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Gornell University Library
Ithaca, New York

j

GEORGE FRANCIS ATKINSON
BOTANICAL LIBRARY
1920

Cornell University

Library

The original of this book is in
the Cornell University Library.

There are no known copyright restrictions in
the United States on the use of the text.

http :/Awww.archive.org/details/cu31924003516923

PUTREFACTION AND INFECTION.

PROFESSOR JOHN TYNDALL'S WORKS.

Essays on the Floating Matter of the Air, in Relation
to Putrefaction and Infection. 12mo. Cloth, $1.50.

On Forms of Water, in Clouds, Rivers, Ice, and Gla-
ciers. With 85 Illustrations, 12mo. Cloth, $1.50.

Heat as a Mode of Motion. New edition. 12mo.

loth, $2.50.

On Sound; A Course of Eight Lectures delivered at
the Royal Institution of Great Britain. Illustrated.
12mo. New edition. Cloth, $2.00.

Fragments of Science for Unscientific People. 12mo.

ew revised and enlarged edition. Cloth, $2.50.

Light and Electricity. 12mo. Cloth, $1.25.

Lessons in Electricity, 1715-16. 12mo. Cloth, $1.00.

Hours of Exercise in the Alps. With Illustrations.
12mo. Cloth, $2.C0.

a rs as @ Discoverer. A Memoir. 12mo. Cloth,

Contributions to Molecular Physics in the Domain of
Radiant Heat. $5.00.

Six Lectures on Light. Delivered in America in
187278. With an Appendix and numerous Illus-
trations. Cloth, $1.50.

Farewell cif ha given to Professor Tyndall, at Del-
monico’s, New York, February 4, 1878. Paper,
50 cents.

Address delivered before the British Association,
assembled at Belfast. Revised, with Additions,

by the author, since the Delivery. 12mo. Paper,
50 cents.

New York: D. Arrieton & Co., 1, 8, & 5 Bond St.

ESSAYS

ON THE

FLOATING-MATTER OF THE AIR

IN RELATION TO

PUTREFACTION AND INFECTION.

BY

JOHN TYNDALL, F.R.S.

(M.D. TUBINGEN).

NEW YORK:

D. APPLETON AND COMPANY,
1, 8, any 5 BOND STREET

1884.

INTRODUCTORY NOTE.

_—

THE VIRTUAL TRIUMPH of the Antiseptic system of
surgery, based as that system is on the recognition of
living contagia as the agents of putrefaction, is of
good augury as regards the receptivity of the public
mind to new views respecting the nature of contagia
generally.

To the credit of English surgeons it stands recorded
that, guided by their practical sagacity, they had
adopted in their hospitals measures of amelioration
which reduced, almost to a minimum, the rate of mor-
tality arising from the ‘mortification’ of wounds.
They had discovered the evils incident to ‘ dirt;’ and,
by keeping dirt far away from them, they had saved
innumerable lives, which would undoubtedly have suc-
cumbed under conditions prevalent in many of the
hospitals of continental Europe.

In thus acting, English surgeons were, for the most
part, ‘ wiser than they knew.’ Their knowledge, how-
ever momentous in its practical applications, was still
empirical knowledge. That dirt was fatal they had
discovered ; but why it was fatal few of them knew.

viii INTRODUCTORY NOTE.

At this point Lister came forward with a scientific
principle which rendered all plain. Dirt was fatal, not
as dirt, but because it contained living germs which,
as Schwann was the first to prove, are the cause of
putrefaction. Lister extended the generalization of
Schwann from dead matter to living matter, and by
this apparently simple step revolutionized the art of
surgery. He changed it, in fact, from an art into a
science.

‘Listerism’ is sometimes spoken of as if it merely
consisted in the application of carbolic acid spray;
but no man of any breadth of vision will regard the
subject thus. The antiseptic system had been enun-
ciated, expounded, and illustrated, prior to the intro-
duction of the spray. The spray is a mere offshoot of
the system—elegant and effective it is true, but still
a matter of detail. In company with my excellent
friend Mr. John Simon, I once visited St. Bar-
tholomew’s Hospital, and became acquainted, in its
wards, with the practice of the late Mr. Callender.
The antiseptic system was there as stringently applied
as at King’s College. Immediately before his departure
to America I spoke to Mr. Callender on this subject ;
and he then told me expressly, that his aim and hope
had been, not to introduce a new principle, but to
simplify the methods of Lister. And yet Mr. Callen-
der’s practice is sometimes spoken of as if it were, in
principle, different from that of his eminent contem-
porary.

It is interesting, and indeed pathetic, to observe
how long a discovery of priceless value to humanity

INTRODUCTORY NOTE. ix

may be hidden away, or rather lie openly revealed,
before the final and apparently obvious step is taken
towards its practical application. In 1837, Schwann
clearly established the connexion between putrefaction
and microscopic life; but thirty years had to elapse
before Lister extended to wounds the researches of
Schwann on dead flesh and animal infusions. Prior to
Lister the possibility of some such extension had
occurred to other minds. Penetrative men had seen
that the germs which produce the putrefaction of meat
might also act with fatal effect in the wards of a
hospital.

Thus, for example, in a paper read before the British
Medical Association at Cambridge in 1864, Mr. Spencer
Wells pointed out that the experiments of Pasteur,
then recent, had ‘all a very important bearing upon
the development of purulent infection, and the whole
class of diseases most fatal in hospitals and other over-
crowded places.’ Mr. Wells did not, as far as I know,
introduce any systematic mode of combating the organ-
isms whose power he so early recognised. But, I
believe, in hardly any other department of surgery has
the success of the antiseptic system been more con-
spicuous and complete than in that particular sphere
of practice in which Mr. Wells has won so great a
name.

A remark in the paper just referred to would seem
to indicate that, in regard to the further possible
influence of germs, the thoughts of Mr. Spencer Wells
had passed beyond the bounds of pure surgical -prac-
tice. ‘Their influence,’ he says, ‘ on the propagation of

x INTRODUCTORY NOTE.

epidemic and contagious diseases has yet to be made
out.’

This shows that at the time here referred to the
Germ Theory, in its wider medical sense, had begun to
ferment in England. Two years, indeed, prior to the
above occasion, and for the use of the same Association
as that addressed by Mr. Wells, the late Dr. William
Budd had drawn up a series of ‘Suggestions towards a
Scheme for the Investigation of Epidemic and Epizootic
Diseases,’ which strikingly illustrate the insight of a
moan of genius, withdrawn from the stimulus of the
metropolis, and working alone, at a time when the
whole medical profession in England entertained views
opposed to his. Budd states in succession, and with
perfect clearness, the points which he considers most
worthy of the attention of the Association. He re-
commends inquiry as to the nature of the evidence
alleged to prove the disease under investigation to be
contagious or communicable. Whether such disease
admits of being artificially propagated by inoculation
or otherwise. Through what surface or surfaces the
virus may be shown to enter the body, and to leave it,
when the disease is taken in the natural way. Whether
the disease is distinguished by eruptions external or
internal. Whether it has a period of true incubation;
and if so, what are the length and limits of that period.
Whether one attack, as in smallpox and many other
contagious diseases, preserves against future attacks.
Whether in the case of human disease animals as well
as man are susceptible, and if so, what animals. What,
is the evidence, if any, as to the particular country or
region in which the disease first appeared. What are

INTRODUCTORY NOTE. xi

its present geographical limits. Whether there is any
evidence of its modern or recent introduction into
countries previously exempt. How far any such disease
may have been prevented from invading new countries,
or from spreading from any particular centre, by
measures directed against contagion. Above all, to
determine what is the nature, and what the true value,
of the evidence supposed to show that the specific
poison of a contagious disease may originate spon-
taneously, or be generated de novo. ‘What we most
want to know,’ adds Budd, ‘in regard to this whole
group of diseases is, where, and how, the specific
poisons which cause them, breed and multiply,’

Budd’s own relation to the question here raised
was distinct and, under the circumstances, impressive.
‘ After giving many years of time and thought to an
examination of the evidence bearing on. this question,’
he comes to the conclusion ‘that there is no proof
whatever’ that the poisons of specific contagious
diseases ever originate spontaneously. ‘That the
evidence on which the contrary conclusion is founded
is negative only; that evidence of precisely the same
order, only to all appeararice still more cogent, would
prove animals and plants, even of large species, to
originate spontaneously; that this evidence is therefore
of no weight ; and, lastly, that all the really important
facts point the other way, and tend to prove that these
poisons (to use a term which is probably provisional
only), like animals and plants, however they may have
once originated, are only propagated now by the law of
continuous succession.’

xii INTRODUCTORY NOTE.

The word ‘ poisons,’ here provisionally employed,
was a concession on Budd’s part to his weaker brethren ;
for he, without a shade of doubt, considered the poison
to be a real living seed. There was, I believe, but
one physician of eminence in England who, at the time
here referred to, shared this conviction, and who im-
parted to Budd the incalculable force derived from the
approbation and encouragement of a wise and cele-
brated man. It gives me singular pleasure to write
down here the name of the venerable Sir Thomas
Watson, who lent to William Budd unfailing counte-
nance and support, and who has lived to see that the
views which commended themselves to his philosophic
judgment are at the present moment advancing with
resistless momentum among the members of the medical
profession. It was far otherwise at the time to which
we here refer. ‘Opinions like these,’ said Budd, ‘are
no doubt, at present, those of a small minority. A
very large, and by far the most influential school in this
country—a school which probably embraces the great
majority of medical practitioners, and the whole of
the “sanitary public”—holds the exact contrary; and
teaches that sundry of these poisons are constantly
being generated de novo by the material conditions
which surround us.’

Budd’s remark regarding the spontaneous generation
of ‘animals and plants, even of large species,’ is both
pregnant and pertinent. In reference to special and
solitary outbreaks of contagious fever, I have frequently
heard physicians of distinction affirm, without apparent
misgiving, the ‘impossibility’ of importation from

INTRODUCTORY NOTE. xiii

without. On such occasions a reply, in the strict sense
affirmed by William Budd, was always at hand; for I
was able to adduce cases of solitary mushrooms, found
upon out of the way Alpine slopes, to which the
evidence would apply with greater force than to the
cases on which the physicians referred to based their
conclusions. With the atmosphere as a vehicle of
universal intercommunication, it is hard to see any
just warrant for the reliance of medical men upon the
negative evidence stigmatized by Budd as valueless.
It is, however, evidence by which many physicians are
still influenced, and the effects of which it will
probably require a generation of doctors, brought up
under other conditions of culture and of practice, to
wholly sweep away.

These conditions are growing up around us, and
their influence will be all-pervading before long. Never
before was medicine manned and officered as it is now.
To name here the workers at present engaged in the
investigation of communicable diseases would be to
extend beyond all reasonable limits this Introductory
Note. On the old Baconian lines of observation and
experiment the work is carried on. The intercommuni-
cation of scientific thought plays here a most important
part. It will probably have been noticed, that while
physiologists and physicians in England and elsewhere
were drawing copiously from the store of facts furnished
by the researches of Pasteur, that admirable investigator
long kept himself clear of physiology and medicine.
There is, indeed, reason to believe that he was spurred
on to his most recent achievements by the papers of

xiv INTRODUCTORY NOTE.

Burdon Sanderson, Koch, and others. The union of
scientific minds is, or ought to be, organic. They are
parts of the same body, in which every memter, under
penalty of atrophy and decay, must discharge its due
share of the duty imposed upon the whole. Of this
‘body,’ a short time since, England provided one of the
healthiest limbs , but round that limb legislation has
lately thrown a ligature, which threatens to damage
its circulation and to divert its energies into foreign
channels. In observational medicine one fine piece of
work may be here referred to—the masterly inquiry of
Dr. Thorne Thorne into the outbreak of typhoid fever
at Caterham and Redhill. Hundreds were smitten by
this epidemic, and many died. The qualities of mind
illustrated in Dr. Thorne’s inquiry match those dis-
played by William Budd in his memorable investigation
of asimilar outbreak in Devonshire. Dr. Budd’s process
was centrifugal—tracing from a single case in the
village of North Tawton, the ravages of the fever far
and wide. Dr. Thorne’s process was centripetal—
tracing the epidemic backwards from the multitude of
cases first: presented, to the single individual whose

infected excreta, poured into the well at Caterham, were
the cause of all.

The Essays here presented to the reader belong to
the A BC of the great subject touched upon in the
foregoing Note. The two principal ones, namely,
Essays II. and III., were prepared for the Royal
Society, and are published in the ‘ Philosophical Trans-
actions’ for 1876 and 1877. But, though written for

INTRODUCTORY NOTE. xv

that learned body, I sought to render their style and
logic so clear as to render them accessible to any fairly
cultivated mind. The Essays on ‘Fermentation’ and
‘Spontaneous Generation’ have already appeared else-
where; while the first Essay, on ‘Dust and Disease,
has been for some years before the public. It may be
regarded as a kind of popular introduction to the more
strenuous and original labours which follow it.

The Essay most likely to try the reader’s patience
is No. JII. On the whole, however, and particularly
in its bearings on the Germ Theory of disease, it is
probably the most important of all. The difficulties
which sometimes beset the experimenter in these in-
vestigations are best illustrated by this Essay. It
shows, to my mind in a very impressive manner, the
analogy of the spread of infection among organic in-
fusions with its mode of propagation among human
beings. The vital resistance of certain germs to heat
is strikingly illustrated in the third Essay, one in-
fusion being there proved to maintain its potentiality
of life intact after eight hours’ continuous exposure to
the temperature of boiling water. Under the plain
guidance of the Germ Theory, it is however shown that
an infusion of this stubborn character may be infallibly
sterilized by discontinuous heating, in one hundredth
part of the time requisite when the boiling is con-
tinuous. Another question, to my mind of fundamental
importance, is also disposed of in Essay III., where it
is shown that the germs which exhibited the foregoing
resistance are neither contained in the air, nor attached
to the surface of the vessel, above the liquid, but that

xvi INTRODUCTORY NOTE,

they manifest their extraordinary vitality in the body
of the liquid itself.

On public sympathy the sanitary physician has
mainly to rely for support, in a country where sanitary
matters are left so much in the hands of the public
itself as they are in England. But sympathy without
cause—that is to say, without some basis of knowledge
—is hardly to be expected. It is as a contribution to
such knowledge that these Essays have been collected,
and thrown into their present handy form.

J. TYNDALL.

Roya INSTITUTION:
August 1881.

CONTENTS.

_—o———

ON DUST AND DISEASE.

Experiments on Dusty Air : 5 . . . .
The Germ Theory of Contagious Didensd . . oe
Parasitic Diseases of Silkworms. Pasteur’s Researches ‘ ‘
Origin and Propagation of Contagious Matter . eo
The Germ Theory applied to Surgery a . ‘ . .

The Luminous Beam as a means of Research : A eas
The Floating-Matter of the Air ‘ 3 . ‘
Dr. Bennett’s Experiments . . . .

OPTICAL DEPORTMENT OF THE ATMOSPHERE
IN RELATION TO PUTREFACTION AND INFEC-

TION.

§ 1. Introduction : : : 2 :

§ 2. Method of Experiment ¢ : - : . .

§ 3. Deportment of Urine . . . : . :

§ 4. Mutton-Infusion . . . . . . . .
§ 5. Beef-Infusion . f . : . 7 oe
§ 6. Haddock-Infusion . a : . 7 a
§ 7. Turnip-Infusion . 3 . ‘ 2 . 5 rae
§ 8. Hay-Infusion . : . : 7 . . : .
§ 9. Infusion of Sole . ¥ ‘ . ‘ : . ae
§ 10. Liver-Infusion . : . a 5
§ 11. Infusions of Hare, Rabbit, Pheasant, and Grouse a
§ 12. Infusions of Codfish, Turbot, Herring, and Mullet .

§ 13. Infusions of Fowland Kidney . . .

§ 14. Boiling by an Internal Source of Heat . ‘ ‘

§ 15. Partial Discussion of the Results. . . .

xviii
§ 16.

§ 17.
§ 18.
§ 19.
§ 20.
§ 21.
§ 22.
§ 23.

§ 24.
§ 26.

§ 26.
§ 27.

CONTENTS.

Suspended Particles in Air and Water; their relation to
Bacteria . ‘ : . . o 25

Recent Experiments on a Heterogenesis . . .

Experiments with Filtered Air . :

Experiments with Calcined Air.

Infusions withdrawn from Air . . . F ae

The Germ Theory of Contagious Disease es 2 ‘

Experiments with Hermetically-sealed Vessels . is

Conditions as to the Temperature and Strength of In-
fusions . .

Developmental Power e Infusions ond Solutions : Air.
germs contrasted with Water-germs c

Diffusion of Germs in the Air .

Tray of one hundred Tubes 3

Some Experiments of Pasteur and ther Relation to Bae-
terial Clouds .

Note I. Action of Basteria apoN a Beara of Light

Note II. Fluorescence of Infusions . 2

FURTHER RESEARCHES ON THE DEPORTMENT AND

Cr tr Lr > wm Murra Cr Lr eh er Mr rar

VITALITY OF PUTREFACTIVE ORGANISMS.

. Introduction . : é . -
. Experiments of Pasteur, Roberts ait Cohn i.
. Hay-Infusions. Preliminary Experiments with Pipette-

bulbs

. Hay-Infusions. Hepariments with Cohn’s Walbes z
. Hay-Infusions (in Closed Chambers) .
. Desiccation of Germs. New Hay and old

Hay-Infusions. Further Experiments with Closed
Chambers . . . - : .

. Experiments with Soaked Hay
. Infusions of Fungi .

. Infusions of Cucumber, Bectioot ie, :
. New Experiments on Animal Infusions. Contradictory
results

. Infusions protected by ‘Glass Shades eontatning Ghlcinea,

Air. F . Z : .

. Further Precautions Gaalnet Tatestion,

. Experiments in the Royal Gardens, Kew

. Experiments on the Roof of the Royal Tdetitution.

. Preliminary Experiments on the Resistance-limit of
Germs to the temperature of Boiling Water

131
135

138
144
146
148

150
164
158
161

165
169
171
174
117

180

CONTENTS. xix

§ 17. Further Experiments on the Resistance-limit of Germs
to the Boiling Temperature é 183

§ 18. Change of Apparatus. New Hxperiments with Filtered
Air

. ;: : 188
§ 19. Final proof that the Resistant Germs are extraned by
the Infusion. Examples of Resistance both in Acid
and Neutral Liquids " - + 194
20. Remarks on Acid, Neutral, and Alkatsaa Infusions - 203
§ 21. Remarks on the Germs of Bacteria as eee
from Bacteria themselves . . : - 205
§ 22. Sterilization by discontinuous Heating . . 210
§ 23. Mortality of Germs through defect of Oxygen produced
by Exhaustion with the Sprengel Pump . : . 216
§ 24. Mortality of Germs through defect of ca conse-
quent on boiling the Infusion . . r + 221
§ 25. Critical Review of the last two Sections . : 5 . 225
§ 26. Mortality of Germs through excess of Oxygen . « » 227
§ 27. Experiments on neutralized Urine . . ‘ . 228
§ 28. Hermetically-sealed Flasks exposed to the Sun of the
Alps . 7 3 . ‘ 5 . - » 231
§ 29, Remarks on Hermetic Sealing : : : . 233
§ 30. Experiments with Turnip-cheese Infusions 3 . . 234
FERMENTATION, AND ITS BEARINGS ON
SURGERY AND MEDICINE . : : . . 287
SPONTANEOUS GENERATION . : ‘ - 277

APPENDIX. . . . . . . . ‘ . « 321

ON DUST AND DISEASE.

—+oe——

I.
Experiments on Dusty Air.

Soar light, in passing through a dark room, reveals
its track by illuminating the dust floating in the air.
‘The sun,’ says Daniel Culverwell, ‘discovers atomes,
though they be invisible by candle-light, and makes
them dance naked in his beams.’

In my researches on the decomposition of vapours
by light, I was compelled to remove these ‘atomes’
and this dust. It was essential that the space con-
taining the vapours should embrace no visible thing—
that no substance capable of scattering light in the
slightest sensible degree should, at the outset of an
experiment, be found in the wide ‘ experimental tube’
in which the vapour was enclosed.

For a long time I was troubled by the appearance
there of floating matter, which, though invisible in
diffuse daylight, was at once revealed by a powerfully
condensed beam. Two U-tubes were placed in suc-
cession in the path of the air, before it entered the
liquid whose vapour was to be carried into the experi-
mental tube. One of the U-tubes contained fragments
ofmarble wetted with a strong solutionof caustic potash ;

2 THE FLOATING-MATTER OF THE AIR.

the other, fragments of glass wetted with concentrated
sulphuric acid which, while yielding no vapour of itsown,
powerfully absorbs the aqueous vapour of the air. To
my astonishment, the air of the Royal Institution, sent
through these tubes at a rate sufficiently slow to dry
it, and to remove its carbonic acid, carried into the
experimental tube a considerable amount of mechani-
cally suspended matter, which was illuminated when
the beam passed through the tube. The effect was
substantially the same when the air was permitted to
bubble through the liquid acid, and through the solu-
tion of potash.

I tried to intercept this floating matter in various
ways; and on October 5, 1868, prior to sending the
air through the drying apparatus, it was carefully
permitted to pass over the tip of a spirit-lamp flame.
The floating matter then no longer appeared, having
been burnt up by the flame. It was therefore organic
matter. I was by no means prepared for this result;
having previously thought that the dust of our air was,
in great part, inorganic and non-combustible.!

I had constructed a small gas-furnace, now much
employed by chemists, containing a platinum tube,
which could be heated to vivid redness.? Within this

1 According to an analysis kindly furnished to me by Dr. Percy,
the dust collected from the walls of the British Museum contains
fully 50 per cent. of inorganic matter. Ihave every confidence in
the results of this distinguished chemist; they show that the jloat-
ing dust of our rooms is, as it were, winnowed from the heavier
matter. As bearing directly upon this point I may quote the fol-
lowing passage from Pasteur: ‘Mais ici se présente une remarque:
la poussiére que l’on trouve a la surface de tous les corps est soumise
constamment 4 des courants d’air, qui doivent soulever-les parti-
cules les plus légéres, au nombre desquelles se trouvent, sans donte,
de préférence les corpuscules organisés, ceufs ou spores, moins lourds
généralement que les particules minérales.’

2 Pasteur was, I believe, the first to employ such a tube.

DUST AND DISEASE. 3

tube was a roll of platinum gauze, which, while it
permitted the air to pass through it, ensured the
practical contact of the dust with the incandescent
metal. The air of the laboratory was permitted to
enter the experimental tube, sometimes through the
cold, and sometimes through the heated, tube of plati-
num. In the first column of the following fragment of
a long table of results, the quantity of air operated on is
expressed by the depression of the mercury gauge of the
air-pump. In the second column the condition of the
platinum tube is mentioned, and in the third the state
of the air in the experimental tube.

Quantity of air State of platinum tube State of experimental tube

l5inches . Cold , a Full of particles.
30 yy , 7 Red-hot . 3 Optically empty.
>

The phrase ‘ optically empty’ shows that when the
conditions of perfect combustion were present, the
floating matter totally disappeared.

In a cylindrical beam, which strongly illuminated
the dust of the laboratory, I placed an ignited spirit-
lamp. Mingling with the flame, and round its rim,
were seen curious wreaths of darkness resembling an
intensely black smoke. On placing the flame at some
distance below the beam, the same dark masses stormed
upwards. They were blacker than the blackest smoke
ever seen issuing from the funnel of a steamer; and
their resemblance to smoke was so perfect as to lead
the most practised observer to conclude that the
apparently pure flame of the alcohol lamp required but
a beam of sufficient intensity to reveal its clouds of
liberated carbon.

But is the blackness smoke? This question pre-
sented itself in a moment and was thus answered: A
red-hot poker was placed underneath the beam: from

4 THE FLOATING-MATTER OF THE AIR.

it the black wreaths also ascended. A large hydrogen
flame was next employed, and it produced those whirl-
ing masses of darkness, far more copiously than either.
the spirit-flame or poker. Smoke was therefore out of
the question.!

What, then, was the blackness? It was simply that
of stellar space; that is to say, blackness resulting
from the absence from the track of the beam of al!
matter competent to scatter its light. When the flame
was placed below the beam the floating matter was
destroyed in situ; and the air, freed from this matter,
rose into the beam, jostled aside the illuminated par-
ticles, and substituted for their light the darkness due
to its own perfect transparency. Nothing could more
forcibly illustrate the invisibility of the agent which
renders all things visible. The beam crossed, unseen,
the black chasm formed by the transparent air, while,
at both sides of the gap, the thick-strewn particles
shone out like a luminous solid under the powerful
illumination.

It is not, however, necessary to burn the particles
to produce a stream of darkness. Without actual
combustion, currents may be generated which shall
displace the floating matter, and appear dark amid the
surrounding brightness. I noticed this effect first. on
placing a red-hot copper ball below the beam, and
permitting it to remain there until its temperature
had fallen below that of boiling water. The dark
currents, though much enfeebled, were still produced.
They may also be produced by a flask filled with hot
water.

1 In none of the public rooms of the United States where I had
the honour to lecture was this experiment made. The organic
dust was too scanty. Certain rooms in England—the Brighton
Pavilion, for example—also lack the necessary conditions.

DUST AND DISEASE. 6

To study this effect a platinum wire was stretched
transversely under the beam, the two ends of the wire
being connected with the two poles of a voltaic battery.
To regulate the strength of the current a rheostat was
placed in the circuit. Beginning with a feeble current
the temperature of the wire was gradually augmented ;
but long before it reached the heat of ignition, a flat
stream of air rose from it, which when looked at edge-
ways appeared darker and sharper than one of the
blackest lines of Fraunhofer in the purified spectrum.
Right and left of this dark vertical band the floating
matter rose upwards, bounding definitely the non-
luminous stream of air. What is the explanation?
Simply this: The hot wire rarefied the air in contact
with it, but it did not equally lighten the floating
matter. The convection current of pure air therefore
passed upwards among the inert particles, dragging
them after it right and left, but forming between them
an impassable black partition. This elementary ex-
periment enables us to render an account of the dark
currents produced by bodies at a temperature below
that of combustion.

When the platinum wire is intensely heated, the
floating matter is not only displaced, but destroyed.
I stretched a wire about 4 inches long through the air
of an ordinary glass shade resting on cotton-wool,
which also surrounded the rim. The wire being raised
to a white heat by an electric current, the air expanded,
and some of it was forced through the cotton-wool.
When the current was interrupted, and the air within
the shade cooled, the returning air did not carry motes
along with it, being filtered by the wool. At the
beginning of this experiment the shade was charged
with floating matter; at the end of half an hour it
was optically empty.

6 THE FLOATING-MATTER OF THE AIR.

On the wooden base of a cubical glass shade, a
cubic foot in volume, upright supports were fixed, and
from one support to the other 38 inches of platinum
wire were stretched in four parallel lines. The ends
of the platinum wire were soldered to two stout copper
wires which passed through the base of the shade
and could be connected with a battery. As in the
last experiment the shade rested upon cotton-wool.
A beam sent through the shade revealed the suspended
matter. The platinum wire was then raised to white-
ness. In five minutes there was a sensible diminution
of the matter, and in ten minutes it was totally con-
sumed.

Oxygen, hydrogen, nitrogen, carbonic acid, so pre-
pared as to exclude all floating particles, produce,
when poured or blown into the beam, the darkness of
stellar space. Coal-gas does the same. An ordinary
glass shade, placed in the air with its mouth down-
wards, permits the track of the beam to be seen
crossing it. When coal-gas or hydrogen is allowed to
enter the shade by a tube reaching to its top, the gas
gradually fills the shade from above downwards. As
soon as it occupies the space crossed by the beam, the
luminous track is abolished. Lifting the shade so as
to bring the common boundary of gas and air above
the beam, the track flashes forth. After the shade is
full, if it be inverted, the pure gas passes upwards like
a black smoke among the illuminated particles.

The Germ Theory of Contagious Disease.

There is no respite to our contact with the floating
matter of the air, We not only suffer from its
mechanical irritation, but it is a growing belief that
a portion of it lies at the root of a class of disorders

DUST AND DISEASE, 7

most deadly toman. And what is this portion? It
was some time ago the current belief that epidemic
diseases generally were propagated by a kind of malaria,
which consisted of organic matter in a state of motor.
decay; that when such matter was taken into the body
through the lungs, skin, or stomach, it had the power
of spreading there the destroying process by which
itself had been assailed. Such a power, it was alleged,
was visibly exerted in the case of yeast. A little leaven
was seen to leaven the whole lump—a mere speck of
matter, in this supposed state of decomposition, being
apparently competent to propagate indefinitely its own
decay. Why should not a bit of rotten malaria within
the human body act in a similar way? In 1836 a
very unexpected reply was given to this question. In
that year Cagniard de la Tour discovered the yeast-
plant—a living organism, which when placed in a
proper medium feeds, grows, and reproduces itself, and
in this way carries on the process which we name
fermentation. Here we have active life instead of
motor-decay. By this discovery fermentation was con-
nected with organic growth.

Schwann, of Berlin, discovered the yeast-plant in-
dependently about the same time; and in February,
1837, he also announced the important result, that
when a decoction of meat is effectually screened from
ordinary air, and supplied solely with calcined air,
putrefaction never sets in. Putrefaction, therefore, he
affirmed to be caused, not by the air, but by something in
the air which could be destroyed by a sufficiently high
temperature. The results of Schwann were confirmed by
the independent experiments of Helmholtz, Ure, and
Pasteur, while other methods, pursued by Schultze,
and by Schroeder and Dusch, led to the same result.
But as regards fermentation, the minds of chemists,

2

8 THE FLOATING-MATTER OF THE AIR.

influenced probably by the great authority of Gay-
Lussae, fell back upon the old notion of matter in a state
of decay. It was not, they said, the living yeast-plant, but
the dead or dying part of it, which, assailed by oxygen,
produced the fermentation, But, as a matter of fact,
when the plant is killed the ferment disappears.
Mediate or immediate, the real ‘ferments’ are living
organisms which find in fermentable substances their
necessary food.

Side by side with these researches and discoveries,
and fortified by them and others, has run the germ
theory of epidemic disease. The notion was expressed
by Kircher, and favoured by Linnzus, that epidemic
diseases may be due to germs which float in the at-
mosphere, enter the body, and produce disturbance by
the development within the body of parasitic life.
The strength of this theory consists in the perfect
parallelism of the phenomena of contagious disease
with those of life. As a planted acorn gives birth to
an oak, competent to produce a whole crop of acorns,
each gifted with the power of reproducing its parent
tree; and as thus from a single seedling a whole forest
may spring ; so, it is contended, these epidemic diseases
literally plant their seeds, grow, and shake abroad new
germs, which, meeting in the human body their proper
food and temperature, finally take possession of whole
populations. There is nothing to my knowledge in
pure chemistry which resembles the power of propaga-
tion and self-multiplication possessed by the matter
which produces epidemic disease. If you sow wheat
you do not get barley; if you sow small-pox you do
not get scarlet-fever, but small-pox indefinitely mul-
tiplied, and nothing else. The matter of each con-
tagious disease reproduces itself as rigidly as if it were
(as Miss Nightingale puts it) dog or cat.

DUST AND DISEASE. 9

Parasitic Diseases of Silkworms. Pasteur’s
Researches.

It is admitted on all hands that some diseases are
the product of parasitic growth. Both in man and in
lower creatures, the existence of such diseases has been
demonstrated. I am enabled to lay before you an ac-
count of an epidemic of this kind, thoroughly investi-
gated and successfully combated by M. Pasteur. For
fifteen years a plague had raged among the silkworms
of France. They had sickened and died in multitudes,
while those that succeeded in spinning their cocoons
furnished only a fraction of the normal quantity of silk.
In 1853 the silk culture of France produced a revenue
of one hundred and thirty millions of franes. During
the twenty previous years the revenue had doubled it-
self, and no doubt was entertained as to its further
augmentation. The weight of the cocoons produced
in 1853 was 52,000,000 pounds; in 1865 it had
fallen to 8,000,000, the fall entailing, in a single year,
a loss of 100,000,000 francs.

The country chiefly smitten by this calamity hap-
pened to be that of the celebrated chemist Dumas, now
perpetual secretary of the French Academy of Sciences.
He turned to his friend, colleague, and pupil, Pasteur,
and besought him, with an earnestness which the cir-
cumstances rendered almost personal, to undertake the
investigation of the malady. Pasteur at this time had
never seen a silkworm, and he urged his inexperience in
reply to his friend. But Dumas knew too well the
qualities needed for such an inquiry to accept Pasteur’s
reason for declining it. ‘Je mets,’ said he, ‘un prix
extréme 4 voir votre attention fixée sur la question qui
intéresse mon pauvre pays; la misére surpasse tout ce

10 THE FLOATING-MATTER OF THE AIR.

que vous pouvez imaginer.’ Pamphlets about the
plague had been showered upon the public, the mono-
tony of waste paper being broken, at rare intervals, by
a more or less useful publication. ‘ The Pharmacopeia
of the Silkworm,’ wrote M. Cornalia in 1860, ‘is now
as complicated as that of man. Gases, liquids, and
solids have been laid under contribution. From
eblorine to sulphurous acid, from nitric acid to rum,
from sugar to sulphate of quinine,—all has been in-
voked in behalf of this unhappy insect.’ The helpless
cultivators, moreover, welcomed with ready trustfulness
every new remedy, if only pressed upon them with
sufficient hardihood. It seemed impossible to diminish
their blind confidence in their blind guides. In 1863
the French Minister of Agriculture signed an agree-
ment to pay 500,000 francs for the use of a remedy,
which its promoter declared to be infallible. It was
tried in twelve different departments of France, and
found perfectly useless. In no single instance was it
successful. It was under these circumstances that M.
Pasteur, yielding to the entreaties of his friend, betook
himself to Alais in the beginning of June, 1865. As
regards silk husbandry, this was the most important
department in France, and it was the most sorely
smitten by the plague.

The silkworm had been previously attacked by
muscardine, a disease proved by Bassi to be caused by
a vegetable parasite. This malady was propagated an-
nually by the parasitic spores. Wafte:l by winds, they
often sowed the disease in places far removed from
the centre of infection. Muscardine is now said to
be very rare, a deadlier malady having taken its
place. This new disease is characterized by the black
spots which cover the silkworms; hence the name pé.
brine, first applied to the plague by M. de Quatrefages,

DUST AND DISEASE. 11

and adopted by Pasteur. Pébrine declares itself in the
stunted and unequal growth of the worms, in the
languor of their movements, in their fastidiousness as
regards food, and in their premature death. The course
of discovery as regards the epidemic is this: In 1849
Guérin Méneville noticed in the blood of silkworms
vibratory corpuscles, which he supposed from their
motions to be endowed with independent life. Filippi,
however, showed that the motion of the corpuscles was
the well-known Brownian motion; but he committed
the error of supposing the corpuscles to be normal to
the life of the insect. Possessing the power of in-
definite self-multiplication, they are really the cause
of its mortality—the form and substance of its
disease. This was well described by Cornalia; while
Lebert and Frey subsequently found the corpuscles not
only in the blood, but in all the tissues of the insect.
Osimo, in 1857, discovered them in the eggs; and on
this observation Vittadiani founded, in 1859, a prac-
tical method of distinguishing healthy from diseased
eggs. The test often proved fallacious, and it was
never extensively applied.

These living corpuscles first take possession of the
intestinal canal, and spread thence throughout the body
of the worm. They fill the silk cavities, the stricken
insect often going automatically through the motions
of spinning, without any material to work upon. Its
organs, instead of being filled with the clear viscous
liquid of the silk, are packed to distension by the
corpuscles. On this feature of the plague Pasteur
fixed his entire attention. The cycle of the silkworm’s
life is briefly this: From the fertile egg comes the
little worm, which grows, and casts its skin. This
process of moulting is repeated two or three times
at intervals during the life of the insect. After

'

12 THE FLOATING-MATTER OF THE AIR.

the last moulting the worm climbs the brambles
placed to receive it, and spins among them its cocoon.
It passes thus into a chrysalis; the chrysalis becomes
a moth, and the moth, when liberated, lays the eggs
which form the starting-point of a new cycle. Now
Pasteur proved that the plague-corpuscles might be
incipient in the egg, and escape detection; they mignt
also be germinal in the worm, and still baffle the
microscope. But as the worm grows, the corpuscles
grow also, becoming larger and more defined. In the
aged chrysalis they are more pronounced than in the
worm; while in the moth, if either the egg or the
worm from which it comes should have been at all
stricken, the corpuscles infallibly appear, offering no
difficulty of detection. This was the first great point
made out in 1865 by Pasteur. The Italian naturalists,
as aforesaid, recommended the examination of the eggs
before risking their incubation. Pasteur showed that
both eggs and worms might be smitten, and still pass
muster, the culture of such eggs or such worms being
sure to entail disaster. He made the moth his starting-
point in seeking to regenerate the race.

Pasteur made his first communication on this sub-
ject to the Academy of Sciences in September, 1865.
It raised a cloud of criticism. Here, forsooth, was a
chemist rashly quitting his proper métier and pre-
suming to lay down the law for the physician and
biologist on a subject which was eminently theirs.
‘On trouva étrange que je fusse si peu au courant de
la question ; on m’opposa des travaux qui avaient paru
depuis longtemps en Italie, dont les résultats montraient
Vinutilité de mes efforts, et Vimpossibilité Warriver A
un résultat pratique dans la direction que je m’étais
engagé. Que mon ignorance fut grande au sujet des
recherches sans nombre qui avaient paru depuis quinze

DUST AND DISEASE. 13

années.’ Pasteur heard the buzz, but he continued his
work. In choosing the eggs intended for incubation,
the cultivators selected those produced in the successful
‘educations’ of the year. But they could not under-
stand the frequent and often disastrous failures of their
selected eggs; for they did not know, and nobody pricr
to Pasteur was competent to tell them, that the finest
cocoons may envelope doomed corpusculous moths. It,
was not, however, easy to make the cultivators accept
new guidance. To strike their imagination, and if
possible determine their practice, Pasteur hit upon the
expedient of prophecy. In 1866 he inspected, at St.
Hippolyte-du-Fort, fourteen different parcels of eggs
intended for incubation. Having examined a sufficient
number of the moths which produced these eggs, he
wrote out the prediction of what would occur in 1867,
and placed the prophecy as a sealed letter in the hands
of the Mayor of St. Hippolyte.

In 1867 the cultivators communicated to the mayor
their results. The letter of Pasteur was then opened
and read, and it was found that in twelve out of fourteen
cases there was absolute conformity between his pre-
diction and the observed facts. Many of the groups
had perished totally; the others had perished almost
totally; and this was the prediction of Pasteur. In
two out of the fourteen cases, instead of the prophesied
destruction, half an average crop was obtained. Now,
the parcels of eggs here referred to were considered
healthy by their owners. They bad been hatched and
tended in the firm hope that the labour expended on
them would prove remunerative. The application of
the moth-test for a few minutes in 1866 would have
saved the labour and averted the disappointment. Two,
additional parcels of eggs were at the same time sub-
mitted to Pasteur. He pronounced them healthy ; and

14 THE FLOATING-MATTER OF THE AIR.

his words were verified by the production of an excellent
crop. Other cases of prophecy still more remarkable,
because more circumstantial, are recorde.1 in Pasteur’s
work on tne Diseases of Silkworms.

Pasteur subjected the development of the corpuscles
to a searching investigation, and followed out with
admirable skill and completeness the various modes by
which the plague was propagated. From moths per-
fectly free from corpuscles he obtained healthy worms,
and selecting 10, 20, 30, 50, as the case might be, he
introduced into the worms the corpusculous matter.
It was first permitted to accompany the food. Let us
take a single example out of many. Rubbing up
a stmoall corpusculous worm in water, he smeared
the mixture over mulberry-leaves. Assuring himself
that the leaves had been eaten, he watched the con-
sequences from day to day. Side by side with the
infected worms he reared their fellows, keeping them as
much as possible out of the way of infection. These
constituted his ‘lot témoin,—his standard of com-
parison. On April 16, 1868, he thus infected thirty
worms. Up to the 23rd they remained quite well.
On the 25th they seemed well, but on that day cor-
puscles were found in the intestines of two of them. On
the 27th, or eleven days after the infected repast, two
fresh worms were examined, and not only was the
intestinal canal found in each case invaded, but the silk
organ itself was charged with corpuscles. On the 28th
the twenty-six remaining worms were covered by the
black spots of pébrine. On the 30th the difference of
size between the infected and non-infected worms was
very striking, the sick worms being not more than two-
thirds of the bulk of the healthy ones. On May 2 a
worm which had just finished its fourth moulting was
examined. Its whole body was so filled with the

DUST AND DISEASE. 15

parasite as to excite astonishment that it could live.
The disease advanced, the worms died and were ex-
amined, and on May 11 only six out of the thirty
remained. They were the strongest of the lot, but on
being searched they also were found charged with cor-
puscles. Not one of the thirty worms had escaped; a
single meal had poisoned them all. The standard lot,
on the contrary, spun their fine cocoons, two only of
their moths being proved to contain any trace of the
parasite, which had doubtless been introduced during
the rearing of the worms.

As his acquaintance with the subject increased,
Pasteur’s desire for precision augmented, and he finally
counted the growing number of corpuscles seen in the
field of his microscope from day to day. After a con-
tagious repast the number of worms containing the
parasite gradually augmented until finally it became
cent. per cent. The number of corpuscles would at the
same time rise from 0 to 1, to 10, to 100, and some-
times even to 1,000 or 1,500 in the field of his micro-
scope. He then varied the mode of infection. He
inoculated healthy worms with the corpusculous matter,
and watched the consequent growth of the disease. He
proved that the worms inoculate each other by the
infliction of visible wounds with their claws. In various
cases he washed the claws, and found corpuscles in the
water. He demonstrated the spread of infection by the
simple association of healthy and diseased worms. By
their claws and their excrement, the diseased worms
spread infection. It was no hypothetical infected
medium-—no problematical pythogenic gas—that killed
the worms, but a definite organism. The question of
infection at a distance was also examined, and its
occurrence demonstrated. As might be expected from
Pasteur’s antecedents, the investigation was exhaustive.

16 THE FLOATING-MATTER OF THE AIR.

the beauty of his manipulation finding a fit correlative
in the clearness of his thought.

The following quotation from Pasteur’s work clearly
shows the relation in which his researches stand to the
important question on which he was engaged :

Place (he says) the most skilful cultivator, even the most
expert microscopist, in presence of large cultivations which
present the symptoms described in our experiments; his
judgment will necessarily be erroneous if he confines him-
self to the knowledge which preceded my researches. The
worms will not present to him the slightest spot of pébrine ;
the microscope will not reveal the existence of ccrpuscles ;
the mortality of the worms will be null or insignificant;
and the cocoons leave nothing to be desired. Our observer
would, therefore, conclude without hesitation that the eggs
produced will be good for incubation. The truth is, on the
contrary, that all the worms of these fine crops have been
poisoned ; that from the beginning they carried in them the
germ of the malady ; ready to multiply itself beyond measure
in the chrysalides and the moths, thence to pass into the
eggs and smite with sterility the next generation. And
what is the first cause of the evil concealed under so deceit-
ful an exterior? In our experiments we can, so to speak,
touch it with our fingers. It is entirely the effect of a
single corpusculous repast; an effect more or less prompt
according to the epoch of life of the worm that has eaten
the poisoned food.

Pasteur describes in detail his method of securing
healthy eggs. It is nothing less than a mode of restor-
ing to France her ancient silk husbandry. The justifi-
cation of his work is to be found in the reports
which reached him of the application and the suc-
cess of his method, while editing his researches for
final publication. In both France and Italy his method
has been pursued with the most satisfactory results.
But it was an up-hill fight which led to this: victory.

DUST AND DISEASE, 17

‘ Since the commencement,’ he says, ‘ of these researches,
I have been constantly exposed to the most obstinate
and unjust contradictions ; but I have made it a duty
to leave no trace of these conflicts in this book.’ And in
reference to parasitic diseases, generally, he uses the
following weighty words: ‘I] est au pouvoir de ’homme
de faire disparaitre de la surface du globe les maladies
parasitaires, si, comme c’est ma conviction, la doctrine
des générations spontanées est une chimére.’

Pasteur dwells upon the ease with which an island
like Corsica might be absolutely isolated from the silk-
worm epidemic. And with regard to other epidemics,
Mr. John Simon describes an extraordinary case of in-
sular exemption, for the ten years extending from 1851
to 1860. Of the 627 registration districts of England,
one only had an entire escape from diseases which, in
whole or in part, were prevalent in all the others: ‘In
all the ten years it had not a single death by measles,
nor a single death by small-pox, nor a single death by
scarlet-fever. And why? Not because of its general
sanitary merits, for it had an average amount of other
evidence of unhealthiness. Doubtless, the reason of its
escape was that it was insular. It was the district of
the Scilly Isles; to which it was most improbable that
any febrile contagion should come from without. And
its escape is an approximative proof that, at least for
those ten years, no contagium of measles, nor any
contagium of scarlet-fever, nor any contagium of small-
pox had arisen spontaneously within its limits. It
may be added that there were only seven districts in
England in which no death from diphtheria occurred,
and that, of those seven, the district of the Scilly Isles
was one.

A second parasitic disease of silkworms, called in
France la flacherie, co-existent with pébrine, but quite

18 THE FLOATING-MATTER OF THE AIR.

distinct from it, has also been investigated by Pasteur.
Enough, however, has been said to send those in-
terested in these questions to the original volumes for
further information. To one important practical point
M. Pasteur, in a letter to myself, directs attention :

Permettez-moi de terminer ces quelques lignes que je
dois dicter, vaincu que je suis par la maladie, en vous faisant
observer que vous rendriez service aux Colonies de la Grande-
Bretagne en répandant la connaissance de ce livre, et des
principes que j’¢tablis touchant la maladie des vers 4 soie.
Beaucoup de ces colonies pourraient cultiver le mirier avec
succés, et, en jetant les yeux sur mon ouvrage, vous vous
convaincrez aisément qu'il est facile aujourd’hui, non-
seulement d’éloigner la maladie régnante, mais en outre de
donner aux récoltes de la soie une prospérité qu’elles n’ont
jamais eue.

Origin and Propagation of Contagious Matter.

Prior to Pasteur, the most diverse and contradictory
opinions were entertained as to the contagious character
of pébrine; some stoutly affirmed it, others as stoutly
denied it. But on one point all were agreed. ‘They
believed in the existence of a deleterious medium,
rendered epidemic by some occult and mysterious
influence, to which was attributed the cause of the
disease.’ Those acquainted with our medical literature
will not fail to observe an instructive analogy here,
We have on the one side accomplished writers, like Dr.
Murchison, ascribing epidemic diseases to ‘ deleterious
media’ which arise spontaneously in crowded hospitals
and ill-smelling drains. According to them, the contagia
of epidemic disease are formed de novo in a putrescent
atmosphere. On the other side we have, writers like

.. Dr. Budd, clear, vigorous, with well-defined ideas and

DUST AND DISEASE, 19

methods of research, contending that the matter which
produces epidemic disease comes always from a parent
stock. It behaves as germinal matter, and they do not
hesitate to regard it as such. They no more believe in
the spontaneous generation of such diseases, than they
do in the spontaneous generation of mice. Pasteur, for
example, found that pébrine had been known for an in-
definite time as a disease among silkworms. The de-
velopment of it which he combated was merely the
expansion of an already existing power—the bursting
into open conflagration of*a previously smouldering fire.
There is nothing surprising in this. For though
epidemic disease requires a special contagium to pro-
duce it, surrounding conditions must have a potent in-
fluence on its development. Common seeds may be
duly sown, but the conditions of temperature and mois-
ture may be such as to restrict, or altogether prevent,
the subsequent growth. Looked at, therefore, from the
point: of view of the germ theory, the exceptional energy
which epidemic disease from time to time exhibits is in
harmony with the method of Nature. We sometimes
hear diphtheria spoken of as if it were a new disease ;
but Mr. Simon tells me that about three centuries ago
tremendous epidemics of it raged in Spain (where it was
named Garrotillo), and soon afterwards in Italy; and
that since that time the disease has been well known to
all successive generations of doctors. In or about 1758,
for instance, Dr. Starr, of Liskeard, in a communication
to the Royal Society, particularly described the disease,
with all the symptoms which have recently again become
familiar to us, but under the name of morbus strangula-
torius, as then severely epidemic in Cornwall. This fact
is the more interesting, as diphtheria, in its more modern
reappearance, again showed predilection for that remote
county. Many also believe that the Black Death, of

20 THE FLOATING-MATTER OF THE AIR.

five centuries ago, has disappeared as mysteriously as it
came; but Mr. Simon finds that it is believed to be
prevalent at this hour in some of the north-western
parts of India.

Let me here state an item of my own experience.
When I was at the Bel Alp in 1869, the English
chaplain received letters informing him of the breaking
out of scarlet-fever among his children. He lived, if I
remember rightly, on the healthful eminence of Dart-
moor, and it was difficult to imagine how scarlet-fever
could have been wafted to the place. A drain ran close
to his house, and on it his suspicions were manifestly
fixed. Some of our medical writers would fortify him
in this notion, and thus deflect him from the truth,
while those of another, and, in my opinion, a wiser
school, would deny to a drain, however foul, the power
of generating de novo a specific disease. After close
inquiry he recollected that a hobby-horse had been
used both by his boy and by another who, a short time
previously, had passed through scarlet-fever.

Drains and cesspools, indeed, are by no means in
such evil odour as they used to be. A fetid Thames
and a low death-rate occur from time to time together
in London. For, if the special matter or germs of
epidemic disorder be not present, a corrupt atmosphere,
dowever obnoxious otherwise, will not produce the
disorder. But, if the germs be present, defective drains
and cesspools become the potent distributors of disease
and death. Corrupted air may promote an epidemic,
but cannot produce it. On the other hand, through
the transport of the special germ oz virus, disease may
develop itself in regions where the drainage is good and
the atmosphere pure.

If you see a new thistle growing in your field, you
feel sure that its seed has been wafted thither. Just as

DUST AND DISEASE. 21

sure does it seem that the contagious matter of epi-
demic disease has been sown in the place where it
newly appears. With aclearness and conclusiveness not
to be surpassed, Dr. William Budd hastraced such diseases
from place to place; showing how they plant them-
selves, at distinct points, among populations subjected
to the same atmospheric influences, just as grains of corn
might be carried in the pocket and sown. Hildebrand,
to whose remarkable work, ‘ Du Typhus contagieux,’ Dr.
de Mussy has directed my attention, gives the following
striking case, both of the transport and the durability
of the virus of scarlatina: ‘Un habit noir que j’avais en
visitant une malade attaquée de scarlatine, et que je
portai de Vienne en Podolie, sans Vavoir mis depuis
plus d’un an et demi, me communiqua, dés que je fus
arrivé, cette maladie contagieuse, que je répandis ensuite
dans cette province, ot elle était jusqualors presque
inconnue.’ Some years ago Dr. de Mussy himself was
summoned to a country house in Surrey, to see a young
lady who was suffering from a dropsy, evidently the
consequence of scarlatina. The original disease, being
of a very mild character, had been quite overlooked ;
but circumstances were recorded which could leave no
doubt upon the mind as to the nature and cause of the
complaint. But then the question arose, How did the
young lady catch the scarlatina? She had come there
on a visit two months previously, and it was only after
she had been a month in the house that she was taken
ill. The housekeeper at length cleared up the mystery.
The young lady, on her arrival, had expressed a wish to
occupy a room in an isolated tower. Her desire was
granted ; and in that room, six months previously, a
visitor had been confined with an attack of scarlatina.
The room had been swept and whitewashed, but the
carpets had been permitted to remain.

22 THE FLOATING-MATTER OF THE AIR.

Thousands of cases could probably be cited in which
the disease has shown itself in this mysterious way, but
where a strict examination has revealed its true parent-
age and extraction. Is it, then, philosophical to take
refuge in the fortuitous concourse of atoms as a cause
of specific disease, merely because in special cases the
parentage may be indistinct? Those best acquainted
with atomic nature, and who are most ready to admit,
as regards even higher things than this, the potentiali-
ties of matter, will be the last to accept these rash
hypotheses.

The Germ Theory applied to Surgery.

Not only medical but still more especially surgical
science is now seeking light and guidance from this
germ theory. Upon it the antiseptic system of Pro-
fessor Lister of Edinburgh is founded. As already
stated, the germ theory of putrefaction was started by
Schwann; but the illustrations of this theory adduced
by Professor Lister are of such public moment as not
only to justify, but to render imperative, their intro-
duction here.

Schwann’s observations (says Professor Lister) did not
receive the attention which they appeared to me to have
deserved, The fermentation of sugar was generally allowed
to be occasioned by the torila cerevisiae; but it was not
admitted that putrefaction was due to an analogous agency.
And yet the two cases present a very striking parallel. In
each a stable chemical compound, sugar in the cne case,
albumen in the other, undergoes extraordinary chemical
changes under the influence of an excessively minute quantity
of a substance which, regarded chemically, we should suppose
inert. Asan example of this in the case of putrefaction,
let us take a circumstance often witnessed in the treatment

DUST AND DISEASE. 23

of large chronic abscesses. In order to guard against the
access of atmospheric air, we used to draw off the matter by
means of a canula and trocar, such as you see here, consist-
ing of a silver tube with a sharp-pointed steel rod fitted
into it, and projecting beyond it. The instrument, dipped
in oil, was thrust into the cavity of the abscess, the trocar
was withdrawn, and the pus flowed out through the canula,
care being taken by gentle pressure over the part to prevent
the possibility of regurgitation. The canula was then drawn
out with due precaution against the reflux of air. This
method was frequently successful as to its immediate object,
the patient being relieved from the mass of the accumulated
fluid, and experiencing no inconvenience from the operation.
But the pus was pretty certain to reaccumulate in course of
time, and it became necessary again and again to repeat
the process. And unhappily there was no absolute security
of immunity from bad consequences. However carefully
the procedure was conducted, it sometimes happened, even
though the puncture seemed healing by first intention, that
feverish symptoms declared themselves in the course of the
first or second day, and, on inspecting the seat of the abscess,
the skin was perhaps seen to be red, implying the presence
of some cause of irritation, while a rapid reaccumulation of
the fluid was found to have occurred. Under these circum-
stances, it became necessary to open the abscess by free
incision, when a quantity, large in proportion to the size of
the abscess, say, for example, a quart, of pus escaped, fetid”
from putrefaction. Now, how had this change been brought
about? Without the germ theory, I venture to say, no
rational explanation of it could have been given. It must
have been caused by the introduction of something from
without. - Inflammation of the punctured wound, even sup-
posing it to have occurred, would not explain the pheno-
menon. For mere inflammation, whether acute or chronic,
though it occasions the formation of pus, does not induce
putrefaction. The pus originally evacuated was perfectly
sweet, and we know nothing to account for the alteration
in its quality but the influence of something derived from

24 THE FLOATING-MATTER OF THE AIR.

the external world. And what could that something be?
The dipping of the instrument in oil, and the subsequent
precautions, prevented the entrance of oxygen. Or even if
you allowed that a few atoms of the gas did enter, it would
be an extraordinary assumption to make that these could
in so short a time effect such changes in so large a mass
of albuminous material. Besides, the pyogenic membrane
is abundantly supplied with capillary vessels, through which
arterial blood, rich in oxygen, is perpetually flowing; and
there can be little doubt that the pus, before it was evacu-
ated at all, was liable to any action which the element
might be disposed to exert upon it.

On the oxygen theory, then, the occurrence of putrefac-
tion under these circumstances is quite inexplicable. But
if you admit the germ theory, the difficulty vanishes at
once. The canula and trocar having been lying exposed to
the air, dust will have been deposited upon them, and will
be present in the angle between the trocar and the silver
tube, and in that protected situation will fail to be wiped
off when the instrument is thrust through the tissues. Then
when the trocar is withdrawn, some portions of this dust will
naturally remain upon the margin of the canula, which is
left projecting into the abscess, and nothing is more likely
than that some particles may fail to be washed off by the
stream of out-flowing pus, but may be dislodged when the
tube is taken out, and left behind in the cavity. The germ
theory tells us that these particles of dust will be pretty
sure to contain the germs of putrefactive organisms, and
if one such is left in the albuminous liquid, it will rapidly
develop at the high temperature of the body, and account
for all the phenomena.

But striking as is the parallel] between putrefaction in this
instance and the vinous fermentation, as regards the greatness
of the effect produced, compared with the minuteness and the
inertness, chemically speaking, of the cause, you will natu-
rally desire further evidence of the similarity of the two
processes. You can see with the microscope the torula of
fermenting must or beer. Is there you may ask, any

DUST AND DISEASE. 25

organism to be detected in the putrefying pus? Yes, gentle-
men, there is. If any drop of the putrid matter is examined
with a good glass, it is found to be teeming with myriads of
minute jointed bodies, called vibrios, which indubitably pro-
claim their vitality by the energy of their movements. It
is not an affair of probability, but a fact, that the entire
mass of that quart of pus has become peopled with living
organisms as the result of the introduction of the canu'a and
trocar; for the matter first let out was as free from vibrios
as it was from putrefaction. If this be so, the greatness of
the chemical changes that have taken place in the pus ceases
to be surprising. We know that it is one of the chief pecu-
liarities of living structures that they possess extraordinary
powers of effecting chemical changes in materials in their
vicinity, out of all proportion to their energy as mere chemical
compounds. And we can hardly doubt that the animalcules
which have been developed in the albuminous liquid, and
have grown at its expense, must have altered its constitu-
tion, just as we ourselves alter that of the materials on which
we feed.!

In antiseptic operations care is taken that every
portion of tissue laid bare by the knife shall be de-
fended from germs; that if they fall upon the wound
they should be killed as they fall. With this in
view he showers upon his exposed surfaces the spray of
dilute carbolic acid, which is particularly deadly to the
germs, and he surrounds the wound in the most careful
manner with antiseptic bandages. To those accustomed
to strict experiment it is manifest that we have a strict
experimenter here—a man with a perfectly distinct
object in view, which he pursues with never-tiring
patience and unwavering faith. And the result, in his
hospital practice, as described by himself, has been,
that even in the midst of abominations too shocking
to be mentioned here, and in the neighbourhood of

1 Introductory Lecture before the University of Edinburgh.

26 THE FLOATING-MATTER OF THE AIR.

wards where death was rampant from pyzmia, erysipe-
las, and hospital gangrene, he was able to keep his
patients absolutely free from these terrible scourges.
Let me here recommend to your attention Professor
Lister’s ‘Introductory Lecture before the University of
Edinburgh,’ which I have already quoted ; his paper on
‘The Effect of the Antiseptic System of Treacment on
the Salubrity of a Surgical Hospital ;’ and the article
in the ‘ British Medical Journal’ of January 14, 1871.

If, instead of using carbolic acid spray, he could
surround his wounds with properly filtered air, the re-
sult would, he contends, be the same. In a room, where
the germs not only float but cling to clothes and walls,
this would be difficult, if not impossible. But surgery
is acquainted with a class of wounds in which the blood
is freely mixed with air that has passed through the
lungs, and it is a most remarkable fact that such air
does not produce putrefaction. Professor Lister, as far
as I know, was the first to give a philosophical interpre-
tation of this fact, which he describes and comments
upon thus:

I have explained to my own mind the remarkable fact
that in simple fracture of the ribs, if the lung be punctured
by a fragment, the blood effused into the pleural cavity,
though freely mixed with air, undergoes no decomposition.
The air is sometimes pumped into the pleural cavity in such
abundance that, making its way through the wound in the
pleura costalis, it inflates the cellular tissue of the whole
body. Yet this occasions no alarm to the surgeon (although
if the blood in the pleura were to putrefy, it would infallibly
occasion dangerous suppurative pleurisy). Why air intro-
duced into the pleural cavity through a wounded lung, should
have such wholly different effects from that entering directly
through a wound in the chest, was to me a complete mystery
until I heard of the germ theory of putrefaction, when it at
once occurred to me that it was only natural that air should

DUST AND DISEASE. 27

be filtered of germs by the air-passages, one of whose offices
is to arrest inhaled particles of dust, and prevent them from
centering the air-cells.

I shall have occasion to refer to this remarkable hypo-
thesis farther on.

The advocates of the germ theory, both of putrefac-
tion and epidemic disease, hold that both arise, not
from the air, but from something contained in the air.
They hold, moreover, that this ‘something’ is not a
vapour nor a gas, nor indeed a molecule of any kind,
but a particle! The term ‘ particulate’ has been used
by Mr. Simon in the Reports of the Medical Department
of the Privy Council to describe this supposed constitu-
tion of contagious matter; and Dr. Sanderson’s experi-
ments render it in the highest degree probable, if they do
not actually demonstrate, that the virus of small-pox is
‘ particulate.’ Definite knowledge upon this point is of
exceeding importance, because in the treatment of par-
ticles methods are available which it would be futile to
apply to molecules.

The Luminous Beam as a means of Research.

My own interference with this great question, while
sanctioned by eminent names, has been also an object
of varied and ingenious attack. On this point I will
only say that when angry feeling escapes trom behind
the intellect, where it may be useful as an urging force,
and places itself athwart the intellect, it is liable to

1 As regards size, there is probably no sharp line of division
between molecules and particles; the one gradually shades into
the other. But the distinction that I draw is this: the atom
or the molecule, if free, is always part of a gas, the particle is never
go, A particle is a bit of liquid or solid matter, formed by the
aggregation of atoms or molecules.

28 THE FLOATING-MATTER OF THE AIR.

produce all manner of delusions. Thus my censors, for
the most part, have levelled their remarks against posi-
tions which were never assumed, and against claims
which were never made. The simple history of the
matter is this: During the autumn of 1868 I was much
occupied with the observations referred to at the be-
‘ ginning of this discourse, and in part described in the
preceding article. For fifteen years it had been my
habit to make use of floating dust to reveal the paths
of luminous beams through the air; but until 1868 I
did not intentionally reverse the process, and employ a
luminous beam to reveal and examine the dust. Ina
paper presented to the Royal Society in December, 1869,
the observations which induced me to give more special
attention to the question of spontaneous generation,
and the germ theory of epidemic disease, are thus
described :

The Floating Matter of the Air.

Prior to the discovery of the foregoing action (the
chemical action of light upon vapours), and also during
the experiments just referred to, the nature of my work
compelled me to aim at obtaining experimental tubes abso-
lutely clean upon the interior surface, and absolutely free
within from suspended matter. Neither condition is, how-
ever, easily attained.

For however well the tubes might be washed and polished,
and however bright and pure they might appear in ordi-
nary daylight, the electric beam infallibly revealed signs and
tokens of dirt. The air was always present, and it was sure
to deposit some impurity, All chemical processes, not con-
ducted in a vacuum, are open to this disturbance. When
the experimental tube was exhausted, it exhibited no trace of
floating matter, but on admitting the air through two U-tubes
containing respectively caustic potash and sulphuric acid, a

DUST AND DISEASE, 29

dust-cone more or less distinct was always revealed by the
powerfully condensed electric beam.

The floating motes resembled minute particles of liquid
which had bien carried mechanically from the U-tubes into
the experimental tube. Precautions were therefore taken to
prevent any such transfer. They produced little or no miti-
gation. I did not imagine, at the time, that the dust of the
external air could find such free passage through the caustic
potash and sulphuric acid. This, however, was the case;
the motes really came from without. They also passed with
freedom through a variety of ewthers and alcohols. In fact,
it requires long-continued action on the part of an acid first
to wet the motes and afterwards to destroy them. By care-
fully passing the air through the flame of a spirit lamp,
or through a platinum tube heated to bright redness, the
floating matter was sensibly destroyed. It was therefore
combustible, in other words, organic, matter. I tried to
intercept it by a large respirator of cotton-woo'. Close pres-
sure was necessary to render the wool effective. A plug
of the wool, rammed pretty tightly into the tube through
which the air passed, was finally found competent to hold
back the motes. They appeared from time to time after-
wards, and gave me much trouble ; but they were invariably
traced in the end to some defect in the purifying apparatus
—to some crack or flaw in the sealing-wax employed to render
the tubes air-tight. Thus through proper care, but not with-
out a great deal of searching out of disturbances, the expe-
rimental tube, even when filled with air or vapour, contains
nothing competent to scatter the light. The space within it
has the aspect of an absolute vacuum.

An experimental tube in this condition I call optically

empty.

The facts here forced upon my attention had a bear-
ing too evident to be overlooked. The inability of air
which had been filtered through cotton-wool to generate
microscopic life, had been demonstrated by Schroeder
and Pasteur: here the cause of its impotence was ren-

30 THE FLOATING-MATTER OF THE AIR.

dered evident to the eye. The experiment proved that
no sensible amount of light was scattered by the mole-
cules of the air; that the scattered light always arose
from suspended particles. The fact moreover that the re-
moval of these abolished simultaneously the power of
scattering light and of originating life, obviously de-
tached the life-originating power from the air, and fixed
it on something suspended in the air. Gases of all
kinds passed with freedom through the plug of cotton-
woul; hence the thing whose removal by the cotton-
wool rendered the gas impotent, could not itself have
been matter in the gaseous condition. It at once
occurred to me that the retina, protected as it was, in
these experiments, from all extraneous light, might be
converted into a new and powerful instrument of demon-
stration in relation to the germ theory.

The observations just described also revealed the
danger incurred in experiments of this nature; showing
that without an amount of care far beyond that hitherto
bestowed upon them, such experiments left the door
open to errors of the gravest description. It was
especially manifest that the chemical method employed
by Schultze in his experiments, and so often resorted
to since, might lead to the most erroneous conse-
quences; that neither acids nor alkalies had the power
of rapid destruction hitherto ascribed to them. In
short, the employment of the luminous beam rendered
evident the cause of success in experiments rigidly con-
ducted like those of Pasteur; while it made equally
evident the certainty of failure in experiments less
severely carried out.

DUST’ AND DISEASE. 31

Dr. Bennett's Kaperiments.

I do not wish to leave an assertion of this kind with-
out proof or illustration. Take, then, the well-conceived
experiments of Dr. Hughes Bennett, described before
the Royal Society of Surgeons in Edinburgh on January
17, 1868.1 Into flasks containing decoctions of liquor-
ice-root, hay, or tea, Mr. Bennett, by an ingenious
method, forced air. The air was driven through two
U-tubes, the one containing a solution of caustic potash,
the other sulphuric acid. ‘All the bent tubes were
filled with fragments of pumice-stone to ‘break up the
air, so as to prevent the possibility of any germs passing
through in the centre of bubbles.’ The air also passed
through a Liebig’s bulb containing sulphuric acid, and
also through a bulb containing gun-cotton.

It was only natural for Dr. Bennett to believe that
his ‘ bent tubes’ entirely cut off the germs. Previous
to the observations just referred to, I also believed in
their efficacy. But these observations destroy any such
notion. The gun-cotton, moreover, will fail to arrest
the whole of the floating matter, unless it is tightly
packed, and there is no indication in Dr. Bennett's
memoir that it was so packed. On the whole, I should
infer, from the mere inspection of Dr. Bennett’s appa-
ratus, the very results which he has described—a retar-
dation of the development of life, a total absence of it
in some cases, and its presence in others.

In his first series of experiments, eight flasks were
fed with sifted air, and five with common air. In
ten or twelve days all the five had fungi in them;
whilst: it required from four to nine months to develop
fungi in the others. In one of the eight, moreover,

1 British Medical Journal, 13, pt. ii. 1868.
3

32 THE FLOATING-MATTER OF THE ATR,

even after this interval no fungi appeared. Ina second
series of experiments there was a similar exception. In
a third series the cork stoppers used in the first and
second series were abandoned, and glass stoppers em-
ployed. Flasks containing decoctions of tea, beef, and
hay were filled with common air, and other flasks with
sifted air. In every one of the former fungi appeared
and in not one of the latter. These experiments
simply ruin the doctrine that Dr. Bennett finally
espouses.

In all these negative cases, the air was forced through
the bent tubes and bulb into the boiling-hot infusion. Dr.
Bennett made a fourth series of experiments, in which,
previous to forcing in the air, he permitted the flasks
to cool. Into four bottles thus treated he forced pre-
pared air, and after a time found fungi in all of them.
What is his conclusion? Not that the boiling-hot
liquid, employed in his first experiments, had destroyed
such germs as had run the gauntlet of his apparatus ;
but that air, which, previous to being sealed up, had
been exposed to a temperature of 212°, is too rare to
support life. This conclusion is so remarkable that it
ought to be stated in Dr. Bennett’s own words. ‘It
may be easily conceived that air subjected to a boiling
temperature is so expanded as scarcely to merit the
name of air, and that it is more or less unfit for the pur-
pose of sustaining animal or vegetable life.’

Numerical data are attainable here, but they are
unnecessary. As a matter of fact, I live and flourish
for a considerable portion of each year in a medium of
less density than that which Dr. Bennett describes as
scarcely meriting the name of air. The inhabitants of
the higher Alpine chalets, with their flocks and herds,
and the grasses which support these, do the same;
while the chamois rears its kids in air rarer still.

DUST AND DISEASE. 33

Insect’ life, moreover, is sometimes exhibited with
monstrous prodigality at Alpine heights.

In a fifth series of experiments sixteen bottles were
filled with infusions. Into four of them, while cold,
ordinary unheated and unsifted air was pumped, and
in these fungi were developed. Into four other
bottles, containing a boiling infusion, ordinary air was
also pumped-——no fungi were here developed. Into
four other bottles containing an infusion which had
been boiled and permitted to cool, sifted air was pumped
—no fungi were developed. Finally, into four bottles
containing a boiling infusion sifted air was pumped—
no fungi were developed. Only, therefore, in the four
cases where the infusions were cold infusions, and the
air ordinary air, did fungi appear.

Dr. Bennett does not draw from his experiments the
conclusion to which they so obviously point. On the
contrary, he founds on them a defence of the doctrine of
spontaneous generation, and a general theory of sponta-
neous development. So strongly was he impressed with
the idea that the germs could not possibly pass through
his potash and sulphuric acid tubes, that the appear-
ance of fungi, even in a small minority of cases, where
the air had been sent through these tubes, was to him
conclusive evidence of the spontaneous origin of such
fungi. And he accounts for the absence of life in many
of his experiments by an explanation which will not
bear a moment’s criticism. But knowing, as we now do,
that organic particles may pass unscathed through
alkalies and acids, the results of Dr. Bennett are pre-
cisely what ought under the circumstances to be ex-
pected. Indeed, their harmony with the conditions
now revealed is a proof of the honesty and accuracy
with which they were executed.

The caution exercised by Pasteur both in the exe-

34 THE FLOATING-MATTER OF THE AIR.

cution of his experiments, and in the reasoning based
upon them, is perfectly evident to those who, through
the practice of severe experimental inquiry, have ren-
dered themselves competent to judge of good experi-
mental work. He found germs in the mercury used to
isolate his air. He was never sure that they did not
cling to the instruments he employed, or to his own
person. Thus when he opened his hermetically-sealed
flasks upon the Mer de Glace, he had his eye upon the
file used to detach the drawn-out necks of his bottles;
and he was careful to stand to leeward when each flask
was opened. Using these precautions, he found the
glacier air incompetent, in nineteen cases out of twenty,
to generate life ; while similar flasks, opened amid the
vegetation of the lowlands, were soon crowded with
living things. M. Pouchet repeated Pasteur’s experi-
ments in the Pyrenees, adopting the precaution of
holding his flasks above his head, and obtaining a
different result. Now great care would be needed to
render this procedure a real precaution. The luminous
beam at once shows us its possible effect. Let smoking
brown paper be placed at the open mouth of a glass
shade, so that the smoke shall ascend and fill the shade.
A beam sent through the shade forms a bright track
through the smoke. When the closed fist is placed
underneath the shade, a vertical wind of surprising
violence, considering the small elevation of temperature,
rises from the hand, displacing by comparatively dark
‘air the illuminated smoke. Unless special care were
taken such a wind would rise from M. Pouchet’s body
as he held his flasks above his head, and thus the pre-
caution of Pasteur, of not coming between the wind
and the flask, would be annulled.

Let me now direct attention to another result of
Pasteur, the cause und significance of which are at once

DUST AND DISEASE. 35

revealed by the luminous beam. He prepared twenty-
one flasks, each containing a decoction of yeast, filtered
and clear. He boiled the decoction so as to destroy
whatever germs it might contain, and while the space
above the liquid was filled with pure steam, he sealed
his flasks with a blow-pipe. He opened ten of them in
the deep, damp caves of the Paris Observatory, and
eleven of them in the courtyard of the establishment.
Of the former, one only showed signs of life subse-
quently. In nine out of the ten flasks no organisms of
any kind were developed. In all the others organisms
speedily appeared.

Now here is an experiment conducted in Paris, on
which we can throw light in London. Causing our
luminous beam to pass through a large flask filled
with the air of this room, and charged with its germs
and its dust, the beam is seen crossing the flask from
side toside. But here is another similar flask, which
cuts a clear gap out of the beam. It is filled with wn-
jiltered air, and still no trace of the beam is visible.
Why? By pure accident I stumbled on this flask in
our apparatus room, where it had remained quiet for
some time. Acting upon this obvious suggestion, I set
aside three other flasks, filled, in the first instance, with
mote-laden air. They are now optically empty. Our
former experiments proved that the life-producing
particles attach themselves to the fibres of cotton-wool.
In the present experiment the motes have been brought
by gentle air-currents, established by slight differences
of temperature within our closed vessels, into contact
with the interior surface, to which they adhere. The
air of these flasks has deposited its dust, germs and all,
and is practically free from suspended matter.

I had a chamber erected, the lower half of whichis
of wood, its upper half being enclosed by four glazed

36 THE FLOATING-MATTER OF THE AIR.

window-frames. It tapers to a truncated cone at the
top. It measures in plan 3 ft. by 2 ft. 6 in., and its
height is 5 ft. 10 in. On February 6 it was closed,
every crevice that could admit dust, or cause displace-
ment of the air, being carefully pasted over with paper.
The electric beam at first revealed the dust within the
chamber as it did in the air of the laboratory. The
chamber was examined almost daily; a perceptible
diminution of the floating matter being noticed as time
advanced. At the end of a week the chamber was
optically empty, exhibiting no trace of matter competent
to scatter the light. Such must have been the case in
the stagnant caves of the Paris Observatory. Were our
electric beam sent through the air of these caves, its
track would, doubtless, save from aqueous haze, be invi-
sible ; thus showing the indissoluble association of the
scattering of light by air and its power to generate life.

I will now turn to what seems to me a more interest-
ing application of the luminous beam than any hitherto
described. My reference to Professor Lister’s interpre-
tation of the fact, that air which has passed through
the lungs cannot produce putrefaction, is fresh in your
memories. ‘Why air, said he, ‘introduced into the
pleural cavity, through a wounded lung, should have
such wholly different effects from that entering through
a permanently open wound, penetrating from without,
was to me a complete mystery, till I heard of the germ
theory of putrefaction, when it at once occurred to me
that it was only natural that the air should be filtered
of germs by the air passages, one of whose offices is to
arrest inhaled particles of dust, and prevent them from
entering the air-cells.’

Here is a surmise which bears the stamp of genius
but which needs verification. If, for the words ‘it is
only natural’ we were authorized to write ‘it is per-

DUST AND DISEASE. 37

fectly certain,’ the demonstration would be complete.
Such demonstration is furnished by experiments with a
beam of light. One evening, towards the close of 1869,
while pouring various pure gases across the dusty track
of a luminous beam, the thought occurred to me of
using my breath instead of the gases. I then noticed,
for the first time, the extraordinary darkness produced
by the expired air, towards the end of the expiration.
Permit me to repeat the experiment in your presence.
I fill my lungs with ordinary air and breathe through a
glass tube across the beam. The condensation of the
aqueous vapour of the breath is shown by the formation
of a luminous white cloud of delicate texture. We
abolish this cloud by drying the breath previous to its
entering the beam; or, still more simply, by warming
the glass tube. The luminous track of the beam is for
atime uninterrupted by the breath, because the dust
returning from the lungs makes good, in great part, the
particles displaced. After a time, however, an obscure
disk appears in the beam, the darkness of which in-
creases, until finally, towards the end of the expiration,
the beam is, as it were, pierced by an intensely black
hole, in which no particles whatever can be discerned.
The deeper air of ihe lungs is thus proved to be abso-
lutely free from suspended matter. It is therefore in
the precise condition required by Professor Lister’s
explanation. This experiment may be repeated any
number of times with the same result. I think it must
be regarded as a crowning piece of evidence both of the
correctness of Professor Lister’s views and of the impo-
tence, as regards vital development, of optically pure air.!

1 Dr. Burdon Sanderson draws attention to the important
observation of Brauell, which shows that the contagium of a preg-
nant animal, suffering from splenic fever, is not found in the blood
of the foetus ; the placental apparatus acting as a filter, and holding
back the infective particles.

38 THE FLOATING-MATTER OF THE AIR..

The foregoing essay, as far as it relates to the
theory which ascribes epidemic disease to the develop-
ment of low parasitic life within the human life, was
embodied in a discourse delivered before the Royal
Institution in January 1870. In June 1871, after a
brief reference to the polarization of light by cloudy
matter, I ventured to recur to the subject in these
terms: What is the practical use of these curiosities ?
If we exclude the interest attached to the observation of
new facts, and the enhancement of that interest through
the knowledge that facts often become the exponents of
laws, these curiosities are in themselves worth little.
They will not enable us to add to our stock of food, or
drink, or clothes, or jewellery. But though thus shorn
of all usefulness in themselves, they may, by carrying
thought into places which it would not otherwise have
entered, become the antecedents of practical conse-
quences. In looking, for example, at our illuminated
dust, we may ask ourselves what it is. How does it
act, not upon a beam of light, but upon our own bodies ?
The question then assumes a practical character. We
find on examination that this dust is mainly organic
matter—in part living, in partdead. There are among
it particles of ground straw, torn rays, smoke, the pollen
of flowers, the spores of fungi, and the germs of other
things. But what have they to do with the animal
economy? Let me give you an illustration to which
my attention has been lately drawn by Mr. George
Henry Lewes, who writes to me thus:

‘I wish to direct your attention to the experiments
of Von Recklingshausen, should you happen not to know
them. They are striking confirmations of what you say
of dust and disease. Last spring, when I was at his
laboratory in Wurzburg, I examined with him blood
that had been three weeks, a month, and five weeks, out

DUST AND DISEASE, 39

of the body, preserved in little porcelain cups under
glass shades. This blood was living and growing. Not
only were the Amcba-like movements of the white
corpuscles present, but there were abundant evidences of
the growth and development of the corpuscles. I also
saw a frog’s heart still pulsating which had been removed
from the body (I forget how many days, but certainly
more than a week). There were other examples of the
same persistent vitality, or absence of putrefaction. Von
Recklingshausen did not attribute this to the absence of
germs—germs were not mentioned by him; but when
I asked him how he represented the thing to himself,
he said the whole mystery of his operation consisted in
keeping the blood free from dirt. The instruments
employed were raised to a red heat just before use; the
thread was silver thread and was similarly treated; and
the porcelain cups, though not kept free from air, were
kept free from currents. He said he often had failures,
and these he attributed to particles of dust having escaped
his precautions.’

Professor Lister, who has founded upon the removal
or destruction of this ‘dirt’ momentous improvements
in surgery, tells us the effect of its introduction into
the blood of wounds. The blood putrefies and he-
comes fetid; and when you examine more closely what
putrefaction means, you find the putrefying substance
swarming with infusorial life, the germs of which have
been derived from the atmospheric dust.

We are now assuredly in the midst of practical mat-
ters; and with your permission I will refer once more to
a question which has recently occupied a good deal of
public attention. As regards the lowest forms of life,
the world is divided, and has for a long time been
divided, into two parties, the one affirming that we
have only to submit absolutely dead matter to certain

40 THE FLOATING-MATTER OF THE AIR.

physical conditions, to evolve from it living things; the

other (without wishing to set bounds to the power of
matter) affirming that, in our duy, life has never been

found to arise independently of pre-existing life. I-
belong to the party which claims life as a derivative of
life. The question has two factors—the evidence, and

the mind that judges of the evidence; and it may be

purely a mental set or bias on my part that causes me,

throughout this long discussion, to see, on the one side,

dubious facts and defective logic, and on the other side

firm reasoning and a knowledge of what rigid experi-

mental inquiry demands. But, judged of practically,

what, again, has the question of Spontaneous Genera-

tion to do with us? Let us see. There are numerous

diseases of men and animals that are demonstrably the

products of parasitic life, and such diseases may take

the most terrible epidemic forms, as in the case of the

silkworms of France, referred to at an earlier part of this

essay. Now it is in the highest degree important to

know whether the parasites in question are spontaneously

developed, or whether they have been wafted from with-

out to those afflicted with the disease. The means of

prevention, if not of cure, would be widely different

in the two cases.

But this is not all. Besides these universally ad-
“mitted cases, there is the broad theory, now broached
and daily growing in strength and clearness—daily, in-
deed, gaining more and more of assent from the most
successful workers and profound thinkers of the medical
profession itself—the theory, namely, that contagious
disease, generally, is of this parasitic character. Had I
any cause to regret having introduced this theory to
your notice more than a year ago, that regret should
now be expressed. I would certainly renounce in your
presence whatever leaning towards the germ theory

DUST AND DISEASE, 4l

my words might then have betrayed. But since the
time referred to nothing has occurred to shake my
conviction of the truth of the theory. Let me briefly
state the grounds on which its supporters rely. From
their respective viruses you may plant typhoid fever,
scarlatina, or small-pox. What is the crop that arises
from this husbandry? As surely as a thistle rises from
a thistle seed, as surely as the fig comes from the fig,
the grape from the grape, the thorn from the thorn,
so surely does the typhoid virus increase and multiply
into typhoid fever, the scarlatina virus into scarlatina,
the small-pox virus into small-pox. What is the con-
clusion that suggests itself here? It is this: That
the thing which we vaguely call a virus is to all
intents and purposes a seed. Excluding the notion
of vitality, in the whole range of chemical science
you cannot point to an action which illustrates this
perfect parallelism with the phenomena of life—this
demonstrated power of self-multiplication and repro-
duction. The germ theory alone accounts for the
phenomena.

In cases of epidemic disease, it is not on bad air or
foul drains that the attention of the physician of the
future will primarily be fixed, but upon disease germs,
which no bad air or foul drains can create, but which
may be pushed by foul air into virulent energy of repro-
duction. You may think I am treading on dangerous
ground, that I am putting forth views that may interfere
with salutary practice. No such thing. If you wish to
learn the impotence of medical practice in dealing with
contagious diseases, you have only to refer to the Har-
veian oration for 1871, by Sir William Gull. Such dis.
eases defy the physician. They must run their course,
and the utmost that can be done for them is careful
nursing. And this, though I do not specially insist

42 THE FLOATING-MATTER OF THE AIR.

upon it, would favour the idea of their vital origin. For
if the seeds of contagious disease be themselves living
things, it may be difficult to destroy either them or their
progeny, without involving their living habitat in the
same destruction.

It has been said, and it is sure to be repeated, that
I am quitting my own métier, in speaking of these
things. Not so. Iam dealing with a question on which
minds accustomed to weigh the value of experimental
evidence are alone competent to decide, and regarding
which, in its present condition, minds so trained are as
capable of forming an opinion as regarding the pheno-
mena of magnetism or radiant heat. ‘ The germ theory
of disease,’ it has been said, * appertains to the biologist
and the physician.’ Where, I would ask in reply, is the
biologist or physician, whose researches, in connection
with this subject, could for one instant be compared to
those of the chemist Pasteur? It is not the philosophic
members of the medical profession who are dull to the
reception of truth not originated within the pale of the
profession itself. I cannot better conclude this portion
of my story than by reading to you an extract froma
letter addressed to me some time ago by Dr. William
Budd, of Clifton, to whose insight and energy the town
of Bristol owes so much in the way of sanitary improve-
ment.

‘As to the germ theory itself, writes Dr. Budd,
‘that is a matter on which I have long since made up
my mind. From the day when I first began to think of
these subjects I have never had a doubt that the specific
cause of contagious fevers must be living organisms.

‘It is impossible, in fact, to make any statement
bearing upon the essence or distinctive characters of
these fevers, without using terms which are of all others
the most distinctive of life Take up the writings of

DUST AND DISEASE. 43

the most violent opponent of the germ theory, and, ten
to one, you will find them full of such terms as “ pro-
pagation,” “ self- propagation,” “ reproduction,” “ self-
multiplication,” and soon. Try as he may—if he has
anything to say of those diseases which is characteristic
of them—he eannot evade the use of these terms, or the
exact equivalents to them. While perfectly applicable
to living things, these terms express qualities which
are not only inapplicable to common chemical agents,
but, as far as I can see, actually inconceivable of
them.’

JPTICAL DEPORTMENT OF THE ATMOSPHERE

IN RELATION TO

PUTREFACTION AND INFECTION.’

a

iT;
§ 1. Introduction.

AN inquiry into the decomposition of vapours by light,
begun in 1868 and continued in 1869,? in which it was
necessary to employ optically pure air, led me to experi-
ment on the floating matter of the atmosphere. A
brief section of a paper published in the Philosophical
Transactions for 18705 is devoted to this subject.

I at that time found that the air of London rooms,
which is always thick with motes, and also with matter
too fine to be described as motes, after it had been
filtered by passing it through densely packed cotton-
wool, or calcined by passing it through a red-hot pla-
tinum-tube containing a bundle of red-hot platinum
wires, or by carefully leading it over the top of a spirit-
lamp flame, showed, when examined by a concentrated
luminous beam, no trace of mechanically suspended
matter. The particular portion of space occupied by
such a beam was not to be distinguished from adjacent,
space.

The purely gaseous portion of our atmosphere was
thus shown to be incompetent to scatter light.

1 Philosophical Transactions, Part L, 1876.
2 Proc. Roy. Soe. vol. xvii. 3 Vol. clx. p. 337,

16 THE FLOATING-MATTER OF THE AIR,

I subsequently found that, to render the air thus
optically pure, it, was only necessary to leave it to itself
for a sufficient time in a small closed chamber, or in a
suitably closed vessel. The floating matter gradually
attached itself to the top and sides, or sank to the
bottom, leaving behind it air possessing no scattering
power. Sent through such air, the most concentrated
beam failed to render its track visible.

I mention ‘top’ and ‘sides,’ as well as ‘ bottom,’
because gravity is not the only agent, perbaps not even
the principal agent, concerned in the removal of the
floating matter. It is practically impossible to sur-
round a closed vessel by an absolutely uniform tempera-
ture; and where differences of temperature, however
small, exist, air-currents will be established. By such
gentle currents the floating particles are gradually
brought into contact with all the surrounding surfaces.
To these they adhere, and, no new supply being ad-
mitted, the suspended matter finally disappears from
the air altogether.

The striking parallelism of these results with those
obtained in the excellent researches of Schwann,}
Schroeder and Dusch,? Schroeder himself,? and Pasteur‘
in regard to the question of ‘spontaneous generation,’
caused me to conclude that the power of scattering
light, and the power of producing life, by atmospheric
air would be found to go hand in hand.

This conclusion was strengthened by an experiment
easily made and of high significance in relation to this
question. It had been pointed out by Professor Lister ®

1 Poge. Ann. 1837, vol. xli. p. 184.

2 Ann. der Pharmacie, vol. lxxxix. p. 232.

3 Ibid. vol. cix. p. 35.

4 Ann. de Chim. ct de Phys. 3rd series, vol. Ixiv. p. 83.

* Introductory Lecture before the University of Edinburgh.

PUTREFACTION AND INFECTION. 47

that air which has passed through the lungs is known
to have lost its power of causing putrefaction. Such air
may mix freely with the blood of an internal wound
without risk of mischief; and that truly great scientific
surgeon had the penetration to ascribe this immunity
from danger to the filtering power of the lungs. Prior
to my becoming acquainted with this hypothesis in
1869, I had demonstrated its accuracy in the following
manner.!

Condensing in a dark room, and in dusty air, a

Fig. 1,

powerful beam of light, and breathing through a glass
tube (the tube actually employed was a lamp-glass, ren-
dered warm in a flame to prevent condensation of the
breath) across the focus, a diminution of the scattered
light was first observed. But towards the end of the
expiration the white track of the beam was broken by a
perfectly black gap, the blackness being due to the
total absence from the expired air of any matter com-
petent to scatter light. The experimental arrangement
is represented in fig. 1, where g represents the heated

1 Proc. Roy. Inst. vol. vi. p. 9.

48 THE FLOATING-MATTER OF THE AIR.

lamp-glass, and b the black gap cut out of the beam
at its brightest point. The deeper portions of the
lungs were thus proved to be filled with optically
pure air, which, as such, had no power to generate the
organisms proved by Schwann to be essential to the
process of putrefaction.!

It seemed that this simple method of examination
could not fail to be of use to workers in this field. They
had hitherto proceeded less by sight than by insight,
being in general unable to observe the physical character
of the medium in which their experiments were con-
ducted. But the method has not been much turned to
account ; and this year (1875) I thought it worth while
to devote some time myself to the more complete
demonstration of its utility.

T also wished to free my mind, and if possible the
minds of others, from the uncertainty and confusion
which now beset the doctrine of ‘spontaneous genera-
tion.’ Pasteur has pronounced it ‘a chimera,’ and ex-
pressed the undoubting conviction that this being’so it is
possible to remove all parasitic diseases from the earth.
To the medical profession, therefore, and through them
to humanity at large, this question, if the illustrious
French philosopher be correct, is one of the last import-
ance. But Pasteur’s labours, which have so long been
considered models by most of us, have been subjected to

1 «No putrefaction,’ says Cohn, ‘can occur in a nitrogenous sub-
stance if it be kept free from the entrance of new Bacteria after
those which it may contain have been destroyed. Putrefaction
begins as soon as Bacteria, even in the smallest numbers, are acci-
dentally or purposely introduced. It progresses in direct proportion
to the multiplication of the Bacteria; it is retarded when the Bac-
teria (for example, by a low temperature) develop a small amount
of vitality, and is brought to an end by all influences which either
stop the development of the Bacteria, or kill them, All bacteri-
cidal media are therefore antiseptic and disinfecting.’ —Beitrige
tur Biologie der Pflanzen, zweites Heft, 1872, p. 203.

PUTREFACTION AND INFECTION. 49

rough handling of late. His reasoning has been criti-
cised, and experiments counter to his have been adduced
in such number and variety, and with such an appear-
ance of circumstantial accuracy, as to render the evi-
dence against him overwhelming to many minds. This,
I have reason to know, has been the effect wrought, not
only upon persons untrained in science, but also upon
biologists of eminence both in this country and America.
The state of medical opinion in England is correctly
described in a recent number of the ‘ British Medical
Journal,’ where, in answer to the question, ‘In what way
is contagium generated and communicated?’ we have
the reply that, notwithstanding ‘an almost incalculable
amount of patient labour, the actual results obtained,
especially as regards the manner of generation of con-
tagium, have been most disappointing. Observers are
even yet at variance whether these minute particles,
whose discovery we have just noticed, and other disease-
germs, are always produced from like bodies previously
existing, or whether they do not, under certain favour-
able conditions, spring into existence de novo.

‘With a view to the possible diminution of the un-
certainty thus described, I beg without further preface
to submit to the Royal Society, and especially to those
who study the etiology of disease, the following descrip-
tion of the mode of procedure followed in this inquiry,
and of the results to which it has led.

§ 2. Method of Experiment.

A chamber, or case, was constructed, with a glass
front, its top, bottom, back, and sides being of wood.
At the back is a little door which opens and closes on
hinges, while into the slides are inserted two panes of
glass, facing each other. The top is perforated in the

50 THE FLOATING-MATTER OF THE AIR.

middle by a hole 2 inches in diameter, closed air-tight
by a sheet of india-rubber. This sheet is pierced in the
middle by a pin, and through the pin-hole is passed the
shank of a long pipette ending above in a small funnel.

Fic, 2.

A circular tin collar, 2 inches in diameter and 13 inch
deep, surrounds the pipette, the space between both
being packed with cotton-wool moistened by glycerine.
Thus the pipette, in moving up and down, is not only
firmly clasped by the india-rubber, but it also passes

PUTREFACTION AND INFECTION, 51

through a stuffing-box of sticky cotton-wool. The width
of the aperture closed by the india-rubber secures the
free lateral play of the lower end of the pipette. Into
two other smaller apertures in the top of the chamber
are inserted, air-tight, the open ends of two narrow
tubes, intended to connect the interior space with the
atmosphere. The tubes are bent several times up and
down, so as to intercept and retain the particles carried
by such feeble currents as changes of temperature might
cause to set in between the outer and the inner air.

» The bottom of the box is pierced with two rows of
holes, six in a row, in which are fixed, air-tight, twelve
test-tubes, intended to contain the liquid to be exposed
to the action of the moteless air.

The arrangement is represented in fig. 2, where ww
are the side windows through which the searching beam
passes from the lamp / across the case c; p is the pi-
pette, and a, b, are the bent tubes connecting the inner
and outer air. The test-tubes passing through the bot-
tom of the case are seen below.

On the 10th of Septemher, 1875, this case was closed.
The passage of a concentrated beam across it through
its two side windows then showed the air within it to be
laden with floating matter. On the 13th it was again
examined. Before the beam entered, and after it quit-
ted the case, its track was vivid in the air, but within
the case it vanished. Three days of quiet had sufficed
to cause all the floating matter to be deposited on the
interior surfaces, where it was retained by a coating of
glycerine, with which these surfaces had been purposely
varnished.

§ 3. Deportment of Urine.

The pipette being dipped into the tubes, fresh urine
was poured into eight of them in succession on the 13th

52 THE FLOATING-MATTER OF THE AIR.

of September. Each tube was about half-filled with
the liquid. The tubes were then immersed in a bath of
brine, raised to ebullition, and permitted to boil for five
minutes. Aqueous vapour rose from the liquid into the
chamber, where it was for the most part condensed, the
uncondensed portion escaping, at a low temperature,
through the bent tubes at the top. Before the brine was
taken away little stoppers of cotton-wool were inserted
in the bent tubes, lest the re-entrance of the air into the
cooling-chamber should at first be forcible enough to
carry motes along with it. As soon, however, as the
outside temperature was assumed by the air within the
case the cotton-wool stoppers were removed.

The front and back of this chamber were squares of
14 inches the side, the depth of the chamber being 8°5
inches. It contained, therefore, 1666 cubic inches of
air, which had unimpeded access to the liquid in the
tubes. No stoppers were employed. The air was un-
affected by calcination, or even by filtering. Neither
cotton-wool nor hermetic sealing was resorted to. Self-
subsidence was the only means employed to rid the
*untortured ’ air of its floating matter.

A second series of eight tubes were filled at the same
time with the same liquid, and subjected to the same
boiling process. The only difference between the two
series was, that these latter tubes were placed in a stand
beside the case containing the former ones and exposed
to the common air of the laboratory.

For the sake of distinction I will call the tubes
opening into the case the protected tubes, and those
openiug into the common air the exposed tubes.

On the 17th of September all the protected tubes
were bright and clear, while all the exposed tubes were
distinctly turbid. Specks of mould, moreover, were in
every case seen on the surface of the exposed liquid.

PUTREFACTION AND INFECTION. 53

These waxed daily larger, and finally formed a thick
layer on the top of every column. The liquid, mean-
while, changed from a pale sherry to a reddish-brown
colour. To me the experiment was impressive in the
highest degree.

On the 27th of September I provided myself with a
microscope having a magnifying power of 1200 diame-
ters. Under its scrutiny the turbidity of the liquid
immediately resolved itself into swarms of Bacteria in
active motion. Cohn correctly explains the turbidity.
The index of refraction of the Bacterium being slightly
different from that of the surrounding medium, a scat-
tering of light is the consequence. This scattering,
however, and the opalescence it produces, are practically
independent of the motions of the Bacteria.

Since the date here referred to the exposed liquid has
been frequently examined, both with the eye and with
the microscope. To the former it is thickly turbid, to
the latter it is swarming with life. Its smell is putrid.
All this time the protected tubes exhibit a liquid per-
fectly unchanged in appearance. For four months it
has remained as transparent and of as rich a colour as
the brightest Amontillado sherry.

On the 1st of October another experiment similar in
principle to that just described was begun. Fresh urine
was employed, and a much smaller case. The capacity
of the latter was 451 cubic inches ; and three test-tubes,
instead of twelve, were passed air-tight through its bot-
tom. Like those in the larger chamber they were filled
by a pipette, and boiled for five minutes in a bath of
brine. Beside them were placed three other tubes con-
taining the same liquid treated in exactly the same way,
but exposed to the common air. On the Sth all the
exposed tubes were turbid, and found by microscopic
examination to be swarming with Bacteria. The colour

54 THE FLOATING-MATTER OF THE AIR.

of the exposed liquid had changed from a pale sherry
colour to a brown orange. On the 25th the tubes were
again examined, and found full of Bacteria. Two
months subsequent to this latter date the infusion,
diminished by evaporation, was found well charged
with Bacterial life.

While this process of putrefaction was goung on
outside, the tubes opening into the moteless air of the
case remained perfectly clear and void of life.

The large chamber represented in fig. 2, and above
described, was the first operated on, and the liquid is
shown by the draughtsman as filling only a small portion
of the test-tubes. This smallness of volume is in part due
to evaporation. Test-tubes 1:2 inch wide and 9 inches
long were, in all subsequent experiments, nearly filled
with the infusions. Strong in the first instance, these
were sometimes kept until slow evaporation through the
bent tubes at the top of the case had reduced them to
one third or one fourth of their original volume. Each
experiment, therefore, was, in reality, a series of experi-
ments, extending over months, on infusions of different
strengths, the concluding ones of the series attaining a
very high degree of concentration.

§ 4. Mutton-Infusion.

A new case was constructed to contain six test-tubes.
It, like the others, had a front of glass, side windows,
anda back door. Its capacity was 857 cubic inches. It
was sealed up on the 21st of September, and found free
from floating matter on the 24th. The lean of mutton,
cut into small pieces, was digested, or soaked, for four
hours in water of a temperature of 120° F.!' The infu-

' The temperature recommended by the supporters of sponta-
neous generation.

PUTREFACTION AND INFECTION, 55

sion was then carefully filtered, and introduced into the
six test-tubes by a pipette which was never removed
from the case.

The mutton-juice was of a fine ruby colour; but on
boiling, its albumen was precipitated, subsequently sank,
and carried the colouring-matter with it. The superna-
tant liquid was perfectly clear. The frothing was con-
siderable when the boiling began. Beside this new case
was placed a stand containing six test-tubes filled with
the same infusion, but exposed to the common air.

On the 27th all the outside flasks were perceptibly
turbid; on the 28th they were found well filled with
Bacteria, which on the 30th had increased to astonishing
swarms. On the 15th of October the tubes were again
examined, and found charged with undiminished life.
They remained thus ‘ putrid’ until the 14th of Novem-
ber.

During the whole of this time the infusion in con-
tact with the moteless air of the chamber remained as
clear as distilled water, and entirely free from life.

On the 14th of November I infected one of the clear
tubes by introducing into it through the pipette a few
drops of mutton-infusion which had been prepared and
exposed upon the 12th of November, and which two
days had sufficed to render turbid. On the 15th the
inoculated infusion showed signs of turbidity, and on
the 16th putrefaction had actively set in, the liquid
heing thickly muddy and full of life.

With a moteless chamber and three tubes, experi-
ments were subsequently made on a second infusion of
mutton. In this case, however, the infusion was boiled,
its albumen was precipitated, and removed by filtration
prior to its introduction into the chamber. The pellucid
liquid was introduced on the Ist of October, boiled for

4

56 THE FLOATING-MATTER OF THE AIR.

five minutes in the brine-bath, and abandoned to the air
ot the case. A series of exposed tubes containing the
same infusion, similarly treated, was placed beside the
protected ones. On the 4th all the outside tubes were
muddy and swarming with Bacteria. Schroeder and
Cohn have shown that different colours are produced by
different kinds of Bacteria. In the three exposed tubes
here referred to a yellow-green pigment was developed.
More than three months after its preparation, the
infusion, considerably diminished by evaporation, re-
mained in all the protected tubes as clear as at first.

§ 5. Beef-Infusion.

A beef-steak, after having its fat removed, was cut
up into small pieces, and digested for three hours at a
temperature of 120° F. The liquid was then poured
off, boiled, and filtered. It was as clear and colourless
as pure water. On the 4th of October it was introduced
into three tubes protected by a chamber of 451 cubic
inches capacity. It was boiled for five minutes in a
brine-bath. Three exposed tubes, containing the same
infusion, were placed beside the protected ones. On the
5th the exposed tubes showed signs of haziness, on the
6th they were turbid, of a green colour, and filled with
Bacteria. They have maintained for months their mud-
diness, colour, and swarming life.

While the exposed beef-infusion putrefied in this
way, all the protected infusions remained perfectly
sweet and clear.

§ 6. Haddock-Infusion.

The haddock was cut up and digested on the 24th
of September; it was afterwards introduced into six
tubes, protected bya chamber. On boiling, its albumen,

PUTREFACTION AND INFECTION. 57

like that of the mutton first referred to, coagulated and
sank to the bottom, leaving a perfectly clear liquid
overhead. Six exposed tubes filled with the same infu-
sion were placed beside the six protected ones.

On the 27th the exposed tubes were all turbid and
swarming with Bacteria. On the 29th one of the
tubes showed a fine green colour; three other tubes
showed the same colour afterwards. The vivacity of
the organisms was extraordinary, and their shapes
various. They darted rapidly to and fro across the
field, clashing, recoiling, and pirouetting—rendering it,
indeed, difficult to believe in the vegetable nature
which the best microscopists assign to them.

For nearly three weeks the protected tubes remained
perfectly clear. To gain room, the case was subse-
quently shifted, and soon afterwards one of the six
tubes became turbid with organisms, the germs of which
had obviously been shaken into the tube.

For more than a month this single infected flask
remained in company with the five healthy ones. The
air containing the gaseous products of putrefaction had
free access to the whole of them, but there was no spread
of the infection. As long as the organisms themselves
were kept out of the flasks, the ‘sewer-gas’ developed
by the putrefaction had no infective power. On the
14th of November I infected two of the five perfectly
pellucid tubes with haddock-infusion which, after boil-
ing, had been exposed for two days to the air. On the
15th the two tubes had obviously yielded to the infec-
tion. On the 16th disease, if I may use the term, had
completely taken possession of them. Into one of them
only one or two drops of the turbid infusion had fallen,
while ten times this amount was introduced into the
other. Nevertheless on the 16th both appeared equally
turbid. The infection acted exactly like the virus of

58 THE FLOATING-MATTER OF THE AIR.

smallpox, a small quantity of which will in the long
run produce the same effect as a large one.

§ 7. Turnip-Infusion.

Turnip-juice had a special interest for me in con-
sequence of the important part it plays in the experi-
ments of heterogenists. I turned to it with the anxious
desire to learn whether the statements made concerning
it were correct.

The conditions laid down as to the strength of the
infusion, the temperature to be maintained during the
process of digestion, and the time it was to be maintained!
were scrupulously adhered to. Thus the turnip was cut
into thin slices, and digested for four hours in a beaker
of water immersed in a water-bath kept at a tempera-
ture close to 120° Fahr. The infusion was then carefully
filtered, introduced through a pipette into its case, and
boiled there for five minutes. Six protected test-tubes
were charged with the infusion on the 24th of Sep-
tember, while six other tubes were placed on a stand
outside, and exposed to the common aur of the labora-
tory.

On the 27th the exposed tubes were distinctly
turbid, and on microscopic examination were found
peopled with Bacteria. The protected tubes, on the
contrary, were perfectly clear. A little distilled water
had been added to one of the outer tubes. The germi-
nal matter, whatever it may be, must have been
copious in the water; for the tube to which it was
added far exceeded the other two in the rapidity of lite-
development. On the 30th this tube contained Bacterict
in swarms, of small size, but of astonishing activity.
The other tubes also were fairly charged with organisms,

' Bastian, ‘Beginnings of Life,’ vol. i. p. 357, note.

PUTREFACTION AND INFECTION. 59

larger and more languid, but not at all so numerous as
in the watered tube. On the 5th of October some of
the exposed tubes began to clear; as if the Bucteria
had died through lack of nutriment, and were falling
as a thick sediment to the bottom.

During these changes the protected tubes were
visibly unaltered, the liquid within every one of them
remaining as clear as it had been on the day of its
introduction.

In this instance I was specially anxious to verify the
result by repetition. Two other cases were therefore
fitted up to contain three tubes each, and instead of a
door a movable panel was placed at the back. After
two or three days’ rest both cases were found free from
floating matter, and on the Ist of October the turnip-
infusion was introduced, and boiled for five minutes in
a bath of brine.

In the former experiment the temperature of di-
gestion was maintained by keeping the beaker contain-
ing the turnip in a bath of warm water. In the present
instance the turnip was sliced in a dish and placed
before a fire. An occult but efficient power like that
already ascribed to the actinic rays', might, I thought,
be ascribed to radiant heat, and I therefore copied to
the letter the mode of digesting pursued by modern
heterogenists.

Adjacent to the closed cases was placed a series of
three exposed tubes, containing a liquid prepared in
precisely the same way. On the 4th of October the
exposed tubes were all turbid, and swarmed with Bacteria.
In two of the tubes they were distinctly more numerous
and lively than in the third. Such differences between
sensibly conterminous tubes, containing the same infu-
sion, are frequent. On the 9th, moreover, the two most

1 «Nature,’ vol. iii. p. 247.

60 THE FLOATING-MATTER OF THE AIR.

actively charged tubes were in part crowned by beautiful
tufts of Penicillium glaucum.! This expanded gra-
dually until it covered the entire surface with a thick
tough layer, which must have seriously intercepted the
oxygen necessary to the Bacterial life. The Bacteria
lost their translatory power, fell to the bottom, and left
the liquid between them and the superficial layer clear.
_ Another difference, pointing to differences in the
unseen life of the air, was shown by these tubes. The
turbidity of the two mould-crowned ones was colourless,
exhibiting a grey hue. The third tube, the middle one
of the three, contained a bright yellow-green pigment,
and on its surface no trace of mould was to be seen.
It never cleared, but maintained its turbidity and its
Bacterial life for months after the other tubes had ceased
to show either. It cannot be doubted that the mould-
spores had fallen into this tube also, but in the fight for
existence the colour-producing Bacteria had the upper
hand. Six other tubes, similarly exposed, showed the
grey muddiness: all of them became thickly covered
with mould, under which the Bacteria died or passed
into a quiescent state, fell to the bottom, and left the
liquid clear.
Up to the 13th of October the purity of the six
protected tubes remained unimpaired.

Here a complementary experiment was made. It
remained to be proved that those long-dormant clear
infusions had undergone no change which interfered
with their ability to develop and maintain life. On the
13th of October, therefore, the small panel was removed
from the back of one of the cases, and with three new
pipettes specimens were taken from the three tubes
within it. The closest search revealed no living thing.

1} Ordinary mould.

PUTREFACIION AND INFECTION. 61

The air of the laboratory being permitted to diffuse
freely into the case, on the day after the removal of the
panel the test-beam showed the case to be charged with
floating: matter.

The access of this matter was the only condition
necessary to the production of life; for on the 17th all
the tubes were muddy and swarming with Bacteria.

A similar experiment, subsequently made, revealed
some of the snares and pitfalls which await an in-
cautious worker. The chamber already referred to
as containing six tubes, filled with turnip-juice, pre-
served the infusion clear for a month. On the 21st
of October the back door of the chamber was opened,
and specimens of the clear infusion were taken out
for examination by the microscope. The first tube
examined showed no signs of life. This result was
expected. Picking up another pipette, I took a
sample from the second tube. Here, to my astonish-
ment, the exhibition of life was monstrously copious.
There were numerous globular organisms, which re-
volved, rotated, and quivered in the most extraor-
dinary manner. There were also numbers of lively
Bacteria darting to and fro. An experimenter who
ponders his work and reaches his conclusions slowly,
cannot immediately relinquish them: and in the pre-
sent instance some time was required to convince me
that no mistake had been made. I could find none,
and was prepared to accept the conclusion that in the
boiled infusion, despite its clearness, life had appeared.

But why, in the protected turnip-infusion, which
had been examined on the 13th of October, could no
trace of life befound? In this case perfect transparency
was accompanied by an utter absence of life. The
selfsame action upon light that enabled the Bacteria
to show themselves in the microscope must, one would

62 THE FLOATING-MATTER OF THE AIR.

think, infallibly produce turbidity. Why, moreover,
should life be absent from the first member of the
present group of tubes? I searched this again, and
found in it scanty but certain signs of life. This
augmented my perplexity. A third tube also showed
traces of life. I reverted to the second tube, where
life had been so copious, and found that in it the
organisms had become as scanty asin the others. I
confined myself for a time to the three tubes of the first
row of the six, going over them again and again;
sometimes finding a Bacterium here and there, but
sometimes finding nothing. The first extraordinary
exhibition of life it was found impossible to restore.
Doubtful of my skill as a microscopist, I took specimens
from the three tubes and sent them to Prof. Huxley,
with a request that he would be good enough to examine
them.

On the 22nd the search was extended to the whole
of the tubes. Early in the day lively Bacteria were
found in one of them; later on, not one of the six
yielded to my closest scrutiny any trace of life. On
the evening of the 22nd a note was received from Prof.
Huxley stating that a careful examination of the speci-
mens sent to him revealed no living thing.

Pipettes had been employed to remove the infusion
from the test-tubes. They were short pieces of narrow
glass tubing, drawn out to a point, with a few inches of
india-rubber tubing attached to them. This was found
convenient for bending so as to reach the bottom of the
test-tubes. Suspicion fell upon this india-rubber. It
was washed, the washing-water was examined, but no
life was found. Distilled water had been used to cleanse
the pipettes, and on the morning of the 23rd I entered
the laboratory intending to examine it. Before dip-
ping a pipette into the water I inspected its point.

PUTREFACTION AND INFECTION. 63

The tiniest drop had remained in it by capillary attrac-
tion from the preceding day. This was blown on toa
slide, covered, and placed under the microscope. An
astonishing exhibition of life was my reward. Thus on
the scent, I looked through my pipettes, and found two
more with the smallest residual drops at the ends: both
of them yielded a field rampant with life. The Bacteria
darted in straight lines to and fro, bending right and
left along the line of motion, wriggling, rotating longi-
tudinally, and spinning round a vertical transverse
axis. Monads also galloped and quivered through the
field. From one of these tiny specks of liquid was
obtained an exhibition of life not to be distinguished
from that which had astonished me on the 21st.

Obviously the phenomenon then observed was due
to the employment of an unclean pipette. Equally
obvious is it that in inquiries of this nature the experi-
menter is beset with danger, the grossest errors being
possible when there is the least lack of care.

The chamber here operated on had been opened
with a view to testing the capacity of the infusions
within it to develop and maintain life. For four weeks
they had remained perfectly clear. Two days after
the door was opened and the common laboratory air
admitted all six tubes were turbid, and swarming with
Bacteria. Some of them were very long, and their wrig-
gling and darting hither and thither very impressive.

The same chamber was again thoroughly cleaned,
sealed, and permitted to remain quiet until the floating
matter had subsided. On the 17th of November a
fresh infusion of turnip was introduced into it through
the pipette, boiled in an oil-bath, and again abandoned
to the air of the case.

After several months the infusion in every tube of
the siz remained as clear as it was on the day of its
introduction.

64 THE FLOATING-MATTER OF THE AIR.

Six other tubes charged with the same infusion,
boiled in the same way, became turbid in a few days,
and subsequently covered with thick layers of Penicii-
lium.

§ 8. Hay-Infusion.

This infusion has been credited with a power of
spontaneous generation similar to that ascribed to
turnip-juice. The hay being chopped into short lengths
was digested for four hours in water kept at a tempera-
ture of 120° Fahr. On the 24th of September the
filtered infusion was introduced into its chamber, and
boiled there for five minutes. Six tubes were charged
with the protected liquid, while six other tubes, filled
with the same infusion, were placed on a stand outside
the case.

On the 27th the inside flasks were clear, the outside
ones faintly turbid. On the 28th spots of mould ap-
peared upon all the exposed surfaces. The infusion in
one of the outside tubes had been diluted with distilled
water, and in it the development of life was far more
rapid than in the five others; all of them, however, on
the 28th contained Bacteria.

On the 29th I noticed a larger organism than the
Bacteria moving rapidly to and fro across the field, the
drop containing it being taken from the dilute infusion.
Several of these monads weré seen upon the 30th gambol-
ling among the smaller Bacteria, appearing bright or”
dark as they sank or rose in the liquid, a film of which,
large as they looked, was to them an ocean. Swarms of
Bacteria were seen on the 2nd of October, their transla-
tory motions being so rapid and varied, and so apparently
guided by a purpose, as to render it difficult to believe
that they could be anything else than animals. On the
15th there was a marvellous exhibition of the larger

PUTREFACTION AND INFECTION. 65

Infusoria, which appeared to have driven the Bucteria
from their habitat, as few of the latter were to be seen.
My inability to find the larger creatures a second time
in such numbers perplexed me, causing me to conclude
that I had accidentally alighted upon a colony of them-
My experience with the unclean pipettes already de-
scribed, pointed, however, to another source.

While three days sufficed to break down their purity,
and to fill the six exposed tubes with Bacterial life, the
six protected ones remained for more than three months
as clear and healthy as they were on the day the infu-
sion was poured into them. Neither a trace of mould
upon the surface of any one of them, nor a trace of tur-
bidity in its mass, was to be seen.

Into another chamber containing three test-tubes a
very strong infusion of hay was introduced on the Ist of
October. It was boiled for five minutes, and then aban-
doned to the air of the case. Three other tubes exposed
to the laboratory air were placed on a stand beside the
case. The colour of the infusion was very deep, but it
was quite transparent. One of the outer tubes was
diluted with distilled water. On the 3rd the infusion
in this tube was turbid, the other exposed ones remain-
ing clear. The unseen germinal matter had in some
way or other invaded the distilled water, and made it
infective. The dilute infusion contained multitudes of
Bacteria, many motionless, but many moving rapidly
about. On the 4th of October all the tubes swarmed
with Bacteria. They continued muddy till the middle
of November, when they were employed for experi-
ments on infection.

Throughout the whole of this time the protected
tubes remained unchanged.

With regard to infection, it may be stated here that

66 THE FLOATING-MATTER OF THE AIR.

the merest speck of a vegetable infusion containing
Bacteria infects all animal infusions, and vice versa.
The bursting of a bubble infects an infusion reached by
the spray. It is the envelope, and not the gas of the
bubble, which produces this result.

Other experiments on hay-infusions, acid, neutral,
and alkaline, placed in contact with air purified in

various ways, yielded in 1875 the same negative re-
sult.

§ 9. Infusion of Sole.

The fish was cut up and digested for three hours in
water kept at 120° Fahr. On the 17th of November it
was introduced into a case containing three test-tubes,
and boiled there for five minutes. Three other tubes
hung outside the case were exposed to the ordinary
laboratory air.

The three exposed tubes were feebly but distinctly
cloudy on the 19th. On the 22nd they were all thickly
turbid. Scattered spots of Penicillium then appeared
on two of them, while the third tube, which stood be-
tween these two, kept the Penicillium down. This
central tube contained the pigment-forming Bacteria,
which have frequently shown a singular power in pre-
venting the development of mould. For nearly two
months the central tube successfully withstood this de-
velopment, while its two neighbours were covered by a
matted layer of Penicillium.

During the whole of this time the protected infusion
continued as clear and colourless as distilled water.

§ 10. Liver-Infusion.

On the 10th of November the infusion was prepared
by the process of digesting already so often described.

PUTREFACTION AND INFECTION. 67

It was introduced into a case containing three protected
tubes, and boiled there for five minutes in the brine-
bath. Hung on to the chamber at the same time were
three tubes containing the same infusion, but exposed to
the common air. On the 13th Bacteria were numerous
in the exposed tubes, and soon afterwards all three of
them became thickly muddy and putrescent. They
continued so for months.

The protected tubes, on the contrary, showed
throughout a bright yellow liquid, as transparent
and fresh as it was on the day of its introduction
into the case.

§ 11. Infusions of Hare, Rabbit, Pheasant, and
Grouse.

For the sake of economy, as so many of them were
employed, the shape of the cases was subsequently varied.
The rounded end of a tall glass shade was cut off, so as
to convert the shade into a hollow cylinder, open at
both ends. This was set upright on a wooden stand,
and cemented to it air-tight. Through the stand passed
three large test-tubes also air-tight: To the top of
the cylinder was cemented a circular piece of wood, the
middle of which was occupied by a pipette passing first
through india-rubber and then through a stuffing-box
of cotton-wool moistened by glycerine.' The air within
the case was connected with the air without by means
of the open bent tubes already described.

In the first experiments made with these cases defects
of construction were revealed during the boiling of the
infusions. But increased experience enabled me to

1 In the earlier experiments the india-rubber formed the bottom
of the stuffing-box, where particles were sometimes detached from

it by the motion of the pipette. To prevent this the positions of
wool and rubber were afterwards reversed.

68 THE FLOATING-MATTER OF THE AIR.

render them secure. The floating matter within the
cases having been permitted to subside, into four of
them, on the 30th of November, infusions of hare, rabbit,
pheasant, and grouse were introduced. The infusions
were boiled in the usual way, and abandoned to the air
of the case. Outside each case, and hung on to it,
were three test-tubes of the same size and containing
the same infusion as that within.

Examined on Christmas-day, the following were the
observed results :—

Pheasant.—The three interior tubes perfectly limpid :
the three exposed ones turbid and covered with Pent-
cillium.

Grouse.—In the same condition as the pheasant.

Hare.—The same as grouse and pheasant.

Rabbit.—The three interior tubes covered with tufts
of particularly beautiful Penicilliwm, some of the tufts
striking deep into the liquid. In two out of the three
tubes, moreover, mycelium was flourishing below. All
the outer tubes were, as usual, turbid and covered with
Penicilliwm.

Is this, then,.a case of spontaneous generation ?
Without further evidence no cautious worker would
draw such a conclusion. Opposed to this isolated in-
stance stand all the others mentioned in these pages,
and their proper action on the mind is to compel it
to demand the closest scrutiny before accepting this
apparent exception as a real one. Subjected to such
scrutiny, it appeared that of the four shades the one
containing the rabbit-infusion, and that only, had
yielded to the heat of boiling. The shade had been
fastened upon its slab with plaster and cement, which
became so loose during the boiling that the steam
issued from the chinks. But crannies which could per-
mit steam to escape could permit air to enter, and to

PUTREFACTION AND INFECTION. 69

the presence of such air the appearance of the Peni-
cilliwm was doubtless due.

I did not, however, rest content with mere inference,
but tested the rabbit-infusion by placing three fresh
tubes of it in one of the firmer cases first described. It
was introduced and boiled on the 5th of January, 1876,
three other tubes filled with the same boiled infusion
being exposed on the same day to the ordinary air. The
three protected tubes remained clear for three months,
while in three days the three exposed ones were charged
with Bacteria.

Salmon.—The colouring-matter of this fish did not
at all affect the infusion ; indeed, no better example of
original freedom from colour or opalescence, and of
persistent purity in contact with the moteless air, has
occurred to me than salmon-infusion. It was introduced
into a cylindrical case on the 13th of December, where
it continued for months to show the brilliant trans-
parency exhibited at first. Three unprotected tubes, on
the other hand, became turbid and covered with mould
in a few days.

Hops.—One tube of this infusion was protected
simply by a lamp-glass, corked and cemented above and
below. Through the lower cork passed the single test-
tube, air-tight ; while through the upper one passed the
pipette and the bent tubes intended to connect the outer
and the inner air. The infusion was prepared and in-
troduced on the 28th of October. In a few days the
exposed tube was found turbid and covered with mould;
the protected tube, on the contrary, remained clear for
several months.

Tea and Coffee.—One tube of each was protected
by a lamp-glass similar to that employed in the infusion
of hops. Both were prepared on the 28th of October,
exposed tubes being hung up at the same time. The

70 THE FLOATING-MATTER OF THE AIR.

protected tea has remained clear, while the exposed tea
is turbid and covered with mould. Both the exposed
coffee and the protected coffee are, on the other hand,
turbid and covered with Penicillium.

The remarks already made with regard to the rabbit-
infusion apply here. The case is one, not for the hasty
admission of spontaneous generation, but for further
scrutiny. JI examined the apparatus as it stood. The
pipette used to introduce the coffee (and this one only
of the three employed in these experiments) rested
against the outer edge of the tube containing the infu-
sion. This had in part evaporated, had been in part
re-condensed, and had trickled down the pipette so as to
form a small drop at the point where pipette and tube
touched each other. The drop had virtually washed the
outer surface of the pipette, carrying with it, in part,
such matter as might have attached itself to that sur-
face. A portion of this washing-water reaching the
infusion was clearly the origin of the life observed.
The sure test, however, was the repetition of the experi-
ment under conditions which should exclude this source
of error. On the 27th of December accordingly two
tubes protected by lamp-glasses were prepared, two
other tubes of the infusion being exposed to the air.
The former remained clear for months, the latter in the
same number of days became turbid and covered with
Penicillium.

§ 12. Infusions of Codfish, Turbot, Herring, and
Mullet.

With a view of causing these experiments on mote-
less and mote-laden air to run parallel with others made
with hermetically-sealed tubes, to be described further
on, I added the fish named in the heading of this section
to the other substances examined. The mullet was in-

PUTREFACTION AND INFECTION. 71

troduced into its case on the 3rd of January. The warm
air of the room had, however, so acted on the wood of
the chamber, which had been employed in former ex-
periments, that the water of condensation trickled from
a chink in the bottom. The other chambers were
mended as far as possible, and into them the infusions
were introduced on the 4th of January. Each chamber,
as before, was provided with three exposed tubes for
comparison with three protected tubes within. On the
morning of the 6th the exposed turbot-infusion was
clear in all the tubes ; a few hours subsequently two out
of the three became cloudy; while on the 7th Bacteria
had taken. possession of all of them. All the unpro-
tected tubes of codfish were cloudy on the 6th, more
cloudy on the 7th, and covered with a soapy layer upon
the 8th. The three exposed herring-tubes were also
cloudy on the 6th, the cloudiness advancing afterwards
to thicker turbidity. The mullet gave way in the same
manner. For more than three months the protected
tubes, including even the wmperfect chamber which
protected the mullet-infusion, have remained as clear
as they were upon the day of their introduction.

To these fish-infusions may be added others of eel
and oyster. Two tubes of each, protected by lamp-
glasses, were charged on the 27th of December. They
remain unchanged. Two other pairs of tubes, prepared
in the same way and exposed to the laboratory air, are
turbid and covered with Penicillium.

§ 13. Infusions of Fowl and Kidney.

Three tubes.of the fowl-infusion were introduced
into a case, and boiled there for five minutes, on the
4th of January. Three similar tubes were at the same
time exposed to the air. On the 6th all the outer

72 THE FLOATING-MATTER OF THE AIR.

tubes were cloudy, the cloudiness becoming denser on
the following days, while disks of Penicillium began
to form on the exposed surfaces. It was found ex-
ceedingly difficult to obtain a clear infusion of kidney.
The liquid, after it had passed through a dozen filters,
was still quite muddy. With considerable labour and
care, and by the employment of 200 filters, the mechani-
cally suspended matter was at length removed, and a
clear infusion obtained. It was introduced into its
case, to which three exposed tubes were attached, on
the 4th of January. On the 7th the latter were per-
ceptibly cloudy, on the 8th distinctly so, while specks
of mould rested upon them all. The protected tubes, on
the contrary, have for months maintained their trans-
parency undimmed.!

The entire number of experiments made to illustrate
the association of scattered light and Bacterial and
fungoid life are not here recounted. Whiting, for
example, may be added to the fish, and pork to the
flesh examined, while many of the other substances
have been tested oftener than I have thought it neces-
sary to record. The method of boiling was also varied
in a manner which may claim a passing reference here.

§ 14. Boiling by an Internal Source of Heat.

Two large test-tubes were fixed air-tight in the
same case. On the 8thof November, after the floating
matter had subsided, infusions of hay and turnip were
introduced. Dipping deep into each infusion were two
tinned copper wires, connected below by a spiral of

1 Kidney has been mentioned by Dr. Bastian as a substance
with which he demonstrates the occurrence of spontaneous genera-
tion. He does not mention the extraordinary turbidity of the
infusion, which proved so troublesome to me.

PUTREFACTION AND INFECTION. 73

platinum wire. The copper wires passed through the
case, and were connected with a voltaic battery outside.
The spiral was heated by the current from this bat-
tery. After a few minutes’ heating ebullition set in,
and was continued for five minutes in each tube. Two
other tubes containing the same infusions were boiled
in the same way, and afterwards hung outside the case
containing the two protected tubes.

In another chamber were placed two tubes con-
taining infusions of beef and mutton. The arrange-
ment and the treatment were precisely the same as
those just described in the case of hay and turnip.

Examined some months subsequently, the exposed
tubes of all four infusions were found turbid and
covered with Penicillium, while all the four protected
tubes remained unchanged. During the boiling process
some flocculi detached themselves from the tinned sur-
faces of the copper wires; but in the protected tubes
these have fallen to the bottom, and left the supernatant
liquid clear. Platinum wires would have been better
than tinned copper ones.

§ 15. Partial Discussion of the Results.

Thus by experiments, reiterated in many cases,
with urine, mutton, beef, pork, hay, turnip, tea, coffee,
hops, haddock, sole, salmon, codfish, turbot, mullet,
herring, eel, oyster, whiting, liver, kidney, hare, rabbit,
fowl, pheasant, grouse, has the induction been established,
that the power of developing Bacterial life by atmospheric
air and its power of scattering light, go hand in hand.
We shall immediately examine more closely what this
means.

The necessity of employing strong infusions has
been frequently dwelt upon, if we would realize the.

74 THE FLOATING-MATTER OF THE AIR.

phenomena of spontaneous generation. I would there-
fore recall to mind what has been stated on a previous
page, that in most of the experiments here described
the infusion at starting was strong, and that it was
permitted to evaporate with extreme slowness until its
concentration became three or four fold what it had
been at starting. Every experiment was thus converted
into an indefinite number of experiments on infusions
of different strengths. Never, in my opinion, was the
requirement as to concentration more completely ful-
filled, and never was the reply of Nature to experiment
more definite and satisfactory. The temperatures,
moreover, to which the infusions have been sub-
jected embrace those hitherto alleged to be effectual,
extending indeed beyond them in both directions.!
They reached from a lower limit of 50° to a higher
limit of more than 100° Fahr. Still higher tempera-
tures were applied in other experiments to be described
subsequently. With regard to the number of the
infusions, more than fifty moteless chambers, each with
its system of tubes, have been tested. There is no
shade of uncertainty in any of the results. In every
instance we have, within the chamber, perfect limpidity
and sweetness—without the chamber, putridity and its
characteristic smells. Inno instance is the least counte-
nance lent to the notion that an infusion deprived by
heat of its inherent life, and placed in contact with air
cleansed of its visibly suspended matter, has any power
whatever to generate life anew.

If it should be asked how I have assured myself
that. the protected liquids do not contain Bacteria, I
would, in the first place, reply that with the most
careful microscopic search I have been unable to find

1 See Proc. of Roy. Soc. vol. xxi. p, 180, where a temperature of
70° is described as effectual.

PUTREFACTION AND INFECTION, 75

them. But much more than this may be affirmed.
The electric or the solar beam is a far more powerful
and searching test in this matter than the microscope.
In the foregoing pages I have more than once described
the clearness of my protected infusions, after months
of exposure, as equal to that of distilled water. So far
is this from being an exaggeration, that it falls short of
the truth; for I have never seen distilled water so free
from suspended particles as the protected infusions
prove themselves tobe. When for months a transparent
liquid thus defies the scrutiny of the searching beam,
maintaining itself free from every speck which could
scatter light asa Bacterium scatters it—when, moreover,
an adjacent infusion, prepared in precisely the same
way, but exposed to the ordinary air, becomes first
hazy, then turbid, and ends by wholly shattering the
concentrated beam into irregularly scattered light, I
think we are entitled to conclude that Bacteria are as
certainly absent from the one as they are present in the
other. (See Note I. at the end of this paper.)

For the right interpretation of scientific evidence
something more than mere sharpness of observation is
requisite, very keen sight being perfectly compatible
with very weak insight. I was therefore careful to have
my infusions inspected by biologists, not only trained
in the niceties of the microscope, but versed in all the
processes of scientific reasoning. Their conclusion is
that it would simply weaken the demonstrative force of
the experiments to appeal to the microscope at all.

§ 16. Suspended Particles in Air and Water ;
their relation to Bacteria.

Examined by the concentrated solar rays, or by the
condensed electric beam, the floating matter of the air

76 THE FLOATING-MATTER OF THE AIR.

is seen to consist :—first, of particles so coarse that their
individual motions can be followed by the eye ; secondly,
of a finer matter which is not to be distinguished as
motes, but which emits a uniform and changeless light.
In this finer matter the coarser motes move as in a
medium.

; As regards the production of colour, the action of
small particles has been examined by Briicke in a paper
‘On the Colours of Turbid Media.’! In relation to the
question of polarization, Professor Stokes has made some
remarks in his memoir ‘ On the Change of the Refrangi-
bility of Light.’? I may also be permitted to refer to
my own papers ‘On New Chemical Reactions by Light’
and ‘On the Blue Colour of the Sky,’ in the Proceed-
ings of the Royal Society for 1868-69, and to a paper
‘On the Action of Rays of High Refrangibility on
Gaseous Matter,’ in the Philosophical Transactions for
1870. M. Soret, Lord Rayleigh, and Mr. Bosanquet
have also worked at this subject, which, as far as it now
concerns us, a few words will render clear.

When the track of a parallel beam in dusty air is
looked at horizontally through a Nicol’s prism, in a
direction perpendicular to the beam, the longer diago-
nal of the prism being vertical, a portion of the light
from the finer matter, being polarized, is extinguished.
The coarser motes, on the other hand, which do not
polarize the light, flash out with greater force, because
of the increased darkness of the space around them.

The individual particles of the finest floating matter
of the air lie probably far beyond the reach of the
microscope. At all events it is experimentally demon-
strable that there are particles which act similarly upon
light, and which are entirely ultra-microscopic. A few

* Pogg. Ann. lxxxviii. p. 363.
2 Philosophical Transactions, vol. 142, pp. 529-530.

PUTREFACTION AND INFECTION, 77

days ago, for example, an inverted bell-jar was filled
with distilled water, into which, while it was briskly
beaten by a glass rod, was dropped a solution of mastic
in alcohol. The proportion was less than that employed
by Briicke, being about ten grains of the gum to 1,000
grains of the alcohol. The jar was placed under a sky-
light, at the height of the eye above the floor. It was
of a beautiful cerulean hue, this colour arising wholly
from the light scattered by the mastic particles.
Looked at horizontally through a Nicol’s prism, with its
shorter diagonal vertical, the blue light passed freely
to the eye. Turning the long diagonal vertical, the
scattered light was wholly quenched, and the jar
appeared as if filled with ordinary pure water.

I tried the effect of a powerful filter upon those parti-
cles, and found that they passed sensibly unimpeded
through forty layers of the best filtering-paper.!

The liquid containing them was examined by a
microscope magnifying 1,200 diameters. The suspended
mastic particles entirely eluded this power, the medium
in which they swam being as uniform as distilled water
in which no mastic whatever had been precipitated.

The optical deportment of the floating matter of
the air proves it to be composed, in part, of particles
of this excessively minute character. The concentrated
beam reveals them collectively, long after the micro-
scope has ceased to distinguish them individually.
In London rooms, moreover, they are for the most part
organic particles, which may be removed from the air
by combustion. In presence of such facts, any argu-
ment against atmospheric germs, based upon their being
beyond the reach of the microscope, loses all validity.

We are here brought face to face with a question

1 There are filters, however, which stop them; but of this
immediately.

78 THE FLOATING-MATTER OF THE AIR.

of extreme importance, which it will be useful to clear
up. ‘Potential germs’ and ‘ hypothetical germs’ have
been spoken of with scorn, because the evidence of the
microscope as to their existence was not forthcoming.
Sagacious writers had drawn from their experiments the
perfectly legitimate inference that in many cases the
germs exist, though the microscope fails to reveal them.
Such inferences, however, have been treated as the pure
work of the imagination, resting, it was alleged, on no
real basis of fact. But in the concentrated beam we
possess what is virtually a new instrument, exceeding
the microscope indefinitely in power. Directing it
upon media which refuse to give the coarser instrument
any information as to what they hold in suspension, these
media declare themselves to be crowded with particles
—not hypothetical, not potential, but actual and myriad-
fold in number—showing the microscopist that there is
a world far beyond his range.

In §§ 6 and 8 experiments on the infection of clear
infusions by others containing visible Bacteria are re-
ferred to. But for the infection to be sure it is not
necessary that the Bacteria should be visible. Over and
over again I have repeated the experiments of Dr. Bur-
don Sanderson on the effective power of ordinary distilled
water, in which the microscope fails to reveal a Bacte-
rium. The water, for example, furnished to the Royal-
Institution laboratory by Messrs. Hopkin and Williams
is sensibly as infectious as an infusion swarming with
Bacteria. The vessels are the source of infection here.

Perhaps the severest experiment of this kind ever
made was one executed by Dr. Sanderson with water
prepared by myself. In 1871 I sought anxiously and
assiduously for water free from suspended particles. The
liquid was obtained in various degrees of purity, but
never entirely pure. Knowing the wonderful power of

PUTREFACTION AND INFECTION. 79

extrusion, as regards foreign matter, brought into play
by water in crystallizing, the thought occurred to me of
examining the liquid derived from the fusion of the
most transparent ice. At my request, therefore, my
assistant arranged the following apparatus for me:—

Fia. 3.

Through the plate of an air-pump (fig. 3) passed air-

tight the shank of a large funnel. A small glass bulb,

B, furnished with a glass stopcock, was attached to the

shank of the funnel below. Prior to being put together

all parts of the apparatus had been scrupulously cleansed.
5 :

80 THE FLOATING-MATTER OF THE AIR.

In the funnel was placed a block of ice, 1, selected for
its transparency, having a volume of 1000 cubic inches
or thereabouts, and over the ice was placed an air-tigh,
receiver. Several times in succession the air was re-
moved from this receiver, its place on each occasion
being takeu by other air carefully filtered through
cotton-wool. The transparent ice was thus surrounded
by moteless air.

The ice was now permitted to melt; its water trickled
into the small glass bulb below, which was filled and
emptied a great number of times. From the very heart
of the block of ice the water was finally taken and sub-
jected to the scrutiny of the concentrated beam. It
proved to be the purest liquid I had ever seen—pro-
bably the purest human eye had ever seen; but still it
contained myriads of ultra-microscopic particles. The
track of the beam through it was of the most delicate
blue, the blue light being perfectly polarized. It could
be wholly quenched by a Nicol’s prism, the beam then
passing through the liquid as through a vacuum. A
comparison of the light with that scattered by mastic
particles such as those above referred to, proved the
suspended particles of the ice-water to be far smaller
than those of the mastic. No microscope, therefore,
could come near them,! Such water, however, was
proved by Dr. Sanderson to be as infectious as the water
from any ordinary tap.

Infinitesimal as these particles are, however, they
may be separated by mechanical means from the liquid
in which they are held in suspension. Filters of porous
earthenware, such as the porous cells of Bunsen’s battery,

1 [ have endeavoured to convey some notion of the smallness of
these scattering particles in ‘Fragments of Science,’ Art. ‘Scientific
Use of the Imagination.’ See note on Mr. Dallinger’s observations
at the end of this Memoir.

PUTREFACTION AND INFECTION 81

have been turned to important account in the researches
of Dr. Zahn, Professor Klebs, and Dr. Burdon Sander-
son. In various instances it has been proved that, as
regards the infection of living animals, the porous
earthenware intercepts contagia. For the living animal,
organic infusions, or Pasteur’s solution, may be substi-
tuted. Not only are ice-water, distilled water, and
tap-water thus deprived of their powers of infection,
but, by plunging the porous cell into an infusion swarm-
ing with Bacterial life, exhausting the cell, and per-
mitting the liquid to be slowly driven through it by
atmospheric pressure, the filtrate is not only deprived of
its Bacteria, but also of those ultra-microscopic germs
which appear to be as potent for infection as the Bac-
teria themselves. The precipitated mastic particles
before described, which pass unimpeded through an in-
definite number of paper filters, are wholly intercepted
by the porous cell.

These germinal particles abound in every pool,
stream, and river. All parts of the moist earth are
crowded with them. Every wetted surface which has
been dried by the sun or air contains upon it the parti-
cles which the unevaporated liquid held in suspension.
From such surfaces they are detached and wafted away,
their universal prevalence in the atmosphere being
thus accounted for. Doubtless they sometimes attach
themselves to coarser particles, organic and inorganic,
which are left behind along with them ; but they need
no such rafts to carry them through the air, being them-
selves endowed with a power of flotation commensurate
with their extreme smallness and the specific lightness
of the matter of which they are composed.

I by no means affirm that the developed Bacterium,
which requires for its maintenance nutriment beyond
that which ordinary water can always supply, is never

82 THE FLOATING-MATTER OF THE AIR.

wafted through the air. Cases may arise favourable
to the growth and dispersion of the full-grown or-
ganism. Whether, after desiccation, it retains the power
of reproduction is another question. But it ought, I
think, to be steadily borne in mind that the complete
Bacteria and the atmospheric matter from which they
spring are, in general, different things. I have care-
fully sought for atmospheric Bacteria, but have never
found them. They have never, to my knowledge, been
found by others; and that they arise from matter which
has not yet assumed the Bacterial form is, as just shown,
capable of demonstration. An organic infusion, boiled
and shielded from atmospheric particles, will remain
clear for an indefinite period, while a fragment of glass
which has been exposed to the air, but on which no trace
of a Bacterium is to be found, will in two or three days
develop in the infusion a multitudinous crop of life.

We have now to look a little more closely at these
particles, foreign to the atmosphere but floating in it,
and proved beyond doubt to be the origin of all the Bac-
terial life which our experiments have thus far revealed.
We must also look at them as they exist in water, in
countless multitudes, being as foreign to this medium as
the floating atmospheric dust is to the air in which it
swims. The existence of the particles is quite as certain
as if they could be felt between the fingers, or seen by
the naked eye. Supposing them to augment in magni-
tude until they come, not only within range of the
microscope, but within range of the unaided senses.
Let it be assumed that our knowledge of them under
these circumstances remains as defective as it is now—
that we do not know whether they are germs, particles
of dead organic dust, or particles of mineral matter.
Suppose a vessel (say a flower-pot) to be at hand filled
with nutritious earth, with which we mix our unknown

PUTREFACTION AND INFECTION. 83

particles, and that in forty-eight hours subsequently buds
and blades of well-defined cresses and grasses appear
above the soil. Suppose the experiment when repeated
a hundred times to yield the same unvarying result.
What would be our conclusion? Should we regard
those living plants as the product either of dead dust,
or of mineral particles? or should we regard them as
the offspring of living seeds? The reply is unavoidable.
We should undoubtedly consider the experiment with the
flower-pot as clearing up our pre-existing ignorance ;
we should regard the fact of their producing cresses and
grasses as proof positive that the particles sown in the
earth of the pot were the seeds of the plants which have
grown from them. It would be simply monstrous to
conclude that they had been ‘spontaneously generated.’

This reasoning applies word for word to the develop-
ment of Bacteria from that floating matter which the
electric beam reveals in the air, and in the absence of
which no Bacterial life has been generated. I cannot
see a flaw in the reasoning; and it is so simple as to
render it unlikely that the notion of Bacterial life being
developed from dead dust can ever gain currency among
the members of the medical profession.

It has been said of those whom the evidence adduced
in favour of spontaneous generation fails to convince,
that they seem willing to believe in almost any infringe-
ment of natural uniformity rather than admit the
doctrine.' This surely is an inversion of the true order
of the facts. Natural uniformity is the record of expe-
rience; and, apart from the phenomena to be accounted
for, there is not a vestige of experience, possessed either
by the man of science or the human race, which warrants
the notion that dead dust, and not living seed, is the
source of the crops which spring from our infusions

1 Transactions of the Pathological Society, vol. xxvi. p. 273.

84 THE FLOATING-MATTER OF THE AIR.

when impregnated by the floating particles of the at-
mosphere.

§ 17. Recent Experiments on Heterogenesis.

The uniform sterility of the boiled infusions described
in the foregoing pages, when protected from the floating
matter of the air, proves that they do not contain germs
capable of generating life. Our most advanced hetero-
genist, indeed, affirms that a temperature of 140° Fahr.
reduces, in all cases, such germs to a state of actual or
potential death; and he ingeniously argues that as,
even in flasks which have been raised to a temperature
of 212°, and hermetically sealed, putrefaction, and its
associated Bacteria, do most certainly arise, such Bac-
teria must be spontaneously generated. ‘We know,’
he says, ‘ that boiled turnip or hay-infusions, exposed to
ordinary air, exposed to filtered air, to calcined air, or
shut off altogether from contact with air, are more or
less prone to swarm with Bacteria and Vibriones in the
course of from two to six days.’!

We are here met by a difficulty at’ the outset. The
proof of Bacterial death at 140° Fahr. consists solely in
the observed fact, that when a certain liquid is heated
to that temperature no life appears in it afterwards ;
while in another liquid life appears two days after it
has been heated to 212°. Instead of concluding that in
the one liquid life is destroyed and in the other not, it
is assumed that 140° Fahr. is the death-temperature for
both ; and this being so, the life observed in the second
liquid is regarded as a case of spontaneous generation.
A great deal of Dr. Bastian’s most cogent reasoning
rests upon this foundation. Assumptions of this kind
guide him in his most serious experiments. He finds,

} «Evolution and the Origin of Life.’ p. 94.

PUTREFACTION AND INFECTION. 85

for example, that a mineral solution does not develop
Bacteria when exposed to the air; and he concludes
from this that an organic infusion also may be thus ex-
posed without danger of infection. He exposes turnip-
juice accordingly, obtains a crop of Bacteria, which, in
the light of his assumption, are spontaneously generated.
Such are the warp and woof of some of the weightiest
arguments on this question which have been addressed
by him to the Royal Society.!

Granting, then, all that Dr. Bastian alleges regard-
ing his experiments to be correct, the logical inference
would be very different from his inference. In a future
essay his position will be more clearly defined. To the
examination of his experiments I now address myself.

§ 18. Experiments with Filtered Air.

A bell-jar containing about 700 cubic inches of air
was firmly cemented to a slab of wood coated with resin,
and supported on three legs.2_ Through the slab passed,
air-tight, three large test-tubes (4, 3, ¢, fig. 4). Prior
to cementing, the tubes had been three-fourths filled,
one with an infusion of hay, another with an infusion of
turnip, and a third with an infusion of mutton. On
the 2nd of November the mote-laden air was pumped
out, air slowly filtered through a long tight plug of
cotton-wool being allowed to take its place. The jar
was emptied and refilled until the closest scrutiny by a
concentrated beam revealed no floating matter within
it. The infusions were then boiled for five minutes,

} Proceedings, vol. xxi. p. 130.

2 Two hoops of sheet iron, with an annular space about an
inch wide, were fastened on to the slab of wood. The annular
space was filled with hot cement, into which the hot bell-jar was
pressed. The circular space within the smaller hoop was also

covered by a layer of cement,

86 THE FLOATING-MATTER OF THE AIR.

and abandoned to the air of the jar. During ebullition
a small quantity of the liquid in one of the tubes boiled
over, and rested upon the interior resinous surface at a
little distance from the mouths of two of the tubes.
The germinal matter, it may be remarked, is not readily
blown away from such a surface, and it certainly was
not wholly removed by our feeble current of filtered air.
Three exposed tubes containing the same infusion were
placed at the same time beside the protected ones

Fie. 4.

In three days these exposed tubes became turbid
and charged with life ; but for three weeks the infusions
in contact with the filtered air remained perfectly
clear.

At the end of three weeks, that is on the 23rd of
November, I desired my assistant to renew the air in the
bell-jar. He pumped it out, and while permitting fresh
air to enter through the cotton-wool filter, my attention

PUTREFACTION AND INFECTION. 87

was directed toa couple of small round patches of Peni-
cilliwm resting in the liquid that had boiled over on the
resin. I at once made the remark that the experiment
was a dangerous one, as the entering air would probably
detach some of the spores of the Penicilliwm and diffuse
them in the bell-jar. This was, therefore, filled very
slowly, so as to render the disturbance a minimum.
Next day, however, a tuft of mycelium was observed at
the bottom of one of the three tubes, namely that con-
taining the hay-infusion. It soon grew large enough
to fill a considerable portion of the tube. For nearly a
month longer the two tubes containing the turnip- and
mutton-infusions maintained their transparency unim-
paired. Late in December the mutton-infusion, which
was in dangerous proximity to the outer mould, showed
a tuft of Penicilliwm upon its surface. The beef-
infusion continued bright and clear for nearly a fort-
night longer. The cold winter weather caused me to
add a third gas-stove to the two which had previously
warmed the room where the experiments are conducted.
The warmth of this stove played upon one side of the
bell-jar ; and on the day after the lighting of the stove,
the beef-infusion gave birth to a tuft of mycelium.
In this case the small spots of Penicillium might have
readily escaped attention; and had they done so we
should have had here three cases of ‘spontaneous gen-
eration’ more striking than most of those that have
been adduced in support of this doctrine.

The experiment was subsequently made upon a
larger scale. Twelve very large test-tubes were caused
to pass air-tight through a slab of wood; the wood was
thickly coated with cement, in which, while it was hot
and soft, a heated ‘ propagating glass,’ resembling a huge
bell-jar, was imbedded. The air within the glass was
pumped out several times, air filtered carefully through

88 THE FLOATING-MATTER OF THE AIR.

a plug of cotton-wool being permitted to supply its
place. The test-tubes contained infusions of hay, tur-
nip, beef, and mutton, three of each, twelve in all.
For two months they remained as clear and cloudless
as they were upon the day of their introduction, while
twelve similar tubes, prepared at the same time, in pre-
cisely the same way, and hung on to the slab of wood
outside the propagating-glass, were, in less than a week,
clogged with mycelium, mould, and Bacteria.

One of the protected tubes was accidentally broken,
and though its aperture was rapidly plugged with
cotton-wool, some common air must at the time have
entered the propagating-glass. Evaporation from the
infusions went on; the vapour was condensed by the
glass above, trickled down its interior surface, carrying
with it, in part, such matter as had attached itself to
that surface. A kind of pool was thus formed upon the
cement below. This after an interval of three months
became spotted with disks of Penicilliwm, by the spores
of which one or two of the infusions have been recently
invaded, the production of very beautiful mycelium-
tufts being the consequence.

§ 19. Hxperiments with Caleined Air.

Six years ago' I showed that the floating matter of
London air could be removed by permitting a platinum
wire heated to whiteness to act upon it for a sufficient
time. I availed myself of this mode of calcining the
air on the present occasion. The apparatus employed
is shown in fig. 5. A glass shade, 8, is placed upon a
slab of wood mounted on a tripod. Through the slab
passes three large test-tubes nearly filled with the in-
fusion to be examined. A platinum spiral, p, unites

' Proc. Roy. Inst. vol. vi. pp. 4 and 5.

PUTKEFACTION AND INFECTION. 89

the ends of two upright copper wires, which pass
through the stand and are seen coiled outside it. The
shade is surrounded below by a tin collar, with a space of
about half an inch all round between it and the shade.
This space is filled with cotton-wool firmly packed.
Connecting the wires with a battery of fifteen cells, the
spiral p was raised to whiteness, and was permitted to
continue so for five minutes. Experiments previously
executed had shown that
this sufficed for the entire
removal of the floating
matter. When the spiral
was heated, a portion of
the expanded air was driven
through the cotton - wool
packing below; and when
the current was interrupted,
this air, returning into the
shade, was prevented by the
cotton-wool from carrying
any floating matter with
it.

The first three substances
brought into contact with
air calcined in this way were damson-juice, pear-juice,
and infusion of yeast. They were boiled for five min-
utes, and for five months they have remained without
speck or turbidity. Other tubes similarly boiled, and
placed underneath shades containing the floating matter
of the air, have long since fallen into mould and rotten-
ness.

Turnip- and hay-infusions, rendered slightly alkaline,
have been mentioned as particularly prone to spon-
taneous generation. I wished to test this. On the
26th of November, therefore, four shades were prepared,

90 THE FLOATING-MATTER OF THE AIR.

two containing strong turnip-infusion and hay-infu-
sion unneutralized, two containing the same infusions
slightly superneutralized by caustic potash. The al-
leged spontaneous development of life was not observed.
The tubes exhibit to this hour the clearness and colour
which they showed on the day they were boiled. Her-
metically-sealed tubes, containing the same infusions,
prepared on the same day, remain equally clear; while
the specimens exposed to the laboratory air have fallen
into rottenness.

The experiments with calcined air were also executed
in another form and on a larger scale. A ‘ propagating-
glass,’ similar to that already described, was cemented
in the same way to a slab of wood through which passed
twelve large test-tubes. The infusions, as before, were
hay, turnip, beef, and mutton. The air being removed
from the propagating-glass by a good air-pump, its place
was supplied by other air which had passed slowly
through a red-hot platinum tube containing a roll of
platinum gauze, also heated to redness. Tested by a
searching beam, this calcined air was found quite free
from floating matter. For two months no speck invaded
the limpidity of the infusions exposed to it, while a
week’s exposure to the ordinary air sufficed to reduce
twelve similar infusions, hung on to the slab of wood
outside the glass, to the muddiness of putrefaction.

§ 20. Infusions withdrawn from Air.

The arrangement here was the same as that adopted
in the first experiment with filtered air, the only dif-
ference being that the bell-jar, with a view to its more
perfect exhaustion, was smaller. It was cemented air-
tight to a slab of wood through which passed three
large test-tubes, filled to about two-thirds of their

PUTREFACTION AND INFECTION. 91

capacity with infusions of beef, mutton, and turnip re-
spectively. The bell-jar was exhausted six times in
succession, and filled after each exhaustion with air
carefully filtered through cotton-wool. While this air
was in contact with the infusions they were boiled in a
brine-bath. The receiver was afterwards exhausted as
perfectly as a good air-pump could exhaust it; while
outside the receiver were hung three tubes to compare
with those within.

Here the protected infusions remained as clear as
they were on the day of their introduction, not only
after the exposed infusions had charged themselves with
life, but for many weeks after they had evaporated
away.

Such, then, are the tests to which I have subjected
the statement that ‘boiled turnip- and hay-infusions
exposed to filtered air, to calcined air, or shut off al-
together from contact with air, are more or less prone to
swarm with Bacteria and Vibriones in the course of
from two to six days.’ These results, and others that
might be adduced, leave no doubt upon my mind that
the deportment of air from which the floating matter
has been removed by filtration or calcination is precisely
the same as that of air from which the particles have
disappeared by self-subsidence. Once really sterilized,
an infusion in .contact with optically pure air, however
obtained, remains sterile.

§ 21. The Germ-theory of Contagious Disease.

It is in connection with the germ-theory of con-
tagious disease that the doctrine of spontaneous genera-
tion assumes its gravest aspect. My interest in the
general question was first excited by the investigations
of Pasteur, while the medical bearings of the doctrine

92 THE FLOATING-MATTER OF THE AIR.

were subsequently made clear to me, mainly, I ought
to say, by the writings and conversation of the late Dr.
William Budd, who was the first of our countrymen
to grasp with true philosophic insight the doctrine of
‘the vitality of contagia,’ which is now every day gain-
ing ground.

At the present moment, indeed, no other medical
principle occupies so much thought, or is the subject of
so much discussion. ‘How does it happen,’ says Dr.
Burdon Sanderson!, ‘that these Bacteria, which we
suppose must have existed half a dozen years ago in as
great numbers as at present, were then scarcely heard
of, and that they now occupy so large a place in the
medical literature of this country and of Germany, and
have lately afforded material for lively discussion in the
French Academy?’ Dr. Sanderson points out the re-
lation of Lister in England, and of Hallier in Germany,
to the movement regarding Bacteria which is now work-
ing likea ferment through the medical world. But to
no other workers in this field are we more indebted
than to Dr. Sanderson himself, and to his colleagues,
for the continued and successful prosecution of re-
searches bearing upon the pathology of contagion.

‘In 1870, writes Mr. John Simon, in one of his
excellent reports to the Privy Council, ‘I had the honour
of presenting Dr. Sanderson’s first. report of researches
made in this matter. At that time general conclusions
seemed justified, first, that the characteristic-shaped
elements which the microscope had shown abounding in
various infective products are self-multiplying organic
forms, not congeneric with the animal body in which
they are found, but apparently of the lowest vegetable
kind; and, secondly, that such living organisms are
probably the essence, or an inseparable part of the

1 British Medical Journal, Janusry 16, 1875.

PUTREFACTION AND INFECTION. 93

essence, of all contagia of disease. . . . This view
of the matter has since then become greatly more dis-
tinct, in consequence of the investigations made by Dr.
Sanderson, particularly in 1871 and 1872, with refer-
ence to the common septic contagium or ferment. For
in that ferment there seems now to be identified a force
which, acting disintegratively upon organic matter,
whether dead or living, can, on the one hand, initiate
putrefaction of what is dead, and, on the other hand,
initiate febrile and inflammatory processes in what is
living.’

At a Meeting of the Pathological Society, held on
the 6th of April, 1875, the germ-theory of disease was
formally introduced as a subject for discussion, the
debate being continued with great ability and earnest-
ness at subsequent meetings. The Conference was
attended by many distinguished medical men, some
of whom were profoundly influenced by the arguments,
and none of whom disputed the facts brought forward
against the theory on that occasion. The leader of
the debate, and the most prominent speaker, was Dr.
Bastian, to whom also fell the task of replying on all
the questions raised. The coexistence of Bacteria and
contagious disease was admitted; but, instead of con-
sidering these organisms as ‘ probably the essence, or
an inseparable part of the essence’ of the contagium,
Dr. Bastian contended that they were ‘ pathological
products,’ spontaneously generated in the body after
it had been rendered diseased by the real contagium.
The grouping of the ultimate particles of matter to
form living organisms, Dr. Bastian considers to be
an operation as little requiring the action of antece-
dent life as their grouping to form any of the ‘ other
less complex chemical compounds.’ Such a position
must, of course, stand or fall by the evidence which its

94 THE FLOATING-MATTER OF THE AIR.

supporter is able to produce; and accordingly Dr.
Bastian appeals to the law and testimony of experiment
as demonstrating the soundness of his view. He seems
quite aware of the gravity of the matter in hand; this
is his deliberate and almost solemn appeal :—‘ With the
view of settling these questions, therefore, we may
carefully prepare an infusion from some animal tissue,
be it muscle, kidney, or liver; we may place it in a
flask whose neck is drawn out and narrowed in the blow-
pipe-flame, we may boil the fluid, seal the vessel during
ebullition, and, keeping it in a warm place, may await
the result, as I have often done. After a variable time
the previously neated fluid within the hermetically
sealed flask swarms more or less plentifully with Bacteria
and allied organisms—even though the fluids have been
so much degraded in quality by exposure to the tempera-
ture of 212° Fahr., and have thereby, in all probability,
been rendered far less prone to engender independent
living units than the unheated fluids in the tissnes
would be.’ !

We have here, to use the words of Dr. Bastian, ‘a
question lying at the root of the pathology of the most
important and most fatal class of diseases to which the
human race is liable.’ Let us now examine his settle-
ment of the question, as described by himself in the
foregoing extract.

§ 22. Experiments with Hermetically-sealed Vessels.

Experiments with hermetically-sealed tubes were
begun by me on the 5th of October, 1875. The shape
of the tubes after sealing is represented in fig.6. Each
of them contained about an ounce of liquid. They

! Transactions of the Pathological Society of London, 1875,
p. 272.

PUTREFACTION AND INFECTION. 95

were boiled for only three minutes in an oil-bath, and
were sealed, during ebullition, not by a blowpipe, but
by the far more effectual spirit-lamp flame.

Hay.—Four tubes were charged on the date
mentioned with a strong infusion, four with a weak
infusion. All eight flasks remain to the present hour
clear.

Turnip.—tTwo kinds of turnip were tried in these
first experiments. Two tubes were charged with a
strong infusion, and two with
a weak infusion of a sound
hard turnip; while two other
pairs of tubes were filled with
strong and weak infusions from
a soft woolly turnip. All the
tubes remain transparent to the
present time. Two or three
days’ exposure to the air of the
laboratory sufficed to cloud all
these infusions and fill them
with life.

On the 8th of October twenty-one tubes were
charged with infusions of the following substances :—
Mackerel, beef, eel, oyster, oatmeal, malt, potato. There
were three tubes of each infusion. All of them remain
to the present hour unchanged.

I had not previously seen a more beautiful illustra-
tion of the dichroitic action which produces the colours
of the sky than in the case of the oyster-infusion. With
reflected light it presented a beautiful cerulean hue,
while it was yellow by transmitted light. This was
due to the action of suspended particles which defied
alike the power of the microscope and of ordinary fil-
tration. At right angles to a transmitted beam the
infusion copiously discharged perfectly polarized light.

Fie. 6,

96 THE FLOATING-MATTER OF THE AIR.

Suspended particles in the potato-infusion produced a
somewhat similar effect, but it was by no means so
fine as that of the oyster-infusion. By ordinary filtra-
tion it was not possible completely to rid the malt and
oatmeal infusions of suspended matter; but both remain
exactly as they were when the flasks containing them
were sealed.

These experiments had been made before the volume
of the Transactions of the Pathological Society con-
taining the discussion referred to above came into my
hands,.' It caused me to turn again to my tubes, seek-
ing further evidence. Onthe 12th of November thirty-
six of them were charged, boiled, and hermetically
sealed ; on the 13th fifty-seven, on the 16th thirty-one,
and on the 17th six tubes were similarly treated. The
entire group of tubes, therefore, numbered one hundred
and thirty. I tried moreover to multiply the chances
of spontaneous generation by making the infusions of
the most diverse materials. The following Table gives

‘the names of the substances operated on, the number

of tubes sealed, and the date of sealing :—
Fowl tubes. | November 12th.
Mutton .
Wild Duck
Beef ;
Herring .
Haddock .
Mullet
Codfish
Pheasant .
Rabbit
Hare
Snipe

” ”

DDADAADAAAAAAaIwWR
S

1 To the courtesy of Dr. Bastian I am indebted for a separate
copy of the report of the discussion here referred to.

PUTREFACTION AND INFECTION. 97

Partridge.
Plover

Liver

Heart

Tongue of Sheep
Brains of Sheep
Sweetbread .
Humour of Ox-eye (anata)
Lens of Ox-eye ,
Lungs of Sheep
Tripe

Sole.

tubes November 13th.

” ”
” ”

»
55 November 16th.

” ”

APAMWNAWA QR AA
7
S

”
a November 17th.

The tubes were immersed in groups of six at a
time in an oil-bath, boiled for three minutes, and then
sealed.

More than one hundred of these flasks were sensibly
transparent and free from turbidity at the outset, and
they remain so to the present hour. In some cases,
however, it was not possible to wholly remove turbidity
by filtration. Ihave already referred to the opalescence
of oyster-infusion, which has invariably appeared when-
ever oyster has been digested. A still more pronounced
case of the kind is furnished by an infusion of the
crystalline lens of the ox. Nothing hitherto encountered
by me imitates the flush of the true opal so closely as this
infusion. Filtration through one hundred layers of paper
was quite incompetent to remove the suspended particles
to which this opalescence is due. Some of the other
infusions remained turbid after filtration, without ex-
hibiting what I should call opalescence. The sheep’s
lungs furnish an example of this. In some cases,
moreover, where repeated filtering failed to remove the
suspended particles, a few weeks’ quiet caused them to
sink, and leave the supernatant liquid clear. It may
be worth remarking that some rabbit-infusions have
shown a decided opalescence, while others have heen

98 FLOATING-MATTER OF THE AIR.

perfectly clear. The same remark applies to turnip-
infusions, some of which have been found as clear as dis-
tilled water, while in general a slight opalescence is not
to be got rid of by filtering.

These later experiments are quite in harmony with
the earlier ones. Not a single flask of this multitude
manifests the deportment alleged to be a matter of
common observation.’ If the power of spontaneous
generation be a scientific verity, surely amid opportu-
nities so multiplied and various it must have exerted
itself. That the infusions employed were not ‘de-
graded’ by the boiling so as to be incapable of sup-
porting life, was proved by the fact that exposed tubes
containing the same infusions, treated in precisely the
same way, resolved themselves with the usual speed
into Bacterial swarms,

§ 23. Conditions as to the Temperature and
Strength of Infusions.

In connection with these experiments, I have sought,
to the best of my ability, to meet every condition and
requirement laid down by others as essential to success.
With regard to warmth, a temperature of 90° was
generally attainable in our laboratory, while on cer-
tain days of mild weather without, and in favourable
positions within, the temperature to which the infu-
sions were subjected reached over 100° Fahr. As
Dr. Bastian, however, had laid considerable stress on
warmth, thougn most of his results were obtained
with temperatures from 15° to 30° lower than mine,? I

1 This group of flasks was submitted to the inspection of the
Fellows of the Royal Society on the 13th of January, 1876.

2 Proc. Roy. Soc. vol. xxi. p. 130. Also ‘ Beginnings of Life,’
vol. i. p. 354.

PUTREFACTION AND INFECTION, 99

thought it desirable to meet this new requirement also.
The sealed tubes, which had proved barren in the Royal
Institution, were suspended in boxes copiously per-
forated, so as to permit of the free circulation of warm
air, and placed under the supervision of an intelligent
assistant in the Turkish Bath in Jermyn Street. The
washing-room of the establishment was found to be
particularly suitable for our purpose; and here, accord-
ingly, the boxes were suspended. From two to six days
are allowed by Dr. Bastian for the generation of
organisms in hermetically-sealed tubes. Mine remained
in the washing-room for nine days. Thermometers
placed in the boxes, and read off twice or three times a
day, showed the temperature to vary from a minimum of
101° to a maximum of 112° Fahr. At the end of nine
days the infusions were as clear as at: the beginning.

They were then removed to a warmer position; the
temperature 115° having been mentioned as favour-
able to spontaneous generation. For fourteen days my
temperatures hovered about this point, falling once as
low as 106°, reaching 116° on three occasions, 118° on
one, and 119° on two. The result was quite the same as
that recorded a moment ago. The higher temperatures
proved perfectly incompetent to develop life.!

Fifty-six observations, including both the maximum
and minimum thermometers, were taken while the tubes
occupied their first position in the washing-room, and
seventy-four while they occupied the second position.
The whole record, carefully drawn out, is before me, but
I trust the statement of the major and minor limits of
temperature will suffice.

Dr. Bastian’s demand for these high temperatures is,
as already remarked, quite recent. Prior to my com-

1 My thanks are due to the managers of the bath for their
obliging kindness in this matter.

100 THE FLOATING-MATTER OF THE AIR

munication to the Royal Society on January 13, he had
successfully worked with temperatures lower than those
within my reach in Albemarle Street. There I followed
his directions, adhered strictly to his prescriptions; bul,
taking care to boil and seal the liquids aright, his results
refused to appear in my experiments. On learning this
“he raised an objection as to temperature, and made a
new demand. With this I have complied ; but bis posi-
tion is unimproved.

With regard to the question of concentration, I have
already referred, in sections 3 and 16 of this memoir,
to the great diversity in this particular presented by
all my infusions, through their slow evaporation.
But more than a general conformity to prescribed con-
ditions was observed here also. The strength of an
infusion is regarded as fixed by its specific gravity ;
and I have worked with infusions of precisely the
same specific gravity as those employed by Dr. Bastian.
This I was specially careful to do in relation to the
experiments described and vouched for, I fear incan-
tiously, by Dr. Burdon Sanderson in vol. vii. p. 180 of
‘Nature.’ It will there be seen that, though failure
attended some of his efforts, Dr. Bastian did satisfy
Dr. Sanderson that in boiled and hermetically-sealed
flasks Bacteria sometimes appear in swarms. With
purely liquid infusions I have failed to reproduce this
result. Hay- and turnip-infusions, of accurately the
same character and strength as those employed on
the occasion referred to, were prepared, boiled in an
oil-bath, carefully sealed up, and subjected to the
proper temperatures. In multiplied experiments they
remained uniformly sterile.'

1 One hundred and twenty flasks, hermetically sealed, contain-
ing animal and vegetable infusions, some two, some three yerrs old,
are now beside me. They show no sign of Bacterial life.

PUTREFACTION AND INFECTION. 101

§ 24. Developmental Power of Infusions and Solu-
tions: Air-germs contrasted with Water-germs.

Wishing to make no experiment, whether with self-
cleansed, filtered, or calcined air, or with infusions with-
drawn from air by the air-pump, or contained in
hermetically-sealed vessels, without exposing the same
infusions to ordinary air, this comparison was instituted
with the substances mentioned at pages 96 and 97.
One hundred test-tubes, an inch wide and 3 inches
deep, were divided into groups, each group being filled
with the same infusion. The groups were sufficiently
numerous to embrace all the substances mentioned in
the Table referred to. Exposed to the uncleansed air,
they were attacked with different degrees of rapidity
and vigour; but in a few days all of them without
exception became muddy and crowded with life. On
the whole, the hare- and pheasant-infusions presented
the greatest contrast. The tubes containing the former
were far gone before those containing the latter were
sensibly invaded. The putrescibility of pheasant, more-
over, was exceeded by that of snipe, partridge, and
plover. The sheep’s heart examined was also slow to
putrefy. A single illustration of this difference of
developmental power may be given here.

On the 13th of November thirty tubes, containing
infusions of partridge, pheasant, snipe, hare, sheep’s
heart, and codfish, five tubes being devoted to each, to-
gether with four tubes of plover, three of mullet, and
three of liver, were exposed to the laboratory air. On
the 15th, 16th, and 22nd the numbers taken possession
of by Bacteria were as follows :—

102 THE FLOATING-MATTER OF THE AIR.

15th. 16th. 22nd,
Partridge . : : . 0 3 all
Pheasant : 0 1 oe
Snipe . Poe) 3 os
Hare . . 2 4 i
Heart . . 0 1 as
Codfish a 2 4 39
Plover. a i 2 ”
Mullet . il 2 55
Liver . rae 3 55

They had doubtless all given way some days before
the 22nd, but I had not taken the precaution to look at
them.

Thus, then, the first two days produced no visible
change in the pheasant-infusion, while in two of the
hare-tubes putrefaction had vigorously set in. Three
days’ exposure caused only one of the pheasant-tubes to
yield ; four of the hare-infusion had yielded in the same
time. The difference between them was also illustrated
by the mould upon their surfaces. Some days after
their exposure four of the five pheasant-tubes were
thickly covered with Penicillium, while the five hare-
tubes, with one exception, which could hardly be con-
sidered such, had repelled that enemy, maintaining their
Bacteria undisturbed.

Still the deportment of the hare-infusion may have
been due, not to any specific difference between hare
and pheasant, but to the circumstances preceding death.
The researches of Dr. Brown-Séquard show that even the
same animal tissue exhibits, under different circum-
stances, very different tendencies to putrefaction. In
guinea-pigs subjected immediately after death to the
action of the magneto-electric current, he found the
rapidity of putrefaction to correspond with the violence
of the tetanization. He also draws attention to the

PUTREFACTION AND INFECTION. 103

influence of muscular exercise on cadaveric rigidity and
putrefaction, showing how quickly they appear in ‘ over-
driven cattle and in animals bunted to death. It is
known, indeed, to sportsmen that a shot hare will remain
soft and limp for a day, while a hunted one becomes
rigid in an hour or two. In September, 1851, two
sheep which had been overdriven to reach a fair were
killed by the section of the carotid arteries. ‘ Putrefac-
tion,’ says Dr. Brown-Séquard, ‘ was manifest before the
end of the day, or in less than eight hours after death.’ !
The deportment of the hare operated upon by me may
therefore depend upon the circumstance of its being
brought down by the greyhound instead of the gun. It
will be interesting to inquire how far the peculiarity of
the animal tissue is transferred to the infusion. This is
a fit subject for further investigation.?

Such observations inculcate caution in drawing in-
ferences from the deportment of any infusion as to the
distribution of germs in the air. The germs may be
demonstrably present while the infusion may not favour
their development. As to the quantity and quality of at-
mospheric germs, the hare and the pheasant might lead
to different conclusions. A passing reference to an im-
portant practical inference may be fitly introduced here.
In one of the earliest of the able series of researches
with which he has enriched medical science, Dr. Burdon
Sanderson exposed to the air ‘Pasteur’s solution,’ which is
capable of vigorously developing and nourishing Bacteria

1 Croonian Lecture, Proc. Roy. Soc. 1862, vol. xi. p. 210.

2 Five-and-twenty flasks containing pheasant-infusion were
compared during the month of December with five-and-twenty
containing infusion of hare, Neither in the rapidity of Bacterial
development, nor in the readiness to support the growth of Peni-
cillium, did the considerable differences between hare and pheasant
first observed repeat themselves.

6

104 THE FLOATING-MATTER OF THE AIR.

when they are communicated to it by inoculation; he
also permitted air to bubble through the liquid, and find-
ing no development in either case, he inferred the entire
absence of Bacteria and their germs from the air, con-
sidering water to be their exclusive habitation. Other
distinguished men have come to the same conclusion ;
while in his books and papers, and in the discussion be-
fore the Pathological Society already referred to, Dr.
Bastian has forcibly dwelt upon the result as justifying
the interpretation which he has affixed to his experi-
ments. If, he rightly urges, the air be ‘ entirely free’
from matter which could produce Bacteria, then their
appearance in boiled infusions exposed to the air must
be due, not to anything contained in the air, but to the
inherent power of the infusions. Spontaneous genera-
tion is undoubtedly the logical outcome of the position
that ‘the germinal matter from which Bacteria spring
does not exist in ordinary air.’ The experiments, how-
ever, recorded in this memoir constitute an ocular
demonstration of the respective parts played by the
infusion and the air. A pinch of fungus-spores, taken
between the fingers, sown in a suitable medium, and
producing their appropriate crop, could not more clearly
indicate the origin of that crop than experiments with
the luminous beam indicate the origin of our harvests
of Bacteria. Dr. Sanderson is, I doubt not, now well
aware that his first statement was founded on an error of
interpretation. In a lecture delivered at Owens College,
Manchester, and published in the ‘British Medical
Journal’ for January 16, 1875, he to a great extent
qualifies and corrects his first inference. He there says
that the Bacteria ‘attach themselves without doubt to
these minute particles, which, scarcely visible in ordinary
light, appear as motes in the sunbeam, or in the beam
of an electric lamp.’ In fact the experiments on which

PUTREFACTION AND INFECTION. 105

he based his first inference owed their barrenness, not to
the absence of Bacteria-germs from the air, but to the
inability or, rather, slowness of his mineral solution to
develop them.

With regard to the part played by the visible motes,
I may repeat here what has been previously stated,
namely, that while the coarser particles could hardly
exist in their midst without loading themselves to some
extent with the minute germs of Bacteria, there is no
reason to think the motes indispensable for the diffusion
of the germs. Whether they are attached to each other
or not, the dryness and the moisture of the air are shared
equally by both. The germs, moreover, float in the air
more readily than the larger particles ; and they, I doubt
not, when properly illuminated, shed forth a portion of
that changeless light to which reference has been already
made, and the perfect polarization of which declares the
smallness of the masses which scatter it.

The prevalence of the germinal matter of Bacteria
in water has been demonstrated by the experiments of
Dr. Burdon Sanderson. But the germs in water, it
ought to be remembered, are in a very different condi-
tion, as regards readiness for development, from those in
air. In water they are already wetted, and ready, under
the proper conditions, to pass rapidly into the finished
organism. In air they are more or less desiccated, and
require a period of preparation more or less long to
bring them up to the starting-point of the water-germs.'

1 The process by which an atmospheric germ is wetted would
be an interesting subject of investigation. A dry microscope
covering-glass may be caused to float on water for a year. A
sewing-needle may be similarly kept floating, though its specific
gravity is nearly eight times that of water. Were it not for some
specific relation between the matter of the germ and that of the
liquid into which it falls, wetting would be simply impossible.
Antecedent to all development there must be an interchange of

106 -THE FLOATING-MATTER OF THE AIR.

The rapidity of development in an infusion infected
by either a speck of liquid containing Bacteria, or by a
drop of distilled water, is extraordinary. On the 4th of
January I dipped a thread of glass almost as fine as a hair
into a cloudy turnip-infusion, and introduced the tip
only of the glass fibre into a large test-tube containing
an infusion of red mullet: twelve hours subsequently
the perfectly pellucid liquid was cloudy throughout. A
second test-tube containing the same infusion was in-
fected with a single drop of the distilled water furnished
by Messrs. Hopkin and Williams; twelve hours also
sufficed to cloud the infusion thus treated. Precisely
the same experiments were made with herring infusion,
with the same result. In the winter season several days’
exposure to warmed air are needed to produce this effect
with air-germs.

On the 31st of December a strong infusion was pre-
pared by digesting turnip in distilled water at a tem-
perature of 120° Fahr. It was divided between four large
test-tubes, in one of which the infusion was left unboiled,
in another boiled for five minutes, in the two remain-
ing ones boiled and, after cooling, infected with one
drop of beef-infusion containing Bacteria. In twenty-
four hours the unboiled tube and the two infected ones
were cloudy, the unboiled tube being the most turbid of
the three. The infusion in the unboiled tube was pecu-
liarly limpid after digestion; for turnip it was quite
exceptional, and no amount of searching with the micro-
scope could reveal in it at first the trace of a living
Bacterium; still germs were there which, suitably
nourished, passed in a single day into Bacterial swarms
without number. Five days failed to produce an effect

matter between the germ and its environment; and this inter-
change must obviously depend upon the character of the encom-
passing liquid.

PUTREFACTION AND INFECTION. 107

approximately equal to this in the uninfected boiled
tube, which was exposed to the common laboratory air.
There cannot, I think, be a doubt that the germs in
the air differ widely among themselves as regards pre-
paredness for development. Some are fresh, others
old; some are dry, others moist. Infected by such germs,
the same infusion would require different lengths of
time to develope Bacterial life. And this remark, I
doubt not, applies to the different degrees of rapidity
with which epidemic disease affects different people.
In some the hatching-period, if I may call it such, is
long, in some short, the differences depending upon the
different degrees of preparedness of the contagium.!

§ 25. Diffusion of Germs in the Air.

During the earlier observations recorded in this
essay, and others not here mentioned, about 100 ex-
posed tubes or flasks had been distributed irregularly in
the rooms where the inquiry is conducted. They ex-
panded to nearly 1000 in the end: not one of them
escaped infection. A few days always sufficed to cloud
the exposed infusions, and fill them with Bacterial life.
I placed tubes at various points in the Royal Institu-
tion—on the roof of the house outside, in my bedroom,
in an upper kitchen, in my study, in the upper and
lower libraries, in the theatre, model-room, reading-room,
managers’ room, and in the kitchen at the bottom of
the house below the level of Albemarle Street. All
were smitten with putrefaction, and with its invariable

1 The medical student of the future will probably connect these
remarks with the following statement of Dr. Murchison :—-‘In
that protean disease typhoid fever, I have repeatedly had occasion
to observe a remarkable similarity in the course, and even in the
complications, according to the source of the poison.’—Trans. Path,
Soc. vol. xxvi. p. 315.

108 THE FLOATING-MATTER OF THE AIR.

associate, Bacteria. In the rooms without fires the
action was slower than in the warmer rooms; but all
the infusions gave way in the end.

In view of the statements which had been made
regarding the scantiness of Bacteriu-germs in the air,
observations outside of London would, I thought, be
interesting. Accordingly, on the 27th of October, a
tube containing an infusion of beef was placed in the
hands of Mr. Darwin, who had the kindness to set it in
his study at Down and observe its changes. In three
days it became cloudy and peopled with Bacteria. The
same result was obtained in the open air. Mr.
Francis Darwin was good enough to expose an infusion
for me in his father’s orchard: the weather was cold,
and the progress, therefore, slow; but the tube which
had been exposed on the 2nd of November was cloudy
and full of Bacteria on the 9th. In Sir John Lubbock’s
study a similar result: was obtained. From Sherwood,
near Tunbridge Wells, infusions of fowl and wild duck
were returned to me by Mr. Siemens thickly turbid
and crowded with Bacteria. From Pembroke Lodge,
Richmond Park, Mr. Russell returned tubes of turnip,
beef, and mutton swarming with life. An infusion
of beef exposed at Heathfield Park, Sussex, for a
week was returned to me by Miss Hamilton muddy
and filled with Bacteria. From Greenwich Hospital]
Mr. Hirst sent me tubes of beef-, mutton-, and turnip-
infusion filled with vigorous Bacteria. Dr. Hooker
was good enough to take charge of three sets of tubes
at Kew, each set embracing beef, mutton, and turnip.
One set was placed in the conservatory, with a tem-
perature of 45° to 50°; one in his own study, with a
temperature of 54° to 60°; a third set was placed in
the orchid-house (the hottest in the gardens), with a
temperature of 62° to 75°.

PUTREFACTION AND INFECTION. 109

The tubes were exposed on the 4th of December, all
of them being then clear. In the orchid-house the
turnip became cloudy on the 7th, the beef and mutton
on the 8th, after which the opacity rapidly increased.
In the study all remained clear until the 9th, when the
turnip began to cloud. On the 11th the beef was still
clear, while the mutton had given way. On the 13th
all of them had yielded. In the conservatory the turnip
began to cloud on the 10th; the others followed in
the same order as in the other cases.

The influence of temperature seems well shown
by these observations. Three days sufficed to cloud the
turnip in the orchid-house, five days in the study, and
six days in the conservatory. The mutton in the study
gathered over it a thick blanket of Penicillium. On
the 13th it had assumed a light brown coleur, ‘as if by
a faint admixture of clay;’ but the infusion became
transparent. The ‘clay’ here was the slime of dormant
or dead Bacteria, the cause of their quiescence being
the blanket of Penicillium. I found no active life in
this tube, while all the others swarmed with Bacteria.
From the Crystal Palace at Sydenham Mr. Price sent
me tubes of mutton, beef, and turnip charged with
Bacteria. The temperature was low at night, the
development of life being thereby considerably retarded.

Thus, wherever it has been tested, the atmosphere
has been found charged with the germs of Bacteria.

I wished, however, to obtain clearer and more defi-
nite insight as to the diffusion of atmospheric germs.
Supposing a large shallow tray to be filled with a suitable
organic infusion and exposed to the ‘air. Into it the
germs would drop; and could the resulting organisms
be confined to the locality where the germs fell, we
should have the floating life of the atmosphere mapped,

110 THE FLOATING-MATTER OF THE AIR.

so to speak, in the infusion. But in such a tray the
organisms would intermingle and thus mar the revela~
tion of their distribution. Valuable information I
thought might be gained by breaking up the infusion
into isolated conterminous patches, and exposing them
to the air.

A square wooden tray was accordingly pierced with
one hundred circular apertures; into each of which
was dropped a test-tube 3 inches long and 1 inch wide,
with its rim resting in each case upon the rim of the
aperture. There were ten rows of tubes, with ten tubes
in each row. On the 23rd of October, 1875, thirty of
these tubes were filled with an infusion of hay, thirty-
five with an infusion of turnip, and thirty-five with an
infusion of beef. The tubes with their infusions had
been previously boiled ten at a time in an oil-bath.

One hundred circles were marked upon paper so as
to form a plan of the tray, and every day the state of
each tube was registered upon the corresponding circle.
Seven such maps or records were executed.

I will use the term ‘cloudy’ to denote the early
stage of turbidity, distinct but not strong. The term
* muddy’ will be used to denote thick turbidity.

§ 26. Tray of one hundred Tubes.

On the 25th of October one or two of the tubes
exposed on the 23rd showed signs of yielding; but the
progress of putrefaction was first registered on the
26th. Fig. 7, embracing the first record, is annexed;
it may be thus described.

Hay.—Of the thirty specimens exposed, one had
become ‘muddy ’—the seventh in the middle row,
reckoning from the side of the tray nearest a stove.
Six tubes remained perfectly clear between this muddy
one and the stove, proving that differences of warmth

PUTREFACTION AND INFECTION. 111

may be overridden by other causes. Every one of the
other tubes containing the hay-infusion showed spots of
mould upon the clear liquid.

Turnip.—F our of the thirty-five tubes were very
muddy, two of them being in the row next the stove,
one four rows distant, and the remaining one nine rows
away. Besides these, seven tubes had become clouded.
There was no mould on any of the tubes.

Beef.—One tube of the thirty-five was quite muddy,
in the seventh row from the stove. There were three
cloudy tubes, while seven of them bore spots of mould.

As a general rule organic infusions exposed to the
air during the autumn remained for two days or more
perfectly clear. Doubtless from the first germs fell
into them, but the germs required time to become or~
ganisms. This period of clearness may be called the
‘period of latency ;’ and, indeed, it exactly corresponds
with what is understood by this term in medicine.
Towards the end of the period of latency the fall into a
state of disease, if I may use the term, is comparatively
sudden ; the infusion passing from perfect clearness to
cloudiness more or less dense in a few hours.

Thus the tube placed in Mr. Darwin’s possession
was clear at 8.33 a.m. on the 19th of October, and
cloudy at 4.30 p.m. Seven hours, moreover, after the
first record of our tray of tubes, a marked change had
occurred. For the purpose of comparison the second
record, fig. 8, is placed beside the first. The change
may be thus described:—Instead of one, eight of the
tubes containing hay-infusion had fallen into uniform
rouddiness. Nineteen of them had produced Bacterial
slime, which had fallen to the bottom, every tube con-
taining the slime being covered by mould. ‘Three tubes
only remained clear, but with mould upon their sur-
faces. The muddy turnip-tubes had increased from four
to ten; seven tubes were clouded, while eighteen of them

112 THE FLOATING-MATTER OF THE AIR.

remained clear, with here and there a speck of mould on
the surface. Of the beef, six were cloudy and one thickly
muddy, while spots of mould had formed on the majority
of the remaining tubes. Fifteen hours subsequent to this
observation, viz. on the morning of the 27th of October,
all the tubes containing hay-infusion were smitten,
though in different degrees, some of them being much

Fic, 7. 26th Oct., noon.

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Mould, Cloudy. Muddy.

more iehag than others, Of the turnip-tubes, three
only remained unsmitten, and two of these had mould
upon their surfaces. Only one of the thirty-five beef-
infusions remained intact. A change of occupancy,
moreover, had occurred in the tube which first gave
way. Its muddiness remained grey for a day and a
half, then it changed to bright yellow-green, and

PUTREFACTION AND INFECTION. 113

maintained this colour to the end. On the evening of
the 27th every tube of the hundred was smitten, the
majority with uniform turbidity, some, however, with
mould above and slime below, the intermediate liquid
being clear. The whole process bore a striking resem-
blance to the propagation of a plague among a popula-
tion, the attacks being successive and of different
Fi, 8, 26th Oct., 7 Px.

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Slime. Slime and Mould. Clear.
degrees of virulence. I annex copies of the fourth and
seventh maps (figs. 9, 10) with their respective dates.
On the 31st of October I finally inspected the tray
of tubes. All those containing the hay-infusion were
turbid, some thicker and much more deeply coloured

114 THE FLOATING-MATTER OF THE AIR.

than others. They had been all at first aliké in colour.
Out of the thirty tubes four only were free from mould.
Three of these were adjacent to each other, the fourth
at a distant portion of the tray.

The Penicillium was exquisitely beautiful. Its
prevalent form was a circular patch made up of alternate

zones of light and deep green. In some cases the liquid
Fig. 9. 27th Oct., 6.30 P.M.

COD OOOQ90C6
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é S97 90809

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oS Q

Cloudy. Green.

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Slime, Slime and mould. Clear.
was covered by a single large patch; in others there
were three or four patches, each made up of its dif-
ferently coloured zones. Reticulated patterns also
occurred, Three kinds of Penicillium seemed strug-
gling for existence, namely:—that just described; a
second kind, of the same consistency and colour, fat

PUTREFACTION AND INFECTION. 115

forming little rounded heaps instead of circles ; thirdly,
a woolly, voluminous, white mould, in the middle of
which a zoned circle of the other mould sometimes
formed a little islet.

All the tubes containing the turnip-infusion were
also turbid on the 3lst. Nine of them were free from
mould. This, where it occurred, exactly resembled

Fia. 10, 29th Oct., 10.30 aa,

@eececeeece
@000000009:

small cocoons in shape. The beef-tubes were also all
turbid on the 31st, and seventeen of them were free
from mould. The mould upon the beef, moreover, was
muck. less luxuriant than that on the hay- and turnip-
infusions. The mould-developing power is obviously
greatest in the hay-, less in the turnip-, and least of all
in the beef-infusion. In every case where the mould

116 THE FLOATING-MATTER OF THE AIR.

was thick and coherent the Bacteria died, or became
dormant, and fell to the bottom as a sediment. The
growth of mould and its effect on the Bacteria are very
capricious. The turnip-infusion, after developing in
the first instance its myriadfold Bacterial life, fre-
quently contracts mould, which stifles the Bacteria and
clears the liquid all the way between the sediment and
the scum. Of two tubes placed beside each other, one
will be taken possession of by Bacteria, which success-~
fully fight the mould and keep the surface perfectly
clean ; while another will allow the mould a footing, the
apparent destruction of the Bacteria being the con-
sequence. This I have proved to be the case with all
infusions, fish, flesh, fowl, and vegetable. At the pre-
sent moment, for example, of three tubes containing an
infusion of sole, placed close together in a row, the two
outside ones are covered by a thick tough blanket of
mould, while the central one has not a single speck
upon its surface. The Bacteria which manufacture a
green pigment appear to be uniformly victorious in
their fight with the Penicillium.

These observations enable us, I think, to draw some
interesting conclusions. From the irregular manner in
which the tubes are attacked we may infer that, as
regards quantity, the distribution of the germs in the
air is not uniform. A single tube will sometimes be a
day or more in advance of its neighbours. The singling
out, moreover, of one tube of the hundred by the par-
ticular Bacteria that develop a green pigment, and
other cases just adverted to, shows that, as regards qual-
ity, the distribution is not uniform. This has been
further illustrated by the following observations :—Of
five-and-twenty tubes of different animal infusions ex-
posed in groups of five, in the middle of November, and

PUTREFACTION AND INFECTION. 117

all swarming with Bacterial life, five were green. They
were distributed as follows:—Beef 2, herring 1, had-
dock 1, fowl 1, wild duck 0. The same absence of
uniformity was manifested in the struggle for existence
between the Bacteria and the Penicillium. In some
tubes the former were triumphant; in other tubes of
the same infusion the latter was triumphant. It would
also seem that a want of uniformity as regards vital
vigour prevailed. With the self-same infusion the
motions of the Bacteria in some tubes were exceedingly
languid; while in other tubes the motions resembled
a rain of projectiles, being so rapid and violent as to be
followed with difficulty by the eye. Reflecting on the
whole of this, I conclude that the germs float through
the atmosphere in groups or clouds, and that now and
then a cloud specifically different from the prevalent ones
is wafted through the air. The touching of a nutritive
fluid by a Bacterial cloud would naturally have a dif-
ferent effect from the touching of it by the sterile air
between two clouds. But, asin the case of a mottled
sky, the various portions of the landscape are succes-
sively visited by shade, so, in the long run, are the various
tubes of our tray touched by the Bacterial clouds, the
final fertilization or infection of them all being the
consequence.’

1 In hospital practice the opening of a wound during the pass-
age of a Bacterial cloud would have an effect very different from
the opening of it in the interspace between two clouds. Certain
caprices in the behaviour of dressed wounds may possibly be ac-
counted for in this way.

Under the heading ‘Nothing New under the Sun,’ Professor
Huxley has lately sent me the following remarkable extract :—
‘ Uebrigens kann man sich die in der Atmosphire schwimmenden
Thierchen wie Wolken denken, mit denen ganz leere Luftmassen,
ja ganze Tage vollig reinen Luftverhiltnisse wechseln.’ (Ehbren-
berg, ‘Infusionsthierchen,’ 1838, p. 525.) The coincidence of
phraseology is surprising, for I knew nothing of Ehrenberg’s con-
ception. My ‘ clouds,’ however, are but small miniatures of his,

118 THE FLOATING-MATTER OF THE AIR.

The tray of tubes proved so helpful in enabling me
to realize mentally the distribution of germs in the air,
that on the 9th of November, 1875, I exposed a second
tray containing one hundred tubes filled with an infusion
of mutton. On the morning of the 11th six of the ten
nearest the stove had given way to putrefaction; three
of the row most distant from the stove had yielded,
while here and there over the tray particular tubes were
singled out and smitten by theinfection. Of the whole
tray of one hundred tubes, twenty-seven were either
muddy or cloudy on the 11th. Thus, doubtless, in
an infective atmosphere, are individuals successively
struck down. On the 12th all the tubes had given
way, but the differences in their contents were extraor~
dinary. All of them contained Bacteria, some few,
others in swarms. In some tubes they were slow and
sickly in their motions, in some apparently dead, while
in others they darted about with rampant vigour. These
differences are to be referred to differences in the ger-
minal matter, for the same infusion was presented
everywhere to the air. Here also I imagine we have a
picture of what occurs during an epidemic, the difference
in number and energy of the Bacterial swarms resem-
bling the varying intensity of the disease. It becomes
obvious from these experiments that of two individuals
of the same population exposed to a contagious atmo-
sphere, the one may be severely, the other lightly
attacked, though, as regards susceptibility, the two
individuals may be as identical as two samples of one
and the same mutton-infusion. What I have already
said regarding the ‘ preparedness’ of contagium has its
application here.

_ The parallelism of these actions with the progress
of infectious disease may be traced still further. The
‘ Times,’ for example, of January 17, 1876, contained a
letter on typhoid fever, signed ‘ M.D.,’ in which occurs

PUTREFACTION AND INFECTION. 119

the following remarkable statement :—‘ In one part of it
[Edinburgh], congregated together and inhabited by the
lowest. of the population, there are, according to the
Corporation return for 1874, no less than 14,319 houses
or dwellings—many under one roof, on the “ flat”
system—in which there are no house connexions what-
ever with the street-sewers, and, consequently, no water-
closets. To this day, therefore, all the excrementitious
and other refuse of the inhabitants is collected in pails
or pans, and remains in their midst, generally in a par-
titioned-off corner of the living-room, until the next
day, when it is taken down to the streets and emptied
into the Corporation carts. Drunken and vicious though
the population be, herded together like sheep, and with
the filth collected and kept for 24 hours in their very
midst, it is a remarkable fact that typhoid fever and
diphtheria are simply unknown in these wretched
hovels.’

The analogy of this result with the behaviour of our
infusions is perfect. On the 30th of last November, for
example, a quantity of animal refuse, embracing beef,
fish, rabbit, hare, was placed in two large test-tubes
opening into a protecting-chamber containing six tubes.
On December 13, when the refuse was in a state of
noisome putrefaction, infusions of whiting, turnip, beef,
and mutton were placed in the other four tubes. They
were then boiled and abandoned to the action of the foul
‘ sewer-gas’ emitted by their two putrid companions.
On Christmas-day, 1875, these four infusions were limpid.
The end of the pipette was then dipped into one of the
putrid tubes, and a quantity of matter, comparable in
smallness to the pock-lymph held on the point of a
lancet, was transferred to the turnip. Its clearness was
not sensibly affected at the time; but on the 26th it
was turbid throughout. On the 27th a speck from the
infected turnip was transferred to the whiting ; on the

120 THE FLOATING-MATTER OF THE AIR.

28th disease had taken entire possession of the whiting.
To the present hour the beef- and mutton-tubes remain
as limpid as distilled water. Just as in the case of the
living men and women in Edinburgh, no amount of
fetid gas had the power of propagating the plague, as
long as the organisms which constitute the true con-
tagium did not gain access to the infusions.

In the foregoing observations the tubes were arranged
in the same horizontal plane; but I also sought to ob-
tain some notion of the vertical distribution of the
germs in the air of the room. Two trays, each contain-
ing 100 tubes, were supported the one above the other
in the same frame. The upper tray had all the air be-
tween it and the ceiling, a height of about 12 feet, from
which the germs might descend upon it; the lower tray
was shaded by the upper, a space of only 6 inches exist-
ing between them. If the number of germs deposited
in the tubes were determined by the air-space above,
the upper tray would be the one most rapidly and
thoroughly taken possession of. The reverse was the
case. As regards the development of Bacterial life, the
lower tray was from first to last in advance of its neigh-
bour. It is not air-space, then, so much as stillness,
that determines the deposition of the germs. The air
between the two trays being less disturbed than the
general air of the room, the germs were less wafted
about, and therefore sank in greater numbers into the
tubes of the lower tray. We have here data which will
enable us to form a rough notion of the lower limit of
the number of germs contained in the room where the
experiments were made.

The floor of the room measured 20 feet by 15 feet ;
its area was therefore 43,200 square inches, and every
square inch would afford room for the section of one of
our test-tubes. The height of the room is 180 inches;

PUTREFACTION AND INFECTION. 121

hence 30 layers of tubes 6 inches apart might be placed
one above the other between the floor and ceiling.
This would make 1,296,000 tubes. If only a single
germ a day fell into each tube, this would be the number
of the germs. If the number deposited were one an
hour, we should have thirty millions a day sown in the
tubes. Probably the average time necessary for infec-
tion is very much less than an hour. At all events,
30,000,000 of germs daily would be an exceedingly
moderate estimate of the number falling into our thirty
layers of tubes. This, moreover, would only be a frac-
tion—probably a small fraction—of the germs really
present in the air. In his Presidential Address to the
British Association at Liverpool, Professor Huxley ven-
tured the statement that myriads of germs are floating
in our atmosphere. Certain experimenters have rashly
ridiculed this statement. In view of the foregoing
calculation it, however, expresses the soberest fact.
Indeed, taking the word myriad in its literal sense of
ten thousand, it would be simple bathos to apply it to
the multitudinous germs of our air.

§ 27. Some Experiments of Pasteur and.their Rela-
tion to Bacterial Clouds.

Quite recently I had occasion to refresh my memory
of Pasteur’s paper published in the ‘ Annales de Chimie’
for 1862. The pleasure I experienced on first reading
it was revived by its reperusal. Clearness, strength, and
caution, with consummate experimental skill for their
minister, were rarely more strikingly displayed than in
this imperishable essay. Hence it is that during recent
discussions, in which this and other labours of the
highest rank met with such scant respect, those in
England most competent to judge of the value of scien-

122 THE FLOATING-MATTER OF THE AIR.

tific work never lost faith in the substantial accuracy of
Pasteur. One striking example of his penetration has
an immediate bearing on the conclusion regarding
Bacterial clouds, independently drawn by me from the
deportment of the tray of one hundred tubes. On the
28th of May, 1860, Pasteur opened, on an uncovered
terrace a few metres above the ground, four flasks con-
taining the water of yeast. Nothing appeared in any
of them until the 5th of June, when a small tuft of
mycelium was observed in one of them. On the 6tha
second tuft appeared in another flask ; the two remaining
flasks continued intact and without organisms. On the
20th of July he opened, in his own laboratory, six flasks
containing water of yeast. Tour of them remained per-
fectly intact, while two of them became promptly charged
with organisms. From these observations Pasteur in-
ferred the non-continuity of the cause to which so-called
spontaneous generation is due. This inference is quite
in accord with the notion of Bacterial clouds suggested
by my observations. Pasteur, in fact, sometimes opened
his flask in the midst of a Bacterial cloud and obtained
life, sometimes in the interspace between two clouds,
and obtained no life.

Not with a view of repeating this observation, which
I had forgotten, but for another reason, I opened on
the 6th of January last a number of hermetically-sealed
tubes in one and the same room of the Royal Institu-
tion. The names of the infusions contained in the
tubes, the date of sealing them up, their condition be-
fore opening on the 6th, and their appearance six days
subsequently are given in the accompanying table.
J chose for these observations tubes which coutained a
little liquid in their drawn-out portions. In every case
the motion of this liquid, when the tube was broken,
indicated a violent inrush of air.

PUTREFACTION AND INFECTION.

123

Tahision. ca aaa gees 7 Oa ae
Grouse Nov. 27th Clear Clear.
Sole . ‘ » 17th +3 Turbid.
Turnip No. 1 Oct. 5th 55 Penicillium
on surface.
Turnip No. 2 sat his 5 Clear.
Tlay . : ” oo” ” Mycelium
at bottom.
Wild Duck Nov. 12th ‘5 Turbid.
Mutton » oo” Cloudy.
Fowl moo” ” Clear.
Beef . Fy Sy 45 Mycelium
at bottom.
Haddock . ube, Eg 55 Clear.
Sweetbread y 16th i Mycelium
at bottom.
Rabbit y 18th +) Clear.
oath yo» ” Curdy layer
at top.
Pheasant . a 755 ” Clear.
Mullet yoo” ” ”
| Hare. » oo” ” ”
Snipe . mo” ” ”
Partridge . no” ” ”
Plover 5 8 93 Mycelium
below.
Codfish aye ae A Clear.
Kidney Jan, 5th ” Mycelium
at bottom.
Salmon Dec. 18th = Clear.
Whiting ” 9 ” ”
Turnip. é : » 29th ” 55
Hay, 4 drops of caustic | Nov, 22nd | Clear with | Mycelium
potash sediment at bottom.
Hay, 2 drops of caustic rae, Clear Mycelium
potash at bottom.
Hay, 5 drops of caustic ae Clear with | Clear.
potash sediment
Hay, 6 drops of caustic $3 Clear with i
potash sediment
Liver Nov. 30th Clear v
Hey . y 18th ” ”
ay. 9” ” ”
Turnip yo” ” Muddy.

124 THE FLOATING-MATTER OF THE AIR.

Thus, out of 31 flasks opened in the same air, 18
remained intact, while 13 were taken possession of by
organisms—a fact obviously the same in character as
that described by Pasteur. Such experiments demon-
strate, if demonstration were needed, that it is not
the air itself, or any gaseous or vaporous substance
" uniformly diffused through it, but some discontinuous
substance floating in it, that is the cause of the infec-
tion. Instead of our tubes, let us suppose thirty-one
wounds to be opened in the same ward of a hospital;
plainly what has occurred with the tubes may occur with
these wounds—some may receive the germs and putrefy,
others may escape. Helped by the conception not only
of germs, but of germ-clouds, the different behaviour of
wounds subjected apparently to precisely the same con-
ditions will cease to be an inscrutable mystery to the
surgeon.!

During the course of this inquiry some eminent
biologists have been good enough, from time to time,
to look in upon my work, and to give me their views

1 «We have ample facts of experiment in our hands,’ said Mr.
Knowsley Thornton (Trans. of the Pathological Society, vol. xxvi.
p. 313), ‘to show that it is not the gases of the air, or any soluble
material in water, but something “particulate ”’ which sets up all
the train of changes in an open wound, which may, after the patient
has passed through a period of more or less constitutional disturb-
ance, end in the healing of the wound, or may end in septicemia
and death. This particulate material, then, I believe we have evi-
dence enough to prove consists of germs of Bacteria and other low
organisms.’ All the evidence points to this conclusion. I may say
that I entirely agree with Mr. Thornton in the distinction he draws
between germs and developed J?acteria floating in the air. It is, in
my opinion, of the very last importance to seize this distinction
with clearness. When it is fully realized we shall probably hear
less of the arguments against Bacterial contagia founded on the
fact that a virus diminishes in strength as the Bactcria multiply.
A portion of the energy of the virus consists in its passage from the
germ state to that of the finished organism.

PUTREFACTION AND INFECTION. 125

regarding the evidential force of the experiments. To
Professor Huxley, moreover, I am indebted for under-
taking the examination of a number of the hermetically-
sealed tubes. Thirty of them were placed in his hands,
none of them being regarded as defective. A close
examination, however, disclosed in one of them a myce-
lium. No faultiness could for a time be discovered in
the tube; the sealing appeared to be quite as perfect as
that of its sterile fellows. Once, however, on shaking it
a minute drop of liquid struck my friend’s face ; and he
soon discovered that an orifice of almost microscopic
minuteness had been left open in the nozzle of the tube.
Through this the common air had been sucked in as
the liquid cooled, and hence the contamination. It was
the only defective tube of the group of thirty, and it
alone showed signs of life.

The statement of this fact before the Royal Society,
by Professor Huxley, brought to my mind a somewhat
similar experience of my own. One morning in Novem-
ber I lifted one of the hermetically-sealed tubes from
the wire on which it was suspended, and, holding it up
against the light, discovered, to my astonishment, a
beautiful mycelium at the bottom. Before restoring
the tube to its place I touched its fused end and
found it cutting sharp. Close inspection showed that
the nozzle had been broken off; the common air had
entered, and the seed of the mycelium had been sown.
Two other instances, one like that observed by Professor
Huxley, have since come to light. In one of thema
minute orifice remained after the supposed sealing of the
tube. The other case was noticed when the tubes were
returned from the Turkish bath. One of them contained
a luxuriant mycelium. It was noticed that the liquid
in this tube had singularly diminished in quantity, and
on turning the tube up it was found cracked at the
bottom.

126 THE FLOATING-MATTER OF THE AIR.

No case of pseudo-spontaneous generation ever
occurred under my hands that was not to be accounted
for in an equally satisfactory manner.

In this inquiry, thus far, I have confined my ob-
servations to purely liquid infusions, purposely exclud-
ing milk, mixtures of turnip-juice and cheese, and,
indeed, mixtures of solids and liquids of all kinds. The
next section of the investigation will be devoted to these
and kindred subjects; and to it I also postpone the
complete examination of pepton, and of the remarkable
experiments described by Dr. William Roberts, a small
residue of which only I have failed to corroborate.

Throughout the whole of this investigation I have
had to congratulate myself on the zealous and efficient
aid of my excellent assistant, Mr. John Cottrell. His
intelligence in seizing my ideas, and his mechanical
skill in realizing them, have rendered me admirable
service. Without such aid, indeed, so much ground
could not have been covered in the time.

Royal Institution, 5th April, 1876.

It gives me special pleasure to direct attention here
to a paper by the Rev. W. H. Dallinger, for an advanced
proof of which I am indebted to the courtesy of Dr.
Lawson, editor of the ‘Popular Science Review.’ Mr.
Dallinger and his colleague Dr. Drysdale are known to
have pushed the microscope to its utmost power of per-
formance at the present time. Their ‘ Researches into
the Life-History of the Monads’ are models of scientitic
thoroughness and concentration. Mr. Dallinger’s review
of the present position of the doctrine of spontaneous
generation, his remarks on Bacterial germs in relation

PUTREFACTION AND INFECTION. 127

to the limits of the powers of the microscope, his
demonstration that the germs of monads survive in a
medium raised to a temperature which destroys the
adult, and that precipitated mastic particles like those
mentioned in § 16 of this paper are not to be discerned
by a magnifying-power of 15,000 diameters, constitute
a most interesting and important communication.

Nore I. Action of Bacteria upon a Beam of Light.

To trace the gradual growth and multiplication of the
Bacteria by their action on a beam of light, an infusion
of beef was prepared on the 5th of October, 1875, placed
in a globular flask of about 50 cubic inches capacity,
and put aside with its mouth open to the laboratory air.
On the 8th, 9th, 10th, 11th, and 12th similar flasks were
prepared and put aside in succession. On the 12th all the
flasks were examined by the concentrated electric light.
The freshest one showed the track of the beam asa richly-
coloured green cone. The green light was unaffected
by a Nicol’s prism, which, however, quenched the ordi-
nary scattered light and augmented the purity and
vividness of the green. It was a case of fluorescence.
In the second flask, one day old, the fluorescent beam
was in great part masked by the scattered light; the
latter, however, could be partially quenched by a Nicol’s
prism, the purity of the fluorescence being thus in part
restored. Through the third flask, two days, and through
the fourth flask, three days old, the track of the beam
was-still discernible; through the fifth flask, four days
old, it was all but obliterated, while in the sixth flask,
seven days old, it was entirely shattered, the turbid
medium being filled uniformly with the laterally scat-
tered light.

Two of these flasks were of a bright yellow-green

7

128 THE FLOATING-MATTER OF THE AIR.

colour, two were milky or white, and two of a dull
brownish hue.

Cohn mentions the bluish tinge of the infusion by
reflected and its yellow tinge by transmitted light when
the Bacteria are incipient. This is due to a dichroitic
action, similar to that which produces the blue of the
sky and the morning and evening red. The blue, how-
ever, though discernible, is not pronounced, for the
Bacteria are too large to scatter the colour in any high
degree of purity; but with a ‘muddy’ infusion a very
fair red may be obtained from transmitted light. I
have used the Bacterial turbidity for photometric put -
poses. On the 9th of October, for example, I ac-
companied Sir Richard Collinson and a Committee of
the Elder Brethren of the Trinity House to Charlton,
with the view of comparing together two lights
mounted at the Trinity Wharf at Blackwall. To imi-
tate a foggy atmosphere, I employed an infusion cloudy
with Bacteria and placed in a glass cell. With it the
beams could be toned gradually down to complete ex-
tinction.

Norte II. Fluorescence of Infusions.

All the animal infusions, both flesh and fish, showed
the same fluorescence. Jt was the same green hue
throughout, though of varying degrees of intensity.
In wild duck, grouse, snipe, hare, partridge, and
pheasant the fluorescence was fine—sometimes exceed-
ingly fine. In rabbit it was less fine than in hare, and
in a tame rabbit less fine than in a warren rabbit.
Fishes also differed from each other. Mullet, for
example, was finer than cod, herring, or haddock.
Beef, mutton, heart, liver, all showed the same green
fluorescence.

Led up to it by a series of remarkable experiments

PUTREFACTION AND INFECTION. 129

on the rapidity of the passage of crystallized substances
into the vascular and non-vascular textures of the body,!
Dr. Bence Jones and Dr. Dupré communicated to the
Royal Society in 1867 a highly interesting paper ‘On
a Fluorescent Substance, resembling Quinine, in Ani-
mals,’* They then showed that ‘from every texture of
man and of some animals a fluorescent substance can
be extracted, which, when extracted, has a very close
optical and chemical resemblance to quinine.’ They
therefore called it animal quinoidine. In dilute solu-
tions they found that the fluorescence of the animal
substance was not to be distinguished from that pro-
duced by quinine. When the solution was concentrated,
the colour of the light was of a decidedly greenish hue.
This latter observation is most in agreement with mine.
In all the infusions examined by me the fluorescent
light was a decided green, and not to be mistaken for
the blue light of quinine.

The green colour is similar to that emitted by the
crystalline lens when a beam of violet light impinges
on it; sending such a beam through any of the infu-
sions, the ‘degradation’ of the violet to green is
strikingly illustrated.

The foregoing statement refers to the deportment
of the infusions after boiling and filtering. Prior to
boiling some of them were of a brilliant ruby colour ;
but even here, when the layer of liquid between the
eye and the beam was not too thick, the green fluor-
escence could be seen through the red liquid.

1 Proceedings of the Royal Society, vol. xiv. 1865.

2 Tbid. vol. xv. p. 73.

3 On plunging the eye into the beam of the electric lamp, trans-
mitted through violet glass, the moment the crystalline lens is seen
to fluoresce by a second observer, a blue shimmer is seen by the eye
on which the beam falls. In the case of my own eye, I can always
readily tell when the fluoresence has set in.

FURTHER RESEARCHES ON THE DEPORT-
MENT AND VITALITY OF PUTREFACTIVE
ORGANISMS."

i aaa

III.
§ 1. Introduction.

On the 13th of January, 1876, I had the honour of
submitting to the Royal Society some account of an
investigation in which the power. of atmospheric air
to produce life in organic infusions and its power to
scatter light were shown to go hand in hand. The
* scattering ” was proved to be due, not to the air itself,
but to foreign matter suspended in the air. It was
moreover proved that air placed under proper conditions
went through a process of self-purification, and that,
when this purification was visibly complete, the power
to scatter light and to generate life disappeared to-
gether.

The form of the experiments here referred to was,
it will be remembered, as follows:—Wooden chambers
were constructed with glass fronts, side windows, and
back doors. Through the bottoms of the chambers
test-tubes passed air-tight, their open ends, for about
one-fifth of the length of the tubes, being within the
chambers. Provision was made fora connexion through
sinuous channels between the outer and the inner air.

1 Philosophical Transactions, Part I., 1877.

132 THE FLOATING-MATTER OF THE AIR.

The chambers, being closely sealed, were permitted to
remain undisturbed for a few days. The floating
matter of the internal air gradually subsided, until at
length an intensely luminous beam failed to show its

Fig. 11,

track within the chamber. Then, and not till then,
were the infusions introduced, by means of a pipette
passing through the top of the chamber. After their
introduction, they were boiled in an oil or brine-bath !

1 From the fact of their being boiled in oil or brine, Professor

VITALITY OF PUTREFACTIVE ORGANISMS. 133

for five minutes, and afterwards placed permanently in
a warm room.

The annexed woodcut (fig. 11), taken from the
‘ Proceedings’ of the Royal Institution, shows a cham-
ber with its six test-tubes, its side windows w w, its
pipette c, and its bent tubes a b, which connect the air
of the chamber with the external air.

In upwards of fifty chambers thus constructed, many
of them used more than once, it was, without excep-
tion, proved that a sterilized infusion in contact with
air shown to be self-cleansed by the luminous beam re-
mained sterile. Never, in a single unexplained instance,
did such an infusion show any signs of life. That the
observed sterility was not due to any lack of nutritive
power in the infusion, was proved by opening the back
door and permitting the uncleansed air to enter the
chamber. The contact of the floating matter with the
infusions was invariably followed by the development of
life. Numerous examples of these results were placed
before the Fellows of the Royal Society at their Meet-
ing on the 13th of January, 1876.

Prior to the date here referred to, great public
interest had been excited, and, I may add, considerable
scientific uncertainty had been produced in reference
to this subject, both in England and America, by the
writings of Dr. Bastian. These writings consisted, in
part, of theoretic considerations and reflections, not
new, but sometimes very ably stated, based on the
general doctrine of Evolution; and, in part, of very
pungent criticisms of those who, though believers in
Evolution, declined to accept the writer’s programme

Cohn has inadvertently inferred that the infusions themselves were
raised above their boiling-points. The tubes being open, the tem-
perature of ebullition is of course independent of the source which
provokes it.

134 THE FLOATING-MATTER OF THE AIR.

of its operations! Passing over both theory and
criticism, I thought it wise to fix upon certain well
defined statements of fact which lay at the basis of the
weighty superstructure raised by their author, and to
bring these statements to the test of strict experiment.

Thus it was affirmed ‘that boiled turnip or hay-
infusions exposed to ordinary air, exposed to filtered
air, to calcined air, or shut off altogether from contact
with air, are more or less prone to swarm with Bacteria
and Vibriones in the course of from two to six days.’ ?
I resorted accordingly to filtered air, calcined air, and
to infusions withdrawn from air, but failed to discover
the alleged‘ proneness’ to run into living forms. It
had also been affirmed that infusions of muscle, kidney,
or liver, placed ‘in a flask whose neck is drawn out and
narrowed in the blowpipe flame, boiled, sealed during
ebullition, and kept in a warm place, swarmed after a .
variable time with Bacteria and allied organisms.’! I
resorted to such flasks, employing infusions of fish, flesh,
fowl, and viscera, and on the 13th of January was able
to place before the Royal Society one hundred and
thirty flasks, every one of which negatived the fore-
going statement.

Two objections were subsequently urged against
these results. The infusions, it was contended, were
not sufficiently concentrated, nor were the temperatures
sufficiently high. Both these objections were met by
the statement that forty-eight hours’ exposure under
the same circumstances to common air sufficed to fill
these same infusions with life. Beyond this, however,
I was able to show that the temperatures employed by
me were exactly those which had previously been found

1 See ‘Evolution, or the Origin of Life,’ pp. 168, 169.
2 « Mvolution,’ p. 94.
» Transactions of the Pathological Society, 1875, p. 272.

VITALITY OF PUTREFACTIVE ORGANISMS. 135

‘most effectual by the writer who urged the objection.
Other temperatures, higher than any previously em-
ployed, were at the same time said to ensure sponta-
neous generation. I exposed my infusions to these
newly-discovered efficient temperatures, but found that
they remained as barren as before.

With regard, moreover, to the question of concen-
tration, it was shown that, owing to their gradual
vaporization, the infusions used by me were probably
unequalled in strength by those employed by any pre-
vious investigator. Some of these infusions remain with
me to the present hour. Concentrated by twelve
months’ slow evaporation, and reduced to one-fifth of
their primitive volume, they still exhibit the purity of
distilled water,

These results proved beyond a doubt that in the
atmospheric conditions existing in the laboratory of
the Royal Institution during the autumn, winter,
and spring of 1875-6, five minutes’ boiling sufficed
to sterilize organic liquids of the most diverse kinds.
Among these may be mentioned urine in its natural
condition, infusions of mutton, beef, pork, hay, turnip,
haddock, sole, salmon, cod-fish, turbot, mullet, her-
ring, eel, oyster, whiting, liver, kidney, hare, rabbit,
barn-door fowl, grouse, and pheasant. Once properly
sterilized, and protected afterwards from the floating
matter of the air, not one of these putrescible infusions
ever manifested the power of generating by its own in-
herent energy putrefactive organisms of any kind. |

§ 2. Experiments of Pasteur, Roberts, and Cohn.

During the investigation just referred to I confined
myself for the most part to animal and vegetable juices
in their natural condition—that. is to say, extracted

136 THE FLOATING-MATTER OF THE ATR.

by distilled water, and not rendered artificially acid,
neutral, or alkaline. I had occasion, however, to repeat
among others some of the very remarkable experiments
on superneutralized hay-infusions described by Dr.
William Roberts in his excellent paper in the Philo-
sophical Transactions for 1874. These experiments I
could not corroborate; for while in his hands such
infusions sometimes required three hours’ boiling to
sterilize them, in mine they behaved like other in-
fusions, and were sterilized in five minutes.

In the abstract of the investigation communicated
to the Royal Society on the 13th of January, 1876, I
mentioned this discrepancy, and pointed out its possible
cause.! But the largeness of the question, which had
been long previously raised by M. Pasteur, and the
limitation of my time, led me to postpone it. This
postponement is mentioned at the conclusion of my
paper in the Philosophical Transactions for 1876, where
the discrepancy referred to is not at all discussed.

In his celebrated paper, ‘Sur les corpuscules orga-
nisés qui existent dans l’Atmosphére,’ published fifteen
years ago,’ M. Pasteur first announced that while acid
infusions had their germinal life destroyed by a tem-
perature of 100° C., a temperature over 100° was
needed to produce the same effect in alkaline infusions.
In his ‘Etudes sur la Biére,’ published in the early
part of 1876, he repeats and illustrates this statement.
Vinegar he finds has the organisms which decompose it
destroyed by a temperature of 50°C. Wine is ren-
dered unchangeable by a slightly higher temperature.
Beerwort without hops requires a temperature of 90°C.
to sterilize it, and milk a temperature of 110°. Fresh
urine has its organisms destroyed at a temperature of

1 Roy. Soc. Proc. vol. xxiv. p. 178.
* Annales de Chimie, 1862, vol. Ixiv.

VITALITY OF PUTREFACTIVE ORGANISMS. 137

100°, while a higher temperature is needed when the
urine has been neutralized by carbonate of lime.! The
resistance of alkalized urine to sterilization is therefore
by no means a new announcement.?

On my return from Switzerland in 1876 the experi-
ments on alkalized hay-infusions were resumed; and
soon afterwards Professor Cohn, of Breslau, so highly
distinguished by his researches on Bacteria, placed in
my hands a memoir * which rendered it doubly incum-
bent on me to examine more strictly the grounds of my
dissidence from Dr. Roberts. Professor Cohn is, on the
whole, emphatic in his corroboration of Dr. Roberts,‘
having found, during a long and varied series of ex-
periments with hay-infusions of divers kinds, that when
the period of boiling did not exceed fifteen minutes
organisms invariably appeared in the infusions after-

1 «Etudes sur la Biare,’ p. 34.

2 With regard to the different action of acid and alkaline
liquids, I put the subject purposely aside with the view to its full
investigation as soon as the first instalment of these researches had
been published. I could find no adequate explanation of the
alleged fact that germs are killed in an acid liquid, while they
survive in an alkaline one of the same temperature; nor could the
well-merited respect that I feel for M. Pasteur cause me to accept
his explanation without further inquiry on my own account. In
due time, therefore, I resolved to examine the question. Various
experiments and explanatory views regarding it are recorded in
the following pages.

3 Beitrige zur Biologie der Pflanzen, July 1876.

« Professor Cohn gently censures me for taking exception to the
cotton-wool plug, seeing that cotton-wool, even in my own experi-
ments, has always proved a trustworthy filter. I did not, however,
object to it asa filter, but on grounds which have in part, at all
events, commended themselves to Professor Cohn himself. With
reference to the method of Dr. Roberts he writes thus :—‘ The de-
fect of this method consists in the difficulty of protecting the
cotton-wool from accidental wetting by the infusion. The steam,
moreover, which rises from the liquid penetrates the cotton-wool,
and, through its partial condensation in the neck of the bulb, might
readily charge itself with germs.’

138 THE FLOATING-MATTER OF THE AIR.

wards. Sixty, eighty, and even one hundred and
twenty minutes’ boiling were found in some cases in-
sufficient to sterilize the infusions. One marked dif-
ference, however, exists between Dr. Roberts and Pro-
fessor Cohn. ‘The former found five minutes’ boiling
sufficient to sterilize unneutralized hay-infusion, but
one, two, and even three hours’ boiling insufficient to
sterilize superneutralized hay-infusion; while the latter
noticed no difference of this kind, but found acid and
neutral infusions equally resistant.

§ 3. Hay-infusions. Preliminary Experiments
with Pipette-bulbs.

I have now the honour to submit to the Royal
Society an investigation which embraces among others
the points here referred to, and which has proved far
more difficult and laborious than I expected it would be.

On the 27th of September, 1876, a quantity of
chopped hay was digested for three hours and a half in
distilled water maintained at a temperature of 120° Fahr.
The infusion was afterwards poured off, and its specific
gravity reduced to the exact figure given by Dr. Roberts,
viz. 1006. It was then filtered and slightly super-
neutralized. Precipitation occurred on the addition of
the potash, and the infusion was boiled for five minutes
to render the precipitation complete. It was then re-
filtered, and introduced into a series of bulbs of the
same size and character as those described by Dr.
Roberts, and called by him ‘ plugged bulbs.’?

Each bulb was a cylinder about four inches high and
upwards of an inch wide, with a long neck attached to

1 «Kin constanter Unterschied in der Zeitdauer zwischen sauren
und neutralen Aufgiissen, wie ihn Roberts gefunden, trat in unseren
Versuchen nicht hervor ’ (p. 259).

2 Phil. Trans. vol. clxiv. p. 460.

VITALITY OF PUTREFACTIVE ORGANISMS. 139

it,! as shown at a, fig. 12, Two-thirds of the cylinder
were occupied by the infusion. After the introduction
of the latter, the neck of the bulb was plugged with
cotton-wool, and hermetically sealed above the plug,
as at B, fig. 12. The bulbs were afterwards plunged in
water deep enough to cover their necks. The water was

Fig. 12.

gradually raised to the boiling-point, and maintained
at the boiling temperature for ten minutes. They

1 JT have called them ‘pipette-bulbs’ because they are formed
by hermetically sealing one shank of a pipette, close to the bulb,
leaving the other shank open for the introduction of the infusions.
German pipettes, on account of their cheapness, were at first com-
monly used; but in cases of long-continued boiling, explosions
were so frequent that bulbs of English glass of specially resistant
quality were resorted to.

140 THE FLOATING-MATTER OF THE AIR.

were then removed and permitted to cool; after
which the sealed end of each neck was broken off by
means of a file, its subsequent appearance being shown
at c, fig. 12. The bulbs, protected by the cotton-wool
plugs in the neck above them, were then exposed to a
tolerably uniform temperature of about 90° Fahr.

At the same time two similar bulbs, charged with
the same infusion, had their necks bent downwards,

Fic, 13. as in fig. 13, the inclined por-
tion being plugged, so that no
impurity could fall into the
liquid from the cotton-wool.
These two bulbs were boiled
for five minutes in an oil-bath,
X33, and plugged while boiling with
cotton-wool. They were then
sealed behind the plugs and
permitted to cool, their sealed
ends being broken off after-
wards.

On the 30th of September
the infusion in all the straight-
necked bulbs was turbid, while
in the two bent-necked ones it
was perfectly clear. On the 2nd
of October the turbidity of the
straight-necked bulbs had in-
creased, while a fatty scum had formed on the sur-
face of each. The two others were at the same time
slightly but distinctly turbid.

My inference from this experiment was that in
neither the straight-necked nor the bent-necked bulbs
bad the germs been wholly killed by the boiling. The
difference between the results obtained with the re-
spective bulbs arises from the different modes of mani-

VITALITY OF PUTREFACTIVE ORGANISMS. 141

pulation pursued in the two cases. For it is to be
aoted that a quantity of air, with its associated floating.
matter, was imprisoned above the infusion in every
straight-necked bulb; that in the case of the two bent-
necked bulbs this air had been in part displaced by
steam, the air which entered on cooling being sifted by
the cotton-wool plugs. To this difference of treatment
is to be attributed the observed difference of deport-
ment. Unlike the thick cloudiness of their neigh-
bours, the turbidity of the bent-necked bulbs, though
distinct, was barely sensible, and in none of them was
any scum ever formed upon the surface of the infusion.

Examined microscopically, numerous Vibrios were
found in the infusions of the straight-necked bulbs,
many of them broken at the centre, with the two halves
apparently trying to separate from each other. There
were also numerous smaller Bacteria, very active and
of various lengths. In the bent-necked bulbs a num-
ber of exceedingly small Bacteria were found, but no
Vibrios.

The deportment of the hay-infusion employed in
these experiments corroborates the results of Dr.
Roberts and Professor Cohn.

On the 2nd of October another infusion of hay was
prepared, and, after neutralization with caustic potash,
was introduced into six pipette-bulbs with straight
necks. The necks, being first plugged with cotton-
wool, were afterwards sealed by the blowpipe. The
infusions were maintained for ten minutes at the tem-
perature of boiling water. Their sealed ends were
afterwards broken off, and they were subjected, like the
former ones, to a temperature of 90° Fahr.

Six other bulbs were charged at the same time with
the same infusion; but, instead of being hermetically
sealed, they were placed in an oil-bath, and boiled there

142 THE FLOATING-MATTER OF THE AIR.

for five minutes. Before the ebullition ceased, the
neck of each was stopped with a plug of cotton-wool.

Up to October 6th all the bulbs continued clear.
On the 6th one bulb of the series last described be-
came turbid, lighter in colour than its neighbours, and
covered with a fatty scum. On the 7th one tube of the
first series (boiled after the fashion of Roberts for ten
minutes) also became turbid and exhibited the same
fatty scum. The remaining ten bulbs maintained per-
manently their deep brown-sherry colour, their high
transparency, and their perfect freedom from Bacterial
life. They are still clear, though seven months have
elapsed since their preparation.

In the great majority of these experiments the de-
portment of alkalized hay-infusion contradicts that
observed by Dr. Roberts and Professor Cohn.

Six other pipette-bulbs, with their necks so bent
and plugged with cotton-wool and asbestos that no
impurity falling from the plug could reach the infusion,
were also charged on the 2nd of October. Three of the
bulbs, with their necks hermetically sealed, were main-
tained for ten minutes at the temperature of boiling
water, the sealed ends being afterwards broken off.
The three other bulbs were boiled in an oil-bath, and
had their necks plugged before ebullition ceased. All
six bulbs have remained perfectly transparent up to the
present time.

Here, again, we have discordance between my re-
sults and those of Dr. Roberts and Professor Cohn.

But on the 6th of October another infusion was
prepared and neutralized, exactly in the same fashion
as before. Five pipette-bulbs were charged with it;
they were hermetically sealed and maintained at the
boiling temperature for ten minutes. The sealed ends
were afterwards broken off, and the bulbs exposed to 2

VITALITY OF PUTREFACTIVE ORGANISMS. 143

temperature of 90° Fahr. On the morning of the 8th
of October (that is to say, two days after their pre-
paration) the infusion in every one of the bulbs was
turbid and covered with scum.

Here once more we have perfect harmony between
my results and those of Dr. Roberts and Professor
Cohn.

On the 2nd of October, moreover, fourteen of our
ordinary small retort-flasks with bent necks (shown
in fig. 14) were charged with
the neutralized hay-infusion.
They were boiled for three mi-
nutes, and hermetically sealed
whilst boiling. Some days after-
wards one tube of the entire
number was observed to have be-
come lighter in colour and sen-
sibly cloudy; but thirteen out of
the fourteen remained unchanged
in colour, brightly transparent,
and entirely free from life.

Here the dissidence between my results and those
of Professor Cohn, who also experimented with her-
metically-sealed flasks, reappears.

Numerous other experiments with pipette-bulbs and
retort-flasks were made at the time here referred to,
but it is unnecessary to record them. Suffice it to say
that, like those just described, some of them corrobo-
rated and some of them contradicted the results of Dr.
Roberts and Professor Cohn.

Fie. 14.

144 THE FLOATING-MATTER OF THE AIR.

§ 4. Hay-infusions. Experiments with Cohn’s
Tubes.

For reasons given by himself,! Professor Cohn de-
viated from the method of experiment pursued by Dr.
Roberts, employing, instead of the pipette-
bulbs, flasks, the nature of which will be under-
stood from the following description. Let a
zone of a common test-tube, about one-third
of its length from its open end, be softened
by heat, and let the softened glass be drawn
out so as to form a tube of much narrower
bore than the original test-tube. Thus modi-
fied, the tube would consist of an elongated
bulb below and an open funnel above, both
being connected, by a narrow neck (see fig. 15).
Professor Cohn filled the elongated bulb to
about two-thirds of its volume with hay-
infusion, plunged his bulbs in water, raised the
water to ebullition, and continued the boiling
for the required time. The tubes were then
removed from their bath, and after being held
open for a minute or two so as to allow the
water condensed in their necks to evaporate,
the funnel was plugged with cotton-wool.

Professor Cohn considers that all possibility
of external contamination is here shut out.2 By
his method, therefore, I wished to check the results above

1 Beitriige, July 1876, p. 256.

2 ¢Bhe ich itiber die Organismen berichte, welche sich in den
gekochten Aufgiissen entwickelten, will ich bemerken, dass an eine
nachtrigliche Infection derselben durch von aussen nach dem
Kochen eingeschleppte Keime bei unseren Versuchen nicht zu
denken ist’ (p. 259). I may remark that, with an atmosphere like
that in which my recent experiments were conducted, there would
be no chance of escape for an infusion thus handled.

VITALITY OF PUTREFACTIVE ORGANISMS. 145

described. Accordingly, on the 24th of October, I had
four groups of Cohn’s tubes (twelve in a group) carefully
charged with two fresh infusions of two different kinds of
hay. Each infusion was divided into two equal parts, one
of which was neutralized and the other left in its natural
acid condition. Twelve of the tubes were charged with
one of the infusions neutralized, and twelve with the
same infusion unneutralized. We will label this in-
fusion A. Twelve other tubes were charged with the
second infusion neutralized, and twelve with it unneu-
tralized. We will call this infusion B. The forty-eight
tubes were subsequently boiled for ten minutes in tin
vessels containing water deep enough nearly to submerge
them. Having proved by previous experiments that it
was dangerous if not fatal to exactness to expose the in-
fusions for one or two minutes to the air after their
removal from the water, I took the precaution of plug-
ging them first and removing them afterwards.

On the 28th of October (that is to say, four days
after their preparation) several of the tubes containing
the unneutralized infusion A were faintly but distinctly
turbid and thinly covered with scum. The twelve
neutralized tubes of the same infusion were at the same
time perfectly clear. This retarding influence of the
alkali has been of frequent occurrence in this inquiry.
That it was simply a case of retardation was proved by
the fact that, on the 30th of October, the twenty-four
tubes, both neutral and acid, of infusion A were tur-
bid and covered with scum.

On the same date the twelve neutralized tubes of
infusion B were perfectly clear and without a trace of
scum. Of the twelve unneutralized tubes three had
given way, and a fourth yielded on the 31st. Four
days later three of the neutralized tubes also yielded.
The permanent state of matters was that eight out of

146 THE FLOATING-MATTER OF THE AIR.

the twenty-four tubes charged with infusion B had
become turbid, while sixteen of them remained perfectly
clear. I do not doubt that the tardy infection of some
of the tubes just referred to arose from external con-
tamination, which is almost inseparable from the method
of experiment.

Here, while infusion A corroborated Professor
Cohn, infusion B in substance contradicted him.

§ 5. Hay-infusions (in Closed Chambers).

In dealing with hay-infusions I also fell back on the
method of experiment which was found so effectual in
1875,' employing closed chambers in which the air had
been permitted to cleanse itself by the gradual subsi-
dence of its floating matter.

On the 3rd of October, 1876, my experiments with
such chambers recommenced. Two of them, containing.
each three large test-tubes, were then charged with an
infusion of hay accurately prepared according to the
prescription of Dr. Roberts. Its specific gravity was
1006; it was superneutralized to the proper extent with
caustic potash, but the period of boiling, instead of being
three hours, was five minutes.

Examined from time to time for more than four
months subsequently, the infusion in both chambers
continued perfectly unchanged. It was free from sus-
pended matter, free also from every trace of scum, main-
taining for the light which passed through it a singular
transparency.

Here, to a certainty, a period of boiling not amount-
ing to one-twentieth of that required by Dr. Roberts,
sufficed to destroy totally the power of generating life
in an alkalized hay-infusion.

1 Briefly described in the Introduction,

VITALITY OF PUTREFACTIVE ORGANISMS. 147

This result is in perfect harmony with all the results
of last year. Chamber after chamber was then charged
with infusions of hay, which were afterwards subjected
to the boiling temperature for five minutes. In every
chamber the infusion remained perfectly clear until
purposely infected from without. There was no instance
observed last year in which five minutes’ boiling failed
to sterilize hay-infusion, whether neutralized or un-
neutralized.

Thus, on the 26th of November, 1875, a group of
three test-tubes was charged with hay-infusion of the
same specific gravity and of the same degree of alkalinity
as that found most resistant by Dr. Roberts. They were
protected by glass shades, the air within the shade being
calcined by an incandescent platinum wire in the man-
ner described in the last essay.! The tubes were boiled
for five minutes, the subsequent intrusion of contami-
nated air being prevented by a ring of cotton-wool.
Thirteen months afterwards the infusion, greatly con-
centrated by evaporation, exhibited its pristine deep
transparency. A second similar group of tubes was
charged with alkalized hay-infusion on the 27th of last
January, and on the 5th of December (that is to say,
after a period of more than ten months) the infusion
was found perfectly clear.

A number of hermetically-sealed tubes charged with
the same infusion, and boiled for only three minutes,
have maintained for more than a year both their primi-
tive transparency and their water-hammer sound. Thus
many of the earliest experiments of the present year,
and the whole body of last year’s experiments, are in
complete harmony with each other.

This harmony was, however, disturbed by some of
the foregoing experiments with bulbs and tubes, and it

1 Phil, Trans., vol. clxvi. p. 50.

148 THE FLOATING-MATTER OF THE AIR.

was soon to be further disturbed by experiments with
closed chambers. On the 6th of October, 1876, for ex-
ample, an infusion was got ready in strict imitation of
that prepared on the 3rd; it was of the same specific
gravity, it was alkaline to the same degree, and it was
, introduced in the same manner into a chamber of three
tubes; but whereas the infusion of the 3rd remained
intact for months, and would have remained so indefi-
nitely, a week had not elapsed before every tube of this
new infusion was turbid and covered with fatty scum.

§ 6. Desiccation of Germs. New Hay and old.

In his work entitled ‘Evolution, and the Origin of
Life,’ Dr. Bastian affirms, with repeated emphasis, that
living matter is unable to maintain its life when exposed
to a temperature even below that of boiling water. He
refers to the scalding of the hand and other destructive
effects, and also to the action of boiling water on eggs.
He also refers to the experiments of Spallanzani on
seeds, and extends the results observed with living
matter of these special kinds, to living matter generally.
‘It has been shown,’ he writes,' ‘ and is believed by the
great majority of biologists, that the briefest exposure
to the influence of boiling water (212° F.) is destructive
of all living matter.’

More than ten years ago an extremely significant
observation directly bearing upon this subject was made
by the wool-staplers of Elbceuf, in France. They were
accustomed to receive dirty fleeces from Brazil, and
among other matters entangled in the wool were the
seeds of a certain plant called Medicago. It had been
repeatedly found by the wool-cleaners that these seeds
sometimes germinated after a period of four hours’

1 ¢ Evolution,’ p. 46,

VITALITY OF PUTREFACTIVE ORGANISMS. 149

boiling. The late M. Pouchet repeated the experiment.
He collected the seeds, boiled them for four hours, and
sowed them afterwards in proper earth. To his aston-
ishment they proved fruitful. He then closely examined
the boiled seeds, and found the great majority of them
swollen and disorganized; but amongst these ruined
seeds he observed others which had refused to imbibe
the water or to swell or break up in any way. These he
carefully picked out, and sowed them and their neigh-
bours separately in the same kind of earth. The swollen
seeds were incapable of germination, while the unaltered
ones rapidly gave birth to a crop. This was the only
instance of such resistance known to Pouchet when
he communicated the fact to the Paris Academy of
Sciences.

The observation here described stands recorded in
the ‘ Comptes Rendus’ for 1866, vol. lxiii. p. 939. It is
not difficult, indeed, to see that the surface of a seed or
germ may be so affected by desiccation and other causes
as practically to prevent contact between it and a sur
rounding liquid.!’ The body of a germ, moreover, may
be so indurated by time and dryness as to resist power-
fully the insinuation of water between its constituent
molecules. It would be difficult to cause such a germ
to imbibe the moisture necessary to produce the swelling
and softening which precede its destruction in a liquid
of high temperature.

In my last’ paper I made some remarks upon this
subject ;? and in relation to our present experiments,

2 In this connexion a remark of Dr. Roberts regarding the re-
sistance of chopped green vegetables merits quotation. ‘The singu-
lar resistance of green vegetables to sterilization appears to be due
to some peculiarity of the surface, perhaps their smooth glistening
epidermis, which prevented complete wetting of their surfaces.’

2 Phil. Trans., vol. clxvi. p. 60.

150 THE FLOATING-MATTER OF THE AIR.

the influence of drying and hardening was brought home
to me by the fact that in all the foregoing cases the
infusions which five minutes’ boiling proved sufficient
to sterilize were, without exception, derived from fresh
hay mown in 1876, while the infusions which five
minutes’ boiling failed to sterilize were derived, with-
out exception, from old hay mown either in 1875 or
some previous year.

In the earlier experiments of the present inquiry
this distinction between old and new hay came most
clearly and definitely out. The result was subsequently
blurred by circumstances which it required time and
labour to unravel, and which will require patience on
the reader’s part if he would thoroughly follow them.
They will, however, throw far more light upon the rea!
character of these inquiries, and do more to reconcile
the discords to which researches on spontaneous genera-
tion have given birth, than if every experiment had
been a success unshaded by doubt.

§ 7. Hay-infusions. Further experiments with
Closed Chambers.

With a view to probing to the uttermost this ques-
tion of drying and hardening, on the 6th of October
an extensive series of experiments with closed chambers
was begun. Three different kinds of hay were em-
ployed:—lst, Old hay, sent to me by Lord Claud
Hamilton, from Heathfield, Sussex;! 2nd, new hay
from Heathfield (both, it may be stated, from a some-
what ungenerous soil); 3rd, new hay purchased in
London, and artificially dried for some days upon a sand-

1 After the possible influence of hard drying and hardening had

suggested itself, I purposely introduced old hay from various locali-
ties into the laboratory.

VITALITY OF PUTREFACTIVE ORGANISMS. 151

bath. For these experiments eleven closed chambers
were prepared, as I wished every result to be based as
far as possible upon the testimony of two chambers.
On the 6th of last October they were carefully charged
with the infusions, the period of boiling afterwards
being five minutes.

Two chambers were devoted to the acid and two to
the alkalized infusion of old hay. Two chambers were
also devoted to the acid and two to the alkalized infu-
sion of dried hay. Two chambers were finally devoted
to the alkalized and one to the natural acid infusion of
new Heathfield hay.

Examined from day to day, differences were svon
observed, not only between the different infusions, but
also between different chambers containing the same
infusion. Thus every tube of both the chambers con-
taining the neutralized infusion of old hay became
turbid, but the three tubes of the one chamber were
loaded in four days with a fatty scum, while the tubes
of the other chamber remained for ten days perfectly
free from scum. The two chambers containing the
acid infusion of old hay exhibited similar differences.
Every tube in both of them became turbid; but in one
of them the infusion was scumless throughout, while
in the other each of the three tubes was heavily laden
with scum.

The two chambers containing the alkalized infusion
of dried London hay had all their tubes turbid and
covered with scum. In the case of the acid infusion of
dried hay, the tubes of one of the chambers became
turbid, while the tubes of the other chamber remained
clear. :

The two chambers of alkalized new Heathfield hay-
infusion were also in disaccord. In the one chamber all
three tubes became turbid and covered with scum,

8

152 THE FLOATING-MATTER OF THE AIR.

while in the other chamber the three tubes remained
sensibly clear and free from scum. Nor did the three
tubes of the single chamber charged with the new
Heathfield acid ififusion present the same appearance ;
for while one tube became thickly turbid, the other two
remained perfectly pellucid.

Amid this confusion, the only point worth dwelling
on is; that while no single case of escape occurred with
the old-hay infusion, whether acid or neutral, with the
infusions of both dried and undried new hay a certain
percentage of the tubes remained sterile.

Reflection on these results naturally drew suspicion
upon the chambers. They had been used before, and,
though carefully cleansed, some unobserved source of
infection may have clung to them. This, at all events,
seemed the most rational way of accounting for the
differences observed between samples of the self-same
infusion placed in different chambers. Hence my desire
to expose a fresh series of infusions in chambers which
had never been used before.

Six new ones were therefore constructed, each of
them containing six tubes. These were charged on the
3rd of November with infusions of old London hay,
old Heathfield hay, new London hay, and dried London
hay. Two chambers were devoted to each infusion,
which in the one chamber was neutralized and in the
other unneutralized.

The six tubes in each chamber were arranged in two
rows of three tubes each. Those nearest to the glass
front were called the front tubes, the others the back
tubes. The infusion intended for the unneutralized
chamber was unboiled before its introduction into the
three back tubes, and boiled in those tubes for five
minutes afterwards: the infusion for the front tubes was

VITALITY OF PUTREFACTIVE ORGANISMS. 153

boiled for fifteen minutes before introduction and for
five minutes afterwards. These differences in the mode
and period of boiling were adopted to ascertain whether
they had any influence on the subsequent development
of life. In the case of the neutralized chambers, the
infusion for the three back tubes was boiled for fifteen
minutes outside before neutralization, and five minutes
in the chamber after neutralization. The infusion for,
the three front tubes was boiled fifteen minutes outside
after neutralization, and five minutes afterwards in the
chamber. If the potash used for neutralization carried
germs into the infusion, the difference between five and
twenty minutes in the period of boiling might, it was
thought, declare itself in the subsequent phenomena.

Four days after its introduction the old Heathfield
acid infusion was found turbid throughout and covered
with scum. The scum and turbidity were sensibly the
same in all the tubes, though the period of boiling
varied from five to twenty minutes. On the same day
the neutralized infusion of the same hay was perfectly
brilliant and free from scum. Three days subsequently,
however (that is to say, on the 10th of November),
the neutralized tubes also became turbid and covered
with scum.

The salient, fact here to be noted is, that in neither
the neutral nor the acid chamber did a single tube of
the old Heathfield hay-infusion maintain its primitive
clearness and freedom from scum.

The old London hay behaved substantially as the
old Heathfield hay, no single tube escaping either in the
neutralized or the unneutralized chamber.

The dried new London hay comes next. A week
after its introduction every one of the six tubes con-
taining the acid infusion was turbid and coated with
scum. In the neutralized chamber, on the contrary,

154 THE FLOATING-MATTER OF THE AIR.

two only of the back tubes gave way, the third back
tube and the three front tubes remaining clear.

On the 8rd of November, moreover, a new chamber of
six tubes was charged with an infusion of new London
hay. Three of the tubes were neutralized and three
unneutralized. Both infusions were introduced into the
chamber unboiled, and were boiled afterwards for five
minutes. Ina week all the tubes had given way, be-
coming turbid in the same degree and covered to the
same extent with scum. The newness of the hay had
failed to secure the sterility of the infusions.

Nothing of this kind occurred in the experiments of
last year. It was then found that hay-infusions of all
kinds were uniformly sterilized by five minutes’ boiling.

Guided by such hints as the experiments furnished,
I continued to work. On the 4th of November four
closed chambers of three tubes each were charged
with infusions of old and new Heathfield hay—two
chambers with the one, and two chambers with the
other. One chamber of each pair contained a neutral-
ized, the other an unneutralized infusion, and the time
of boiling was ten minutes. Six days subsequently the
infusion of new hay, both neutralized and unneutralized,
was found perfectly unchanged. Of the old-hay in-
fusion, on the other hand, only one of the six tubes
escaped. The three acid tubes became completely tur-
bid, while two out of the three neutral ones fell into the
same condition.

§ 8. Expervments with Soaked Hay.

Pondering still further on the influence of drying
and hardening, and recognizing the necessity of not
only wetting but also softening the germs, the thought

VITALITY OF PUTREFACTIVE ORGANISMS. 155

occurred to me of soaking the hay for some days prior
to digesting it. Old London hay was accordingly
chopped up and placed in three glass vessels—one con-
taining distilled water, another acidulated water, and a
third alkalized water. The superior extractive power
of the alkalized liquid was at once manifest ; it rapidly
assumed a dark colour. The distilled water came next,
yielding a colour less deep than that of the alkalized,
but more deep than that of the acidulated water. The
alkaliné and distilled-water infusions emitted a rich
odour of hay, while the smell of the acid infusion was
very faint, and not like that of hay. The hay was per-
mitted to soak from the 8th to the 11th of November.
It was then digested for three hours in the same liquid
at a temperature of 120° F., boiled, filtered, and intro-
_ duced into the closed chambers, where it was reboiled in
each case for five minutes.

Prior to digesting the hay in the liquid in which it
had been soaked, Bacteria had developed in swarms.
These, of course, were killed by the boiling, and they
were not entirely removed by the filtration. The alka-
line infusion, indeed, though filtered repeatedly, was
sufficiently turbid to prevent the flame of a candle
placed behind the tubes containing it from being seen.
The same to a less extent was true of the distilled-
water infusion. This latter had been divided into two
portions, one of which was accurately neutralized, and
the other left unneutralized, a separate chamber being
devoted to each.

From the 11th to the 18th of November the only
change observed in any of the infusions was in the
direction of increased transparency. They all became
clearer with time, the distilled-water infusions becoming
particularly clear and brilliant at the top. After two or
three days’ quiet the alkaline infusion allowed a flame

156 THE FLOATING-MATTER OF THE AIR.

placed behind it to be seen of a deep red. The acidu-
lated-water infusion remained entirely unchanged ; but
this is not worth dwelling on, for in this case, even
when exposed to the common air, the infusion resisted
infection for a considerable time.

In no case was the fatty scum which had been
already so frequently observed formed in any one of the
tubes. Some change inimical to the particular organ-
isms which produce this scum must have been caused by
the soaking of the hay.

Examined microscopically on the 18th of November
these infusions, I thought, exhibited undoubted evi-
dences of Bacterial life. Bacterial forms were unques-
tionably there in considerable numbers, more particularly
in the sediment at the bottoms of the tubes. Nor dol
now see any valid grounds for doubting the presence of
life; but I was warned against drawing too hastily the
conclusion which first prompted itself, by boiling an in-
fusion swarming with active Bacteria, and submitting
the liquid after cooling to microscopic examination.
Here also the dead Bacterial forms were preserved, and
it was extremely difficult to distinguish their motions,
which were certainly Brownian motions, from those ob-
served in the protected infusions of soaked hay.

The experiment was thought worth repeating. On
the 16th of November accordingly chopped bundles of
old Heathfield hay and new Heathfield hay, and of old
London hay and new London hay, were placed in glass
dishes containing distilled water, and were thus soaked
until the 18th. They were then moved from the lower
laboratory, and taken, with their glass covers, to a dis-
tant room at the top of the Royal Institution. Here
the four specimens of hay were digested for three hours
at a temperature of 120° Fahr. They were filtered,
boiled, refiltered, some of them through 100 layers of

VITALITY OF PUTREFACTIVE ORGANISMS. 157

filter-paper ; after which they were introduced into four
closed chambers of six tubes each, and then boiled for
five minutes.

On the 20th of November. the infusions in all the
chambers appeared to be as free from organisms as at
first. The new Heathfield and the new London hay-
infusions in their respective chambers had their some-
what turbid columns surmounted by an exceedingly
clear zone of liquid, due, I should consider, to the me-
chanical subsidence of the particles, had vot subsequent
experience taught me to regard this appearance as a sign
of life.

On the 23rd scum had begun to gather on every
tube of the case containing the infusion of old Heath
field hay. On the 30th this scum continued, but there
was no trace of it in any of the chambers containing
new Heathfield hay, new London hay, and old London
hay. These infusions were all somewhat turbid ; but the
turbidity differed very little from that exhibited when
the infusions were prepared.

I spent a good deal of time over these infusions of
soaked hay, both with the microscope and otherwise,
but the recorded observations would not add materially
to our knowledge. I therefore dismiss them with the
remark that their general drift was in favour of the idea
that the extraordinary resistance to sterilization mani-
fested by the old-hay infusions is the result of hardening
and desiccation. The foregoing observations, however,
have been noted, more with the view of indicating my
line of thought than of claiming for them any value
whatever as a demonstration.

158 THE FLOATING-MATTER OF THE AIR.

§ 9. Infusions of Fungi.

Turning from hay to substances in which germs, if
they existed, could not be desiccated, I felt pretty sure
that infusions of such substances would be unable to
resist the boiling temperature. To test the correctness
of this view the following experiments were made :—
Three different kinds of fungi (red, black, and yellow)
were gathered in Heathfield Park on the 13th of Octo-
ber, and digested separately in London on the following
day. Three tubes of a closed chamber containing six
tubes were charged with the red-fungus infusion and
three with the black, while a second chamber of three
tubes was charged with the yellow-fungus infusion.
They were all boiled for five minutes after their intro-
duction into the chambers.

For two or three days all the infusions continued
clear; but they subsequently broke down, every tube
of the nine becoming-turbid with organisms and covered
with scum.

Examined microscopically on the 8th of November
the red-fungus infusion was found charged with a mul-
titude of spore-like bodies, massed in some places con-
tinuously together, in others floating freely in the liquid.
Among these ran long filaments, dotted with spore-like
specks from beginning to end. There was a consider-
able number of Vibrios in one of the tubes. The black-
fungus infusion contained a mixed population of Vibrios
and Bacteria with spore-filled filaments. Swarms of
Bacteria were observed in the red-fungus infusion.

Suspicious of the chambers in which these infusions
had been exposed, I had three new ones constructed
and provided with new tubes. A fresh supply of fungi
was sent to me from Heathfield, a tree fungus being,

VITALITY OF PUTREFACTIVE ORGANISMS. 159

however, substituted for the black one used in the
former experiments. On the 1st of November the
three infusions were very carefully introduced into
three chambers, a chamber being devoted to each in-
fusion. I thought it advisable to vary the period of
subsequent boiling. One tube of the yellow fungus was
therefore boiled for five, one for ten, and one for fifteen
minutes; but as it was difficult to save the infusion
from waste when the boiling was long continued, one
tube of each of the other two infusions was boiled for
five minutes, and the other two for ten. Tubes charged
with the respective infusions were exposed at the same
time to the common air.

In two days the outside tubes containing the red-
and yellow-fungus infusion became turbid and covered
with the fatty scum so prevalent in our laboratory this
year. No scum had formed on the surface of the ex-
posed tree-fungus infusion, which, to casual observation,
appeared quite black. Closer scrutiny, however, showed
that it transmitted the deepest red of the spectrum, and
was apparently quite free from floating matter. It
changed rapidly during the night of the 3rd, and on the
morning of the 4th of November the bottom of this
tube was found laden with a heavy dark-brown precipi
tate, while numerous dark-brown flocculi floated in the
liquid overhead, which had become almost as clear and
colourless as water. Under the microscope the dark-
brown mass resolved itself into confused moss-like
patches and long cylindrical sheaths dotted throughout
with small dark specks. These filaments with spore-
like specks have been of very frequent occurrence in
this inquiry.

The deportment. of the closed chambers was as fol-
lows:— 1. Yellow fungus: the liquid in the three tubes
remained perfectly and permanently clear and without

160 THE FLOATING-MATTER OF THE AIR,

a trace of the scum which loaded the infusion outside.
2. Red fungus: one of the three tubes became thickly
turbid, while the two others maintained their pristine
brilliancy. 3. Tree fungus: one of the tubes became
thickly turbid, the two others remained permanently clear.
Iasked myself why should one tube of the red-fungus
give way and the others remain intact? The answer
seemed at hand. The turbid tube had been boiled for
only five minutes, while the clear ones had been boiled
for ten. On consulting the adjacent chamber this pos-
sible explanation was blown to the winds, for here the
turbid tube had been boiled for ten minutes, while its
untainted neighbour had been boiled for only five.
Thus, although the more careful repetition of the
experiments did not secure every tube from infection,
the escape of seven out of nine tubes entirely destroys
the presumption of spontaneous life-development which
the first experiments might suggest to some minds.
Wishing to observe more attentively the action of
common uncleansed air upon boiled fungus-infusions, a
tray of 100 tubes was charged with them on the 14th
of October. Thirty-five tubes were filled with black,
thirty-five with yellow, and thirty with red-fungus in-
fusion. On the 16th of October every one of the yellow-
fungus tubes was turbid and covered with a thick, cohe-
rent, cobweb-like scum. The surfaces of the black-
fungus tubes were also sprinkled with spots of white
scum. Turbidity was the only change observed in the
red-fungus tubes. They were wholly free from scum.
Examined microscopically on the 2nd of November
the yellow-fungus tubes were for the most part found
swarming with exceedingly small and active Bacteria;
the red-fungus tubes also swarmed with Bacteria, some
beaded Vibrios being mingled with them. In many of
the tubes examined galloping monads appeared, attain-

VITALITY OF PUTREFACTIVE ORGANISMS. 161

ing an astounding development in the black-fungus infu-
sion. Patches of moss-like matter would appear here
and there in the field of the microscope; and it was no
uncommon thing to see from ten to twenty monads
nestling and quivering in this ‘moss,’ and darting
actively in and out of it. They put me in mind of
frogs amid their spawn; and as I looked at them my
belief in the animality of the one was almost as strong
as in that of the other. Almost every patch of spawn-
like matter had its colony. In some cases hardly any
thing but monadz was to be seen; but in others the
crowding of active Vibrios was so great that the monads
wholly retreated from the field.

§ 10. Infusions of Cucumber, Beetroot, &e.

The fungi having disappeared on the approach of
winter, I turned to cucumber and beetroot, not expecting
that their sterilization would offer any difficulty. Two
closed chambers were accordingly prepared, left for the
proper time in quietness, and on the 7th of November
were charged, the one with the cucumber- and the other
with the beet-root infusion. In a few days the infu-
sions in both chambers broke down, first losing their
transparency and afterwards loading themselves with
fatty scum. Thus perplexities accumulated.

On the 18th of November twenty-four Cohn’s tubes!
were charged with infusions of cucumber, beetroot, par-
snep, and turnip, six tubes being devoted to each infu-
sion. They were placed in a vessel of cold water, raised
‘gradually to the boiling-point, and maintained at the
builing temperature for ten minutes. Before their re-
moval from the hot liquid they were one and all plugged
with cotton-wool.

1 See § 4.

162 THE FLOATING-MATTER OF THE AIR.

On the 30th of November all the infusions were
thickly turbid throughout and heavily coated with scum.

From some of the precautions already mentioned it
may be inferred that before this point of the inquiry
had been reached, I had begun to suspect the atmo-
sphere in which I worked. Hay of various kinds, both
old and new, had been exposed and shaken about in the
laboratory, the air of which doubtless contained multi-
tudes of spores which diffused and insinuated themselves
everywhere. So, at all events, I reasoned. On the
20th of November, therefore, I had infusions of cucum-
ber, beetroot, parsnep, and turnip prepared, far from the
laboratory, in one of the highest rooms of the Royal
Institution, and introduced into four new chambers of
three tubes each. JI deemed the precaution of prepar-
ing the infusions and introducing them in the distant
room sufficient. Accordingly, when the chambers were
charged they were carried down, and the infusions boiled
in the laboratory.

Two days afterwards the parsnep alone remained clear
This, however, was only a respite, for a day or two sub
sequently it fell into the condition of its neighbours.
On the 30th of November both turnip- and parsnep-
infusions were turbid throughont, and laden at the
surface with thick fatty scum. The cucumber was also
heavily laden with scum, which sent long streamer-like
filaments into the subjacent liquid. The beetroot agreed
with the others in becoming turbid, but differed from
them in remaining free fromscum. In no case last year
did turnip-infusion show the deportment here described.
Knowing, then, from multiplied experiments, that turnip
possessed no inherent power of life-development, the
conclusion was irresistible that its present behaviour,
and with it the behaviour of cucumber, beetroot, and
parsnep, were due to infection from without.

VITALITY OF PUTREFACTIVE ORGANISMS. 163

I once more tried removal to a distant room, with
the added precaution of not only introducing the infu-
sions into the chambers upstairs, but of boiling them
there. It had been noticed that when the test-tubes
were withdrawn from the oil-bath, and the discharge
of steam into the chambers ceased, a somewhat violent
entrance of the air into the cooling chamber was the
consequence. To sift such air of its germs, both the
funnel of the pipette and the open ends of the bent
tubes were carefully stopped with cotton-wool. The
wool was never removed from the funnel, and it was
not removed from the bent tubes until the chamber had
thoroughly cooled. The same vegetables were operated
on, viz. cucumber, beetroot, turnip, and parsnep. On
the 25th of November four chambers were charged with
the infusions. On the 30th they were one and all covered
with a layer of deeply pitted and corrugated fatty
scum. Thus far, then, I was defeated in my efforts to
escape contamination.

During these experiments a fact was observed which
repeated itself afterwards in other instances. Samples
of the different infusions were always exposed to the
common air beside their respective chambers, and in
general these outside samples became turbid and covered
with scum a day or so before the interior tubes gave
notice of breaking down; but here, in the case of the
turnip, the outside tube continued pellucid and free
from life for some time after the inside ones had become
turbid with organisms. How could this be? The case
of my two trays placed one above the other last year!
suggested itself to my memory. In regard to life-de-
velopment it was then found that the lower tray was
always in advance of the upper one. As pointed out

1 Phil, Trans., vol. clxvi. p. 68.

164 THE FLOATING-MATTER OF THE AIR.

at the time, the absence of agitation which permitted
the germs to sink into its tubes was the cause of the
quicker contamination of the lower tray. No other
cause appeared to me assignable in the present instance.
By some means or other germs had insinuated them-
selves into my closed chamber, where the tranquillity of
the air permitted them to sink into the infusion, and
thus produce effects in advance of those produced by
the unquiet air outside. So, at all events, I reasoned.

But how could the germs get into the chamber? I
could, at the moment, fix only upon one way. The
weather had changed from warm to cold and from cold
to warm. This genial outside temperature sometimes
caused the air surrounding the infusions to rise to up-
wards of 90° Fahr., and we had often to work in this
heat. To moderate it, I sometimes partially turned off
the gas, thus lowering the temperature of the room 10°
or more. The contraction of the air within the closed
chambers followed as a matter of course, and the bent
tubes being open, I thought the entrance of the external
air might be sufficiently rapid to carry germs along
with it.

A new chamber of six tubes was therefore prepared
upstairs, three of its tubes being charged with cucum-
ber- and three with turnip-infusion on the 27th of
November. The pipette funnel and the bent tubes
were plugged above with cotton-wool, which was not
removed from them afterwards. I took care, moreover,
not to alter the gas-stoves in any way. My care was
nugatory. In three days every tube of the six was
laden with life. Another chamber of six tubes, charged
on the 30th of November with cucumber-infusion, and
two additional ones prepared on December 1st, shared
the same fate.

Slices of cucumber were next digested for three

VITALITY OF PUTREFACTIVE ORGANISMS. 165

hours ; the infusion was filtered, boiled, and such pre-
cipitated matter as appeared on boiling was removed by
refiltering. The liquid thus prepared was introduced
into five thick glass tubes, which were hermetically
sealed, placed in a cold oil-bath, gradually heated to
230°, and maintained at that temperature for a quarter
of an hour. The tubes being removed and permitted
to cool, the infusion was introduced into a chamber of
six tubes, and boiled there for five minutes.

The previous superheating of the infusion did not
even retard the development of life, for in less than two
days every tube in the chamber swarmed with Bacteria.
Thus far, then, every attempt ata solution was unsuc-
cessful.

But why, it may be asked, attempt such solutions ?
Was it not mere prejudice against the doctrine of spon-
taneous generation that prevented me from frankly
submitting to the apparent logic of facts, and admitting
the experiments just recorded to be a demonstration of
the doctrine? By no means. The only prejudice I
feel is the wholesome repugnance to accepting momen-
tous conclusions on insufficient grounds. Hume's cele-
brated argument has its application here. Taking an-
tecedent experience fully into account, it was far easier
for me to believe my knowledge imperfect, or my
present work erroneous, than to believe the doctrine of
spontaneous generation true.

§ 11. New Experiments on Animal Infusions.
Contradictory results.

In the course of this inquiry I was continually re-
minded of my experiments in 1875, when the most
complete immunity from Bacterial or fungoid life was
so readily secured. I had operated many times with

166 THE FLOATING-MATTER OF THE AIR.

turnip, never finding the least difficulty as to its steriliza-
tion. It is certain that the care bestowed in preparing
the turnip-infusion on the 20th of November, 1876, was
greater than that bestowed upon the same infusion in
1875. But whereas the latter was invariably sterilized
by five minutes’ boiling, remaining afterwards as pel-
lucid as distilled water, the former, three days after its
preparation, became thickly turbid and swarming with
life. I extended the present inquiry to other substances
whose deportment was familiar to me last year, some of
whose infusions, indeed, still remain with me as clear as
they were on the day of their preparation.

On the Ist of December. for example, infusions of
beef, mutton, pork, herring, haddock, and sole were
prepared, and introduced into six closed chambers, each
containing three tubes. On the 5th of December the
pork, beef, mutton, and haddock were all covered with
a fatty corrugated scum. A second chamber, containing
artichoke-infusion, prepared at the same time, was found
on the 5th more turbid than any of the animal infu-
sions, and equally covered with scum. In the animal
infusions, indeed, the body of the liquid underneath the
scum maintained a surprising brilliancy, the develop-
ment of life being confined to the layer in immediate
contact with the atmospheric oxygen.

On the 5th of December the herring- and sole-infu-
sions were both clear; but this was only a respite, for
on the 6th white spots appeared on the latter, which
extended until they covered the whole surface. The
herring-infusion remained clear for a week, after which
small specks began to appear on its surface. They
never reached the development of the scum which
coated the other infusions. It sometimes occurred to
me that the oil of this fish exercises a certain antiseptic
action. -

VITALITY OF PUTREFACTIVE ORGANISMS. 167

Last year I preserved infusion of herring perfectly
pellucid for months, even in a chamber so leaky that
the light could be seen through its chinks. I had,
moreover, no failure with any of the animal infusions
here enumerated. Last year they all remained sweet
and clear; this year, with far greater precaution, I
failed to protect any of them from putrefaction. Re-
flection on these results, renders, I think, but one con-
clusion possible to the scientific mind. It will be loth
to assume that mutton, beef, pork, haddock, herring,
and sole had totally changed their natures, and con-
tracted qualities and powers in 1876 which they did
not possess in 1875. But if the origination of the
observed life be denied to the infusions themselves,
there is but one other source to which it could be re-
ferred, namely, atmospheric contamination.

It became, indeed, more and more obvious to me that,
in consequence of increased vitality or virulence in the
contagia afloat this year, liberties in the preparation of
the infusions or defects in the construction of closed
chambers which would have been of no moment a year
ago were sufficient to ruin the experiments, and render
nugatory the usual means of sterilization. Against
such defects I continued to struggle. With a view to
stopping all chinks and crannies which might permit
of the entrance of contamination, I had some of the
chambers carefully coated with oil-silk and others
covered with three coatings of strong paint; and as
failure had attended my efforts to procure an uninfected
atmosphere upstairs, I had the entire apparatus used
for digesting, filtering, and boiling removed to a store~
room at the base of the Royal Institution. The floor
of the room was of stone, and it was covered by no
carpet. Prior to going into it, moreover, I caused my
assistant to remove the clothes which he had previously

168 THE FLOATING-MATTER OF THE AIR.

worn in the laboratory and to dress himself in others.
The infusions prepared under these conditions were
cucumber, melon, turnip, and artichoke, which, from
beginning te end, were operated on below stairs. Two
chambers were devoted to each infusion, and after the
usual boiling in the chambers they were permitted to
remain in the store-room throughout the night, being
transferred to the warm laboratory next morning.

I fully expected that the majority of these chambers
would prove sterile. I did not expect to find them all
in this condition, because the chambers had been put
together in the laboratory, the air of which must have
deposited its germs not only on the glycerine-coated
interior of the chambers, but also on the inner surfaces
of the test-tubes. My expectation, moderate as it was,
was not realized. The only noticeable peculiarity in
the deportment of the infusions was that they yielded
tardily, but in the end every one of: them, without
exception, broke down.

Was the infection in this case aaa from the air
of the store-room? I think not; and for this reason :—
On the 27th of December four hermetically-sealed flasks,
charged with a cucumber-infusion which had remained
perfectly pellucid for some weeks, were opened in the
store-room; four similar flasks, charged with the same
infusion, were opened at the same time in the laboratory.
On the 31st of December the whole group of the latter
four was found invaded by organisms, while those
opened in the store-room contracted no infection and
developed no life. Ido not imagine, therefore, that the
air of the store-room had anything to do with the con-
tamination of the infusions contained in the closed cham-
bers, but conclude that the contagium already existed
in the chambers when they were taken down stairs.
They acted as infected houses placed in salubrious air.

VITALITY OF PUTREFACTIVE ORGANISMS, 169

§ 12. Infusions protected by Glass Shades
containing Calcined Air.

I have already described this mode of experiment.!
The shades stood upon circular plates of wood, each
supported on a tripod (see fig. 16). Under each shade
were two upright rods of stout copper wire, and stretch-
ing from rod to rod was a spiral (p) of platinum wire.
The copper wires passed
through the slab of wood, .
their free ends being in
the air. The rim of each
shade was surrounded bya
collar of tin attached by
wax to the slab, with a
space of about half an
inch between the collar
and the glass. After the
introduction of the infu-
sions and the mounting of
the shades, this annular
space was packed with
cotton-wool. The aim
here was to destroy the
floating matter of the air by the incandescent pla-
tinum spiral. The air heated by the spiral would of
course expand, passing outwards through the cotton-
wool, while the air re-entering, on the cooling of
the shade, would be duly sifted by the wool. In my
former experiments five minutes’ incandescence sufficed
to render the air absolutely inoperative on infusions
exposed to its action. ©

In the present experiments the period of incan-

} Phil, Trans. vol. clxvi. p. 50.

170 THE FLOATING-MATTER OF THE AIR.

descence was doubled, ten minutes being allowed in-
stead of five, while the wire was raised to the highest
possible degree of incandescence. The infusions em-
ployed were turnip and cucumber, a group of three
tubes being charged with each. After the air had been
calcined, the infusions were boiled for five minutes in
an oil-bath. With this mode of treatment not a single
failure occurred in 1875, turnip-infusion being among
the number of liquids thus treated. This year two days
sufficed to render every one of the six tubes turbid with
organisms and to cover the infusion with a heavy scum.

I, however, had occasion to doubt the closeness of
these shades. The wax intended to seal the junction
of the tin collar with the plate of wood had cracked and
yielded here and there, and the entry of contamination
through such cracks was possible. - Six new shades were
therefore mounted and surrounded by collars which were
imbedded in white lead and firmly screwed down to
the plate of wood. The height of the collar, which
measured the depth of the filtering layer of wool, was
much greater than it had ever been last year. As
before, the period of incandescence was ten minutes,
during which the platinum spiral was brought as close
as possible to its point of fusion.

Each of these six shades covered a group of three
test-tubes. Two such groups were charged with turnip,
two with cucumber, and two with artichoke-infusion.
The infusions, as usual, were boiled for five minutes
after calcination. They were all brilliant when pre-
pared; but in two days every one of them had become
turbid, and had covered itself with a fatty scum. This
gradually augmented until it reached in some of the
tubes a thickness of half an inch. The weight of the
scum caused it in some cases to bag downwards, form-
ing a kind of inverted cone, the apex of which was

VITALITY OF PUTREFACTIVE ORGANISMS. 171

more than an inch from its base. These bags finally
broke and scattered their organisms in the subjacent
liquid. Thus the conflict went on.

§ 13. Further precautions against Infection.

At the beginning of December, my attention being
keenly aroused by those successive failures, I watched
more closely than I had previously done the filling of
the test-tubes through the pipette. Now and then I
noticed minute bubbles of air carried down with the
descending infusion. On escaping from the end of the
pipette, these small bubbles, I concluded, would break,
and scatter such germs as they contained in the air of
the chamber. Last year I should have found it difficult
to believe that a cause so small could lie at the root of
the observed anomalies; but this year I had learned to
respect small causes, and accordingly took measures to
effectually exclude the air.

On December 4th three chambers, which had been
previously left quiet for several days, were charged with
carefully prepared cucumber-infusion, and two other
chambers with turnip-infusion prepared with equal
care. The following precautions were taken :—The
funnel of the pipette formerly employed was broken
off from its shank, and for it was substituted a ‘ separa-
tion-funnel’ with a glass stopcock. This was connected
by closely fitting india-rubber tubing with the shank of
the pipette. But before the connexion was made, the
funnel was filled with the infusion, and the stopcock
turned on for a moment, until the liquid issued from
the orifice below. The stopcock being then turned off,
the flow of the liquid ceased, and the column in the
shank below the stopcock was supported by atmospheric
pressure. A pinchcock nipped the india-rubber tube at

172 THE FLOATING-MATTER OF THE AIR.

its centre. The portion of tubing above the pinchcock
was then filled with the infusion, and the end of the
separation-funnel introduced into the tube, all air being
thus excluded. On turning on the stopcock and releasing
the pinchcock, the liquid passed slowly down the shank
of the pipette, filling it wholly. The point of the shank
was then placed in succession over the test-tubes, the
infusion entering them witbout a single associated
bubble. The arrangement was not absolutely perfect,
but it was an improvement upon previous ones. As
before, the charged chambers were placed in a room
the air of which was maintained at a temperature of
about 90° Fahr.

The result was as follows :—Of the two turnip cham-
bers prepared as just described, on the 4th, one had
completely given way on the 6th. In the other cham-
ber two out of the three tubes had given way, but the
third remained permanently brilliant. Previous to this
series of experiments I had never succeeded in saving
even a single tube of cucumber-infusion ; here, how-
ever, two out of the three chambers charged with it
remained perfectly clear for many days. Subsequently
one of these chambers yielded in part, through an
accident, but the other chamber is as brilliant at this
moment as it was on the day of its preparation many
months ago.

Now, as regards inherent power to generate life, the
infusion of this chamber was in precisely the same
condition as its two neighbours. They, one and all,
contained the same infusion; and there is no way of
accounting for the observed difference of deportment
save by reference to contamination from without. Here
we are certainly on the trace of the enemy which has
given us so much trouble.

On the 5th of December two additional cases were

VITALITY OF PUTREFACTIVE ORGANISMS. 173

charged with infusion of melon prepared in the usual
way; and on the 12th of December I subjected both
these chambers, and those prepared upon the 4th, to a
very close scrutiny. The result was instructive. After
the introduction of the infusions, and prior to the re-
moval of the separation-funnel, the india-rubber tubing
connecting the latter with the shank of the pipette
was perfectly closed by the pinchcock. Provided the
clasping of the india-rubber tube round the shank of
the pipette were perfectly air-tight, the liquid contained
in the shank ought to remain there, supported by
atmospheric pressure. If, however, the india-rubber
tube failed to clasp with sufficient tightness the pipette-
shank, air would insinuate itself between the two, and
the depression of the liquid would be the consequence.
The result, observed upon the 12th was this:—In two
only of the seven chambers prepared on the 4th and
5th was the liquid column found perfectly supported ;
and only in these two chambers were the test-tubes,
which contained cucumber-infusion, without exception
pellucid.

In the five remaining chambers the liquid columns,
which had completely filled the pipette-shanks on the
4th and 5th, were found more or less depressed. The
tubes in one of the chambers, containing melon-infusion,
had become rapidly turbid and covered with scum. The
pipette-shank in this case was found entirely emptied of
its liquid and filled with air. Another chamber had
nine inches, while a third had seven inches of its
pipette-shank filled with air. In a fourth chamber
only one inch of the pipette-shank was filled with air;
here one out of a total of three tubes remained pellucid.
Thus, where the closure above was perfect, we had in
this instance perfectly pellucid infusions ; where it was
grossly defective, the infusions gave way in all the tubes ;

174 THE FLOATING-MATTER OF THE AIR.

while where the closure was but slightly defective we
had the escape of a fraction.

The defects thus revealed came, I concluded, into
play when the infusions were introduced, the descending
column of liquid sucking in minute air-bubbles between
the india-rubber tubing and the pipette, thus carrying
with it the external contagium. Few seem aware of the
precautions which are sometimes essential to save the
experimenter from error in inquiries of this nature.
Even with some of our best and most celebrated observers
I find no adequate sense of the danger involved in their
modes of experimentation.

§ 14. Eaperiments in the Royal Gardens, Kew.

But it was only in exceptional instances, dependent
on the state of the air, that even precautions such as
those described in the foregoing section secured freedom
from contamination. The contagium seemed omni-
present and persistent, and whether it was local or
general—due to the accidental condition of our labora-
tory, or to an epidemic of the air—became a question
with me, not by any means to be decided offhand. On
this point, then, I held judgment in suspense. The in-
fection was, to all appearance, fully accounted for by
reference to the conditions under which I worked; but
as regards outbreaks of epidemics the autumn had been
a remarkable one, and it seemed well worth investigating
whether it was not also a period prolific generally in the
germs of putrefaction.

I resolved therefore to break away wholly from the
Royal Institution, and, thanks to the friendly permission
of Sir Joseph Hooker, I was enabled to transfer my
apparatus to Kew Gardens. By the enlightened mu-

VITALITY OF PUTREFACTIVE ORGANISMS. 175

nificence of Mr. Jodrell, a new and very complete labo-
ratory had been just erected there, and in it I sought a
purer air than I could find at home.

My chambers hitherto had been constructed of wood,
but those to be tested at Kew were made of block-tin,
and they were carried direct from the tinman’s to the
gardens without being permitted to come near the in-
fected air of Albemarle Street. At Kew the test-tubes
- employed were first cleansed with carbolic acid, then
washed with a solution of caustic potash, afterwards
swept out with distilled water, and finally raised almost
lo the temperature of redness bya Bunsen-flame. They
were then fitted air-tight into the chambers with white-
lead and tow.

The chambers were closed on the 3rd of January,
and allowed to remain quiet until the 8th, when the
two most refractory liquids that I had encountered in
the laboratory of the Royal Institution were introduced
into them. These were infusions of cucumber and
melon. There were two chambers devoted to each
infusion—four in all; and each chamber embraced three
large test-tubes. The period of boiling was that found
effectual last year, i.e. five minutes. The temperature
of the room in which the chambers were placed was
maintained, partly by hot-water pipes and partly by a
gas-stove, at about 90° Fahr.—-a temperature which had
been proved eminently favourable to the development of
Bacteria.

Tubes containing the same infusions were at the same
time exposed to the common air of the Jodrell labora-
tory. These became rapidly turbid and covered with
scum. My interest and anxiety during the early days
of the trial of the protected tubes may be imagined.
After eleven days’ exposure they showed no signs of
giving way. On the 19th of January the four chambers

9

176 THE FLOATING-MATTER OF THE AIR.

were removed ina van from Kew, and shown in the
evening of that day to the members of the Royal
Institution, including many eminent Fellows of the
Royal Society. The infusions were one and all brilliant,
no trace either of turbidity or scum being found associ-
ated with any of them. During all my previous efforts
(and they had been very numerous) I had never suc-
ceeded in saving a single tube of melon-infusion ; here,
however, every tube of both chambers was intact. The
epidemic was thus localized, the obvious cause of it
being the contaminated air of our laboratory. _

A couple of days subsequent to the removal of the
chambers from Kew, a single tube of the cucumber-
infusion became turbid, its two neighbours in the same
chamber remaining intact. Not one of the other tubes,
either of melon or cucumber, gave way. They all
remained as pellucid in London as they had been at
Kew. Their removal from Albemarle Street to the
city last year ruined many of our sterilized chambers.
I was not therefore prepared to see so little damage
done by the transport from Kew,

It may be remarked, in passing, that this infection
of an infusion by mere mechanical shaking is an obvious
proof that the contagium is not a gas or vapour, but
that it consists of particles capable of being detached
from the interior surface of the chamber, and endowed
with the power of passing into active life.

Two other chambers were exposed at the same time
in the Jodrell laboratory, the one containing beef- and
the other sole-infusion. They are by no means so
sensitive as the cucumber and melon, still one of the
three beef-tubes broke down, becoming thickly turbid
throughout. Right and left of this tube its two com-
panions remained perfectly transparent. Asan illustra-
tion of the externality of the contagium, the result was

VITALITY OF PUTREFACTIVE ORGANISMS. 177

more conclusive than it would have been had all three
tubes remained intact; for had the power of developing
the organisms which produced the turbidity been in-
herent in the infusions, its action would not have been
confined to a single tube.

It will be understood that when the chamber is
lifted from the oil-bath in which its infusions are boiled,
the air within the chamber contracts, and an indraught
is the consequence. If the entering air be properly
sifted, by passing it through cotton-wool plugs, no harm
is done; but if it enter an aperture unsifted, it carries
its motes along with it. In the beef-chamber just re-
ferred to an aperture of this kind, about the size of a
pin-hole, was detected. This obviously was the door
through which the contagium entered. Through a
similar but graver defect in its chamber the sole-
infusion also broke down; but in a subsequent experi-
ment with sole-infusion in the Jodrell laboratory, two-
thirds of the whole number of tubes charged with it
remained free from all trace of life.

§ 15. Haperiments on the Roof of the
Royal Institution.

With a view to making, nearer home, experiments
similar to those made at Kew, I had a wooden shed
erected on the roof of our laboratory. The shed was
provided with benches, water and gas-pipes, and a stove
for heating. To an infusion of cucumber, which I had
found extremely intractable in the laboratory, my atten-
tion was first directed. Two tin chambers of three
tubes each were prepared, and transferred to the shed
fiom the workshop where they were made, without

178 THE FLOATING-MATTER OF THE AIR.

being permitted to enter our laboratory. The cucumber
used for the infusion was also kept clear of the infected
air; it was sliced and digested in the shed, the infusion
was there filtered, introduced into the tin chambers, and
boiled subsequently for five minutes.

The result was not that expected. Not a single
tube of either of these two chambers escaped con-
tamination. They one and all behaved like the
same infusion in the infected laboratory, becoming
in three days turbid throughout and laden with fatty
scum.

I have been daily and hourly impressed with the
parallelism between these phenomena of putrefaction
and those of infectious disease. A further illustration
of this parallelism is here presented to us. The clothes
of my assistants who prepared the infusion in the shed
had been worn in the laboratory, a transfer of infection
by one of the modes of transport known to every
physician being the result. The thoughtful physician
cannot indeed fail to see the absolute identity of deport-
ment between the contagia with which he is familiar,
and those assailants of my infusions against which I
have been contending so long.

With regard to the shed my first step, after this
preliminary failure, was to disinfect it. This was done
by washing every part of it, first with a mixture of
carbolic acid and water, and secondly with a solution of
caustic potash. When the whole was well dried, new
tin chambers furnished with new tubes were introduced.
Cucumbers and beef fresh from the market were also
digested in the shed, my assistant taking care to cover
his legs with clean linen trowsers, and his body with a
new blouse. There was one chamber devoted to the
cucumber and another to the beef. Into the former
the infusion was introduced on the 19th, and into the

VITALITY OF PUTREFACTIVE ORGANISMS. 179

latter on the 20th of March; each infusion was boiled
for five minutes after its introduction.

Let us compare results and draw conclusions. Ata
distance of eight yards from the shed, viz. in the labora-
tory, infusions both of beef and cucumber refused to
be sterilized by three hours’ boiling. Indeed I have
samples of both infusions which have borne five hours’
boiling and developed multitudinous life afterwards.
But the upshot of this experiment in the disinfected
shed is, that every tube of the two chambers, though
boiled for only five minutes, contains an infusion which,
at the present hour, is as limpid as the puvest distilled
water.

What shall we say, then? is the infusion in the
laboratory endowed with a generative force denied to
the same infusion in the shed? Irrespective of the
condition of the air, can a linear space of eight yards
produce so remarkable a difference? It is only the
confusion of mind still prevalent in relation to this sub-
ject that renders such a question necessary. Let me
add that it suffices simply to wave a bunch of hay in
the air of the shed to make it as infective as the labora-
tory air. Even the unprotected head of my assistant
when his body was carefully covered sufficed in some
cases to carry the infection.

If anything were needed to illustrate the extra-
ordinary care necessary on the part of physicians and
surgeons, both as regards the clothes they wear and the
instruments they use, such illustrations are copiously
furnished by the facts brought to light in this inquiry.

180 THE FLOATING-MATTER OF THE AIR.

§ 16. Preliminary Experiments on the Resistance~
limit of Germs to the temperature of Boiling Water.

While continuing the conflict and experiencing the
defeats recorded in the foregoing pages, a remark of
Professor Lister’s sometimes occurred to me. To apply
the antiseptic treatment with success, the surgeon must,
he holds, be interpenetrated with the conviction that
the germ theory of putrefaction is true. He must not
permit occasional failures to produce scepticism, but, on
the contrary, must probe his failures, in the belief that
his manipulation, and not the germ-theory, is at fault.
This may look like operating under a prejudice; but
Professor Lister’s maxim is nevertheless consistent with
sound philosophy and good sense; and if I permitted a
bias to influence me in this inquiry, it was one fairly
founded on antecedent knowledge, which led me to
conclude that the long line of failures above referred
to would eventually be traced to my ignorance of the
conditions wherehy perfect freedom from contamination
was to be secured.

I laboured to discover these conditions, and to learn
something more regarding the nature of the contami-
nation—its origin, persistence, and manner of action.
When these researches began, five minutes’ boiling, as
I have frequently stated, sufficed to sterilize the most
diversified infusions. Here we have frequently extended
the time of boiling to ten and fifteen minutes, and,
in some cases glanced at above, to immensely longer
periods, without producing this result. I desired more
exact knowledge as to the limit of endurance, and with
this view, on the 22nd of December, had six ‘ pipette
bulbs’ charged with an infusion of cucumber, sp. gr. 1004.
They were then plugged with cotton-wool, hermetically
sealed, and subjected to the boiling temperature for 10

VITALITY OF PUTREFACTIVE ORGANISMS. 181

minutes. Six other bulbs, charged with the same in-
fusion and treated in the same way, were boiled for
30 minutes. Finally eight bulbs, similarly charged,
were boiled for 120 minutes.

On the 23rd of December three of the first group of
bulbs, three of the second, and five of the third, had
their sealed ends filed off, and were afterwards exposed
to a tolerably constant temperature of about 90° Fahr.
Not one of these twenty bulbs preserved itself free from
life. On the 25th of December every one of them had
given way to cloudiness and turbidity.

There was, however, a marked difference between
the sealed and the unsealed bulbs. To the latter, it
will be remembered, the air had access through the
plug of cotton-wool, while to the former no air had
access, save the small quantity imprisoned above the
infusion when the necks of the bulbs were sealed. The
aerated bulbs grew rapidly and thickly turbid, while a
passing cloudiness was all that showed itself in the
sealed ones. This soon disappeared, and left the in-
fusions apparently intact. In fact it required some
attention to detect the appearance of this fugitive life,
which existed only so long as there was oxygen to sus-
tain it. I have ranged the sealed and unsealed tubes
side by side in groups. To the most cursory observa-
tion the difference between them is obvious. The ex-
periment strikingly illustrates the dependence of the
special organisms here implicated on the oxygen of the
air.

The experiments were pushed still further on the
28th of December. Two bulbs of cucumber, two of
melon, two of turnip, and two of artichoke were then
plugged, sealed, and maintained at the boiling tem-
perature for four hours. Six of the eight bulbs burst in
the operation, but two of them, a bulb of melon and

182 THE FLOATING-MATTER OF THE AIR.

one of cucumber, bore the ordeal uninjured. After
cooling, their sealed ends being broken off, they were
placed in the warm room. The melon remained per-
manently sterile, but in two days the cucumber-infusion
became turbid and laden with fatty scum.

Eight similar bulbs were boiled on the same day for
five hours and a half. Four of them burst, but four
remained intact. Of these, two contained cucumber-,
one melon-, and one turnip-infusion. Three out of
the four bulbs were sterilized by the long-contibued
boiling, but one cucumber-bulb passed through the
ordeal unscathed. Two days after the operation it
swarmed with life, and was covered with a fatty scum
formed of matted Bacteria.

Many similar experiments were subsequently made.
On the 27th of January, for example, six bulbs of
turnip infusion were boiled for 220 minutes, six for
300 minutes, and two for 305 minutes. Suspended in
the air above each infusion was a sprig of old Colchester
hay, this being purposely introduced to augment the
chance of infection. Notwithstanding its presence the
bulbs were one and all permanently sterilized. The
specific gravity of the infusion was in all cases 1007.

The sprigs of old hay were afterwards shaken into
the liquid, but they produced no effect. For weeks
afterwards the infusion remained clear. Was this im-
potence to generate life due to the fact that the nutri-
tive power of the infusion had been destroyed by the
‘blighting influence of heat’? Not so; for when the
same infusion was infected by a sprig of fresh hay, by a
small pellet of cotton-wool rubbed against the dusty
shelves of the warm room, or by a speck of another
infusion containing Bacteria, it never failed to develop
life. The only observed difference between the effect
produced by the dry hay or dust and the living Bacteria

VITALITY OF PUTREFACTIVE ORGANISMS. 183

was purely a difference of time. Inoculation with the
finished organisms acted more rapidly than infection
with the dust, but the effects were the same in the end.

On the 27th of January also nine melon-bulbs were
treated exactly like the turnip, being furnished with
sprigs of old Colchester hay, plugged with cotton-wool,
and hermetically sealed above the plugs. Six of them
were boiled for 215 minutes, and three for 220 minutes.
They were one and all permanently sterilized ; but, like
the turnip, all of them were open to infection by fresh
hay, dry dust, or living Bacteria. The specific gravity
of the melon-infusion was 1008.

§ 17. Further Experiments on the Resistance-limit
of Germs to the Boiling Temperature.

The amount of boiling which turnip-infusion failed
to withstand is shown by some of the foregoing experi-
ments; but to determine the limit of its resistance we
must begin with shorter periods. On the 1st of March,
therefore, eight groups of pipette-bulbs were charged
with turnip-infusion which had been prepared in an
atmosphere purposely infected with the germs of old
Heathfield hay. In every case, moreover, a sprig of the
same hay was placed in the air above the infusion.
The bulbs had their necks plugged with cotton-wool,
and were hermetically sealed above the plug. In this
condition the respective groups were boiled for the fol-
lowing times :—

1st. group ‘ : 5 i . 15 minutes.
2nd ,, cs @ @ «© «6 180 34
8rd, cS ee wR, TRB ae
4th ,, . . . 6 ,
bth ,, 75 oy
6th ,, ; 90 ~«,
7th =, ' 105,
Sth " 120 Si

184 THE FLOATING-MATTER OF THE AIR.

After boiling they were removed, permitted to
cool, had their necks broken off by a file, and were
afterwards exposed to the temperature of our warm
room. It may be remarked that the infusion gradually
deepened in colour from the 15-minute period, where
the colouring was hardly sensible, to the 2-hour period,
where the colouring became deep yellow. The effect
was doubtless due to the oxidation of the infusion,
which, notwithstanding the colour, was in all cases
highly transparent.

Two days after their preparation, every tube of the
series had become turbid and had begun to cover itself
with scum.

On March the 6th the periods of boiling were pro-
longed with a fresh infusion. Two groups of tubes
were, on that day, exposed to boiling water for the fol-
lowing times :—

Ist group é : 5 . - 180 minutes.
2nd ,, ge Sage cael. “hg Sd hg

On the 8th of March all the members of the
first group were turbid and covered with scum. The
second group was completely sterilized. This latter
result is quite in accordance with the experiments made
on the 27th of January. Turnip-infusion was then
boiled for periods varying from 220 minutes to 305
minutes, complete sterilization being in all cases the
consequence. These results were subsequently checked
by a continuous series of experiments extending over
periods of boiling varying from one to six hours. Up
to three hours the infusion resisted sterilization ; but
when the periods of boiling were prolonged to four,
five, and six hours respectively, all the bulbs became
permanently barren. The liquid continued in the
highest degree transparent, and in colour a brilliant
orange-brown.

VITALITY OF PUTREFACTIVE ORGANISMS. 185

Experiments intended to determine the limit of
resistance of cucumber-infusion were made on the 24th
of February. Nine pipette-bulbs were then charged,
plugged, hermetically sealed, and subjected to the boil-
ing temperature for the following times :—

1st bulb F ‘ : ‘ $ 15 minutes.
2nd ,, ‘ : : ; : 30 3
3rd, > So al Jo Abe
4th ,, ; § : ‘ ‘ 60 .
bth ,, Lg oe tet fel. Geer.
6th ,, eh A cae gl Jat Ha a
7th ,, : ; : : . 240 5
8th ,, al fel a tnt Jel ees 3,
oth ,, Fst. mn. Jat let eggs

After boiling and cooling they had as usual their
ends broken off by a file. The result here was that at
the 5th bulb, which corresponded to a boiling for two
hours, the life-development suddenly ceased. All the
tubes boiled from three to six hours inclusive were com-
pletely sterilized.

The infusion in this case had been diluted by an
accident, so that its specific gravity was not much above
that of distilled water. On the 28th of February,
therefore, a fresh infusion having a specific gravity of
1006 was prepared, and introduced into a series of
bulbs exactly as in last experiment. The bulbs were
exposed to the boiling temperature for the following
times :—

1st bulb : ‘ é 5 A 15 minutes.
Qnd ,, ‘ F i ‘ F 80 53
8rd, . ‘ : 3 . 45 -
4th ,, et 2, cts oh SOE Ge
5th ,, ‘ : g ‘ . 120
6th ,, - 3 A ; . 180 is
7th ae a ea |) ae
8th ,, ; , 3 j . 800

oth ,, ey Gh he ce REE OG,

186 THE FLOATING-MATTER OF THE AIR.

The result here was that at the 6th bulb, which cor-
responded to three hours’ boiling, the life-development
suddenly ceased. All the bulbs boiled from 15 minutes
to 180 minutes inclusive proved fruitful; while from 240
minutes to 360 inclusive all were completely sterilized.
As in the case of the turnip-infusion, the cucumber sub-
jected to long periods of boiling assumed an orange-
brown tinge.

Comparing these results with those obtained with
the turnip-infusion, it will be observed that cucumber
and turnip exhibit about the same resistant power:
three hours’ boiling, and less, failed to sterilize both of
them; four hours’ boiling, and more, rendered both of
them permanently barren.

The cucumber-infusions prepared on the 22nd and
28th of February were connected with the atmosphere
through the cotton-wool plugs; but no attempt had
been made to remove its floating matter from the air
above the infusions. On the 22nd, however, four bulbs
of the infusion were also prepared, charged with filtered
air, left unplugged, and hermetically sealed. The same
was done with four bulbs on the 28th of February. Each
group was subjected to periods of boiling of 15, 30,
45, and 60 minutes respectively. All of them became
turbid; but it was interesting to notice the gradual and
obvious fall of life from the 15-minute to the 60-minute
period. Could the Bacteria have been counted, and
the result graphically represented, the ordinate corre-
sponding to the abscissa 15 would have been found very
considerably longer than that corresponding to the
abscissa 60.

The method of experiment here for the most part pur-
sued was employed by Spallanzani and Needham. It
was afterwards extensively applied by the late excellent

VITALITY OF PUTREFACTIVE ORGANISMS. 187

Professor Wyman, of Harvard College, while in 1874
it was materially refined and improved upon by Dr.
William Roberts, of Manchester. The method is ham-
pered by one grave doubt. The air, plus its floating
matter, is imprisoned in the sealed bulbs, so that the
heat applied has not only to destroy the germs clasped
by the infusion, but also those diffused through the
supernatant atmosphere. Now it is not certain whether
an amount of heat which would be absolutely destruc-
tive to a germ embraced by a hot liquid may not be
wholly ineffectual when acting on a germ floating in
vapour or air. Throughout Spallanzani’s and Needham’s
experiments, throughout those of Wyman and Roberts,
and throughout my own, as reported in this section
and the last, this possibility of error runs. Such ex~
periments, in short, do not enable us to state with
certainty the temperature at which an infusion is steri-
lized, because the germs which most pertinaciously
oppose sterilization may not belong to the infusion at
all, but to the adjacent air.

The most astonishing cases of resistance to steriliza-
tion observed by Wyman were associated with this
particular mode of experiment. The et}
possible action of the uncleansed air,
moreover, was in his case augmented by
the fact that he employed quantities
of liquid, very small in comparison
with the size of his flasks. In some of
his earlier experiments the volume of
air was more than thirty times that of
the infusion. These relative volumes
are represented in the annexed figure \_

(fig. 17), copied from Wyman’s Memoir 7
of 1862.'

1 Silliman’s American Journal, vol. xxiv. p. 80.

188 THE FLOATING-MATTER OF THE ATR.

§ 18. Change of Apparatus. New Experiments
with Filtered Air.

The source of possible error referred to in the last
section had been long present to my mind, and I had
already taken measures to avoid it. On the 2nd of
January, 1877, an infusion of turnip (sp. gr. 1006) and
an infusion of melon (sp. gr. 1008) were prepared and
introduced into a series of pipette-bulbs in the follow-
ing manner :—One end a, fig. 18, of a glass T-tube was
connected with an air-pump, the other end 6 was
closely plugged with cotton-wool, while to the third
branch of the T-tube the neck of the pipette-bulb A
was attached by india-rubber tubing. A piece of the
same tubing, furnished with a pinchcock p, was also
attached to the free end of the T-tube beyond the
cotton-wool.

The bulb A was exhausted three times in succession,
the pinchcock p being closed, and was three times filled
with filtered air, the pincheock being opened. At the
third exhaustion the bulb was raised to a very high
temperature by a Bunsen flame, and finally filled with
filtered air. It was then plunged for a minute into ice-
cold water, from which it was afterwards removed,
detached from the T-tube, and then charged with the
infusion by means of a narrow pipette, fe, shown at the
top of B, fig. 18.

The rationale of the above proceeding is this:—On
quitting the ice-cold water for the warmer air of the
laboratory, expansion of the air within the bulb would
occur. This would cause a gentle motion from within
outwards, opposing all indraught of contaminated air.
The entry of the infusion into the bulb would, I thought,
also promote this outward motion. On the removal of
the pipette, which occupied but a very small portion of the

VITALITY OF PUTREFACTIVE ORGANISMS. 189

neck of the bulb, a little warmth was applied to the
latter, and during its application the neck was plugged
with cotton-wool. The air entering through this plug
to supply the place of the small quantity displaced by

Fig. 18.

the warmth would, I concluded, reach the interior of the
bulb perfectly sifted of its floating matter. The necks
of the bulbs were hermetically sealed, and the infusions

190 THE FLOATING-MATTER OF THE AIR.

maintained for ten minutes at the temperature of boil-
ing water. After a lapse of twelve hours their sealed
ends were broken off by means of a file.

In our experiments on the 28th of December tumnia
and melon subjected to ten minutes’ boiling entirely
gave way. In these present experiments, where greater
care was taken, two out of the six turnip-bulbs and
three out of the six melon-bulbs remained permanently
barren. Even this amount of success proved afterwards
so exceptional that it might be fairly regarded as
accidental.

On the 4th of January the experiments were con-
tinued. The pipette-bulbs employed were first carefully
washed with carbolic acid, which was removed as far as
possible with ordinary water. They were then washed
with a solution of caustic potash, and finally rinsed out
with distilled water. They were not subjected to the
action of the Bunsen flame. The infusions employed
were turnip (sp. gr. 1006) and melon (sp. gr. 1008),
eight bulbs being filled with each infusion.

I could not be certain that the motion of the liquid
fillet at the end e of the pipette with which the bulb s,
fig. 18, had been charged, had not drawn into the neck
of the bulb a modicum of the external air. In the pre-
sent experiments, therefore, the method of charging the
bulbs was modified in the following way:—The glass
T-tube employed in our last experiments had its end a,
which was to be connected with the air-pump, drawn
out to a small orifice and bent as in fig. 19. The branch
connected with the bulb was also drawn out to a tube
of fine bore, which entered the neck of the bulb for
some distance to ¢, the thicker part above being con-
nected with the neck of the bulb by india-rubber
tubing. The end b, as before, was plugged with cotton-
wool and provided with a pinchcock, p. The object

VITALITY OF PUTREFACTIVE ORGANISMS. 191

here aimed at was that the liquid should be discharged
into the bulb far below the india-rubber connecting-

piece, and that during the discharge it should pass only
through filtered air.

Fig. 19,

SJ

Each bulb was exhausted in the manner already
described, and refilled three times in succession. When
last filled it was plunged for a minute or so into

192 THE FLOATING-MATTER OF THE AIR.

iced water, with the view of rendering the air within
the bulb denser than that without. The pinchcock p
being closed, the whole apparatus was then detached
from the air-pump. On being lifted from the iced
water into the warmer air there was a gentle outflow of
air from a.

The mode of charging the bulb was this:—The point
a was well sunk into the infusion, and the associated
bulb, B, was plunged into boiling water. There was an
immediate outrush of air from a which bubbled through
the liquid. As soon as the bubbling had relaxed a
little, a being still submerged, the bulb was transferred
to iced water. A shrinking of the warm air was the
consequence, and through a the infusion was forced by
atmospheric pressure. It descended the middle branch
of the T-tube, and was discharged from its end e into
the bulb. The quantity of liquid obtained by a first
immersion in the iced water was not sufficient to charge
the bulb; but by repeating the process of heating and
chilling two or three times, the point @ never being
permitted to quit the infusion, any required quantity
was with ease and accuracy introduced. The neck of
the bulb was finally detached from the T-piece by
loosening the india-rubber tube. The bulb was then
slightly warmed so as to cause an outflow of air from
within, and while this outflow continued the neck was
plugged with cotton-wool. It was sealed above the
plug, and after the cooling of the infusion the sealed
end was broken off with a file.

It is not my intention to take up time in
describing in detail the numerous experiments made
in accordance with this method, or the variety of
infusions employed in testing its efficacy. Suffice
it to say that, notwithstanding all my care, the
results were chequered throughout. Sometimes success

VITALITY OF PUTREFACTIVE ORGANISMS. 193

would seem complete, but a repetition of the experi-
ments—and I never felt safe without frequent and varied
repetition—would, as before, present the success in the
light of an accident. Iam, however, secure in stating
that while pursuing this plan I have in some cases
effected complete sterilization by an amount of boiling
which, in other cases, though twenty times multiplied,
has failed to produce this effect. I have, for example,
placed side by side in my collection two series of organic
infusions, one as pellucid as distilled water, having
been rendered permanently sterile by an exposure to
the boiling temperature for five and ten minutes, and
a second series containing the same infusions boiled for
30, 120, and 330 minutes respectively, and which never-
theless are muddy throughout and covered with scum.
Even here, however, causes, other than differences of
manipulation, may have contributed to the result.
Weeks of labour have been devoted to these experi-
ments, nor did they exhaust the trials actually made.
Another mode of proceeding was this. Pipette-bulbs
were prepared by having a portion of their necks drawn
out to a tube of very fine bore. The open end being
connected with an air-pump, the bulb was exhausted
and filled with filtered air several times in succession.
In the final experiment the bulb was charged with one-
third of an atmosphere of cleansed air; and while this
pressure was maintained by the air-pump the narrow
tube was hermetically sealed. Each bulb was after-
wards heated almost to redness in the flame of a Bunsen
lamp. It was charged by inverting the bulb, dipping
the sealed end into the infusion, and breaking it off
underneath the surface. The liquid entered until the
bulb was two-thirds filled, when the narrow tube was
again sealed. A great number of experiments were

194 THE FLOATING-MATTER OF THE AIR.

thus executed, the results of which distinctly favoured
the conclusion, though they did not to my satisfaction
prove it, that the resistaut germs were not to be wholly
ascribed to the air, but that they had survived in the
liquid.

§ 19. Final proof that the Resistant Germs are em-
braced by the Infusion. Examples of Resistance
both in Acid and Neutral Liquids.

We here face a question which greatly harassed
me at the time to which I now refer. It was this:—
Have the germs, which under the circumstances here
described produced life, been really embraced by the
infusion itself during the time of heating? The liquid,
it will be remembered, had to pass through the neck
of the pipette-bulb, and it could not descend from the
neck into the bulb without leaving a film adherent to
the internal surface of the neck. This film, I reflected,
might dry in part by evaporation; and it might, in doing
so, leave germs behind which would be very differently
circumstanced from those in the liquid. To germs thus
exposed, not to the heat of water, but to the possibly
less effective heat of vapour and air, the observed life
might I thought be due. Before closing definitely with
the proposition that the surviving germs had actually
been in the liquid, the possibility to which I have just
referred had to be inexorably shut out.

The evil was to some extent mitigated by charging
the bulb, not through its own neck, but through a
narrow tube issuing at right angles to the neck. But
even here a portion of the neck and of the higher
interior surface of the bulb was trickled over by the
infusion. The difficulty was finally met, and completely
surmounted, by causing the lateral tube to issue from

VITALITY OF PUTREFACTIVE ORGANISMS. 195

the centre of the bulb itself, and forcing the infusion
into the bulb by atmospheric pressure, until the surface
of the liquid stood clearly above the lateral orifice.
To this level the liquid rose without wetting any
portion of the surface against which it did not per-
manently rest.

The precise method pursued in preparing and
charging the bulbs was this:—First, the bulb as sent to
us by the glass-blower is represented at a, fig. 20. Its
neck is first plugged with cotton-wool (c) and hermetic-
ally sealed as at B, fig. 20. The lateral tube is then
drawn out to almost capillary narrowness at o and p.
The end 7 is connected with an air pump, by which
the bulb is exhausted, and after two or three emptyings
and fillings, it is finally charged with one-third of an
atmosphere of thoroughly filtered air. While the pump
attached to » maintains this pressure within the bulb,
the capillary tube p is sealed with a lamp. The bulb
and its appendages are then heated nearly to redness in
a Bunsen flame, all life adherent to the interior surface
being thus destroyed.

The end p is then introduced into the infusion,
pressed against the bottom of the vessel that contains
it, and thus broken. The external pressure of a whole
atmosphere, having but one-third of an atmosphere
within the bulb to oppose it, forces the liquid through
the lateral tube. It enters the bulb, gradually rising
until it reaches the orifice, and rises above it. When
the pressure within is exactly equal to the pressure
without, two-thirds of the bulb are occupied by the
liquid.

The infusion then extends without breach of con-
tinuity from the bulb B to the vessel in which the end
p is immersed, the uncleansed air being thus completely

196 THE FLOATING-MATTER OF THE AIR.

excluded. A small gas flame is carefully applied at o.
The liquid within the narrow tube vaporizes, and the
vapour drives the liquid to some distance right and left
from the place of heating. In the absence of the liquid
the fine tube reddens, fuses, and is hermetically sealed.

Fie. 20.

The aspect of the bulb after it has been thus charged is
shown at ©, fig. 20.

By this method, on the 20th of February sixteen
bulbs were charged with infusions of old Heathfield hay
and of a hard wiry hay from Guildford, not old. They
weré divided into four groups, four bulbs in a group.

VITALITY OF PUTREFACTIVE ORGANISMS. 197

Each group embraced two acids and two neutral in-
fusions. They were boiled for the following times:—

Ist group. tl, oS: . 10 minutes,
2nd, me cher <> rn ory SROe a,
3rd, . = 8» «+» « 80 y,
4th ,, see ee DF"

After the bulbs had sufficiently cooled, their sealed
ends were removed by a file.

On the 21st of February, less than 24 hours after
their preparation, all these bulbs showed signs of yield-
ing. On the 22nd they were all turbid, while as
regards the comparison of acid and neutral infusions,
their condition was this:—

( Guildford neutral distinctly more turbid
than Guildford acid. Scum on for-
mer, none on latter.

Ist group. 10 minutes.’ Old Heathfield neutral not to be dis-
tinguished from old Heathfield acid.
Both turbid and covered with scum.
Much lightened in colour.

Guildford neutral distinctly more turbid

ond 20 minut than the acid liquid.

and group, <U minutes. 1 Qld Heathfield neutral more turbid than

the acid infusion.

Guildford neutral a little more turbid

{ than Guildford acid: difference small.

8rd group. 30 minutes. Old Heathfield neutral more turbid than

the acid infusion; the former with
scum, the latter none.

, Guildford neutral distinctly more turbid
than Guildford acid ; the former with
scum, the latter free from scum.

Old Heathfield neutral somewhat more
turbid and scummy than the acid
liquid: difference not great.

Here I take it to be absolutely certain that the
germs which resisted sterilization were contained in the

4th group. 60 minutes. ,

198 THE FLOATING-MATTER OF THE AIR.

liquid—a proof necessary to the argument, and admit-
ting of no question, being thus offered to the reader.

On the 22nd of February four groups of bulbs were
charged as above described with the same two infusions,
and the periods of boiling prolonged as follows :—

me prop ew be minutes.
ny ” . . . . . ”
srd,, Ge ee gs ap SEBO oy
4th ,, ete oe el, dg, CE

As in the last case, neutral and acid infusions of
each kind of hay were operated on. This was the re-
sult:—On the evening of the 23rd, that is to say, 24
hours after their preparation, every one of these bulbs
disclosed to the practised eye that organisms existed
within it. At 2 p.m. on the 24th they all swarmed
with life. The old Heathfield bulbs, both acid and
neutral, were turbid and covered with scum, the very
weakly-acid infusions being indistinguishable in appear-
ance from the neutral ones. In the case of the
Guildford infusion, however, the scum of the neutral
infusions was richer and heavier than that on the acid
ones.

Four hours mark the limit to which the boiling was
carried in these experiments. Onthe 27th of February
the periods of boiling were still further prolonged.
Four groups of bulbs charged with infusions of the
same two kinds of hay, both acid and neutral, were on
that day boiled for the following times:—

lst group. ‘ ‘ ‘ . 800 minutes.
2nd_(, : : a ; . 3860 ,,
3rd, : ‘ ; ‘ . 420 y
4th ,, . . 4 . 480,

I had previously boiled infusions of old Heathfield,
old London, and old Colchester hay for 5 hours, and

VITALITY OF PUTREFACTIVE ORGANISMS. 199

found them afterwards permanently barren. In the
present instance, also, all the bulbs boiled for 5 hours,
6 hours, and 7 hours were completely sterilized. They
remained ever afterwards perfectly brilliant. This, with
one exception, was also the deportment of the group of
bulbs boiled for 8 hours. The exception was a neutral-
ized bulb of the Guildford infusion, which became turbid
and covered with scum. Considering the severity with
which the bulb had been treated prior to charging,
and considering the mode of charging it, the life
developed could not possibly have been the product of
external germs. Through profound and thorough hard-
ening and desiccation, through defect of contact with
the liquid or some other cause, some germs in the
infusion itself had, I doubt not, been enabled to with-
stand the extraordinary ordeal here described.

Was it. ‘the blighting influence of heat’ that de-
prived the great majority of these 8-hour bulbs of the
power of spontaneous generation? Whatever be the
meaning attached to such language the reply is ob-
vious, that the ‘blighting’ was the same for all the
bulbs; and yet we find one of them which, when taken
from the boiling water, was perfectly brilliant, rendered
in two days muddy with organisms. Further, it was only
necessary to wash with perfectly sterilized distilled water
the adherent germs from a small bunch of hay, and to
inoculate the clear infusion in an 8-hour bulb with the
washing-water, to cause it within four-and-twenty hours
to become turbid throughout. To speak more definitely,
14 hours in the warm room were found sufficient to
cloud the infected 8-hour bulb with Bacteria. Thus
the infusion, when living germs are restored to it, shows
its perfect competence to develop them, and it was
solety th destruction of the germs which it possessed
before it was boiled that rendered it sterile afterwards.

10

200 THE FLOATING-MATTER OF THE AIR.

It is worth bearing in mind that the particular kinds
of hay whose germs manifested these extraordinary
powers of resistance were so sapless and indurated that
the specific gravity of their infusions, even after five
hours’ digesting, could not without difficulty be sensibly
raised above that of distilled water. This was more
especially the case with old Heathfield and old Col-
chester hay, the infusions of which, though highly
coloured, were marked, almost without exception, ‘spe-
cific gravity 1000.’ Old London hay-infusion was
usually 1003, while infusions of new Heathfield hay
were raised without difficulty to 1007.!

As already stated, I never felt safe in these experi-
ments until they were checked by careful repetition. A
partial corroboration has been already adverted to. But
on the 2nd of March I had the same infusions prepared,
kept in a cool place throughout the night, and intro-
duced into four groups of bulbs next morning. The infu-
sions were all brilliant. During the process of boiling
one group of bulbs blew up, hence one link is absent from
the series. I thought the 4-hour group could be best
spared, and therefore selected it for omission. We had
thus the infusions subjected for one, two, three, five and
six hours respectively to the boiling temperature. The
three first hours agree exactly with their predecessors.
No single bulb within these limits was sterilized, all of
them became turbid throughout and loaded with scum.

1 A comparative experiment on dried and undried peas, de-
scribed in the Proceedings of the Royal Society (1877, vol. xxv.
p. 503), may be referred to here as illustrating the manner in which
desiccation restricts diffusion, and thus tends to preserve the in-
tegrity of the desiccated germ. I suppose the original mineral
salts of the hay were still retained in the old samples; but hot
water appeared to have little power of extracting them. The resist-
ance of the hay in this respect appeared to be shared by its
germs.

VITALITY OF PUTREFACTIVE ORGANISMS, 201

One bulb of the 5-hour group and one of the 6-hour
group also became turbid and flocculent within, but
without any scum upon the surface. As in the case of
the 8-hour bulb already mentioned, this appearance
of life was, I doubt not, due to stray germs of excep-
tional resisting power, which maintained theinselves
unscathed in the infusions after their fellows had been
destroyed.

By multiplied experiments of a similar character
executed subsequently, and fortified by others made in
a different way, all doubts as to the real ordeal to which
the germs had been exposed were set at rest. A flood
of light, moreover, was thrown upon the difficulties
recorded in the foregoing pages. Prior to the intro-
duction into our laboratory of the particular samples of
desiccated hay whose adherent germs had manifested
such extraordinary powers of resistance, infusions of all
kinds, even those of hay itself, were sterilized. with ease
and certainty. But the old London, the old Heathfield,
the Guildford, and the old Colchester hay brought a
plague into our atmosphere, and thus the infusions of
other substances, some samples of hay included, became
the victims of a pest entirely foreign to themselves.
The failure to sterilize cucumber, turnip, beetroot,
artichoke, melon, beef, mutton, haddock, herring, sole,
was plainly due to the fact that their infusions had been
prepared in an atmosphere, or brought into contact
with vessels, contaminated with germs which have been
here shown capable of resisting 240 minutes’ boiling.
It is obvious from all this that to speak of an infusion
being rendered barren by such or such a temperature,
is simply to use words without definite meaning; be-
cause the temperature at which any infusion is sterilized
depends upon the character and condition of the germs
which find access to it. The death-temperature, for

*

202 THE FLOATING-MATTER OF THE AIR,

example, may be more than three hours in London, and
less than three minutes at Kew.!

I will cite here two conspicuous illustrations of the
infective energy of those desiccated hay-germs in two
infusions which, under ordinary atmospheric conditions,
are very easily sterilized. On the 30th of March five
pipette-bulbs were charged with clear beef-infusion and
boiled for the following times :—

1st bulb ‘i : : : . 60 minutes.
ond ,, Be ca ee e- Let TBO ey
3rd, @. one let ae. ie SBOE) ce
4th ,, van tes, EAL us Vena
5th ,, A, ig Mel Ce Sie SOR: Fe

After cooling, the sealed ends were broken off, the
air being admitted through cotton-wool plugs. Every
one of these bulbs became charged with organisms. In
the shed, eight yards off, this beef-infusion was, as
already reported, sterilized by five minutes’ boiling.

Precisely the same experiment was made on March
30 with pellucid mutton-infusion. Not one of the five
bulbs was sterilized. All of them are at this moment
charged with life. It behoves those engaged in the
industry of preserved meat and vegetables to keep clear
of the old-hay contamination. Probably they from
time to time have encountered difficulties and dis-
appointments which they could not explain, but which
may be solved by reference to the results here set forth.

‘I have already described the distribution of Bacteria-germs
in the air as ‘Bacterial clouds.’ Were our vision sufficiently
sharpened to see the manner in which such germs are distributed
over the surface of a meadow, we should not, I am persuaded, find
that distribution uniform. We should, in my opinion, find the
germs grouped in crowds, with comparatively free interspaces, like
violets on an alp, or mushrooms in a field. It is therefore con-
ceivable that two bunches of hay from the same meadow may
differ from each other in deportment.

VITALITY OF PUTREFACTIVE ORGANISMS. 203

But above all the practical question arises :—May not
the surgeon have to fight sometimes against enemies
like those here described? The particular germs with
which I have been so long contending act on both fish
and flesh in the manner described. How would they
behave in the wards of an hospital? Can they cause
wounds to putrefy? and if so, would they succumb to
the disinfectants usually applied? These are questions
the weighty import of which will be best understood by
the enlightened follower of the antiseptic system, and
which he will know how to answer for himself.

§ 20. Remarks on Acid, Neutral, and Alkaline
Infusions.

In the foregoing section reference was made to the
comparative deportment of acid and neutral infusions.
There can be no doubt of the fact that, for the nutrition
and multiplication of Bacteria, acid infusions are less
suitable than neutral or slightly alkaline ones. In
acid infusions exposure to the common air sometimes
copiously developes Penicillium, while it fails to de-
velope Bacteria. Itis also true that exposure for a
certain time to a certain temperature may in many
cases prevent the appearance of life in an acid infusion,
and fail to prevent it in a neutral or slightly alkaline
one.

In the present inquiry this has been frequently
found to be the case. I have many closed chambers,
for example, to which the process of ‘discontinuous
heating,’ to be subsequently described, has been applied;
and with them it has proved a common experience that
an amount of heating which has rendered acid infusions
of hay permanently barren has failed to sterilize the
corresponding neutral infusions. Moreover, in the

204 THE FLOATING-MATTER OF THE AIR.

cases just recorded, where single bulbs escaped steriliz-
ation though exposed for five, six, and eight hours to
the boiling temperature, it was always a neutral bulb
that kindled into life. To these instances another may
be added here. On the 22nd of March an infusion of
the wiry Guildford hay already referred to was divided
into two parts, one of which was neutralized and the
other left acid. Five pipette-bulbs were filled with the
one infusion and five with the other. After hermetic
sealing they were all completely submerged in water
and boiled for six hours. Every one of the acid bulbs
was sterilized by this process, while in two days three
of the five neutral ones became turbid and covered with
scum.

The best thought that I have been able to bestow
upon this subject does not induce me to lean towards
the explanation suggested by M. Pasteur, namely, that
the germs escape the destructive action of the heat
because they are not wetted by the alkaline or neutral
liquid. From the comparative action of alkalized and
acidulated water upon hay, I should be inclined to infer
that the wetting of its germs by the former would be
more prompt than by the latter. The question, I think, is
not one of wetting, but of relative nutritive power. Two
Bacteria-germs of equal vital vigour dropping from the
atmosphere, the one into a neutral or slightly alkaline,
the other into an acid infusion, soon cease to be equal
in vigour. The life of the one is promoted, the life of
the other only tolerated by its environment. When
the temperature surrounding both is raised to a pre
judicial height the one will suffer more than the other,
because equally inclement conditions are brought to
bear upon constitutions of different strengths; and if
the temperature be sufficiently exalted or sufficiently
prolonged to become fatal, the more weakly organism

\

VITALITY OF PUTREFACTIVE ORGANISMS. 205

will be the first to give way. A germ, moreover, brought
close to the death-point in a neutral or in an alkaline in-
fusion may revive, while in an acid one it may perish—
just as proper nutriment may rescue a dying man, while
improper nutriment would fail to doso. These elemen-
tary considerations, founded on the demonstrable fact
that Bacteria-germs are more fully vivified and better
nourished in neutral infusions than in acid ones, snffice,
I think, to explain the observed difference of action.
At all events, these are the thoughts which have be-
come rooted in my mind, through long observation and
long pondering of this question.!

§ 21. Remarks on the Germs of Bacteria as
distinguished from Bacteria themselves.

The failure to distinguish between these stubborn
germs and the soft and sensitive organisms which
spring from them has been a source of error in writings
on Biogenesis. In his able and important paper,
*On the Origin and Distribution of Bacteria in Water,
and the circumstances which determine their exist-
ence in the Tissues and Liquids of the Living Body,’
Dr. Burdon Sanderson, for example, has described ex-
periments from which, in my opinion, very incorrect
conclusions have been drawn. He exposed to the com-
mon air vessels containing Pasteur’s solution, which
when inoculated with fully developed Bacteria enables
them freely and copiously to increase and multiply;

1 From their deportment in boiling, I should infer that the air
dissolved in an alkaline liquid is in a different physical condition
from that dissolved in an acid liquid; and to this, in some measure,
the difference of nutritive power may be due. I have been unable
to find any experiments on the comparative absorption of air by

acid and neutral liquids. The subject is, I think, well deserving of
attention.

206 .THE FLOATING-MATTER OF THE AIR.

he even caused the air to bubble through the solution, .
and finding that though Torula and Penicilliwm were
luxuriantly developed in the liquid, Bacteria never
made their appearance, he concluded, ‘not merely that
the conditions of origin and growth of Bacteria and
fungi are considerably different, but that, as regards
the former, the germinal matter from which they spring
does not exist in ordinary air.”!

Dr. Sanderson subsequently reaffirmed the position
here laid down. ‘In my preceding experiments,’ he
says, ‘it has been shown that, although Torula-cells and
Penicillium appear invariably, and without exception,
on all nutritive liquids of which the surfaces are ex-
posed to the air, without reference to their mode of
preparation, no amount of exposure has any effect in
determining the evolution of Bacteria’? And, again,
with reference to another experiment:—‘The result
shows that ordinary air is entirely free from living
Bacteria.* His general conclusion is that, as regards
the development of Bacteria in organic liquids, ‘water
is the contaminating agent.’

Upon these experiments, and the conclusion drawn
from them, an argument has been founded by Dr.
Bastian, which would be weighty were its basis sure.
In reference to the Presidential Address of the British
Association in Liverpool,’ he argues thus:—‘Speaking
of living Bacteria-germs, Professor Huxley summed
up by saying, “considering their lightness, and the

1 Appendix to the Thirteenth Report to the Medical Officer of
the Privy Council for 1871, p. 335.

2 ¢ Appendix,’ p. 338. Though Dr. Sanderson speaks of ‘all
nutritive liquids,’ if I understand him aright, he really tried but
one, and that was a mineral solution, not an animal or vegetable
infusion.

3 ¢ Appendix,’ p. 339. * ¢ Evolution,’ p. 44.

% Brit, Assoc. Report, 1870.

VITALITY OF PUTREFACTIVE ORGANISMS. 207

wide diffusion of the organisms which produce them,
it is impossible to conceive that they should not
be suspended in the atmosphere in myriads.” Had
Professor Huxley himself made some careful and dis-
criminating experiments on this part of the subject, he
might have found that the supposed impossibility of
conception was entirely delusive..... What has been
the subsequent progress of events? In the first place,
it has been shown by Professor Burdon Sanderson, my-
self, and others, that the living Bucterta-germs are
not diffused through the air to any appreciable extent;
and this is now a very widely accepted doctrine, in spite
of its being, as Professor Huxley imagined, an im-
possible conception.’ The ‘others’ referred to by Dr.
Bastian embrace among them, it is to be admitted, the
celebrated naturalist Cohn.

Dr. Bastian was quite correct in saying that the
‘doctrine’ he enunciated was, at that time, ‘ widely
accepted.’ But the deportment of almost any sterilized
animal or vegetable infusion exposed to common air
will disprove the doctrine. It is irreconcileable with
the experiments on melon-, turnip-, cucumber-, and
hay-infusions, alluded to in this memoir. Such in-
fusions, after having been sterilized by exposure for six
or eight hours to the boiling-temperature, remain, if
protected from the Bacteria-germs of the air, for ever
barren; but when infected spontaneously, or purposely,
by atmospheric germs, they are found, within eight and
forty hours after such infection, thickly crowded with
Bacteria. That London air is laden with living Bac-
teria-germs is as certain as that London chimneys are
laden with smoke. What Dr. Sanderson’s extremely
important experiments really prove is, that a mineral
solution competent to nourish the Bacteria, after they
have been fully developed, is not competent (or, rather,

208 THE FLOATING-MATTER OF THE AIR.

is but very feebly competent) to effect the transfer from
the germ state to that of the finished organism. It
can feed the chick, but it cannot hatch the egg. As I
have already expressed it, the experiment proves, not
the absence of Bucteria-germs from the air, but the
inability of the mineral solution to develop them.

Another experiment, described by Dr. Sanderson in
the paper above referred to, is this:—‘ A glass rod was
charged with Bacteria by dipping it into a solution on
the surface of which there was a viscous scum, consist-
ing entirely of these bodies imbedded in a gelatinous
matrix. The rod was allowed to dry in the air for a
few days. It was then introduced into boiled test-
solution contained in a superheated glass. On February
6th the liquid was already milky, and teemed with
Bacteria. ;

‘To determine the effect of more complete desicca-
tion, an éprouvette containing one cubic centimeter of
cold water, previously ascertained to be zymotic, was
evaporated to dryness in the incubator, and kept. for
some days at a temperature of 40° Cent. On February
20th the dried glass was charged with boiled and
cooled solution, and plugged with cotton-wool in the
usual way. The liquid was examined microscopically
on March 2nd, when it contained numerous Torula-
cells, but no trace of Bacteria. It therefore appears
that the germinal particles of Bacteria are rendered
inactive by drying without the application of heat.’

These experiments have been quoted as conclusive
in reference to the influence of desiccation. They are
quoted, moreover, as applicable not only to the de-
veloped Bacterium, but also, without restriction, to
the germs from which Bacteria spring. ‘To main-
tain,’ says Dr. Bastian,’ ‘his Panspermism in the face

1 ¢ Evolution,’ p. 156,

VITALITY OF PUTREFACTIVE ORGANISMS. 209

of his own experiments, Spallanzani was compelled to
assume that the germs of the lower infusoria do possess
this seed-like property of developing after desiccation.
Modern science, however, declares that they have no
such property. We are told most unreservedly by
Professor Burdon Sanderson, not only that the germinal
particles of Bacteria are rendered inactive by thorough
drying, without the application of heat, i.e. by mere
exposure to air for two or three days at a temperature
of 104° Fahr., but also that fully-formed Bacteria are
deprived of their power of further development by
thorough desiccation.’ In this unqualified sense the
conclusion is untenable. I could cite a multitude of
experiments to prove this, but a reference to one or
two of them will here suffice. 7

A small bunch of old Heathfield hay was washed
with distilled water, which was received into a cham-
pagne-glass. The glass was placed on a stove until]
the water had all evaporated, and the dried residue
was permitted to remain upon the stove for several
days. Dr. Sunderson’s drying temperature was 104°
Fahr., mine was 120° Fahr., and my period of drying
was longer than his. Scraping a little of the dry sedi-
ment treated as above from the bottom of the cham-
pagne-glass, I infected with it a bulb containing
hay-infusion which had been completely sterilized by
eight hours’ boiling. When infected, the infusion was
brightly transparent, but forty-eight hours afterwards
it was teeming with Bacteria. With regard to
the doctrine that these organisms arise from * dead
organic particles,’ instead of from living germs,! no
scientific man at the present day ought, I submit, to
be called upon to spend a moment’s thought upon it.

One other reference will suffice. I have had bun-

1 «Hyvolution,’ p. 44.

210 THE FLOATING-MATTER OF THE AIR.

dles of hay hung up for seven or eight weeks in the hot
rooms of the Turkish Bath in Jermyn Street, and ex-
posed during the whole of this time to a temperature
of 140° Fahr. and upwards. The germs adherent to this
hay were not killed by even this amount of desiccation.
When a sterilized animal or vegetable infusion was
infected with them they gave birth in the usual time
to swarms of Bacteria.

§ 22. Sterilization by discontinuous Heating.

Keeping the distinction between germs and de-
veloped organisms here insisted on, and the probable
changes that occur in passing from the one to the other,
clearly in view, I have been able to sterilize with in-
fallible certainty the most obstinate infusions referred
to in this paper, without either raising the tempera-
ture of the infusions beyond their ordinary boiling-
point, or inordinately prolonging the application of
heat. The infusions may be sterilized by a tempera-
ture even below that of boiling water, while the time
of its application may be but an extremely minute
fraction of that resorted to in some of the foregoing
experiments.

It is an undisputed fact that active Bacteria are
killed by a temperature far below that of boiling water.
It is also a fact that a certain period, which I have
called the period of latency, is necessary to enable the
hardy and resistant germ to pass into that organic con-
dition in which it is so sensitive to heat. There can
hardly be a doubt that the nearer the germ approaches
the moment when it is to emerge as the finished organ-
ism, the more susceptible it is to that influence by
which that organism is so readily destroyed. We may
learn from experience, aided by the power of search

VITALITY OF PUTREFACTIVE ORGANISMS. 211

which the concentrated luminous beam places in our
hands, what is the approximate time required for the
Bacterial germ to pass into the Bacteriwm. Say that
it is twenty-four hours. Supposing the heat of bviling
water, or even a lower heat than that of boiling water,
to be applied to the germ immediately before its final
development, when all its parts are plastic, when it is,
in short, on the point of reaching a stage at which a
temperature of 140° Fahr. is demonstrably fatal. It
is in the highest degree probable that a temperature of
212°, or of 200°, or, indeed, a temperature of 150°, if
applied sufficiently often or for a sufficient length of
time, will prove fatal to the germ, and prevent the
appearance of the still more sensitive organism to
which the germ is on the point of giving birth.

Here, at all events, we have a theoretic finger-post
pointing out a course which experiment may profitably
pursue. Itis not to be expected that the germs with
which our infusions are charged all reach their final
development at the same moment. Some are drier
and harder than others, and some, therefore, will be
rendered plastic and sensitive to heat before others.
Hence the following procedure,

Four-and-twenty small retorts were charged with
hay-infusions on the Ist of February, and subjected
morning and evening to the boiling temperature for
one minute. The last heating took place on the even-
ing of the 3rd of February. The retort-necks had been
plugged with cotton-wool; the air within them, how-
ever, had not been filtered, and there was comparatively
little care bestowed on their preparation. After the
final heating they were abandoned to the temperature
of a room kept close to 90° Fahr. A series of similar
retorts charged at the same time with the same infu-
sions were boiled continuously for ten minutes, plugged

212 THE FLOATING-MATTER OF THE AIR.

while boiling, and placed in the same warm room. Two
days after their preparation the retorts last mentioned
had, without a single exception, given way to turbidity
and scum. On the other hand, twelve of the twenty-four
retorts which had been subjected for a much shorter
period to the discontinuous boiling remained perma-
nently brilliant and free from scum.

On the same 1st of February eight pipette-bulbs were
charged with two hay-infusions, four bulbs being de-
voted to each. The air above the infusions was the
unfiltered air of the laboratory. They were subjected
to the temperature of boiling water for a minute; at the
same time four other bulbs containing the same infu-
sions were boiled continuously for ten minutes and sus-
pended beside their neighbours. Twelve hours subse-
quent to their first brief heating the eight bulbs were
perfectly brilliant, and while in this condition they were
again subjected to the boiling temperature for a minute.
On the evening of the same day they were subjected to
the boiling temperature for half a minute, and on the
following morning the process was repeated. Two
additional heatings of the same brief character were
resorted to. The result of the whole experiment was
that two days after their preparation the four bulbs
which had been boiled for ten minutes were found tur-
bid and covered with scum, while two months after their
preparation the eight bulbs whose periods of boiling
added together amounted only to four minutes were
perfectly brilliant ana free from scum.

The reason of this procedure is plain. By the first
brief application of heat the germs, which are at that
moment plastic, are killed; and before any of the re-
maining germs can develop themselves into Bacteria
they are subjected to another brief period of heating.
This again kills such germs as are sufficiently near their

VITALITY OF PUTREFACTIVE ORGANISMS, 213

final development. At each ‘subsequent period of heat-
ing the number of living germs is diminished, until
finally they are completely destroyed. The infusion, if
protected from external contamination, remains for ever
afterwards unchanged, although, when living Bacteria,
a sprig of hay, or even the dry dust particles of the
laboratory are sown in it, the sterilized liquid shows its
power both of enabling the fully developed organism to
increase and multiply, and of developing the desiccated
Bacterial germ into multitudinous Bacterial life.

On the same date an experiment was made with a
series of pipette-bulbs, whose necks were so bent and
plugged with cotton-wool that no imptrity from the
wool could fall into the infusion. Four bulbs were
charged with an infusion of Heathfield and four with an
infusion of London hay, samples of the same infusions
being introduced at the same time into another series
of bulbs which were plugged like their neighbours and
subjected continuously to the boiling temperature for
ten minutes. The eight bulbs first referred to were, on |
the contrary, discontinuously boiled, the sum of their
periods of boiling being four minutes. The result is
that while the entire series of bulbs boiled for ten
miuutes gave way within forty-eight hours after their
preparation, seven out of the eight bulbs which had been
subjected to discontinuous boiling remained permanently
brilliant.

On the 3rd of February, with the view of testing the
new method still further, infusions of our most refrac-
tory kinds of hay were prepared. There were five bulbs
of neutralized Guildford infusion, and five of a neutral-
ized infusion formed from a mixture of old Colchester
and old Heathfield hay. Two bulbs of each infusion
were at the same time charged and subjected to the
boiling temperature for ten minutes, The ten bulbs

214 THE FLOATING-MATTER OF THE AIR.

first mentioned were never raised to the boiling tempe-
rature at all, the maximum to which they were exposed
being some degrees below their boiling-point. The
result is that while every one of the four bulbs boiled
for ten minutes has become turbid and covered with
scum, one only of the ten discontinuously heated bulbs
has given way; nine of them remain as brilliant as at
first.

It is obvious from what has gone before that two
hundred and forty minutes might have been substituted
for ten minutes without altering this result. Five
minutes of discontinuous heating can accomplish more
than five hours’ continuous heating.

On the same date three bulbs charged with an acid
infusion of London hay were subjected to the same dis-
continuous treatment. They all remain brilliant to the
present hour.

On the 7th of February four of Cohn’s tubes were
charged with turnip-infusion, which was heated discon-
tinuously night and morning up to a temperature of
205° Fahr. The total time during which they were
exposed to this temperature was about three minutes.
They were permanently sterilized, and exhibit a singular
brilliancy to the present hour.

The discontinuous method of heating has also been
applied with success to the closed chambers. One mode
of operation is this :—An oil-bath is heated to a tempe-
rature of 300° Fahr. The charged test-tubes of the
closed chamber are then plunged in the oil, which clasps
the tubes to the level of the surface of the infusion.
They are either raised to incipient boiling and then re-
moved, or suffered actually to boil for thirty seconds
and then removed. Another mode of heating is this:
instead of being plunged into hot oil, the test-tubes are
plunged for two or three minutes into boiling water,

VITALITY OF PUTREFACTIVE ORGANISMS. 215

taken out, wiped dry, the actual boiling being finished
by a spirit-lamp. This is a very handy method, and
more under the experimenter’s control than the oil-bath.
When the latter is employed, the infusions sometimes in
great part waste themselves by leaping from their
tubes; but the spirit-lamp enables us to humour the
infusions by occasionally withdrawing the flame and
moderating the ebullition. The lamp, of course, may
be employed alone without the preliminary immersion
of the tubes in hot water. Usually the process of heat-
ing is repeated at intervals of twelve hours, but in the
case of very nutritive infusions in a very warm room the
interval ought to be shorter. Practice must inform the
experimenter on this point. The reheating must always
occur before the infusions show the slightest visible
tendency to change.

In the early days of February a closed chamber of
six tubes was treated in the manner here described.
Three of the tubes were charged with strong turnip- and
the three others with strong artichoke-infusion. After
two days’ discontinuous heating night and morning, they
were allowed to remain undisturbed in the warm room.
The six tubes remain perfectly brilliant to the present
hour.

On the 12th of February a closed chamber of three
tubes was charged with cucumber-infusion. Heated
discontinuously in the manner described, and abandoned
afterwards to a warm temperature, the three tubes re-
mained perfectly sterile.

Any process competent to sterilize very old hay can
sterilize with greater ease any other infusion. The fact,
therefore, that only a few days ago three closed chambers
charged with our most refractory hay-infusions were
sterilized by discontinuous heating proves the power of
the method over infusions of all kinds.

216 THE FLOATING-MATTER OF THE AIR.

By this method very instructive comparative experi-~
ments might be made, and the resistant power of dif-
ferent germs might be expressed in terms of the heatings
necessary for their sterilization. I possess, for example,
two test-tubes, containing the same infusion and asso-
ciated with the same closed chamber, one of which has
been heated five times and the other six. The former
is quite turbid, while the latter is perfectly clear. In
this case five heatings had left some of the more resist-
ant germs still unkilled, which were destroyed by the
sixth heating. Of two other tubes charged with a
different infusion, one has been heated seven times and
is now full of life; the other has been heated eight
times and is perfectly barren.

With due care the method of sterilization here de-
scribed is infallible, however highly infective the sur-
rounding atmosphere may be. But here, as elsewhere in
these difficult inquiries, the sagacity which comes in
great part from nature, the skill which comes from
training, and the care which ought to root itself in his
moral constitution, are all necessary to save the experi-
menter from error and to lead him to the truth.

§ 23. Mortality of Germs through defect of Oxy-
gen produced by Exhaustion with the Sprengel

Pump.

An equally striking mode of sterilization is now to
be described. The crowding together of the organisms
so as to form in a multitude of cases a heavy, corrugated,
fatty scum upon the surface of the infusions obviously
indicated that air was a necessity of their life. In some
cases the oxygen dissolved in the infusions sufficed to
enable the Bacteria to cloud them from top to bottom;
but in many cases they gathered at the top, and formed

VITALITY OF PUTREFACTIVE ORGANISMS. 217

there a living layer through which no oxygen could pass
to the liquid underneath, which, thus surmounted,
remained as clear as water. The observation of these
facts, and many others of a similar bearing, suggested
inquiry into the effect which the more or less perfect
withdrawal of the air from the infusions would have
upon the development of life.

A few experiments with an ordinary air-pump were,
in the first instance, made. The necks of a series of
pipette bulbs charged with turnip-infusion were drawn
out at the middle to a tube of very small diameter.
The open end of the neck being connected with the
air-pump, the bulbs were exhausted. In some cases,
to render the removal of the air mpre perfect, hydrogen
was admitted into the bulb and was afterwards with-
drawn by the air-pump. Before they were detached
from the pump the bulbs were immersed in lukewarm
water. They boiled freely, and after a minute’s ebul-
lition the narrowed necks were hermetically sealed.
The bulbs were then submerged in cold water, which
was gradually raised to 212° F. and kept boiling for
ten minutes; they were afterwards removed and placed
in a room with a temperature of about 90° Fahr.

Four bulbs were thus treated in a preliminary expe-
riment on the 7th of March. Two of them remain
crystal clear to the present hour; the two others became
cloudy, but remained entirely free from scum. The
cloudiness, I may add, was barely perceptible, but it
was perfectly distinct to the practised eye.

By such means, however, the removal of the air
must have been more or less imperfect, and I therefore
resorted to the far more effective Sprengel pump. To
connect them with the pump, the bulbs were thrown
into the form represented in fig. 21. After the neck of
the bulb had been plugged with cotton-wool it was bent

218 THE FLOATING-MATTER OF THE AIR.

at right angles above the plug, and a portion of it was
drawn out to a tube of capillary diameter, represented
at o. The end a@ was connected with the Sprengel
pump, and after the exhaustion had been continued for
the required interval, the neck of the bulb was sealed
at o.

On the 14th of March three bulbs charged with
turnip-infusion, from which the air had been as far as
possible removed by the ordinary air-pump, were con-
nected with the Sprengel, which continued the exhaus-
tion uninterruptedly for three hours. The air dissolved
in the liquid freely escaped from it at first, and it con-
tinued to appear in minute bubbles long after the
exhaustion had reached a considerable degree of perfec-
tion. The drawn-out necks of the bulbs being hermetic-
ally sealed, the infusion within them was maintained
as before for ten minutes at the boiling temperature.

It will be remembered that when the infusion and
the air above it possessed their ordinary supply of oxy-
gen, 180 minutes’ boiling failed to sterilize the turnip-
infusion. Here, when the air was withdrawn from the
liquid, exposure for one-eighteenth of the foregoing
interval sufficed to produce perfect barrenness. The
infusion in the three bulbs here operated on remains to
the present hour clear in body and perfectly free from
scum.

On the 15th of March seven bulbs charged with in-
fusion of turnip were treated in the manner just de-
scribed, being purged of their air by three hours’ action
of the Sprengel pump, and boiled for ten minutes after-
wards. Six out of the seven remain perfectly pellucid.

On the 16th of March the result was still further
verified. Seven bulbs were then charged with turnip-
infusion, exhausted first by the air-pump, and afterwards
by five hours’ action of the Sprengel pump. Hermetic-

VITALITY OF PUTREFACTIVE ORGANISMS. 219

ally sealed and boiled as before, six out of the seven
remain as clear as distilled water.

On the 20th of March seven bulbs were charged with
infusion of cucumber, and subjected to the action of the
Sprengel pump for seven hours. They were afterwards
treated in the manner just
described. They were all
completely sterilized.

On the 27th of March
three bulbs were charged
with cucumber -infusion
and subjected to the ac-
tion of the Sprengel pump
for five hours. One of them
was subsequently boiled for
five minutes, another for
one minute, while the third
was left unboiled. This
third tube became faintly
cloudy, but the two others
remain perfectly free from
life.

This result invited re-
petition. On the 29th
accordingly six bulbs of
cucumber -infusion were
exhausted for five hours,
and afterwards sealed and
boiled for a single minute.
Five of the six bulbs re-
mained permanently clear ; one became cloudy.

On the 30th of March six bulbs containing turnip-
infusion were exhausted for five hours and boiled after-
wards for a minute. Five remain perfectly clear, one
has become muddy.

220 THE FLOATING-MATTER OF THE AIR.

On the 6th of April five bulbs of beef-infusion were
subjected for three hours to the action of the Sprengel
pump and boiled for a minute afterwards. They all
remain brilliant.

On the 7th of April five bulbs of mutton-infusion
were treated like the beef-bulbs, being exhausted for
three hours and boiled for a minute. All remain clear.
This experiment was repeated and confirmed on the
20th of April.

On the 14th of April three bulbs of pork-infusion
were exhausted for four hours and boiled for a minute.
They all remain pellucid.

On the 17th of April four bulbs of accurately neu-
tralized urine were exhausted for five hours and boiled
fora minute. Three of them remain bright; one has
become cloudy.

This does not exhaust the list of instances. Many
other infusions have been sterilized by this method since
the 17th of April.

It is perfectly certain that in most, if not all, of
these cases 200 minutes’ boiling would have proved in-
sufficient to sterilize the infusion if it had been supplied
with air.

Here the question naturally arises :—What would
happen if the bulbs were exhausted and left unboiled ?
Probably with sufficiently perfect exhaustion all infu-
sions would be sterilized. But in the trials I have thus
far made some of the unboiled infusions have become
cloudy, while others have remained clear. Thus three
bulbs of mutton-infusion exhausted for four hours, two
bulbs of beef-infusion exhausted for three hours, four
bulbs of pork-infusion exhausted for four hours and left
unboiled remain as transparent and as free from life as
their boiled companions. Various other instances of
sterilization without boiling might be cited. On the

VITALITY OF PUTREFACTIVE ORGANISMS. 221

other hand, three bulbs of neutralized urine, exhausted
for five hours and left unboiled, became cloudy. A case
of cucumber-infusion which behaved similarly has been
cited above. It is difficult, if not impossible, to remove
from the infusion and the space above it the last traces
of air; and when backed by a highly nutritive liquid
an infinitesimal residue of oxygen can develop a sensible
amount of life. I may add that I have tested the ex-
haustion of some of the cloudy bulbs, and have found it
in every case defective.

The foregoing instances sufficiently illustrate the
dependence of the organisms here under review upon the
supply of oxygen.! I think it probable that the prin-
ciple thus indicated is capable of useful and extensive
practical application.

§ 24. Mortality of Germs through defect of Oxygen
consequent on boiling the Infusion.

Long prior to these experiments with the Sprengel
pump, the influence of atmospheric oxygen on the life
of these organisms had been brought home to me. It
revealed itself in a striking manner in experiments with
infusions purged of air by boiling, the vessels containing
them being carefully sealed during ebullition. At a
time when the atmosphere of our laboratory was so laden
with infection that no escape for animal or vegetable
liquids introduced in the usual way into closed chambers
was possible, it was perfectly easy to keep the same in-
fusions pellucid for an indefinite time in vessels purged
of air by boiling and properly sealed. I will give afew

1 In search of this gas they sometimes rise into the liquid film
which covers the interior of the bulb to the height of an inch and
more above the surface of the liquid, forming within the bulb »
gauzy scum which appears as if lifted by capillary attraction,

222 THE FLOATING-MATTER OF THE AIR.

out of the multitude of examples that might be cited in
proof of this statement.
Fra. 22. On the 2ud of October four-
=~ teen of our ordinary retort-flasks
(fig. 22) were charged with a
neutralized infusion of hay. They
were boiled for three minutes in
an oil-bath, and hermetically
sealed whilst boiling. Thirteen
out of the fourteen tubes re-
mained perfectly barren, retain-
ing for months their pristine
colour and transparency.

On the 18th of November six retort-flasks were filled
with turnip-, five with cucumber-, five with beetroot-,
and four with parsnep-infusion. The six turnip-flasks
remained permanently pellucid, yielding a clear water-
hammer ring. The five beetroot-flasks remained also
permanently barren, all yielding the water-hammer
sound. Of the parsnep-flasks, two became turbid, but
two remained clear. Of the cucumber-flasks, three
became cloudy, while three remained permanently clear.
Neither in the case of the parsnep nor in that of the
cucumber could the water-hammer sound be obtained
from the cloudy flasks, and when their sealed ends were
broken under water, the vacuum was found defective.
In the clear tubes, on the contrary, it was found practi-
cally perfect.

Again, on the 20th of November, seventeen retort-
flasks were charged with infusions of turnip, cucumber,
and parsnep. They were boiled for three minutes in an
oil-bath, and carefully sealed while boiling. The six
turnip-flasks remained permanently clear, maintaining
for months their sharp water-hammer sound. Of the
five parsnep- flasks, one became turbid and four remained

VITALITY OF PUTREFACTIVE ORGANISMS. 223

permanently clear. These latter only yielded the water-
hammer sound. The turbid flask, on the contrary,
when shaken yielded no such sound, and when its sealed
end was broken under water, its vacuum proved defec-
tive. Of the six cucumber-flasks, two became turbid,
the remaining four being perfectly clear. On breaking
their sealed ends under water, one-third of one of the
turbid flasks and one-fourth of the other remained un-
filled by the liquid.

On the 6th of December eighteen retort-flasks were
charged with cucumber-infusion. They were boiled for
the usual time, that is three minutes, extreme care
being taken to seal them during the issue of the steam.
The water-hammer sound in all these flasks was parti-
cularly sharp and clear. Exposed to a temperature of
90° Fahr. for many weeks, seventeen of them remained
perfectly pellucid; while the same infusion in a sealed
bulb with filtered air above it, and dissolved in it,
swarmed with life after boiling for sixty times the
interval here found effectual.

On the day subsequent to its preparation, one of
these well-exhausted flasks was unexpectedly found tur-
bid and covered with scum. But on examining the
sealed end it was found snipped off. The laboratory air
had thus entered the flask and given birth to the ob-
served organisms. Failures of this sort have a demon-
strative force greater even than successes ; they render so
obviously plain the external source of the contamination.

It is worth saying here that the observation just
recorded was of frequent occurrence. The fineness of
the sealed points of our retort-flasks renders them very
liable to be snipped off if they are not handled with
care. After preparation they are usually suspended on
a wire or on a wooden support; and in frequent in-
stances, after such suspension, I have found a flask

11

224 THE FLOATING-MATTER OF THE AIR.

differentiating itself by thick turbidity from a number’
of perfectly pellucid neighbours, the yielding of the flask
being immediately traced to the fracture of its sealed
end.

With the view of showing how readily, unless ex-
treme care is taken, contamination may enter her-
metically-sealed vessels, the following experiment was
made on the 6th of December. Four retort-flasks
were charged with cucumber-infusion, boiled for the
usual time and sealed, not during the outrush of the
steam, but a moment after ebullition had ceased. On
the 9th of December three of these four flasks were
faintly but distinctly turbid. The reason is obvious.
On the cessation of the ebullition, a momentary conden-
sation of the steam above the infusion caused an
indraught—slight, no doubt, but still sufficient to
contaminate or vivify the infusion.

The source of the contagium was also indicated by
the following experiments. A large number of retort-
flasks, embracing infusions of snipe, wild duck, partridge,
hare, rabbit, mutton, turbot, salmon, whiting, mullet,
turnip, and hay, had remained over from my stock of
1875. After a year’s exposure to the temperature of
our warm room not one of these flasks showed the
slightest trace of turbidity or life. On the 7th of De-
cember the sealed ends of forty of them were snipped
off in the laboratory. Five days afterwards twenty-
seven of them were found swarming with organisms—a
considerably higher percentage than that obtained by
the same process in the same laboratory a year pre-
viously.

It is needless to dwell with any emphasis on the
obvious inference from all this, namely, that the conta-
gium is external to the infusions, that it is something
in the air, and that at different times we have different

VITALITY OF PUTREFACTIVE ORGANISMS, 225

amounts of aerial interspace free from the floating con-
tagium.

§ 25. Critical Review of the last two Sections.

It has been my desire and aim throughout this
inquiry to free it as much as possible from uncer-
tainty and doubt. I have tried to render the facts
safe by laborious repetition, and the interpretations
of those facts secure by close and constant criticism.
Thus, in reference to our present subject, I had to put
to myself very definitely the question whether the per-
manent clearness of an infusion exposed to a very
moderate amount of heat, after having been freed from
air by boiling or by the Sprengel pump, was really due
to the destruction of the germs in the infusion. Even
in a highly infective atmosphere, from three to five
minutes’ boiling in an oil-bath suffices to sterilize our
retort-flasks, while it is perfectly certain that exposure
to the boiling temperature for fifty times this interval
may fail to kill the germs of an infusion containing
a good supply of atmospheric air. A similar remark
applies to our experiments with the Sprengel pump.
I asked myself whether in these cases the life of the
germs was not suspended merely, instead of being
destroyed. It was quite conceivable that germs en-
dowed with vital power, ready to act under proper
conditions, might still exist in our hermetically-sealed
flasks, although the entire absence of oxygen rendered
their further development impossible.

That something more than a mere temporary hind-
rance to development is here involved was, however,
proved by many of the experiments just recorded.
These experiments showed that after hermetically-seaied
flasks had remained pellucid, not only for days but for

226 THE FLOATING-MATTER OF THE AIR.

weeks and months, and in some cases for more than a
year, on their sealed ends being broken off, even in
ordinary air, they by no means invariably showed signs
of life afterwards. Many of them remained permanently
barren while copiously supplied with oxygen.

Special experiments were, however, made to illus-
trate this point. First of all, as I have already re-
counted, hermetically-sealed retort-flasks were opened
in one of our lower store-rooms, and though supplied
with oxygen from this source they showed subsequently
no signs of life. A considerable number of retort-flasks
had also their sealed ends broken off in the midst of a
spirit-lamp flame. It is known that gunpowder can be
dropped through such a flame without ignition ; and in
a few rare instances the infusions which had their first
supply of air thus passed through a flame showed subse-
quent signs of life. In such cases the germinal matter
had been sucked so rapidly through the flame that it
escaped destruction; but in the vast majority of in-
stances the sterilized infusions remained sterile.

Mechanical arrangements were also made for the
breaking off of the sealed ends in a receiver filled with
filtered air. But it is by no means easy to perfectly
cleanse from infectious matter the instruments used in
such experiments, though with sufficient practice this
might certainly be done. The consequence was that
some of the flasks opened in filtered air yielded subse-
quently. The following is an illustrative case :—On the
3rd of January ten flasks were charged with cncumber-,
turnip-, artichoke-, and melon-infusions. They were
boiled for the usual time, sealed during ebullition, and
exposed afterwards to a warmtemperature. Their sealed
ends were then broken off by a mechanical contrivance
placed in a receiver containing filtered air. The two
artichoke-flasks remained permanently barren after-

VITALITY OF PUTREFACTIVE ORGANISMS. 227

wards. Of the two melon-flasks, one remained barren
and the other developed life. Of the two cucumber-
flasks, one became turbid, the other remained clear. Of
the four turnip-flasks, two became turbid and two re-
mained clear. Out of the ten flasks, therefore, all freely
connected with the external air, six remained perma-
nently barren. By further practice barrenness in almost
every instance has been secured. The conclusion, I
think, is obvious. It is not the heat alone that destroys
these germs, for fifty times the amount of heat will not
accomplish this when oxygen in due quantity is pre-
sent: the heat must be aided by the withdrawal of the
oxygen.

§ 26. Mortality of Germs through excess of Oxygen.

The foregoing remarks lead naturally to a brief
reference to the important experiments of M. Paul Bert!
on the toxic influence of compressed oxygen. From the
imperfect account of these experiments which first
reached me, I inferred that the germs of putrefaction
had been destroyed by mere mechanical pressure, and
more than a year and a half ago I placed turnip-infu-
sions in strong iron bottles, and subjected them for several
days to an air-pressure of twenty-three atmospheres,
When taken from the bottles the infusions were found
one and all swarming with life. Last October I made
a series of similar experiments with infusions of hay and
turnip, subjecting them for several days to an air-pres-
sure of twenty-seven atmospheres. When taken from
their iron bottles the infusions were found one and all
teeming with Bacteria.

I then resorted to pure oxygen, and found the same
to be true of my infusions that M. Paul Bert had found

1 Comptes Rendus, vol, Ixxx. p. 1579,

228 THE FLOATING-MATTER OF THE AIR.

true of his flesh, moist bread, boiled starch, strawberries,
cherries, wine, and urine. Pressures varying from
twenty-seven atmospheres to ten atmospheres of oxygen
were employed. In all cases, however long the pressure
was continued, or however favourable to putrefaction the
surrounding temperature might be, the infusions (which
embraced those of beef, mutton, and turnip) were found,
when taken from the bottles, as clear as crystal and
entirely free from life. It required, indeed, long subse-
quent exposure to the common air to infect infusions
which had been thus surcharged with oxygen. Other
bottles containing the same infusions were simultane-
ously subjected to a like pressure, not of oxygen, how-
ever, but. of atmospheric air. When removed from the
bottles they were one and all found in a state of putre-
faction and swarming with life.

Thus when oxygen is wholly withdrawn from organic
infusions, the life with which we are here concerned
ceases. When, on the other hand, the gas is in con-
siderable excess, it becomes a deadly poison to organisms
which, in moderate quantities, it sustains. As in the
case of temperature, so in regard to the supply of oxygen,
there is a medial zone favourable to the play of vitality,
beyond which, on both sides, life cannot exist.

The present memoir virtually ends here; but I will
append a few brief sections which, though incomplete,
are not without instruction.

§ 27. Experiments on neutralized Urine.

I have already communicated to the Royal Society
the result of some experiments made with this liquid,!
in which the potash employed for neutralization was
subjected to a temperature of 220° Fahr. The alkali

1 Proceedings, vol. xxv. p. 457.

VITALITY OF PUTREFACTIVE ORGANISMS. 229

was contained in tubes drawn out finely at the end,
which were introduced int» the flasks containing the
urine, and broken by shaking after the acid urine had
been completely sterilized by heat. The cases were ex-
ceedingly rare in which life showed itself in the urine
thus neutralized. The preponderance of sterilized flasks
over unsterilized ones was very great.

In the experiments now to be glanced at, neither
the urine nor the potash was raised to a temperature
higher than 212°. Wishing to ascertain how the refrac-
tory germs of our laboratory would fare in neutralized
urine, on the 16th of February I had five pipette-bulbs
charged with the liquid. It was neutralized by caustic
potash, which on boiling produced copious precipitation.
It was afterwards filtered and rendered very transparent.
The bulbs had been well cleansed, filled with one-third
of an atmosphere of filtered air, hermetically sealed,
and exposed afterwards to the heat of a Bunsen flame.
They were charged with the urine by breaking off their
finely drawn out points in the body of the liquid. They
were then again sealed, and subjected to the boiling
temperature for ten minutes.

Not one of these bulbs remained sterile. Two days
subsequent to their preparation they were all swarming
with organisms.

Three other bulbs were on the same occasion charged
with precisely the same infusion, only instead of being
associated with air they were well purged of air by five
minutes’ boiling in an oil-bath. While the steam was
issuing they were hermetically sealed.

Not one of these bulbs has proved fruitful. They are
all as brilliant and as free from life as they were after
they had passed through the filter.

The difference here indicated is worthy of notice.
In the one case five minutes’ action completely steril-

230 THE FLOATING-MATTER OF THE AIR.

izes; in the other ten minutes’ action fails to do so.
This latter interval indeed might be multiplied twenty-
fold and still prove ineffectual. In the one case the
process of boiling purged the liquid of its air; in the
other case the air was retained within and above the
liquid. The case therefore connects itself with our
former illustrations.

On the 21st of February six bulbs were charged
with fresh urine carefully neutralized and boiled for five
minutes in an oil-bath. Of the six flasks, four remain
perfectly clear and brilliant, one is slightly cloudy, and
one turbid.

The urine here referred to was neutralized in our
own laboratory; but as the importance of accurate neu-
tralization has been much insisted on, I wished to check
myself. At my request, therefore, Dr. Debus was good
enough to send me from Greenwich a quantity of urine
carefully neutralized by him. On the Ist of March
seven retort-flasks were charged with the neutralized
liquid. These were boiled for five minutes in an oil-
bath and sealed during ebullition. Three of these flasks
have become turbid, but four remain perfectly clear.

On the 5th of March Dr. Williamson was good
enough to send me a supply of neutralized urine collected
in a public urinal in University College. The colour
was very deep, the odour was very bad, and the precipi-
tation on boiling very copious. Fourteen retort-flasks
were charged with this liquid on the 6th of March.
Seven of them have gone bad, but seven of them remain
clear.

On the 10th of March Dr. Frankland was good
enough to send me a supply of urine neutralized by
himself. It was introduced into four retort-flasks, which,
like the others, were boiled for five minutes in hot oil
and sealed during ebullition. None of these flasks have

VITALITY OF PUTREFACTIVE ORGANISMS. 231

shown the slightest sign of yielding. The liquid within
all of them is as brilliant as it was when first intro- -
duced.

In every case here mentioned the liquid, after boil-
ing, was exposed for several days to a temperature of
50° C,

The conflict described in the foregoing pages and
the search for principles to reconcile the results occupied
me too long to permit of my doing more than break
ground on the subject of urine. I entertain, however, a
strong opinion that by a little practice with this liquid,
its sterilization by five minutes’ boiling might be ren-
dered certain in every case. As the experiments stand,
they sufficiently negative the conclusion that neutralized
urine furnishes a specially convincing illustration of
spontaneous generation.

§ 28. Hermetically-sealed Flasks exposed to the Sun
of the Alps.

A remark of Dr. Bastian’s, wherein he refers to the
power of the actinic rays of the sun to promote spon-
taneous generation,’ caused me to take with me to
Switzerland a number of flasks hermetically sealed with
special care and charged with infusions of various kinds.
Eighty of them were carefully packed in sawdust in
London; but on my arrival at the Bel Alp, which
stands at an elevation of some 7,000 feet above the
sea, I found only forty-five of them unbroken. They
were thus distributed :—

Beef . . ; ‘ : ; 12 flasks.
Mackerel , ‘ ; - : 12 ,
Turnip . : : a : 12. 5
Fowl . . «© «© «©. 9 y

' «Nature,’ vol, iii. p. 247.

232 THE FLOATING-MATTER OF THE AIR,

For ten days of the splendid summer with which we
were favoured during a portion of last July, these flasks
were exposed daily to the sunlight upon the roof of the
Bel Alp hotel. The sky during many of these days was
of a deep and cloudless blue; and certainly in London
the actinic rays never approached the power of those
here brought to bear upon the infusions. The tempera-
ture for many hours of each day was about 120° Fahr.
Every evening, when the thermometer had fallen to
about 70°, the flasks were removed and suspended above
the kitchen-range of the hotel, the temperature gene-
rally varying throughout the night from 70° to 80°
Fahr. Such variations of temperature, it may be re-
marked, are deemed favourable to spontaneous genera-
tion.

After the sunny weather had disappeared, the flasks
were allowed to remain for three weeks suspended in
the kitchen, with occasional exposures to the sun; the
average temperature of the kitchen where the flasks
were hung was about 90° F. The result of the observa-
tions was that not one of these forty-five flasks yielded
the slightest evidence of spontaneous generation. From
first to last they all continued as limpid as distilled
water.

The sealed ends of these flasks were afterwards nipped
off under various circumstances, some on the Sparren-
horn, some on the glacier, some in the Massa Gorge,
some amid the hair of my own head, and some in the
rooms of the hotel. Many of them, moreover, were
infected with water of various kinds—spring-water, lake-
water, and glacier-water. It is not my object to give
a detailed account of these experiments, but simply to
say that it was not lack of nutritive power on the pari
of the infusions which prevented the appearance of or-
ganisms in the first instance; for when brovght into

VITALITY OF PUTREFACTIVE ORGANISMS. 233

contact with infectious matter every one of the flasks
showed its power of sustaining and multiplying life.

§ 29. Remarks on Hermetic Sealing.

A few brief remarks on this subject may, I think,
be fitly interpolated here. Hermetic sealing during
ebullition is an operation requiring some apprenticeship
to perform it aright. The neck of the flask ought to
be so narrow that the pressure of the steam within shall
be always sensibly greater than that of the atmosphere
without. This condition would be readily fulfilled if
the liberation of the steam were absolutely uniform, and
not by fits and starts. But it never is uniform, and if
the channel through which the steam issues be wide, it
is scarcely possible to avoid regurgitation. Sometimes
the pressure within is above that of the atmosphere, and
steam freely issues; but at the next moment, through
liquid adhesion to the flask, and partial condensation
above, the internal pressure may be below that of the
atmosphere and permit air to enter. This alternate
triumph of the inner and the outer pressure may be
rendered plainly evident by the motions of the water
condensed in the neck of the flask. The liquid acts as
an index which moves to and fro, sometimes forward,
sometimes backward, as the pressure varies. It is quite
evident that contamination may be, and it is quite cer-
tain that contamination has been, thus introduced into
flasks reputed to be free from air.

Even with considerable care and fairly disciplined
manipulatory skill success is not invariable. Ten per
cent. is not at all a large allowance to set down as
defective in ordinary hermetically-sealed flasks. The
recent opening of about two hundred flasks employed in
my earlier experiments, under water and under caustic-

234 THE FLOATING-MATTER OF THE aIR.

potash solution, furnishes the basis of this conclusion.
Even in a comparatively pure atmosphere success does
not in every instance attend the experimenter. At Kew,
for example, on the 8th of January, thirteen retort-flasks
were charged with infusions of cucumber, melon, beef,
andsole. Twelve out of the thirteen remained perfectly
limpid, but one of them (a cucumber-flask) became dis-
tinctly cloudy, and this one alone refused, when tested,
to yield the water-hammer sound. With due training,
however, success may be rendered invariable.

§ 30. Experiments with Turnip-cheese Infusions.

Iam unwilling to omit all reference to experiments
which have cost considerable labour, and which, though
they have not been repeated and controlled to the extent
that I could wish, contribute nevertheless to our know-
ledge of the present question. This unwillingness causes
me to introduce here, in the briefest manner possible, a
reference to a series of experiments made with turnip-
cheese infusions, which have been so frequently cited as
offering a conspicuous proof of the doctrine of-sponta-
neous generation.

The experiments to which I refer were made in part
with closed chambers, and in part with hermetically-
sealed retort-flasks. The specific gravity of the infu-
sions varied from 1008 to 1012. The cheeses employed
were Cheshire, Cheddar, Gloucester, Dutch cheese,
American cheese, Roquefort, and Parmesan, the quantity
varying from half a grain to two grains for every ounce
of the infusion. The cheese being first well triturated
in a mortar, so as to render its particles very minute,
was intimately mixed with the infusion, which was then
boiled for a few minutes and passed through a filter.
The filtered liquid was then introduced into its closed
chamber, and boiled there for five minutes.

VILALITY OF PUTREFACTIVE ORGANISMS, 235

Sixteen such chambers were employed, one of them
containing twelve test-tubes, each of the others only
three. There were therefore fifty-seven test-tubes in
all. The result of the experiment was, that out of the
fifty-seven tubes, twenty-seven became turbid in a few
days, while thirty remained for months without sensible
alteration.}

A considerable number of retort-flasks were charged
at the same time with the same infusions, and boiled for
five minutes in an oil-bath. The great majority of
these flasks remained perfectly intact.

Here, then, as elsewhere, the ground on which the
doctrine of spontaneous generation has sought to plant
itself slips from under it; for assuredly the scientific
mind will attribute to other causes than to it the pro-
duction of organisms in the minority of cases above
referred to.

One likely cause may here be signalized and illus-
trated. The experiments of Spallanzani on the action
of heat upon seeds are well known, and they have
been frequently cited in support of the thesis that
the briefest exposure to the temperature of 212° Fahr.
suffices to destroy all living matter. I have repeated
many of Spallanzani’s experiments, and will here
briefly refer to one series which bear upon the present
point. Peas, kidney-beans, cress- and mustard-seed
were tied up in small calico bags, and boiled for in-
tervals varying from half a minute to five minutes.
They were then carefully sown in flower-pots filled with
well-prepared earth, and placed in a shed kept at a

1 These chambers were prepared and their tubes charged prior
to the introduction of hay into our laboratory last autumn, other-
wise the immunity of a single one of them could not have been
secured. The chambers employed had stood over from my last in-
vestigation, and no pains had been taken to render them air-tight.

236 THE FLOATING-MATTER OF THE AIR.

temperature of 70° Fahr. An unboiled sample of every
seed was sown at the same time beside the boiled ones.
The unboiled seeds sprouted vigorously. Thirty seconds’
exposure to the boiling temperature deprived both the
peas and the beans of their power of germination. A
few of the cress-seeds exposed for this interval sprouted,
but the majority were killed, and all were killed by a
minute’s boiling. On the other hand, a very large pro-
portion of the mustard-seeds boiled for thirty seconds
germinated. The time of exposure in the case of this
seed was doubled, trebled, and quadrupled, leaving still
a residue of life. The fertile mustard-seeds gradually
diminished in number as the time of boiling increased,
but even after two minutes’ boiling many of them
germinated.

And now comes a fact which I deem of some im-
portance as regards the present inquiry. When the
calico bag was abandoned, and the mustard-seeds were
placed loosely in water, so as to ensure not only the free
communication to them of its temperature, but free
diffusion between the soluble portions of the seeds and
the surrounding liquid, not one of them escaped the
ordeal of thirty seconds’ boiling. In the first series of
experiments, the bag which held the seeds together not
only exercised a protecting influence itself, but it en-
abled the outside seeds to act as shields to the inside
ones Assuredly in a far higher degree will cheese
shield germs contained within it. Unlike fruit and
meat, it is highly impervious to water. It thus wards
off the liquid on which the softening and swelling of the
germ depend, so that within such a substance the life of
a germ might be indefinitely prolonged.

FERMENTATION, AND ITS BEARINGS ON
SURGERY AND MEDICINE.

IV.

Onz of the most remarkable characteristics of the age
in which we live, is its desire and tendency to connect
itself organically with preceding ages—to ascertain
how the state of things that now is came to be what it
is. And the more earnestly and profoundly this pro-
blem is studied, the more clearly comes into view the
vast and varied debt which the world of to-day owes to
that fore-world, in which man by skill, valour, and
well-directed strength first replenished and subdued
the earth. Our prehistoric fathers may have been
savages, but they were clever and observant ones.
They founded agriculture, by the discovery and develop-
ment of seeds whose origin is now unknown. They
tamed and harnessed their animal antagonists, and sent
them down to us as ministers, instead of rivals in the
fight for life. Later on, when the claims of luxury
added themselves to those of necessity, we find the
same spirit of invention at work. We have no historic
account of the first. brewer, but we glean from history
that his art was practised, and its produce relished,
more than two thousand years ago. Theophrastus,
who was born nearly four hundred years before Christ,

1A Discourse delivered before“the Glasgow Science Lectures
Association, October 19 1876.

238 THE FLOATING-MATTER OF THE AIR.

described beer as the wine of barley. It is extremely
difficult to preserve beer in a hot country, still, Egypt
was the land in which it was first’ brewed, the desire of
man to quench his thirst with this exhilarating beverage
overcoming all the obstacles which a hot climate threw
in the way of its manufacture.

Our remote ancestors had also learned by experience
that wine maketh glad the heart of man. Noah, we
are informed, planted a vineyard, drank of the wine,
and experienced the consequences. But, though wine
and beer possess so old a history, a very few years ago
no man knew the secret of their formation. Indeed, it
might be said that until the present year no thorough
and scientific account was ever given of the agencies
which come into play in the manufacture of beer, of
the conditions necessary to its health, and of the
maladies and vicissitudes to which it is subject.
Hitherto the art and practice of the brewer have re-
sembled those of the physician, both being founded on
empirical observation. By this is meant the observa-
tion of facts, apart from the principles which explain
them, and which give the mind an intelligent mastery
over them. The brewer learnt from long experience
the conditions, not the reasons, of success. But he had
to contend, and has still to contend, against unexplained
perplexities. Over and over again his care has been
rendered nugatory ; his beer has fallen into acidity or
rottenness, and disastrcus losses have been sustained,
of which he has been unable to assign the cause. It is
the hidden enemies against which the physician and the
brewer have hitherto contended, that recent researches
are dragging into the light of day, thus preparing the
way for their final extermination.

Let us glance for a moment at the outward and

FERMENTATION. 239

visible signs of fermentation. A few weeks ago IJ paid
a visit to a private still in a Swiss chalet; and this is
what I saw. In the peasant’s bedroom was a cask with
a very large bunghole carefully closed. The cask con-
tained cherries which had lain in it for fourteen days.
It was not entirely filled with the fruit, an air-space
being left above the cherries when they were put in. I
had the bung removed, and a small lamp dipped into
this space. Its flame was instantly extinguished. The
oxygen of the air had entirely disappeared, its place
being taken by carbonic acid gas.' I tasted the
cherries: they were very sour, though when put into
the cask they were sweet. The cherries and the liquid
associated with them were then placed in a copper
boiler, to which a copper head was closely fitted. From
the head proceeded a copper tube which passed straight
through a vessel of cold water, and issued at the other
side. Under the open end of the tube was placed a
bottle to receive the spirit distilled. The flame of
small wood-splinters being applied to the boiler, after
a time vapour rose into the head, passed through the
tube, was condensed by the cold of the water, and fell
in a liquid fillet into the bottle. On being tasted, it
proved to be that fiery and intoxicating spirit known in
commerce as Kirsch or Kirschwasser.

The cherries, it should be remembered, were left to
themselves, no ferment of any kind being added to
them. In this respect what has been said of the cherry
applies also to the grape. At the vintage the fruit of
the vine is placed in proper vessels, and abandoned to
its own action. It ferments, producing carbonic acid ;
its sweetness disappears, and at the end of a certain

1 The gas which is exhaled from the lungs after the oxygen of
the air has done its duty in purifying the blood; the same also which
effervesces from soda water and champagne.

240 THE FLOATING-MATTER OF THE AIR.

time the unintoxicating grape-juice is converted into
intoxicating wine. Here, as in the case of the cherries,
the fermentation is spontaneous—in what sense sponta-
neous will appear more clearly by-and-by.

It is needless for me to tell a Glasgow audience that
the beer-brewer does not set to work in this way. In
the first place the brewer deals not with the juice of
fruits, but with the juice of barley. The barley having
been steeped for a sufficient time in water, it is drained
and subjected to a temperature sufficient to cause the
moist grain to germinate; after which, it is completely
dried upon a kiln. It then receives the name of malt.
The malt is crisp to the teeth, and decidedly sweeter to
the taste than the original barley. It is ground, mashed
up in warm water, then boiled with hops until all the
soluble portions have been extracted; the infusion thus
produced being called the wort. This is drawn off, and
cooled as rapidly as possible ; then, instead of abandon-
ing the infusion, as the wine-maker does, to its own
action, the brewer mixes yeast with his wort, and places
it in vessels each with only one aperture open to the
air. Soon after the addition of the yeast, a brownish
froth, which is really new yeast, issues from the aper-
ture, and falls like a cataract into troughs prepared to.
receive it. This frothing and foaming of the wort is a
proof that the fermentation is active.

Whence comes the yeast which issues so copiously
from the fermenting tub? What is this yeast, and how
did the brewer become possessed of it? Examine its
quantity before and after fermentation. The brewer
introduces, say 10 cwts. of yeast; he collects 40, or it
may be 50, ewts. The yeast has, therefore, augmented
from four to five fold during the fermentation. Shall
we conclude that this additional yeast has been sponta-
neously generated by the wort? Are we not rather re-

FERMENTATION. 241

minded of that seed which fell into good ground, and
brought forth fruit, some thirty fold, some sixty fold,
some an hundred fold? On examination, this notion
of organic growth turns out to be more than a mere
surmise. In the year 1680, when the microscope was
still in its infancy, Leeuwenhoek turned the instru~
ment upon yeast, and found it composed of minute
globules suspended in a liquid. Thus knowledge rested
until 1835, when Cagniard de la Tour in France, and
Schwann in Germany, independently, but animated by
a common thought, turned microscopes of improved
definition and heightened powers upon yeast, and
found it budding and sprouting before their eyes. The
augmentation of the yeast alluded to above was thus
proved to arise from the growth of a minute plant now
called Torula (or Saccharomyces) Cerevisie. Sponta-
neous generation is therefore out of the question. The
brewer deliberately sows the yeast-plant, which grows
and multiplies in the wort as its proper soil. This dis-
covery marks an epoch in the history of fermentation.
But where did the brewer find his yeast? The reply
to this question is similar to that which must be given
if it were asked where the brewer found his barley. He
has received the seeds of both of them from preceding
generatious. Could we connect without solution of con-
tinuity the present with the past, we should probably
be able to trace back the yeast employed by my friend
Sir Fowell Buxton to-day to that employed by some
Egyptian brewer two thousand years ago. But you may
urge that there must have been a time when the first
yenst-cell was generated. Granted—exactly as there
was a time when the first barley-corn was generated.
Let not the delusion lay hold of you thata living thing
is easily generated because it is small. Both the yeast-
plant and the barley-plant lose themselves in the dim

242 THE FLOATING-MATTER OF THE AIR.

twilight of antiquity, and in this our day there is no
more proof of the spontaneous generation of the one
than there is of the spontaneous generation of the
other.

I stated a moment ago that the fermentation of
grape-juice was spontaneous; but I was careful to add,
‘in what sense spontaneous will appear more elearly
by-and-by.’ Now this is the sense meant. The wine-
maker does not, like the brewer and distiller, delibe-
rately introduce either yeast, or any equivalent of yeast,
into his vats; he does not consciously sow in them any
plant, or the germ of any plant; indeed, he has been
hitherto in ignorance whether plants or germs of any
kind have had anything to do with his operations.
Still, when the fermented grape-juice is examined, the
living TYorula concerned in alcoholic fermentation
never fails to make its appearance. How is this? If
no living germ has been introduced into the wine-vat,
whence comes the life so invariably developed there ?

You may be disposed to reply, with Turpin and
others, that in virtue of its own inherent powers, the
grape-juice when brought into contact with the vivi-
fying atmospheric oxygen, runs spontaneously and of
its own accord into these low forms of life. I have not
the slightest objection to this explanation, provided
proper evidence can be adduced in support of it. But
the evidence adduced in its favour, as far as I am ac-
quainted with it, snaps asunder under the strain of
scientific criticism. It is, as far as I can see, the evi-
dence of men who, however keen and clever as ob-
servers, are not rigidly trained experimenters. These
alone are aware of the precautions necessary in investi-
gations of this delicate kind. In reference, then, to the
life of the wine-vat, what is the decision of experiment
when carried out by competent men? Let a quantity

FERMENTATION. 243

of the clear, filtered ‘must’ of the grape be so boiled
as to destroy such germs asit may have contracted from
the air or otherwise. In contact with germless air the
uncontaminated must never ferments. All the mate-
rials for spontaneous generation are there, but so long
as there is no seed sown, there is no life developed, and
no sign of that fermentation which is the concomitant
of life. Nor need you resort to a boiled liquid. The
grape is sealed by its own skin against contamination
from without. By an ingenious device Pasteur has ex-
tracted from the interior of the grape its pure juice,
and proved that in contact with pure air it never
acquires the power to ferment itself, nor to produce
fermentation in other liquids.! It is not, therefore, in
the interior of the grape that the origin of the life
observed in the vat is to be sought.

What then is its true origin? This is Pasteur’s
answer, which his well-proved accuracy renders worthy
of all confidence. At the time of the vintage micro-
scopic particles are observed adherent, both to the outer
surface of the grape and to the twigs which support the
grape. Brush these particles into a capsule of pure
water. It is rendered turbid by the dust. Examined
by a microscope, some of these minute particles are
seen to present the appearance of organized cells.
Instead of receiving them in water, let them be brushed
into the pure inert juice of the grape. Forty-eight
hours after this is done, our familiar Torwlais observed
budding and sprouting, the growth of the plant being
accompanied by all the other signs of active fermenta-
tion. What is the inference to be drawn from this

t The liquids of the healthy animal body are also sealed fror
external contamination. Pure blood, for example, drawn with due
precautions from the veins, will never ferment or putrefy in contact
with pure air.

244 THE FLOATING-MATTER OF THE ATR,

experiment? Obviously that the particles adherent
to the external surface of the grape include the germs
of that life which, after they have been sown in the
Juice, appears in such profusion. Wine is sometimes
objected to on the ground that fermentation is < arti-
ficial ;” but we notice here the responsibility of nature.
The ferment of the grape clings like a parasite to the
surface of the grape; and the art of the wine-maker
from time immemorial has consisted in bringing—and
it may be added, ignorantly bringing—two things thus
closely associated by nature into actual contact with
each other. For thousands of years, what has been
done consciously by the brewer, has been done uncon-
sciously by the wine-grower. The one has sown his
leaven just as much as the other.

Nor is it necessary to impregnate the beer-wort
with yeast to provoke fermentation. Abandoned to
the contact of our common air, it sooner or later
ferments; but the chances are that the produce of that
fermentation, instead of being agreeable, would be
disgusting to the taste. By a rare accident we might
get the true alcoholic fermentation, but the odds against
obtaining it would be enormous. Pure air acting upon
a lifeless liquid will never provoke fermentation; but
our ordinary air is the vehicle of numberless germs
which act as ferments when they fall into appropriate
infusions. Some of them produce acidity, some putre-
faction. The germs of our yeast-plant are also in the
air; but so sparingly distributed that an infusion like
beer-wort, exposed to the air, is almost sure to be taken
possession of by foreign organisms. In fact, the mala-
dies of beer are wholly due to the admixture of these
objectionable ferments, whose forms and modes of
nutrition differ materially from those of the true
leaven.

FERMENTATION. 245

Working in an atmosphere charged with the germs
of these organisms, you can understand how easy it is
to fall into error in studying the action of any one
of them. Indeed it is only the most accomplished
experimenter, who, moreover, avails himself of every
means of checking his conclusions, that can walk with-
out tripping through this land of pitfalls. Such a man
the French chemist Pasteur has hitherto proved himself
to be. He has taught us how to separate the com-
mingled ferments of our air, and to study their pure
individual action. Guided by him, let us fix our
attention more particularly upon the growth and action
of the true yeast-plant under different conditions. Let
it be sown in a fermentable liquid, which is supplied
with plenty of pure air. The plant will flourish in
the aérated infusion, and produce large quantities of
carbonic acid gas—a compound, as you know, of carbon
and oxygen. The oxygen thus consumed by the plant
is the free oxygen of the air, which we suppose to be
abundantly supplied to the liquid. The action is so
far similar to the respiration of animals, which inspire
oxygen and expire carbonic acid. If we examine the
liquid even when the vigour of the plant has reached
its maximum, we hardly find in it a trace of alcohol.
The yeast has grown and flourished, but it has almost
ceased to act as a ferment. And could every individual
yeast-cell seize, without any impediment, free oxygen
from the surrounding liquid, it is certain that it would
cease to act as a ferment altogether.

What, then, are the conditions under which the
yeast-plant must be placed so that it may display its
characteristic quality ? Reflection on the facts already
referred to suggests a reply, and rigid experiment
confirms the suggestion. Consider the Alpine cherries
in their closed vessel. Consider the beer in its barrel,

246 THE FLOATING-MATTER OF THE AIR.

with a single small aperture open to the air, through
which it is observed not to imbibe oxygen, but to pour
forth carbonic acid. Whence come the volumes of
oxygen necessary to the production of this latter gas ?
The small quantity of atmospheric air dissolved in the
wort and overlying it would be totally incompetent to
supply the necessary oxygen. In no other way can the
yeast-plant obtain the gas necessary for its respiration
than by wrenching it from surrounding substances in
which the oxygen exists, not free, but in a state of
combination. It decomposes the sugar of the solution
in which it grows, produces heat, breathes forth car-
bonie acid gas, and one of the liquid products of the
decomposition is our familiar alcohol. The act of fer-
mentation, then, is a result of the effort of the little
plant to maintain its respiration by means of combined
oxygen, when its supply of free oxygen is cut off.
As defined by Pasteur, fermentation is life without
air.

But here the knowledge of that thorough investi-
gator comes to our aid to warn us against possible error.
It is not, he says, all yeast-cells that can thus live without
air and provoke fermentation. They must be young cells
which have caught their vegetative vigour from contact
with free oxygen. But once possessed of this vigour the
yeast, he alleges, may be transplanted into a saccharine
infusion absolutely purged of air, where it will con-
tinue to live at the expense of the oxygen, carbon,
and other constituents of the infusion. Under these
new conditions its life, as a plant, will be by no
means so vigorous as when it had a supply of free
oxygen, but its action as a ferment will be indefinitely
greater.

Does the yeast-plant stand alone in its power of
provoking alcoholic fermentation? It would be sin-

FERMENTATION. 247

gular if amid the multitude of low vegetable forms no
other could be found capable of acting in a similar way.
And here again we have occasion to marvel at that
sagacity of observation among the ancients to which we
owe so vast a debt. Not only did they discover the
alcoholic ferment of yeast, but they had to exercise a
wise selection in picking it out from others, and giving
it special prominence. Place an old boot in a moist
place, or expose common paste or a pot of jam to the
air; it soon becomes coated with a blue-green mould,
which is nothing else than the fructification of a little
plant called Penicillium glaucum. Do not imagine
that the mould kas sprung spontaneously from boot, or
paste, or jam; its germs, which are abundant in the
air, have been sown, and have germinated, in as legal
and legitimate a way as thistle-seeds wafted by the
wind to a proper soil. Let the minute spores of Peni-
cillium be sown in a fermentable liquid, which has
been previously so boiled as to kill all other spores or
seeds which it may contain; let pure air have free
access to the mixture; the Penicillium will grow
rapidly, striking long filaments into the liquid, and
fructifying at its surface. Test the infusion at various
stages of the plant’s growth, you will never find in it
a trace of alcohol. But forcibly submerge the little
plant, push it down deep into the liquid, where the
quantity of free oxygen that can reach it is insufficient
for its needs, it immediately begins to act as a ferment,
supplying itself with oxygen by the decomposition of
the sugar, and producing alcohol as one of the results
of the decomposition. Many other low microscopic
plants act in a similar manner. In aérated liquids
they flourish without any production of alcohol, but cut
off from free oxygen they act as ferments, producing:
alcohol exactly as the real alcoholic leaven produces it.
12

248 THY FLOATING-MATTER OF THE AIR.

only less copiously. For the discovery and apprehension
of these facts we are indebted to Pasteur.

In the cases hitherto considered, the fermentation
is proved to be the invariable correlative of life, being
produced by organisms foreign to the fermentable sub-
stance. But the substance itself may also have within
it, to some extent, the motive power of fermentation.
The yeast-plant, as we have learned, is an assemblage
of living cells; but so at bottom, as shown by Schleiden
and Schwann, are all living organisms. Cherries,
apples, peaches, pears, plums, and grapes, for example,
are composed of cells, each of which is a living unit.
And here I have to direct your attention to a point of
extreme interest. In 1821, the celebrated French
chemist, Bérard, established the important fact that all
ripening fruits, exposed to the free atmosphere, absorb
the oxygen of the atmosphere and liberate an approxi-
mately equal volume of carbonic acid. He also found
that when ripe fruits were placed in a confined at-
mosphere, the oxygen of the atmosphere was first
absorbed, and an equal volume of carbonic acid given
out. But the process did not end here. After the
oxygen had vanished, carbonic acid, in considerable
quantities, continued to be exhaled by the fruits, which
at the same time lost a portion of their sugar, becoming
more acid to the taste, though the absolute quantity of
acid was not augmented. This was an observation of
capital importance, and Bérard had the sagacity to
remark that the process might be regarded as a kind of
fermentation.

Thus the living cells of fruits can absorb oxygen and
breathe out carbonic acid, exactly like the living cells
of the leaven of beer. Supposing the access of oxygen
suddenly cut off, will the living fruit cells as suddenly
die, or will they continue to live as yeast lives, by

FERMENTATION, 249

extracting oxygen from the saccharine juices round
them? This is a question of extreme theoretic signi-
ficance. It was first answered affirmatively by the
able and conclusive experiments of Lechartier and
Bellamy, and the answer was subsequently confirmed
and explained by the experiments and the reasoning of
Pasteur. Bérard only showed the absorption of oxygen,
and the production of carbonic acid; Lechartier and
Bellamy proved the production of alcohol, thus com-
pleting the evidence that it was a case of real fermen-
tation, though the common alcoholic ferment was absent.
So full was Pasteur of the idea that the cells of a fruit
.would continue to live at the expense of the sugar of
the fruit, that once in his laboratory, while conversing
on these subjects with M. Dumas, he exclaimed, ‘I will
wager that if a grape be plunged into an atmosphere
of carbonic acid, it will produce alcohol and carbonic
acid by the continued life of its own cells—that they
will act for a time like the cells of the true alcoholic
leaven.’ He made the experiment, and found the result
to be what he had foreseen. He then extended the
inquiry. Placing under a bell-jar twenty-four plums,
he filled the jar with carbonic acid gas; beside it he
placed twenty-four similar plums uncovered. At the
end of eight days, he removed the plums from the jar,
and compared them with the others. The difference
was extraordinary. The uncovered fruits had become
soft, watery, and very sweet; the others were firm and
hard, their fleshy portions being not at all watery. They
had, moreover, lost a considerable quantity of their
sugar. They were afterwards bruised, and the juice
was distilled. It yielded six and a half grammes of
alcohol, or one per cent. of the total weight of the
plums. Neither in these plums, nor in the grapes first
experimented on by Pasteur, could any trace of the

250 THE FLOATING-MATTER OF THE AIR.

ordinary alcoholic leaven be found. As previously
proved by Lechartier and Bellamy, the fermentation
was the work of the living cells of the fruit itself, after
air had been denied to them. When, moreover, the cells
were destroyed by bruising, no fermentation ensued.
The fermentation was the correlative of a vital act,
and it ceased when life was extinguished.

Liidersdorf was the first to show by this method
that yeast acted, not, as Liebig had assumed, in virtue
of its organic, but in virtue of its organized character.
He destroyed the cells of yeast by rubbing them on a
ground glass plate, and found that with the destruction
of the organism, though its chemical constituents re-
mained, the power to act as a ferment totally dis-
appeared.

One word more in reference to Liebig may find a
place here. To the philosophic chemist thoughtfully
pondering these phenomena, familiar with the concep-
tion of molecular motion, and the changes produced
by the interactions of purely chemical forces, nothing
could be more natural than to see in the process of
fermentation a simple illustration of molecular insta-
bility, the ferment propagating to surrounding molecular
groups the overthrow of its own tottering combinations.
Broadly considered, indeed, there is a certain amount
of truth in this theory; but Liebig; who propounded
it, missed the very kernel of the phenomena when he
overlooked, or contemned, the part played in fermenta-
tion by microscopic life. He looked at the matter too
little with the eye of the body, and too much with the
spiritual eye. He practically neglected the microscope,
and was unmoved by the knowledge which its revelations
would have poured in upon his mind. His hypothesis,
as I have said, was natural—nay, it was a striking
illustration of Liebig’s power to penetrate and unveil

FERMENTATION. 251

molecular actions; but it was an error, and as such has
proved an ignis fatuus instead of a pharos to some
of his followers.

I have said that our air is full of the germs of
ferments differing from the alcoholic leaven, and some-
times seriously interfering with the latter. They are
the weeds of this microscopic garden which often over-
shadow and choke the flowers. Let us take an illus-
trative case. Expose milk to the air. It will, after a
time, turn putrid or sour, separating like blood into clot
and serum. Placeadrop of such milk under a powerful
microscope and watch it closely. You see the minute
butter-globules animated by that curious quivering
motion called the Brownian motion. But let not this
attract your attention too much, for it is another
motion that we have now to seek. Here and there you
observe a greater disturbance than ordinary among
the globules; keep your eye upon the place of tumult,
and you will probably see emerging from it a long eel-
like organism, tossing the globules aside and wriggling
more or less rapidly across the field of the microscope.
Part of the change wrought in the milk is due to this
organism, which from its motions receives the name of
vibrio. In curdled milk you find other organisms,
small, motionless, and usually linked together like
beads on a string. It is these which cause the milk to
separate jnto clot andserum. They constitute the lactic
ferment of milk, as the yeast-plant does the alcoholic
ferment of sugar. But milk may become putrid without
' hecoming sour. Examine putrid milk microscopically,
and you find it swarming with shorter organisms, some-
times associated with the vibrios, sometimes alone, and
often manifesting a wonderful alacrity of motion. Keep
these organisms and their germs out of your milk and it

252 THE FLOATING-MATTER OF THE AIR.

will never putrefy. Expose a mutton-chop to the air
and keep it moist; in summer weather it soon stinks.
Placea drop of the juice of the fetid chop under a power-
ful microscope; it is seen swarming with organisms
resembling those in the putrid milk. These organisms,
which receive the common name of bacteria,! are the
agents of all putrefaction. Keep them and their germs
from your meat and it will remain for ever sweet. Thus
we begin to see that within the world of life to which we
ourselves belong, there is another living world requiring
the microscope for its discernment, but which, never-
theless, has the most important bearing on the welfare
of the higher life-world.

And now let us reason together as regards the origin
of these bacteria. A granular powder is placed in your
hands, and you are asked to state what it is. You
examine it, and have, or have not, reason to suspect that
seeds of some kind are mixed up init. To determine
this point you prepare a bed in your garden, sow in it
the powder, and soon after find a mixed crop of docks
and thistles sprouting from your bed. Until this powder
was sown neither docks nor thistles ever made their ap-
pearance in your garden. You repeat the experiment
once, twice, ten times, fifty times. From fifty different
beds after the sowing of the powder, you obtain the same
crop. What will be your response to the question pro-
posed to you? ‘Iam not in a condition,’ you would
say, ‘to affirm that every grain of the powder is a
dock-seed, or a thistle-seed ; but I am in a condition
to affirm that both dock and thistle-seeds form, at all
events, part of the powder.’ Supposing a succession of
such powders to be placed in your hands with grains
becoming gradually smaller, until they dwindle to the

1 Doubtless organisms exhibiting grave specific differences are
grouped together under this common name.

FERMENTATION 253

size of impalpable dust particles; assuming that you
treat them all in the same way, and that from every
one of them in a few days you obtain a definite crop —
it may be clover, it may be mustard, it may be mignon-
_ette, it may be a plant more minute than any of these—
the smallness of the particles, or of the plants that
spring from them, does not affect the validity of the
conclusion. Without a shadow of misgiving you would
conclude that the powder must have contained the
seeds or germs of the life observed. There is not in
the range of physical science, an experiment more con-
clusive nor an inference safer than this one.

Supposing the powder to be light enough to float in
the air, and that you are enabled to see it there just as
plainly as you saw the heavier powder in the palm of
your hand. If the dust sown by the air instead of by
the hand produce a definite living crop, with the same
logical rigour you would conclude that the germs of
this crop must be mixed with the dust. To take an
illustration: the spores of the little plant Penicillium
glaucwm, to which I have already referred, are light
enough to float in the air. A cut apple, a pear, a
tomato, a slice of vegetable marrow, or, as already men~
tioned, an old moist boot, a dish of paste, or a pot of
jam, constitutes a proper soil for the Penicillium. Now,
if it could be proved that the dust of the air when
sown in this soil produces this plant, while, wanting the
dust, neither the air, nor the soil, nor both together
can produce it, it would be obviously just as certain, in
this case, that the floating dust contains the germs of
Penicillium, as that the powders sown in your garden
contained the germs of the plants which sprung from
them.

But how is the floating dust to be rendered visible ?
In this way. Build a little chamber and provide it

254 THE FLOATING-MATTER OF THE AIR.

with a door, windows, and window-shutters. Let an
aperture be made in one of the shutters through which
a sunbeam can pass. Close the door and windows so
that no light shall enter save through the hole in the
shutter. The track of the sunbeam is at first per-
fectly plain and vivid in the air of the room. If all
disturbance of the air of the chamber be avoided, the
luminous track will become fainter and fainter, until at
last it disappears absolutely, and no trace of the beam
is to be seen. What rendered the beam visible at first ?
The floating dust of the air, which, when thus illuminated
and observed, is as palpable to sense as dust or powder
placed on the palm of the hand. In the still air the dust
gradually sinks to the floor or sticks to the walls and
ceiling, until finally, by this self-cleansing process, the
air is entirely freed from mechanically suspended matter.

Thus, far, I think, we have made our footing sure.
Let us proceed. Chop up a beefsteak and allow it to
remain for two or three hours just covered with warm
water; you thus extract the juice of the beef in a con-
centrated form. By properly boiling the liquid and
filtering it, you can obtain from it a perfectly trans-
parent beef-tea. Expose a number of vessels containing
this tea to the moteless air of your chamber; and
expose a number of vessels containing precisely the
same liquid to the dust-laden air. In three days every
one of the latter stinks, and examined with the micro-
scope every one of them is found swarming with the
bacteria of putrefaction. After three months, or three
years, the beef-tea within the chamber, if properly
sterilized in the first instance, will be found as sweet
and clear, and as free from bacteria, as it was at the
moment when it was first put in. There is absolutely
no difference between the air within and that without,
save that the one is dustless and the other dust-

FERMENTATION. 255

laden. Clinch the experiment thus: Open the door of
your chamber and allow the dust to enter it. In three
days afterwards you have every vessel within the chamber
swarming with bacteria, and in a state of active putre-
faction. Here, also, the inference is quite as certain
as in the case of the powder sown in your garden.
Multiply your proofs by building fifty chambers instead
of one, and by employing every imaginable infusion of
wild animals and tame; of flesh, fish, fowl, and viscera ;
of vegetables of the most various kinds. If in all these
cases you find the dust infallibly producing its crop of
bacteria, while neither the dustless air nor the nutritive
infusion, nor both together, are ever able to produce
this crop, your conclusion is simply irresistible that the
dust of the air contains the germs of the crop which
has appeared in your infusions. I repeat there is no
inference of experimental science more certain than
this one. In the presence of such facts, to use the
words of a paper lately published in the ‘ Philosophical
Transactions,’ it would be simply monstrous to affirm
that these swarming crops of bacteria are spontaneously
generated.

Is there then no experimental proof of spontaneous
generation? I answer without hesitation, none! But
to doubt the experimental proof of a fact, and to deny
its possibility, are two different things, though some
writers confuse matters by making them synonymous,
In fact, this doctrine of spontaneous generation, in one
form or another, falls in with the theoretic beliefs of
some of the foremost workers of this age; but it is
exactly these men who have the penetration to see, and
the honesty to expose, the weakness of the evidence
adduced in its support.

And here observe how these discoveries tally with

256 THE FLOATING-MATTER OF THE AIR.

the common practices of life. Heat kills the bacteria,
colds numbs them. When my housekeeper has pheasants
in charge which she wishes to keep sweet, but which
threaten to give way, she partially cooks the birds, kills
the infant bacteria, and thus postpones the evil day.
By boiling her milk she also extends its period of
sweetness. Some weeks ago in the Alps I made a few
experiments on the influence of cold upon ants. Though
the sun was strong, patches of snow still maintained
themselves on the mountain slopes. The ants were found
in the warm grass and on the warm rocks adjacent.
Transferred to the snow the rapidity of their paralysis
was surprising. In a few seconds a vigorous ant, after
a few languid struggles, would wholly lose its power
of locomotion, and lie practically dead upon the snow.
Transferred to the warm rock, it would revive, to be
again smitten with death-like numbness when retrans-
ferred to the snow. What is true of the ant is specially
true of our bacteria. Their active life is suspended
by cold, and with it their power of producing or con-
tinuing putrefaction. This is the whole philosophy of
the preservation of meat by cold. The fishmonger, for
example, when he surrounds his very assailable wares
by lumps of ice, stays the process of putrefaction by
reducing to numbness and inaction the organisms which
produce it, and in the absence of which his fish would
remain sweet and sound. It is the astonishing activity
into which these bacteria are pushed by warmth that
renders a single summer’s day sometimes so disastrous
to the great butchers of London and Glasgow. The
bodies of guides lost in the crevasses of Alpine glaciers
have come to the surface forty years after their in-
terment, without the flesh showing any sign of putre-
faction. But the most astonishing case of this kind
is that of the hairy elephant of Siberia which was

FERMENTATION. 257

found incased in ice. It had been buried for ages, but
when laid bare its flesh was sweet, and for some time
afforded copious nutriment to the wild beasts which fed
upon it.

Beer is assailable by all the organisms here referred
to, some of which produce acetic, some lactic, and some
butyric acid, while yeast is open to attack from the
bacteria of putrefaction. In relation to the particular
beverage the brewer wishes to produce, these foreign
ferments have been properly called ferments of disease.
The cells of the true leaven are globules, usually some-
what elongated. The other organisms are more less
rod-like or eel-like in shape, some of them being beaded
so as to resemble necklaces. Each of these organisms
produces a fermentation and a flavour peculiar to itself.
Keep them out of your beer and it remains for ever
unaltered. Never without them will your beer contract
disease. But their germs are in the air, in the vessels
employed in the brewery; even in the yeast used to
impregnate the wort. Consciously or unconsciously, the
art of the brewer is directed against them. His aim is
to paralyse, if he cannot destroy them.

For beer, moreover, the question of temperature is
one of supreme importance; indeed, the recognized
influence of temperature is causing on the Continent
of Europe a complete revolution in the manufacture of
beer. When I was a student in Berlin, in 1851, there
were certain places specially devoted to the sale of
Bavarian beer, which was then making its way into
public favour. This beer is prepared by what is called
the process of low fermentation ; the name being given
partly because the yeast of the beer, instead of rising
to the top and issuing through the bunghole, falls to
the bottom of the cask; but partly, also, because it is
produced at a low temperature. The other and older

258 THE FLOATING-MATTER OF THE AIR.

process, called high fermentation, is far more handy,
expeditious, and cheap. In high fermentation eight
days suffice for the production of beer ; in low fermenta-
tion, ten, fifteen, even twenty days are found necessary.
Vast quantities of ice, moreover, are consumed in the
process of low fermentation. In the single brewery of
Dreher, of Vienna, a hundred million pounds of ice are
consumed annually in cooling the wort and beer. Not-
withstanding these obvious and weighty drawbacks, the
low fermentation is rapidly displacing the high upon
the Continent. Here are some statistics which show the
number of breweries of both kinds existing in Bohemia
in 1860, 1865, and 1870 :—

1860. 1865. 1870.
High Fermentation . . 281 81 18
Low Fermentation . . 135 459 831

Thus in ten years the number of high-fermentation
breweries fell from 281 to 18, while the number of low-
fermentation breweries rose from 135 to 831. The sole
reason for this vast change—a change which involves a
great expenditure of time, labour, and money—is the
additional command which it gives the brewer over the
fortuitous ferments of disease. These ferments, which,
it is to be remembered, are living organisms, have their
activity suspended by temperatures below 10° C., and
as long as they are reduced to torpor the beer remains
untainted either by acidity or putrefaction. The beer
of low fermentation is brewed in winter, and kept in
cool cellars; the brewer being thus enabled to dispose
of it at his leisure, instead of forcing its consumption
to avoid the loss involved in its alteration if kept too
long. Hops, it may be remarked, act to some extent
as an antiseptic to beer. The essential oil of the hop
is bactericidal ; hence the strong impregnation with hop
juice of all beer intended for exportation.

FERMENTATION. 259

These low organisms, which one might be disposed
to regard as the beginnings of life, were we not warned
that the microscope, precious and perfect as it is, has
no power to show us the real beginnings of life, are
by no means purely useless or purely mischievous in
the economy of nature. They are only noxious when
out of their proper place. They exercise a useful
and valuable function as the burners and consumers
of dead matter, animal and vegetable, reducing such
matter, with a rapidity otherwise unattainable, to in-
nocent carbonic acid and water. Furthermore, they
are not all alike, and it is only restricted classes of
them that are really dangerous to man. One difference
in their habits is worthy of special reference here.
Air, or rather the oxygen of the air, which is absolutely
necessary to the support of the bacteria of putre-
faction, is, according to Pasteur, absolutely deadly to
the vibrios which provoke the butyric acid fermentation.
This has been illustrated by the following beautiful
observation.

A drop of the liquid containing those small organisms
is placed upon glass, and on the top is placed a circle
of exceedingly thin glass; for, to magnify them suffi-
ciently, it is necessary that the object-glass of the
microscope should come very close to the organisms.
Round the edge of the circular plate of glass the liquid
is in contact with the air, and incessantly absorbs it,
including the oxygen. Here, if the drop be charged
with bacteria, we have a zone of very lively ones. But
through this living zone, greedy of oxygen and appro-
priating it, the vivifying gas cannot penetrate to the
centre of the film. In the middle, therefore, the
bacteria die, while their peripheral colleagues continue
active. Ifa bubble of air chance to be enclosed in the
film, round it the bacteria will pirouette and wabble

260 THE FLOATING-MATTER OF THE AIR.

until its oxygen has been absorbed, after which all
their motions cease. Precisely the reverse of all this
occurs with the vibrios of butyric acid. In their case
it is the peripheral organisms that are first killed, the
central ones remaining vigorous while ringed by a zone
of dead: Pasteur, moreover, filled two vessels with a
liquid containing these vibrios; through one vessel he
led air, and killed its vibrios in half an hour; through
the other he led carbonic acid, and after three hours
found the vibrios fully active. It was while observing
these differences of deportment fifteen years ago that
the thought of life without air, and its bearing upon
the theory of fermentation, flashed upon the mind of
this admirable investigator.

We now approach an aspect of this question which
concerns us still more closely, and will be best illustrated
by an actual fact. A few years ago I was bathing in
an Alpine stream, and returning to my clothes from
the cascade which had been my shower-bath, I slipped
upon a block of granite, the sharp crystals of which
stamped themselves into my naked shin. The wound
was an awkward one, but being in vigorons health at
the time, I hoped for a speedy recovery. Dipping a
clean pocket-handkerchief into the stream, I wrapped
it round the wound, limped home, and remained for
four or five days quietly in bed. There was no pain,
and at the end of this time I thought myself quite fit
to quit my room. The wound, when uncovered, was
found perfectly clean, uninflamed, and entirely free from
pus. Placing over it a bit of goldbeater’s-skin, I
walked about all day. Towards evening itching and
heat were felt ; a large accumulation of matter followed,
and I was forced to go to bed again. The water-
bandage was restored, but it was powerless to check

FERMENTATION, 261

the action now set up; arnica was applied, but it made
matters worse. The inflammation increased alarmingly,
until finally I had to be carried on men’s shoulders
down the mountain and transported to Geneva, where,
thanks to the kindness of friends, I was immediately
placed in the best medical hands. On the morning
after my arrival in Geneva, Dr. Gautier discovered an
abscess in my instep, at a distance of five inches from
the wound. The two were connected by a channel, or
sinus, as it is technically called, through which he was
able to empty the abscess, without the application of
the lance.

By what agency was that channel formed—what
was it that thus tore asunder the sound tissue of my
instep, and kept me for six weeks a prisoner in bed?
In the very room where the water dressing had been
removed from my wound, and the goldbeater’s-skin
applied to it, I opened this year a number of tubes,
containing perfectly clear and sweet infusions of fish,
flesh, and vegetable. These hermetically-sealed infusions
had been exposed for weeks, both to the sun of the
Alps and to the warmth of a kitchen, without showing
the slightest turbidity or sign of life. But two days
after they were opened the greater number of them
swarmed with the bacteria of putrefaction, the germs
of which had been contracted from the dust-laden air
of the room. And had the matter from my abscess
been examined, my memory of its appearance leads
me to infer that it would have been found equally
swarming with these bacteria—that it was their germs
which got into my incautiously opened wound, and that
they were the subtile workers that burrowed down my
shin, dug the abscess in my instep, and produced effects
which might easily have proved fatal.

This apparent digression brings us face to face with

262 THE FLOATING-MATTER OF THE AIR.

the labours of a man who combines the penetration of
the true theorist with the skill and conscientiousness
of the true experimenter, and whose practice is one
continued demonstration of the theory that the putre-
faction of wounds is to be averted by the destruction
of the germs of bacteria. Not only from his own
reports of his cases, but from the reports of eminent
men who have visited his hospital, and from the
opinions expressed to me by continental surgeons, do
I gather that one of the greatest steps ever made in
the art of surgery was the introduction of the anti-
septic system of treatment, for which we are indebted
to Professor Lister.

The interest of this subject does not slacken as we
proceed. We began with the cherry-cask and beer-vat;
we end with the body of man. There are persons born
with the power of interpreting natural facts, as there
are others smitten with everlasting incompetence in
regard to such interpretation. To the former class in
an eminent degree belonged the illustrious philosopher
Robert Boyle, whose words in relation to this subject
have in them the forecast of prophecy. ‘And let me
add,’ writes Boyle in his ‘Essay on the Pathological
Part of Physik, ‘that he that thoroughly understands
the nature of ferments and fermentations shall probably
be much better able than he that ignores them, to give
a fair account of divers phenomena of several diseases
(as well fevers as others), which will perhaps be never
properly understood without an insight into the doctrine
of fermentations.’

Two hundred years have passed since these pregnant
words were written, and it is only in this our day that
men are beginning to fully realize their truth. In the
domain of surgery the justice of Boyle’s surmise has
been most strictly demonstrated. But we now pass

FERMENTATION. 263

the bounds of surgery proper, and enter the domain of
epidemic disease, including those fevers so sagaciously
referred to by Boyle. The most striking analogy between
a contagiwm and a ferment is to be found in the power
of indefinite self-multiplication possessed and exercised
by both. You know the exquisitely truthful figures
regarding leaven employed in the New Testament. A
particle hid in three measures of meal leavens it all. A
little leaven leaveneth the whole lump. In a similar
manner, a particle of contagiwm spreads through the
human body and may be so multiplied as to strike down
whole populations. Consider the effect produced upon
the system by a microscopic quantity of the virus of
smallpox. That virus is, to all intents and purposes,
a seed. It is sown as yeast is sown, it’ grows and
multiplies as yeast grows and multiplies, and it always
reproduces itself. To Pasteur we are indebted for a
series of masterly researches, wherein he exposes the
looseness and general baselessness of prevalent notions
regarding the transmutation of one ferment into another.
He guards himself against saying it is impossible. The
true investigator is sparing in the use of this word,
though the use of it is unsparingly ascribed to him;
but, as a matter of fact, Pasteur has never been able to
effect the alleged transmutation, while he has been
always able to point out the open doorways through
which the affirmers of such transmutations had allowed
error to march in upon them.!

The great source of error here has been already
alluded to in this discourse. The observers worked in

1 Those who wish for an illustration of the care necessary in
these researches, and of the carelessness with which they have in
some cases been conducted, will do well to consult the Rev. W. H.
Dallinger’s excellent ‘Notes on Heterogenesis’ in the October
number of the Popular Science Review.

264 THE FLOATING-MATTER OF THE AIR.

an atmosphere charged with the germs of different
organisms; the mere accident of first possession ren-
dering now one organism, now another, triumphant.
In different stages, moreover, of its fermentative or
putrefactive changes, the same infusion may so alter
as to be successively taken possession of by different
organisms. Such cases have been adduced to show that
the earlier organisms must have been transformed into
the later ones, whereas they are simply cases in which
different germs, because of changes in the infusion,
render themselves valid at different times.

By teaching us how to cultivate each ferment in its
purity—in other words, by teaching us how to rear the
individual crganism apart from all others,—Pasteur has
enabled_us to avoid all these errors. And where this
isolation of a particular organism has been duly effected
it grows and multiplies indefinitely, but no change of
it into another organism is ever observed. In Pasteur’s
researches the Bacterium remained a Bacterium, the
Vibrio a Vibrio, the Penicillium a Penicillium, and the
Torula a Torula. Sow any of these in a state of purity
in an appropriate liquid; you get it, and it alone, in
the subsequent crop. In like manner, sow smallpox
in the human body, your crop is smallpox. Sow there
scarlatina, and your crop is scarlatina. Sow typhoid
virus, your crop is typhoid—cholera, your crop is
cholera. The disease bears as constant a relation to its
contagium as the microscopic organisms just enumerated
do to their germs, or indeed as a thistle does to its seed.
No wonder then, with analogies so obvious and so
striking, that the conviction is spreading and growing
daily in strength, that reproductive parasitic life is at
the root of epidemic disease—that living ferments find-
ing lodgment in the body increase there and multiply,
directly ruining the tissue on which they subsist, or

FERMENTATION. 265

destroying life indirectly by the generation of poisonous
compounds within the body. This conclusion, which
comes to us with a presumption almost amounting to
demonstration, is clinched by the fact that virulently
infective diseases have been discovered with which
living organisms are as closely and as indissolubly as-
sociated as the growth of Torula is with the fermentation
of beer.

And here, if you will permit me, I would utter a
word of warning to well-meaning people. We have now
reached a phase of this question when it is of the very
last importance that light should once for all be thrown
upon the manner in which contagious and infectious
diseases take root and spread. To this end the action
of various ferments upon the organs and tissues of the
living body must be studied ; the habitat of each special
organism concerned in the production of each specific
disease must be determined, and the mode by which its
germs are spread abroad as sources of further infection.
It is only by such rigidly accurate inquiries that we can
obtain final and complete mastery over these destroyers.
Hence, while abhorring cruelty of all kinds, while
shrinking sympathetically from all animal suffering—
suffering which my own pursuits never call upon me
to inflict,—an unbiassed survey of the field of research
now opening out before the physiologist causes me to
conclude, that no greater calamity could befall the
human race than the stoppage of experimental inquiry
in this direction, A lady whose philanthropy has
rendered her illustrious said to me some time ago, that
science was becoming immoral: that the researches of the
past, unlike those of the present, were carried on with-
out cruelty. I replied to her that the science of Kepler
and Newton, to which she referred as moral, dealt with
the laws and phenomena of inorganic nature; but that

266 THE FLOATING-MATTER OF THE AIR.

one great advance made by modern science was in the
direction of biology, or the science of life; and that in
this new direction scientific inquiry, though at the
outset pursued at the cost of some temporary suffering,
would in the end prove a thousand times more benefi-
cent than it had ever hitherto been. I said this because
I saw that the very researches which the lady deprecated
were leading us to such a knowledge of epidemic diseases
as will enable us finally to sweep these scourges of the
human race from the face of the earth.

This is a point of such capital importance that I
should like to bring it home to your intelligence by a
single trustworthy illustration. In 1850, two distin-
guished French observers, MM. Davainne and Rayer,
noticed in the blood of animals which had died of the
virulent disease called splenic fever, small microscopic
organisms resembling transparent rods; but neither of
them at that time attached any significance to the
observation. In 1861, Pasteur published a memoir on
the fermentation of butyric acid, wherein he described
the organism which provoked it; and after reading this
memoir it occurred to Davainne that splenic fever might
be a case of fermentation set up within the animal body,
by the organisms which had been observed by him and
Rayer. This idea has been placed beyond all doubt by
subsequent research.

Observations of the highest importance have also
been made on splenic fever by Pollender and Brauell.
Two years ago, Dr. Burdon Sanderson gave us a very
clear account of what was known up to that time of
this disorder. With regard to the permanence of the
contagium, it had been proved to hang for years about
localities where it had once prevailed; and this seemed
to show that the rod-like organisms could not con-
stitute the contagium, because their infective power

FERMENTATION, 267

was found to vanish in a few weeks. But other facts
established an intimate connexion between the organ-
isms and the disease; so that a review of all the facts
caused Dr. Sanderson to conclude that the contagium
existed in two distinct forms: the one ‘fugitive’ and
visible as transparent rods; the other permanent but
‘latent,’ and not yet brought within the grasp of the
microscope.

At the time that Dr. Sanderson was writing this re-
port, a young German physician, named Koch, occupied
with the duties of his profession in an obscure country
district, was already at work, applying, during his spare
time, various original and ingenious devices to the
investigation of splenic fever. He studied the habits of
the rod-like organisms, and found the aqueous humour
of an ox’s eye to be particularly suitable for their
nutrition. With a drop of the aqueous humour he
mixed the tiniest speck of a liquid containing the rods,
placed the drop under his microscope, warmed it suit-
ably, and observed the subsequent action. During the
first two hours hardly any change was noticeable; but
at the end of this time the rods began to lengthen,
and the action was so rapid that at the end of three
or four hours they attained from ten to twenty times
their original length. At the end of a few additional
hours they had formed filaments in many eases a
hundred times the length of the original rods. The
same filament, in fact, was frequently observed to
stretch through several fields of the microscope. Some-
times they lay in straight lines parallel to each other,
in other cases they were bent, twisted, and coiled into
the most graceful figures; while sometimes they formed
knots of such bewildering complexity that it was im-

1 This, I believe, was the first reference to the researches of Koch
made in this country. 1879.

268 THE FLOATING-MATTER OF THE AIR.

possible for the eye to trace the individual filaments
through the confusion.

Had the observation ended here an interesting
scientific fact would have been added to our previous
store, but the addition would have been of little practical
value. Koch, however, continued to watch the filaments,
and after a time noticed little dots appearing within
them. These dots became more and more distinct, until
finally the whole length of the organism was studded
with minute ovoid bodies, which lay within the outer
integument like peas within their shell. By-and-bye
the integument fell to pieces, the place of the organisms
being taken by a long row of seeds or spores. These
observations, which were confirmed in all respects by
the celebrated naturalist, Cohn of Breslau, are of the
highest importance. They clear up the existing per-
plexity regarding the latent and visible contagia of
splenic fever; for in the most conclusive manner, Koch
proved the spores, as distinguished from the rods, to
constitute the contagium of the fever in its most deadly
and persistent form.

How did he reach this important result? Mark the
answer. There was but one way open to him to test
the activity of the contagium, and that was the inocu-
lation with it of living animals. He operated upon
guinea-pigs and rabbits, but the vast majority of his
experiments were made upon mice. Inoculating them
with the fresh blood of an animal suffering from splenic
fever, they invariably died of the same disease within
twenty or thirty hours after inoculation. He then
sought to determine how the contagium maintained its
vitality. Drying the infectious blood containing the
rod-like organisms, in which, however, the spores were
not developed, he found the contagium to be that which
Dr. Sanderson calls ‘ fugitive.’ It maintained its power

FERMENTATION. 269

of infection for five weeks at the furthest. He then
dried blood containing the fully developed spores, and
exposed the substance to a variety of conditions. He
permitted the dried blood to assume the form of dust ;
wetted this dust, allowed it to dry again, permitted it.
to remain for an indefinite time in the midst of putre-
fying matter, and subjected it to various other tests.
After keeping the spore-charged blood which had been
treated in this fashion for four years, he inoculated a
number of mice with it, and found its action as fatal as
that of blood fresh from the veins of an animal suffering
from splenic fever. There was no single escape from
death after inoculation by this deadly contagium. Un-
counted millions of these spores are developed in the
body of every animal which has died of splenic fever,
and every spore of these millions is competent to produce
the disease. The name of this formidable parasite is
Bacillus anthracis.

Now the very first step towards the extirpation of
these contagia is the knowledge of their nature; and
the knowledge brought to us by Dr. Koch will render
as certain the stamping out of splenic fever as the
stoppage of the plague of pébrine by the researches of
Pasteur.? One small item of statistics will show what

1 Koch found that to produce its characteristic effects the con-
tagium of splenic fever must enter the blood; the virulently in-
fective spleen of a diseased animal may be eaten with impunity
by mice. On the other hand, the disease refuses to be communi-
cated by inoculation to dogs, partridges, or sparrows. In their blood
Bacillus anthracis ceases to act asa ferment. Pasteur announced
more than six years ago the propagation of the vibrios of the silk-
worm disease called flacherie, both by fission and by spores. He
also made some remarkable experiments on the permanence of the
contagium in the form of spores. See ‘Etudes sur la Maladie des
Vers a Soie,’ pp. 168 and 256.

2Surmising that the immunity enjoyed by birds might arise
from the heat of their blood, which destroyed the bacillus, Pasteur

270 THE FLOATING-MATTER OF THE AIR.

this implies. In the single district of Novgorod in
Russia, between the years 1867 and 1870, over fifty-six
thousand cases of death by splenic fever, among horses,
cows, and sheep were recorded. Nor did its ravages
confine themselves to the animal world, for during the
time and in the district referred to, five hundred and
twenty-eight human beings perished in the agonies of
the same disease.

A description of the fever will help you to come to
aright decision on the point which I wish to submit
to your consideration. ‘An animal,’ says Dr. Burdon
Sanderson, ‘ which perhaps for the previous day has de-
clined food and shown signs of general disturbance,
begins to shudder and to have twitches of the muscles
of the back, and soon after becomes weak and listless.
In the meantime the respiration becomes frequent and
often difficult, and the temperature rises three or four
degrees above the normal; but soon convulsions, affect-
ing chiefly the muscles of the back and loins, usher
in the final collapse, of which the progress is marked
by the loss of all power of moving the trunk or
extremities, diminution of temperature, mucous and
sanguinolent alvine evacuations, and similar discharges
from the mouth and nose.’ In a single district of
Russia, as above remarked, fifty-six thousand horses,
cows, and sheep, and five hundred and twenty-eight
men and women, perished in this way during a period
of two or three years. What the annual fatality is
throughout Europe I have no means of knowing.
Doubtless it must be very great. The question, then,
which I wish to submit to your judgment is this :—Is

lowered their temperature artificially, inoculated them, and killed
them. Healso raised the temperature of guinea-pigs after inocu-
lation, and saved them. It is needless to dwell for a moment on the
importance of this experiment.

FERMENTATION. 271

the knowledge which reveals to us the nature, and
which assures the extirpation, of a disorder so virulent
and so vile, worth the price paid for it? S? It is exceed-
ingly important that assemblies like the present should
see clearly the issues at stake in such questions as this,
and that the properly informed sense of the community
should temper, if not restrain, the rashness of those
who, meaning to be tender, become agents of cruelty
by the imposition of short-sighted restrictions upou
physiological investigations. It is a modern instance
of zeal for God, but not according to knowledge, the
excesses of which must be corrected by an instructed
public opinion. ;

And now let us cast a backward glance on the field
we have traversed, and try to extract from our labours
such further profit as they can yield. For more than
two thousand years the attraction of light bodies by
amber was the sum of human knowledge regarding
electricity, and for more than two thousand years fer-
mentation was effected without any knowledge of its
cause. In science one discovery grows out of another,
and cannot appear without its proper antecedent. Thus,
before fermentation could be understood, the micro-
scope had to be invented, and brought to a considerable
degree of perfection. Note the growth of knowledge.
Leeuwenhoek, in 1680, found yeast to be a mass of
floating globules, but he had no notion that the globules
were alive. This was proved in 1835 by Cagniard de la
Tour and Schwann. Then came the question as to the
origin of such microscopic organisms, and in this con-
nexion the memoir of Pasteur, published in the
« Annales de Chimie’ for 1862, is the inauguration of a
new epoch.

On that investigation all Pasteur’s subsequent

18

272 THE FLOATING-MATTER OF THE AIR.

labours were based. Ravages had over and over again
occurred among French wines. There was no guarantee
that they would not become acid or bitter, particularly
when exported. The commerce in wines was thus
restricted, and disastrous losses were often inflicted on
the wine-grower. Every one of these diseases was
traced to the life of an organism. Pasteur ascertained
the temperature which killed these ferments of disease,
proving it to be so low as to be perfectly harmless to
the wine. By the simple expedient of heating the
wine to a temperature of fifty degrees Centigrade, he
rendered it inalterable, and thus saved his country the
loss of millions. He then went on to vinegar—vin
aigre, acid wine—which he proved to be produced by
a fermentation set up by a little fungus called
Mycoderma aceti. Torula, in fact, converts the grape
juice into alcohol, and Mycoderma aceti converts the
alcohol into vinegar. Here also frequent failures
occurred, and severe losses were sustained. Through
the operation of unknown causes, the vinegar often
became unfit for use, sometimes indeed falling into utter
putridity. It had been long known that mere exposure
to the air was sufficient to destroy it. Pasteur studied
all these changes, traced them to their living causes,
and showed that the permanent health of the vinegar
was ensured by the destruction of this life. He passed
from the diseases of vinegar to the study of a malady
which a dozen years ago had all but ruined the silk
husbandry of France. This plague, which received the
name of pébrine, was the product of a parasite which
first took possession of the intestinal canal of the silk-
worm, spread throughout its body, and filled the sack
which ought to contain the viscid matter of the silk.
Thus smitten, the worm would go automatically through
the process of spinning, when it had nothing to spin.

FERMENTATION, 273

Pasteur followed this parasitic destroyer from year to
year, and led by his singular power of combining facts
with the logic of facts, discovered eventually the
precise phase in the development of the insect when
the disease which assailed it could with certainty be
stamped out. Pasteur’s devotion to this inquiry cost
him dear. He restored to France her silk husbandry,
rescued thousands of her population from ruin, set the
looms of Italy also to work, but emerged from his
labours with one of his sides permanently paralyzed.
His last investigation is embodied in a work entitled
‘Studies on Beer,’ in which he describes a method
of rendering beer permanently unchangeable. That
method is not so simple as those found effectual with
wine and vinegar, but the principles which it involves
are sure to receive extensive application at some future
day.

There are other reflections connected with this sub-
ject which, even were they now passed over without re-
mark, would sooner or later occur to every thoughtful
mind in this assembly. I have spoken of the floating
dust of the air, of the means of rendering it visible, and
of the perfect immunity from putrefaction which accom-
panies the contact of germless infusions and moteless air.
Consider the woes which these wafted particles, during
historic and pre-historic ages, have inflicted on man-
kind ; consider the loss of life in hospitals from putre-
fying wounds; consider the loss in places where there
are plenty of wounds, but no hospitals, and in the ages
before hospitals were anywhere founded ; consider the
slaughter which has hitherto followed that of the battle-
field, when those bacterial destroyers are let loose, often
producing a mortality far greater than that of the
battle itself; add to this the other conception that in
times of epidemic disease the self-same floating matter

274 THE FLOATING-MATTER OF THE AIR.

has mingled with it the special germs which produce
the epidemic, being thus enabled to sow pestilence and
death over nations and continents—consider all this,
and you will come with me to the conclusion that
all the havoc of war, ten times multiplied, would be
evanescent if compared with the ravages due to atmo-
spheric dust.

This preventible destruction is going on to-day, and
it has been permitted to go on for ages, without a whis-
per of information regarding its cause being vouchsafed
to the suffering sentient world. We have been seourged
by invisible thongs, attacked from impenetrable ambus-
cades, and it is only to-day that the light of science is
being let in upon the murderous dominion of our foes.
Facts like these excite in me the thought that the rule
and governance of this universe are different from what
we in our youth supposed them to be—that the inscrut-
able Power, at once terrible and beneficent, in whom we
live and move and have our being and our end, is to be
propitiated by means different from those usually re-
sorted to. The first requisite towards such propitiation
is knowledge; the second is action, shaped and illumi-
nated by that knowledge. Of knowledge we already
see the dawn, which will open out by-and-by to perfect
day ; while the action which is to follow has its un-
failing source and stimulus in the moral and emotional
nature of man—in his desire for personal well-being,
in bis sense of duty, in his compassionate sympathy
with the sufferings of his fellow-men. ‘ How often,’ says
Dr. William Budd in his celebrated work on Typhoid
Fever,—‘ How often have I seen in past days, in the
single narrow chamber of the day-labourer’s cottage the
father in the coffin, the mother in the sick-bed in mut-
tering delirium, and nothing to relieve the desolation
of the children but the devotion of some poor neigh-

FERMENTATION. 275

bour, who in too many cases paid the penalty of her
kindness in becoming herself the victim of the same
disorder!’ From the vantage ground already won I look
forward with confident hope to the triumph of medical
art over scenes of misery like that here described. The
cause of the calamity being once clearly revealed, not.
only to the physician, but to the public, whose intelli-
gent co-operation is absolutely essential to success, the
final victory of humanity is only a question of time. We
have already a foretaste of that victory in the triumphs
of surgery as practised at your doors. '

SPONTANEOUS GENERATION.

Vv.

Wirnin ten minutes’ walk of a little cottage which
I have recently built in the Alps, there is a small lake,
fed by the melted snows of the upper mountains.
During the early weeks of summer no trace of life
is to be discerned in this water; but invariably to-
wards the end of July, or the beginning of August,
swarms of tailed organisms are seen enjoying the sun’s
warmth along the shallow margins of the lake, and
rushing with audible patter into deeper water at the
approach of danger. The origin of this periodic crowd
of living things is by no means obvious. For years I
had never noticed in the lake either an adult frog, or
the smallest fragment of frog spawn; so that were I
not otherwise informed, I should have found the conelu-
sion of Mathiole a natural one, namely, that tadpoles
are generated in lake mud by the vivifying action of
the sun.

The checks which experience alone can furnish
being absent, the spontaneous generation of creatures
quite as high as the frog in the scale of being was
assumed for ages to be a fact. Here, as elsewhere, the
dominant mind of Aristotle stamped its notions on
the world at large. For nearly twenty centuries after
him men found no difficulty in believing in cases of

1 ¢ The Nineteenth Century,’ January 1878.

278 THE FLOATING-MATTER OF THE AIR.

spontaneous generation which would now he rejected
as monstrous by the most fanatical supporter of the
doctrine. Shell-fish of all kinds were considered to
be without parental origin. Eels were supposed to
spring spontaneously from the fat ooze of the Nile.
Caterpillars were the spontaneous products of the leaves
on which they fed ; while winged insects, serpents, rats,
and mice were all thought capable of being generated
without sexual intervention.

The most copious source of this life without an
ancestry was putrefying flesh ; and, lacking the checks
imposed by fuller investigation, the conclusion that
flesh possesses and exerts this generative power is a
natural one. I well remember when a child of ten or
twelve seeing a joint of imperfectly salted beef cut into,
and coils of maggots laid bare within the mass.
Without a moment’s hesitation I jumped to the con-
clusion that these maggots had been spontaneously
generated in the meat. I had no knowledge which
could qualify or oppose this conclusion, and for the
time it was irresistible. The childhood of the indi-
vidual typifies that of the race, and the belief here
enunciated was that of the world for nearly two thou-
sand years.

To the examination of this very point the celebra-
ted Francesco Redi, physician to the Grand Dukes
Ferdinand II. and Cosmo III. of Tuscany, and a
member of the Academy del Cimento, addressed him-
self in 1668. He had seen the maggots of putrefying
flesh, and reflected on their possible origin. But he
was not content with mere reflection, nor with the
theoretic guesswork which his predecessors had founded
upon their imperfect observations. Watching meat
during its passage from freshness to decay, prior to the
appearance of maggots he invariably observed flies

SPONTANEOUS GENERATION. 279

buzzing round the meat and frequently alighting on it.
The maggots, he thought, might be the half-developed
progeny of these flies.

The inductive guess precedes experiment, by which,
however, it must be finally tested. Redi knew this, and
acted accordingly. Placing fresh meat in a jar and
covering the mouth with paper, he found that, though
the meat putrefied in the ordinary way, it never bred
maggots, while the same meat placed in open jars soon
swarmed with these organisms. For the paper cover
he then substituted fine gauze, through which the
odour of the meat could rise. Over it the flies buzzed,
and on it they laid their eggs, but, the meshes being too
small to permit the eggs to fall through, no maggots
were generated in the meat. They were, on the con-
trary, hatched upon the gauze. By a series of such
experiments Redi destroyed the belief in the sponta-
neous generation of maggots in meat, and with it
doubtless many related beliefs. The combat was con-
tinued by Vallisneri, Schwammerdam, and Réaumur,
who succeeded in banishing the notion of spontaneous
generation from the scientific minds of their day.
Indeed, as regards such complex organisms as those
which formed the subject of their researches, the notion
was banished for ever.

But the discovery and improvement of the micro-
scope, though giving a death-blow to much that
had been previously written and believed regarding
spontaneous generation, brought also into view a world
of life formed of individuals so minute—so close as it
seemed to the ultimate particles of matter—as to sug-
gest an easy passage from atoms to organisms. Animal
and vegetable infusions exposed to the air were found
clouded and crowded with creatures far beyond the
reach of unaided vision, but perfectly visible to an eye

280 THE FLOATING-MATTER OF THE AIR.

strengthened by the microscope. With reference to
their origin these organisms were called ‘ Infusoria.’
Stagnant pools were found full of them, and the
obvious difficulty of assigning a germinal origin to
existences so minute furnished the precise condition
necessary to give new play to the notion of hetero-
genesis or spontaneous generation.

The scientific world was soon divided into two hos-
tile camps, the leaders of which only can here be
briefly alluded to. On the one side, we have Buffon
and Needham, the former postulating his ‘ organic
molecules,’ and the latter assuming the existence of a
special ‘vegetative force’ which drew the molecules
together so as to form living things. On the other side,
we have the celebrated Abbé Lazzaro Spallanzani, who
in 1777 published results counter to those announced
by Needham in 1748. They were obtained by methods
so precise as to completely overthrow the convictions
based upon the labours of his predecessor. Charging his
flasks with organic infusions, he sealed their necks with
the blowpipe, subjected them in this condition to the
heat of boiling water, and subsequently exposed them
to temperatures favourable to the development of life.
The infusions continued unchanged for months, and
when the flasks were subsequently opened no trace of
life was found.

Here I may forestall matters so far as to say that
the success of Spallanzani’s experiments depended wholly
on the locality in which he worked. The air around
him must have been free from the more obdurate in-
fusorial germs, for otherwise the process he followed
would, as was long afterwards proved by Wyman, have
infallibly yielded life. But his refutation of the doc-
trine of spontaneous generation is not the less valid on
this account. Nor is it in any way upset by the fact,

SPONTANEOUS GENERATION. 281

that others in repeating his experiments obtained life
where he obtained none. Rather is the refutation
strengthened by such differences. Given two experi-
menters equally skilful and equally careful, operating
in different places on the same infusion, in the same
way, and assuming the one to obtain life while the other
fails to obtain it; then its well-established absence in
the one case proves that some ingredient foreign to the
infusion must be its cause in the other.

Spallanzani’s sealed flasks contained but small quan-
tities of air, and as oxygen was afterwards shown to
be generally essential to life, it was thought that the
absence of life observed by Spallanzani might have
been due to the lack of this vitalizing gas. To dissi-
pate this doubt, Schulze in 1836 half filled a flask with
distilled water to which animal and vegetable matters
were added. First boiling his infusion to destroy what-
ever life it might contain, Schulze sucked daily into
his flask air which had passed through a series of
bulbs containing concentrated sulphuric acid, where all
germs of life suspended in the air were supposed to be
destroyed. From May to August this process was
continued without any development of infusorial life.

Here again the success of Schulze was due to his
working in comparatively pure air, but even in such
air his experiment is a very risky one. Germs will
pass unwetted and unscathed through sulphuric acid
unless the most special care is taken to detain them.
I have repeatedly failed, by repeating Schulze’s experi-
ments, to obtain his results. Others have failed like-
wise. The air passes in bubbles through the bulbs, and
to render the method secure, the passage of the air must
be so slow as to cause the whole of its floating matter,
even to the very core of each bubble, to touch the sur-
rounding liquid. But if this precaution be observed,

282 THE FLOATING-MATTER OF THE AIR.

water will be found quite as effectual as sulphuric acid.
By the aid of an air-pump, in an highly infective atmo-
sphere I have thus drawn air for weeks without inter-
mission, first through bulbs containing water, and
afterwards through vessels containing organic infusions,
without any appearance of life. The germs were not
killed by the water, but they were effectually intercepted,
while the objection that the air had been injured by
being brought into contact with strongly corrosive sub-
stances was annulled.

The brief paper of Schulze, published in Poggen-~
dorf's Annalen for 1836, was followed in 1837 by
another short and pregnant communication by Schwann.
Redi, as we have seen, traced the maggots of putrefying
flesh to the eggs of flies. But he did not and he could
not know the meaning of putrefaction itself.. He had
not the instrumental means to inform him that it also
is a phenomenon attendant on the development of life.
This was first proved in the paper now alluded to.
Schwann placed flesh in a flask filled to one-third of its
capacity with water, sterilized the flask by boiling, and
then supplied it for months with calcined air. Through-
out this time there appeared no mould, no infusoria,
no putrefaction; the flesh remained unaltered, while
the liquid continued as clear as it was immediately
after boiling. Schwann then varied his experimental
argument, with no alteration in the result. His final
conclusion was, that putrefactionis due to decompositions
of organic matter attendant on the multiplication there-
in of minute organisms. These organisms were derived
- not from the air, but from something contained in the
air, which was destroyed by a sufficiently high tempera-
ture. There never was a more determined opponent of
the doctrine of spontaneous generation than Schwann,
though a strange attempt was made a year and a half

SPONTANEOUS GENERATION. 283

ago to enlist him and others equally opposed to it on
the side of the doctrine.

The physical character of the agent which produces
putrefaction was further revealed by Helmholtz in 1843.
By means of a membrane he separated a sterilized
putrescible liquid. from a putrefying one. The steril-
ized infusion remained perfectly intact. Hence it was
not the liquid of the putrefying mass—for that could
freely diffuse through the membrane—but something
contained in the liquid, and which was stopped by
the membrane, that caused the putrefaction. In 1854
Schroeder and Von Dusch struck into this inquiry,
which was subsequently followed up by Schroeder alone.
These able experimenters employed plugs of cotton-wool
to filter the air supplied to their infusions. Fed with
such air, in the great majority of cases the putrescible
liquids remained perfectly sweet after boiling. Milk
formed a conspicuous exception to the general rule. It
putrefied after boiling, though supplied with carefully
filtered air. The researches of Schroeder bring us up
to the year 1859.

In that year a book was published which seemed to
overturn some of the best established facts of previous
investigators. Its title was Hétérogénie, and its author
was F, A. Pouchet, Director of the Museum of Natural
History at Rouen. Ardent, laborious, learned, full not
only of scientific but of metaphysical fervour, he threw
his whole energy into the inquiry. Never did a subject
require the exercise of the cold critical faculty more
than this one—calm study in the unravelling of com-
plex phenomena, care in the preparation of experiments,
care in their execution, skilful variation of conditions,
and incessant questioning of results until repetition had
placed them beyond doubt or question. Toa man of
Pouchet’s temperament the subject was full of danger

284 THE FLOATING-MATTER OF THE AIR.

—danger not lessened by the theoretic bias with which
he approached it. This is revealed by the opening
words of his preface: ‘Lorsque, par la méditation, il
fut évident pour moi que la génération spontanée était
encore l’un des moyens qu’emploie la nature pour la re-
production des étres, je m’appliquai 4 découvrir par
quels procédés on pouvait parvenir 4 en mettre les
phénoménes en évidence.’ It is needless to say that
such a prepossession required a strong curb. Pouchet
repeated the experiments of Schulze and Schwann with
results diametrically opposed to theirs. He heaped ex-
periment upon experiment and argument upon argu-
ment, spicing with the sarcasm of the advocate the
logic of the man of science. In view of the multitudes
required to produce the observed results, he ridiculed
the assumption of atmospheric germs. This was one
of his strongest paints. ‘Si les Proto-organismes que
nous voyons pulluler partout et dans tout, avaient leurs
germes disséminés dans l’atmosphére, dans la propor-
tion mathématiquement indispensable 4 cet effet, lair
en serait totalement obscurci, car ils devraient sy
trouver beaucoup plus serrés que les globules d’eau qui
forment nos nuages épais. I] n’y a pas la la moindre
exagération.’ Recurring to the subject, he exclaims:
‘L’air dans lequel nous vivons aurait presque la den-
sité du fer.’ There is often a virulent contagion in a
confident tone, and this hardihood of argumentative
assertion was sure to influence minds swayed not by
knowledge, but by authority. Had Pouchet known
that *the blue ethereal sky’ is formed of suspended
particles, through which the sun freely shines, he would
hardly have ventured upon this line of argument.
Pouchet’s pursuit of this inquiry strengthened the
conviction with which he began it, and landed him in
downright credulity in the end. I do not question

SPONTANEOUS GENERATION, 285

his ability as an observer, but the inquiry needed a
disciplined experimenter. This latter implies not mere
ability to look at things as Nature offers them to our
inspection, but to force her to show herself under con-
ditions prescribed by the experimenter himself. Here
Pouchet lacked the necessary discipline. Yet the
vigour of his onset raised clouds of doubt, which for a
time obscured the whole field of inquiry. So difficult
indeed did the subject seem, and so incapable of definite
solution, that when Pasteur made known his intention
to take it up, his friends Biot and Dumas expressed
their regret, earnestly exhorting him to set a definite
and rigid limit to the time he purposed spending in
this apparently unprofitable field.

Schooled by his education as a chemist, and by
special researches on the closely related question of
fermentation, Pasteur took up this subject under par-
ticularly favourable conditions. His work and _ his
culture had given strength and finish to his natural
aptitudes. In 1862, accordingly, he published a paper
‘On the Organized Corpuscles existing in the Atmo-
sphere,’ which must for ever remain classical. By the
most ingenious devices he collected the floating par-
ticles of the air surrounding his laboratory in the Rue
d’Ulm, and subjected them to microscopic examination.
Many of them he found to be organized particles.
Sowing them in sterilized infusions, he obtained abund-
ant crops of microscopic organisms. By more refined
methods he repeated and confirmed the experiments
of Schwann, which had been contested by Pouchet,

1 «Je ne conseillerais 4 personne,’ said Dumas to his already
famous pupil, ‘ de rester trop longtemps dans ce sujet.’ Annales de
Chimie et de Physique, 1862, vol. lxiv. p. 22. Since that time the
illustrious Perpetual Secretary of the Academy of Sciences has had
good reason to revise this ‘counsel.’

286 THE FLOATING-MATTER OF THE AIR.

Montegazza, Joly, and Musset. He also confirmed the
experiments of Schroeder and Von Dusch. He showed
that the cause which communicated life to his infusions
was not uniformly diffused through the air; that there
were aérial interspaces which possessed no power to
generate life. Standing on the Mer de Glace, near the
Montanvert, he snipped off the ends of a number of
hermetically-sealed flasks containing organic infusions.
One out of twenty of the flasks thus supplied with
glacier air showed signs of life afterwards, while eight
out of twenty of the same infusions, supplied with the
air of the plains, became crowded with life. He took
his flasks into the caves under the Observatory of Paris,
and found the still air in these caves devoid of genera-
tive power. These and other experiments, carried out
with a severity perfectly obvious to the instructed
scientific reader, and accompanied by a logic equally
severe, restored the conviction that, even in these lower
reaches of the scale of being, life does not appear with-
out the operation of antecedent life.

The main position of Pasteur has been strengthened
by practical researches of the most momentous kind.
He has applied the knowledge won from his inquiries
to the preservation of wine and beer, to the manufacture
of vinegar, to the staying of the plague which threatened
utter destruction of the silk husbandry of France, and
to the examination of other formidable diseases which
assail the higher animals, including man. His relation to
the improvements which Professor Lister has introduced
into surgery is shown by a letter quoted in his Htudes
sur la Biére.! Professor Lister there expressly thanks
Pasteur for having given him the only principle which
could have conducted the antiseptic system to a suc-
cessful issue. The strictures regarding defects of
reasoning, to which we have been lately accustomed,

1 P. 43,

SPONTANEOUS GENERATION. 287

whatever light they may shed upon their author, throw
no shade upon Pasteur.

Redi, as we have seen, proved the maggots of putre-
fying flesh to be derived from the eggs of flies; Schwann
proved putrefaction itself to be the concomitant of
far lower forms of life than those dealt with by Redi.
Our knowledge here, as elsewhere in connexion with
this subject, has been vastly extended by Professor
Cohn, of Breslau. ‘ No putrefaction,’ he says, ‘ can occur
in a nitrogenous substance if its bacteria be destroyed
and new ones prevented from entering it. Putrefaction
begins as soon as bacteria, even in the smallest numbers,
are admitted either accidentally or purposely. It pro-
gresses in direct proportion to the multiplication of
the bacteria, it is retarded when they exhibit low
vitality, and is stopped by all influences which either
hinder their development or kill them. All bactericidal
media are therefore antiseptic and disinfecting.’ It
was these organisms acting in wound and abscess which
so frequently converted our hospitals into charnel-
houses, and it is their destruction by the antiseptic
system that now renders justifiable operations which no
surgeon would have attempted a few yearsago. The
gain is immense—to the practising surgeon as well as
to the patient practised upon. Contrast the anxiety of
never feeling sure whether the most brilliant operation
might not be rendered nugatory by the access of a few
particles of unseen hospital dust, with the comfort
derived from the knowledge that all power of mischief
on the part of such dust has been surely and certainly

1 In his last excellent memoir Cohn expresses himself thus:
‘Wer noch heut die Fiulniss von einer spontanen Dissociation der
Proteinmolecule, oder von einem unorganisirten Ferment ableitet,
oder gar aus “Stickstoffsplittern” die Balken zur Stiitze seiner

Faulnisstheorie zu zimmern versucht, hat zuerst den Satz “keine
Faulniss ohne Bacterium Termo” zu widerlegen.’

288 THE FLOATING-MATTER OF THE AIR.

annihilated. But the action of living contagia extends
beyond the domain of the surgeon. The power of re-
production and indefinite self-multiplication which it
characteristic of living things, coupled with the
undeviating fact of contagia ‘ breeding true,’ has given
strength and consistency to a belief long entertained by
penetrating minds, that epidemic diseases generally are
the concomitants of parasitic life. ‘There begins to be
faintly visible to us a vast and destructive laboratory of
nature wherein the diseases which are most fatal to ani-
mal life, and the changes to which dead organic matter
is passively liable, appear bound together by what must
at least be called a very close analogy of causation.”!
According to this view, which, as I have said, is daily
gaining converts, a contagious disease may be defined
as a conflict between the person smitten by it and a
specific organism which multiplies at his expense,
appropriating his air and moisture, disintegrating his
* tissues, or poisoning him by the decompositions incident
to its growth.

During the ten years extending from 1859 to 1869,
researches on radiant heat in its relations to the gas-
eous form of matter occupied my continual attention.
When air was experimented on, I had to cleanse it
effectually of floating matter, and while doing so I was
surprised to notice that, at the ordinary rate of transfer,
such matter passed freely through alkalis, acids, alcohols,
and ethers. The eye being kept sensitive by darkness,
a concentrated beam of light was found to be a most
searching test for suspended matter both in water
and in air—a test indeed indefinitely more searching
and severe than that furnished by the most powerful
microscope. With the aid of such a beam I examined

1 Report of the Medical Officer of the Privy Council, 1874, p. 5.

SPONTANEOUS GENERATION. 289

air filtered by cotton-wool; air long kept free from agita-
tion, so as to allow the floating matter to subside; cal-
cined air, and air filtered by the deeper cells of the human
lungs. In all cases the correspondence between my ex-
periments and those of Schwann, Schroeder, Pasteur, and
Lister in regard to spontaneous generation was perfect.
The air which they found inoperative was proved by
the luminous beam to be optically pure and therefore
germless. Having worked at the subject both by expe-
riment and reflection, on Friday evening, January 21,
1870, I brought it before the members of the Royal
Institution. Two or three months subsequently, for
sufficient practical reasons, I ventured to direct public
attention to the subject in a letter to the Times.
Such was my first contact with this important question.
This letter, I believe, gave occasion for the first
public utterance of Dr. Bastian in relation to this
subject. He did me the honour to inform me, as others
had informed Pasteur, that the subject ‘pertains to the
biologist and physician.’ He expressed ‘amazement’
at my reasoning, and warned me that before what I had
done could be undone ‘ much irreparable mischief might
be occasioned.’ With far less preliminary experience to
guide and warn him, the English heterogenist was far
bolder than Pouchet in his experiments, and far more
adventurous in his conclusions. With organic infusions
he obtained the results of his celebrated predecessor,
but he did much more—the atoms and molecules of in-
organic liquids passing under his manipulation into
those more ‘ complex chemical compounds,’ which we
dignify by calling them ‘living organisms.” As re-
1 ¢Jt is further held that bacteria or allied organisms are prone

to be engendered as correlative products, coming into existence in
the several fermentations, just as independently as other less

complex chemical compounds.’—Bastian, Trans. of Pathological
Society, vol. xxvi. 258.

290 THE FLOATING MATTER OF THE AIR.

gards the public who take an interest in such things,
and apparently also as regards a large portion of the
medical profession, our extremely clever countryman
succeeded in restoring the subject to a state of uncer-
tainty similar to that which followed the publication of
Pouchet’s volume in 1859.

It is desirable that this uncertainty should be
removed from all minds, and doubly desirable on
practical grounds that it should be removed from the
minds of medical men. In the present article, there-
fore, I propose discussing this question face to face with
some eminent and fair-minded member of the medical
profession who, as regards spontaneous generation, en-
tertains views adverse to mine. Such a one it would
be easy to name; but it is perhaps better to rest in the
impersonal, I shall therefore simply call my proposed
co-inquirer my friend. With him at my side, I shal]
endeavour, to the best of my ability, so to conduct this
discussion that he who runs may read and that he who
reads may understand.

Let us begin at the beginning. I ask my friend

to step into the laboratory of the
~ Royal Institution, where I place
_ before him a basin of thin turnip
slices barely covered with distilled
water kept at a temperature of
120° Fahr. After digesting the
* turnip for four or five hours we
pour off the liquid, boil it, filter
it, and obtain an infusion as clear
as filtered drinking water. We
cool the infusion, test its specific
praiity, and find it to be 1006 or higher—water
being 1000. A number of small clean empty flasks, of
the shape shown on the margin, are before us. One of

Fia. 23.

SPONTANEOUS GENERATION, 291

them is slightly warmed with a spirit-lamp, and its open
end is then dipped into the turnip infusion. The warmed
glass is afterwards chilled, the air within the flasks
cools, contracts, and is followed in its contraction by
the infusion. Thus we get a small quantity of liquid
into the flask. We now heat this liquid carefully.
Steam is produced, which issues from the open neck,
carrying the air of the flask along with it. After a few
seconds’ ebullition, the open neck is again plunged
into the infusion. The steam within the flask con-
denses, the liquid enters to supply its place, and in
this way we fill our little flask to about four-fifths of
its volume. This description is typical; we may thus
fill a thousand flasks with a thousand different infusions.

I now ask my friend to notice a trough made of
sheet copper, with two rows of handy little Bunsen
burners underneath it. This trough, or bath, is nearly
filled with oil; a piece of thin plank constitutes a kind
of lid for the oil-bath. The wood is perforated with
circular apertures wide enough to allow our small flask
to pass through and plunge itself in the oil, which has
been heated, say, to 250° Fahr. Clasped all round by
the hot liquid, the infusion in the flask rises to its
boiling point, which is not sensibly over 212° Fahr.
Steam issues from the open neck of the flask, and the
boiling is continued for five minutes. With a pair of
small brass tongs, an assistant now seizes the neck near
its junction with the flask, and partially lifts the latter
out of the oil. The steam does not cease to issue, but
its violence is abated. With a second pair of tongs held
in one hand, the neck of the flask is seized close to its
open end, while with the other hand a Bunsen’s flame
or an ordinary spirit flame is brought under the middle
of the neck. The glass reddens, whitens, softens, and
as it is gently drawn out the neck diminishes in dia-

292 THE FLOATING-MATTER OF THE AIR.

meter, unti] the canal is completely blocked up. The
second pair of tongs with the fragment of severed neck
being withdrawn, the flask, with its contents diminished
by evaporation, is lifted from the oil-bath perfectly
sealed hermetically.

Sixty such flasks filled, boiled, and sealed in the
manner described, and containing strong infusions of
beef, mutton, turnip, and cucumber, are carefully packed
in sawdust, and transported to the Alps. Thither, to
an elevation of about 7,000 feet above the sea, I invite
my co-inquirer to accompany me. It is the month of
July, and the weather is favourable to putrefaction.
We open our box at the Bel Alp, and count out fifty-
four flasks, with their liquids as clear as filtered drink-
ing water. In six flasks, however, the infusion is found
muddy. We closely examine these, and discover that
every one of them has had its fragile end broken off in
the transit from London. Air has entered the flasks,
and the observed muddiness is the result. My colleague
knows as well as I do what this means. Examined with
a pocket-lens, or even with a microscope of insufficient
power, nothing living is seen in the muddy liquid; but
regarded with a magnifying power of athousand diameters
or so, what an astonishing appearance does it present !
Leeuwenhoek estimated the population of a single drop
of stagnant water at 500,000,000: probably the popu-
lation of a drop of our turbid infusion would be this
many times multiplied. The field of the microscope
is crowded with organisms, some wabbling slowly, others
shooting rapidly across the microscopic field. They
dart hither and thither like a rain of minute projectiles ;
they pirouette and spin so quickly round, that the
retention of the retinal impression transforms the little
living rod into a twirling wheel. And yet the most
celebrated naturalists tells us they are vegetables.

SPONTANEOUS GENERATION. 293

From the rod-like shape which they so frequently
assume, these organisms are called ‘ bacteria ’—a term,
be it here remarked, which covers organisms of very
diverse kinds.

Has this multitudinous life been spontaneously
generated in these six flasks, or is it the progeny of
living germinal matter carried into the flasks by the
entering air? If the infusions have a self-generative
power, how are the sterility and consequent clearness
of the fifty-four uninjured flasks to be accounted for ?
My colleague may urge—and fairly urge—that the
assumption of germinal matter is by no means neces-
sary; that the air itself may be the one thing needed
to wake up the dormant infusions. We will examine
this point immediately. But meanwhile I would remind
him that Iam working on the exact lines laid down
by our most conspicuous heterogenist. He distinctly
affirms that the withdrawal of the atmospheric pressure
above the infusion favours the production of organisms ;
and he accounts for their absence in tins of preserved
meat, fruit, and vegetables, by the hypothesis that
fermentation has begun in such tins, that gases have
been generated, the pressure of which has stifled the
incipient life and stopped its further development.!
This is the new theory of preserved meats. Had Dr.
Bastian pierced a tin of preserved meat, fruit, or vege-
table under water with the view of testing its truth,
he would have found it erroneous. In well-preserved
tins he would have found, not an outrush of gas, but an
inrush of water. I have noticed this recently in tins
which have lain perfectly good for sixty-three years in
the Royal Institution. Modern tins, subjected to the
same test, yielded the same result. From time to time,
moreover, during the last two years, I have placed glass

1 ¢ Beginnings of Life,’ vol. i. p. 413,

294 THE FLOATING-MATTER OF THE AIR.

tubes, containing clear infusions of turnip, hay, beef,
and mutton, in iron bottles, and subjected them to air-
pressures varying from ten to twenty-seven atmospheres
—pressures, it is needless to say, far more than sufficient
to tear a preserved meat tin to shreds. After ten days
these infusions were taken from their bottles rotten with
putrefaction and teeming with life. Thus collapses an
hypothesis which had no rational foundation, and which
could never have seen the light had any well-directed
attempt been made to verify it.

Our fifty-four vacuous and pellucid flasks also declare
against the heterogenist. We expose them to a warm
Alpine sun by day, and at night we suspend them in a
warm kitchen. Four of them have been accidentally
broken; but at the end of a month we find the fifty
remaining ones as clear as at the commencement.
There is no sign of putrefaction or of life in any of
them. We divide these flasks into two groups of
twenty-three and twenty-seven respectively (an accident
of counting rendered the division uneven). The question
now is whether the admission of air can liberate any
generative energy in the infusions. Our next experi-
ment will answer this question and something more.
We carry the flasks to a hayloft, and there, with a pair
of steel pliers, snip off the sealed ends of the group
of three-and-twenty. Each snipping off is of course
followed by an inrush of air. We now carry our twenty-
seven flasks, our pliers, and a spirit-lamp, to a ledge
overlooking the Aletsch glacier, about 200 feet above
the hayloft, from which ledge the mountain falls almost
precipitously to the north-east for about a thousand
feet. A gentle wind blows towards us from the north-
east—that is, across the crests and snow-fields of the
Oberland mountains. We are therefore bathed by air
which must have been for a good while out of practical

SPONTANEOUS GENERATION. 295

contact with either animal or vegetable life. I stand
carefully to leeward of the flasks, for no dust or particle
from my clothes or body must be blown towards them.
An assistant ignites the spirit-lamp, into the flame of
which I plunge the pliers, thereby destroying all attached
germs or organisms. Then I snip off the sealed end
of the flask. Prior to every snipping the same process
is gone through, no flask being opened without the
previous cleansing of the pliers by the flame. In this
way we charge our seven-and-twenty flasks with clean
vivifying mountain air.

We place the fifty flasks, with their necks open,
over a kitchen stove, in a temperature varying from
50° to 90° Fahr., and in three days find twenty-one out
of the twenty-three flasks opened on the hayloft invaded
by organisms—two only of the group remaining free
from them. After three weeks’ exposure to precisely
the same conditions, not one of the twenty-seven flasks
opened in free air had given way. No germ from the
kitchen air had ascended, the narrow necks, the flasks
being shaped so as to avoid this contingency. They
are still in the Alps, as clear, I donbt not, and as free
from life as they were when sent off from London.!

What is my colleague’s conclusion from the experi-
ment before us? Twenty-seven putrescible infusions,
first in vacuo, and afterwards supplied with the most
invigorating air, have shown no sign of putrefaction
or of life. And as to the others, I almost shrink from
asking him whether the hayloft has rendered them
spontaneously generative. Is not the inference here
imperative that it is not the air of the loft—which is
connected through a constantly open door with the
general atmosphere—but something contained in the

- An actual experiment made at the Bel Alp is here described,
14

296 THE FLOATING-MATTER OF THE AIR,

air, that has produced the effects observed? What is
this something? A sunbeam entering through a chink
in the roof or wall, and traversing the air of the loft,
would- show it to be laden with suspended dust particles.
Indeed the dust is distinctly visible in the diffused day-
light. Can ithave been the origin of the observed life ?
If so, are we not bound by all antecedent experience to
regard these fruitful particles as the germs of the life
observed ?

The name of Baron Liebig has been constantly
mixed up with these discussions. ‘We have,’ it is said,
‘his authority for assuming that dead decaying matter
can produce fermentation.” True, but with Liebig
fermentation was by no means synonymous with life.
It meant, according to him, the shaking asunder by
chemical disturbance of unstable molecules. Does the
life of our flasks, then, proceed from dead particles ?
If my co-inquirer should reply ‘ Yes,’ then I would ask
him, ‘ What warrant does Nature offer for such an
assumption? Where, amid the multitude of vital
phenomena in which her operations have been clearly
traced, is the slightest countenance given to the notion
that the sowing of dead particles can produce a living
crop?’ With regard to Baron Liebig, had he studied
the revelations of the microscope in relation to these
questions, a mind so penetrating could never have
missed the significance of the facts revealed. He, how-
ever, neglected the microscope, and fell into error—but
not into error so gross as that in support of which his
authority has been invoked. Were he now alive, he
would, I doubt not, repudiate the use often made of his
name—Liebig’s view of fermentation was at least a
scientific one, founded on profound conceptions of
molecular instability. But this view by no means
involves the notion that the planting of dead particles

SPONTANEOUS GENERATION. 297

—‘ Stickstoffsplittern,” as Cohn contemptuously calls
them—is followed by the sprouting of infusorial life.

Let us now return to London and fix our attention
on the dust of ats air. Suppose a room in which the
housemaid has just finished her work to be completely
closed, with the exception of an aperture in a shutter
through which a sunbeam enters and crosses the room.
The floating dust reveals the track of the light. Let
a lens be placed in the aperture to condense the beam.
Its parallel rays are now converged to a cone, at the
apex of which the dust is raised to almost unbroken
whiteness by the intensity of its illumination. Defended
from all glare, the eye is peculiarly sensitive to this
scattered light. The floating dust of London rooms is
organic, and may be burned without leaving visible
residue. The action of a spirit-lamp flame upon the
floating matter has been elsewhere thus described :—

In a cylindrical beam which strongly illuminated the
dust of our laboratory, I placed an ignited spirit lamp.
Mingling with the flame, and round its rim, were seen
curious wreaths of darkness resembling an intensely black
smoke. On placing the flame at some distance below the
beam, the same dark masses stormed upwards. They were
blacker than the blackest smoke ever seen issuing from the
funnel of a steamer; and their resemblance to smoke was
so perfect as to prompt the conclusion that the apparently
pure flame of the alcohol-lamp required but a beam of
sufficient intensity to reveal its clouds of liberated carbon.

But is the blackness smoke? This question presented
itself in a moment, and was thus answered’: A red-hot
poker was placed underneath the beam; from it the black
wreaths also ascended. A large hydrogen flame, which
emits no smoke, was next employed, and it also produced
with augmented copiousness those whirling masses of dark-
ness. Smoke being out of the question, what is the black-

298 THE FLOATING-MATTER OF THE AIR.

ness? It is simply that of stellar space; that is to say,
blackness resulting from the absence from the track of the
beam of all matter competent to scatter its light. When
the flame was placed below the beam, the floating matter
was destroyed in situ; and the heated air, freed from this
matter, rose into the beam, jostled aside the illuminated
particles, and substituted for their light the darkness due to
its own perfect transparency. Nothing could more forcibly
illustrate the invisibility of the agent which renders all
things visible. The beam crossed, unseen, the black chasm
formed by the transparent air, while, at both sides of the
gap, the thick-strewn particles shone out like a luminous
solid under the powerful illumination.!

Supposing an infusion intrinsically barren, but
readily susceptible of putrefaction when exposed to
common air, to be brought into contact with this un-
illuminable air, what would be the result? It would
never putrefy. It might, however, be urged that the
air is spoiled by its violent calcination. Oxygen passed
through a spirit-lamp flame is, it may be thought, no
longer the oxygen suitable for the development and
maintenance of life. "We have an easy escape from this
difficulty, which is based, however, upon the unproved
assumption that the air has been affected by the flame.
Let a condensed beam be sent through a large flask or
bolthead containing common air. The track of the
beam is seen within the flask—the dust revealing the
light, and the light revealing the dust. Cork the flask,
stuff its neck with cotton-wool, or simply turn it mouth
downwards and leave it undisturbed for a day or two.
Examined afterwards with the luminous beam, no track
is visible; the light passes through the flask as through
a vacuum. The floating.matter has abolished itself,
being now attached to the interior surface of the flask.

1 Sce pp. 3 and 4 of this volume.

SPONTANEOUS GENERATION. 299

Were it our object, as it will be subsequently, to effec-
tually detain the dirt, we might coat that surface with
some sticky substance. Here, then, without ‘ torturing’
the air in any way, we have found a means of ridding

Fig. 24,

it, or rather of enabling it to rid itself, of floating
matter.

We have now to devise a means of testing the action
of such spontaneously purified air upon putrescible
infusions. Wooden chambers, or cases, are accordingly

300 THE FLOATING-MATTER OF THE AIR.

constructed, having glass fronts, side-windows, and
back-doors. Through the bottoms of the chambers
test-tubes pass air-tight; their open ends, for about
one-fifth of the length of the tubes, being within the
chambers. Provision is made for a free connexion
through sinuous channels between the inner and the
outer air. Through such channels, though open, no
dust will reach the chamber. The top of each chamber
is perforated by a circular hole two inches in diameter,
closed air-tight by a sheet of india-rubber. This is
pierced in the middle by a pin, and through the pin-
hole is pushed the shank of a long pipette, ending
above in a small funnel. The shank also passes through
a stuffing-box of cotton-wool moistened with glycerine ;
so that, tightly clasped by the rubber and wool, the
pipette is not likely in its motions up and down to carry
any dust into thechamber. The annexed woodcut (fig. 24)
shows a chamber, with six test-tubes, its side-windows
w w,its pipette p c, and its sinuous channels a b which
connect the air of the chamber with the outer air.

The chamber is carefully closed and permitted to
remain quiet for two or three days. Examined at the
beginning by a beam sent through its windows, the air
is found laden with floating matter, which in three
days has wholly disappeared. To prevent its ever
rising again, the internal surface of the chamber was
at the outset coated with glycerine. The fresh but
putrescible liquid is introduced into the six tubes in
succession by means of the pipette. Permitted to
remain without further precaution, every one of the
tubes would putrefy and fill itself with life. The liquid
has been in contact with the dust-laden air outside by
which it has been infected, and the infection must be
destroyed. This is done by plunging the six tubes into
a bath of heated oil and boiling the infusion. The time

SPONTANEOUS GENERATION. 301

requisite to destroy the infection depends wholly upon
its nature. Two minutes’ boiling suffices to destroy some
contagia, whereas two hundred minutes’ boiling fails to
destroy others. After the infusion has been sterilized,
the oil-bath is withdrawn, and the liquid, whose putre-
scibility has been in no way affected by the boiling, is
abandoned to the air of the chamber.

With such chambers I tested, in the autumn and
winter of 1875-6, infusions of the most various kinds,
embracing natural animal liquids, the flesh and viscera
of domestic animals, game, fish, and vegetables. More
than fifty chambers, each with its series of infusions,
were tested, many of them repeatedly. There was no
shade of uncertainty in any of the results. In every
instance we had, within the chamber, perfect limpidity
and sweetness, which in some cases lasted for more than
a year—without the chamber, with the same infusion,
putridity and its characteristic smells. In no instance
was the least countenance lent to the notion that an
infusion deprived by heat of its inherent life, and placed
in contact with air cleansed of its visibly suspended
matter, has any power to generate life anew.

Remembering then the number and variety of the
infusions employed, and the strictness of our adherence
to the rules of preparation laid down by the hetero-
genists themselves ; remembering that we have operated
upon the very substances recommended by them as
capable of furnishing, even in untrained hands, easy and
decisive proofs of spontaneous generation, and that we
have added to their substances many others of our own
—if this pretended generative power were a reality,
surely it must have manifested itself somewhere.
Speaking roundly, I should say that in such closed
chambers at least five hundred chances have been given
to it, but it has nowhere appeared.

302 THE FLOATING-MATTER OF THE AIR.

The argument is now to be clenched by an experi-
ment which will remove every residue of doubt as to the
ability of the infusions here employed to sustain life. We
open the back doors of our sealed chambers, and permit
the common air with its floating particles to have access
to our tubes. For three months they have remained
pellucid and sweet—flesh, fish, and vegetable extracts
purer than ever cook manufactured. Three days’
exposure to the dusty air suffices to render them
muddy, fetid, and swarming with infusorial life. The
liquids are thus proved, one and all, ready for putre-
faction when the contaminating agent is applied. I
invite my colleague to reflect on these facts. How will
he account for the absolute immunity of a liquid
exposed for months in a warm room to optically pure
air, and its infallible putrefaction in a few days when
exposed to dust-laden air? He must, I submit, bow
to the conclusion that the dust-particles are the cause
of putrefactive life. And unless he accepts the hypo-
thesis that these particles, being dead in the air, are
in the liquid miraculously kindled into living things,
he must conclude that the life we have observed springs
from germs or organisms diffused through the atmo-
sphere.

The experiments with hermetically-sealed flasks
have reached the number of 940. A sample group of
130 of them were laid before the Royal Society on
January 13, 1876. They were utterly free from life,
having been completely sterilized by three minutes’
boiling. Special care had been taken that the tempe-
ratures to which the flasks were exposed should include
those previously alleged to be efficient. The conditions
laid down by the heterogenist were accurately copied,
but there was no corroboration of his results. Stress
was then laid on the question of warmth, thirty degrees

SPONTANEOUS GENERATION. 303

being suddenly added to the temperatures with which
both of us had previously worked. Waiving all protest
against the caprice thus manifested, I met this new
requirement also. The sealed tubes, which had proved
barren in the Royal Institution, were suspended in per-
forated boxes, and placed under the supervision of an
intelligent assistant in the Turkish Bath in Jermyn
Street. From two to six days had been allowed for
the generation of organisms in hermetically-sealed
tubes. Mine remained in the washing-room of the
bath for nine days. Thermometers placed in the boxes,
and read off twice or three times a day, showed the
temperature to vary from a minimum of 101° to a
maximum of 112° Fahr. At the end of nine days the
infusions were as clear as at the beginning. They
were then removed to a warmer position. A tempera-
ture of 115° had been mentioned as particularly favour-
able to spontaneous generation. For fourteen days
the temperature of the Turkish Bath hovered about
this point, falling once as low as 106°, reaching 116°
on three occasions, 118° on one, and 119° on two. The
result was quite the same as that just recorded. The
higher temperatures proved perfectly ineompetent to
develope life.

Taking the actual experiment we have made as a
basis of calculation, if our 940 flasks were opened on
the hayloft of the Bel Alp, 858 of them would become
filled with organisms. The escape of the remaining 82
strengthens our case, proving as it does conclusively
that not in the air, nor in the infusions, nor in anything
continuous diffused through the air, but in discrete
particles, suspended in the air and nourished by the
infusions, we are to seek the cause of life. Our experi-
ment proves these particles to be in some cases so far
apart on the hayloft as to permit 10 per cent. of our

304 THE FLOATING-MATTER OF THE AIR.

flasks to take in air without contracting contamination.
A quarter of a century ago Pasteur proved the cause of
‘so-called spontaneous generation ’ to be discontinuous.
I have already referred to his observation that 12 out
of 20 flasks- opened on the plains escaped infection,
while 19 out of 20 flasks opened on the Mer de Glace
escaped. Our own experiment at the Bel Alp is a
more emphatic instance of the same kind, 90 per cent.
of the flasks opened in the hayloft being smitten, while
not one of those opened on the free mountain ledge was
attacked.

The power of the air as regards putrefactive infec-
tion is incessantly changing through natural causes, and
we are able to alter it at will. Of a number of flasks
opened in 1876 in the laboratory of the Royal Institu-
tion, 42 per cent. were smitten, while 58 per cent. es-
caped. In 1877 the proportion in the same laboratory
was 68 per cent. smitten, to 32 intact. The greater
mortality, so to speak, of the infusions in 1877 was due
to the presence of hay which diffused its germinal dust
in the laboratory air, causing it to approximate as re-
gards infective virulence to the air of the Alpine loft.
I would ask my friend to bring his scientific penetration
to bear upon all the foregoing facts. They do not
prove spontaneous generation to be ‘impossible.’ My
assertions, however, relate not to ‘ possibilities,’ but to
proofs, and the experiments just described do most
distinctly prove the evidence on which the heterogenist
relies to be written on waste paper.

My colleague will not, Iam persuaded, dispute these
results ; but he may be disposed to urge that other able
and honourable men working at the same subject have
arrived at conclusions different from mine. Most freely
granted ; but let me here recur to the remarks already
made in speaking of the experiments of Spallanzani,

SPONTANEOUS GENERATION. 305

to the effect that the failure of others to confirm his
results by no means upsets their evidence. To fix the
ideas, let us suppose that my colleague comes to the
laboratory of the Royal Institution, repeats there my
experiments, and obtains confirmatory results; and
that he then goes to University or King’s College,
where, operating with the same infusions, he obtains
contradictory results. Will he be disposed to conclude
that the selfsame substance is barren in Albemarle
Street and fruitful in Gower Street or the Strand?
His Alpine experience has already made known to him
the literally infinite differences existing between diffe-
rent samples of air as regards their capacity for putre-
factive infection. And, possessing this knowledge, will
he not substitute for the adventurous conclusion that
an organic infusion is barren at one place and sponta-
neously generative at another, the more rational and
obvious one that the atmospheres of the two localities
which have had access to the infusion are infective in
different degrees ?

As regards workmanship, moreover, he will not fail
to bear in mind, that fruitfulness may be due to errors
of manipulation, while barrenness involves the pre-
sumption of correct experiment. It is only the careful
worker that can secure the latter, while it is open to
every novice to obtain the former. Barrenness is the
result at which the conscientious experimenter, whatever
his theoretic convictions may be, ought to aim, omit-
ting no pains to secure it, and resorting, only when
there is no escape from it, to the conclusion that the
life observed comes from no source which correct experi-
ment could neutralize or avoid.

Let us again take a definite case. Supposing my
colleague to operate with the same apparent care on
100 infusions—or rather on 100 samples of the same

306 THE FLOATING-MATTER OF THE AIR.

infusion—and that 50 of them prove fruitful and 50
barren. Are we to say that the evidence for and against
heterogeny is equally balanced? There are some who
would not only say this, but who would treasure up the
50 fruitful flasks as ‘ positive’ results, and lower the
evidential value of the 50 barren flasks by labelling
them ‘negative’ results. This, as shown by Dr.
William Roberts, is an exact inversion of the true order
of the terms positive and negative.! Not such, I trust,
would be the course pursued by my friend. As regards
the 50 fruitful flasks he would, I doubt not, repeat the
experiment with redoubled care and scrutiny, and not
by one repetition only, but by many, assure himself
that he had not fallen into error. Such faithful scru-
tiny, fully carried out, would infallibly lead-him to the
conclusion that here, as in all other cases, the evidence
in favour of spontaneous generation crumbles in the
grasp of the competent inquirer.

The botanist knows that different seeds possess
different powers of resistance to heat.2 Some are
killed by a momentary exposure to the boiling tem-
perature, while others withstand it for several hours.
Most of our ordinary seeds are rapidly killed, while
Pouchet made known to the Paris Academy of Sciences
in 1866, that certain seeds, which had been transported
in fleeces of wool from Brazil, germinated after four
hours’ boiling. The germs of the air vary as much
among themselves as the seeds of the botanist. In
some localities the diffused germs are so tender that

! See his truly philosophical remarks on this head in the British
Medical Journal, 1876, p. 282.

2 Tam indebted to Dr. Thiselton Dyer for various illustrations
of such differences. It is, however, surprising that a subject of such
high scientific importance should not have been more thoroughly
explored. Here the scoundrels who deal in killed seeds might be
able to add to our knowledge.

SPONTANEOUS GENERATION. 307

boiling for five minutes, or even less, would be sure to
destroy them all; in other localities the diffused germs
are so ebstinate, that many hours’ boiling would be
requisite to deprive them of their power of germina-
tion. The absence or presence of a truss of desiccated
hay would produce differences as great as those here
described. The greatest endurance that I have ever
observed—and I believe it is the greatest on record—
was a case of survival after eight hours’ boiling.

As regards their power of resisting heat, the in-
fusorial germs of our atmosphere might be classified
under the following and intermediate heads :—Killed in
five minutes; not killed in five minutes but killed in
fifteen; not killed in fifteen minutes but killed in
thirty ; not killed in thirty minutes but killed in an
hour; not killed in an hour but killed in two hours;
not killed in two but killed in three hours; not killed
in three but killed in four hours. I have had several
cases of survival after four and five hours’ boiling, some
survivals after six, and one after eight hours’ boiling.
Thus far has experiment actually reached; but there is
no valid warrant for fixing upon even eight hours as
the extreme limit of vital resistance. Probably more
extended researches (though mine have been very exten-
sive) would reveal germs more obstinate still. It is
also certain that we might begin earlier, and find germs
which are destroyed by a temperature far below that of
boiling water. In the presence of such facts, to speak
of a death-point of bacteria and their germs would be
unmeaning—but of this more anon.

‘What present warrant,’ it has been asked, ‘is there
for supposing that a naked, or almost naked, speck of
protoplasm can withstand four, six, or eight hours’
boiling?’ Regarding naked specks of protoplasm I
make no assertion. I know nothing about them, save

308 THE FLOATING-MATTER OF THE AIR.

as the creatures of fancy. But I do affirm, not as a
‘supposition,’ nor an ‘assumption,’ nor a ‘ probable
guess,’ nor as ‘a wild hypothesis, but as a matter of
the most undoubted fact, that the spores of the hay
bacillus, when thoroughly desiccated by age, have
withstood the ordeal mentioned. And I further affirm
that these obdurate germs, under the guidance of the
knowledge that they are germs, can be destroyed by
five minutes’ boiling, or even less. This needs explana-
tion. The finished bacterium perishes at a temperature
far below that of boiling water, and it is fair to assume
that the nearer the germ is to its final sensitive condi-
tion the more readily will it succumb to heat. Seeds
soften before and during germination. This premised,
the simple description of the following process will
suffice to make its meaning understood.

An infusion infected with the most powerfully re-
sistent germs, but otherwise protected against the
floating matters of the air, is gradually raised to its
boiling-point. Such germs as have reached the soft.
and plastic state immediately preceding their develop-
ment into bacteria are thus destroyed. The infusion is
then put aside in a warm room for ten or twelve hours.
If for twenty-four, we might have the liquid charged
with well-developed bacteria. To anticipate this, at
the end of ten or twelve hours we raise the infusion a
second time to the boiling temperature, which, as
before, destroys all germs then approaching their point
of final development. The infusion is again put aside
for ten or twelve hours, and the process of heating is
repeated. We thus kill the germs in the order of
their resistance, and finally kill the last of them. No
infusion can withstand this process if it be repeated a
sufficient number of times. Artichoke, cucumber, and
turnip infusions, which had proved specially obstinate

SPONTANEOUS GENERATION. 309

when infected with the germs of desiccated hay, were
completely broken down by this method of discontinuous
heating, three minutes being found sufficient to accom-
plish what three hundred minutes’ continuous boiling
failed to accomplish. I applied the method, moreover,
to infusions of various kinds of hay, including those
most tenacious of life. Not one of them bore the
ordeal. These results were clearly foreseen before they
were realized, so that the germ theory fulfils the test
of every true theory, that test being the power of
prevision.

When ‘naked or almost naked specks of protoplasm ’
are spoken of, the imagination is drawn upon, not the
objective truth of Nature. Such words sound like the
words of knowledge where knowledge is really nil. The
possibility of a ‘thin covering’ is conceded by those
who speak in this way. Such a covering may, however,
exercise a powerful protective influence. A thin pellicle
of india-rubber, for example, surrounding a pea keeps
it hard in boiling water for a time sufficient to
reduce an uncovered pea to a pulp. The pellicle pre-
vents imbibition, diffusion, and the consequent dis-
integration. A greasy or oily surface, or even the layer
of air which clings to certain bodies, would act to some
extent ina similar way. ‘The singular resistance of
green vegetables to sterilization, says Dr. William
Roberts, ‘appears to be due to some peculiarity of the
surface, perhaps their smooth glistening epidermis
which prevented complete wetting of their surfaces.’
I pointed out in 1876 that the process by which an
atmospheric germ is wetted would be an interesting
subject of investigation. A dry microscope covering-
glass may be caused to float on water for a year. A
sewing-needle may be similarly kept floating, though
its specific gravity is nearly eight times that of water.

310 THE FLOATING-MATTER OF THE AIR.

Were it not -for some specific relation between the
matter of the germ and that of the liquid into which
it falls, wetting would be simply impossible. Antece-
dent to all development there must be an interchange
of matter between the germ and its environment;
and this interchange must obviously depend upon the
relation of the germ to its encompassing liquid. Any-
thing that hinders this interchange retards the de-
struction of the germ in boiling water. In my paper,
published in the ‘ Philosophical Transactions’ for 1877,
I add the following remark :—

It is not difficult to see that the surface of a seed or germ
may be so affected by desiccation and other causes as practi-
cally to prevent contact between it and the surrounding
liquid. The body of a germ, moreover, may be so indurated
by time and dryness as to resist powerfully the insinuation
of water between its constituent molecules. It would be
difficult to cause such a germ to imbibe the moisture neces-
sary to produce the swelling and softening which precede its
destruction in a liquid of high temperature.

However this may be—whatever be the state of the
surface, or of the body, of the spores of Bacillus subtilis,
they do as a matter of certainty resist, under some
circumstances, exposure for hours to the heat of boiling
water. No theoretic scepticism can successfully stand
in the way of this fact, established as it has been by
hundreds—nay thousands, of rigidly conducted expe-
riments.

We have now to test one of the principal founda-
tions of the doctrine of spontaneous generation as
formulated in this country. With this view, I place
before my friend and co-inquirer two liquids which
have been kept for six months in one of our sealed
chambers, exposed to optically pure air. The one is a

SPONTANEOUS GENERATION. 311

mineral solution containing in proper proportions all
the substances which enter into the composition of
bacteria, the other is an infusion of turnip—it might
be any one of a hundred other infusions, animal or
vegetable. Both liquids are as clear as distilled water,
and there is no trace of life in either of them. They
are, in fact, completely sterilized. A mutton-chop, over
which a little water has been poured to keep its juices
from drying up, has lain for three days upon a plate in
our warm room. It smells offensively. Placing a drop
of the fetid mutton-juice under a microscope, it is found
swarming with the bacteria of putrefaction. Witha
speck of the swarming liquid I inoculate the clear
mineral solution and the clear turnip infusion, as a
surgeon might inoculate an infant with vaccine lymph.
In four-and-twenty hours the transparent liquids have
become turbid throughout, and instead of being barren
as at first, they are teeming with life. The experiment
may be repeated a thousand times with the same
invariable result. To the naked eye the liquids at the
beginning were alike, being both equally transparent—
to the naked eye they are alike at the end, being both
equally muddy. Instead of putrid mutton-juice, we
might take as a source of infection any one of a
hundred other putrid liquids, animal or vegetable. So
long as the liquid contains living bacteria, a speck of it
communicated either to the clear mineral solution, or to
the clear turnip infusion, produces in twenty-four hours
the effect here described.

We now vary the experiment thus :—Opening the
back-door of another closed chamber which has con-
tained for months the pure mineral solution and the
pure turnip infusion side by side, I drop into each of
them a small pinch of laboratory dust. The effect here
is tardier than when the speck of putrid liquid was

312 THE FLOATING-MATTER OF THE AIR.

employed. In three days, however, after its infection
with the dust, the turnip infusion is muddy, and swarm-
ing as before with bacteria. But what about the mineral
solution which, in our first experiment, behaved in a
manner undistinguishable from the turnip-juice? At
the end of three days there is not a bacterium to be
found in it. At the end of three weeks it is equally
innocent of bacterial life. We may repeat the experi-
ment with the solution and the infusion a hundred
times with the same invariable result. Always in the
case of the latter the sowing of the atmospheric dust
yields a crop of bacteria—never in the former does the
dry germinal matter kindle into active life.! What
is the inference which the reflecting mind must draw
from this experiment? Is it not as clear as day that
while both liquids are able to feed the bacteria and to
enable them to increase and multiply, after they have
been once fully developed, only one of the liquids is
able to develope into active bacteria the germinal dust
of the air?

I invite my friend to reflect upon this conclusion ;
he will, I think, see that there is no escape from it.
He may, if he prefers, hold the opinion, which I
consider erroneous, that bacteria exist in the air, not
as germs but as desiccated organisms. The inference
remains, that while the one liquid is able to force the
passage from the inactive to the active state, the other
is not..

But this is not at all the inference which has been
drawn from experiments with the mineral solution.
Seeing its ability to nourish bacteria when once inocu-
lated with the living active organism, and observing

1 This is the deportment of the mineral solution as described by
others. My own experiments would lead me to say that the de-
velopment of the hacteria, though exceedingly slow and difficult, is
not impossible.

SPONTANEOUS GENERATION. 313

that no bacteria appeared in the solution after long
exposure to the air, the inference was drawn that neither
bacteria nor their germs existed in the air. Through-
out Germany the ablest literature of the subject, even
that opposed to heterogeny, is infected with this error ;
while heterogenists at home and abroad have based upon
it a triumphant demonstration of their doctrine. It is
proved, they say, by the deportment of the mineral
solution that neither bacteria nor their germs exist in
the air; hence, if, on exposing a thoroughly sterilized
turnip infusion to the air, bacteria appear, they must of
necessity have been spontaneously generated. In the
words of Dr. Bastian: ‘We can only infer that whilst
the boiled saline solution is quite incapable of engen-
dering bacteria, such organisms are able to arise de nove
in the boiled organic infusion.’ !

I would ask my eminent colleague what he thinks
of this reasoning now? The datum is—‘A mineral
solution exposed to common air does not develope
bacteria;’ the inference is—‘ Therefore if a turnip
infusion similarly exposed develope bacteria, they must
be spontaneously generated.’ The inference, on the face
of it, is an unwarranted one. But while as matter of
logic it is inconclusive, as matter of fact it is chimerical.
London air is as surely charged with the germs of
bacteria as London chimneys are with smoke. The
inference just referred to is completely disposed of
by the simple question: ‘Why, when your sterilized
organic infusion is exposed to optically pure air, should
this generation of life de novo utterly cease? Why
should I be able to preserve my turnip-juice side by
side with your saline solution for the three hundred and
sixty-five days of the year, in free connexion with the
general atmosphere, on the sole condition that the

1 Proceedings of the Royal Society, vol. xxi. p. 130.

314 THE FLOATING-MATTER OF THE AIR,

portion of that atmosphere in contact with the juice
shall be visibly free from floating dust, while three days’
exposure to that dust fills it with bacteria?’ Am I
over-sanguine in hoping that as regards the argument
here set forth he who runs may read, and he who reads
mnay understand ?

We now proceed to the calm and thorough con-
sideration of another subject, more important if pos-
sible than the foregoing one, but like it somewhat
difficult to seize by reason of the very opulence of the
phraseology, logical and rhetorical, in which it has been
set forth. The subject now to be considered relates to
what has been called ‘the death-point of bacteria.’
Those who happen to be acquainted with the modern
English literature of the question will remember how
challenge after challenge has been issued to pansperm-
atists in general, and to one or two home workers in
particular, to come to close quarters on this cardinal
point. It is obviously the stronghold of the English
heterogenist. ‘Water, he says, ‘is boiling merrily
over a fire when some luckless person upsets the vessel
so that the heated fluid exercises its seathing influence
upon an uncovered portion of the body—hand, arm, or
face. Here, at all events, there is no room for doubt.
Boiling water unquestionably exercises a most per-
nicious and rapidly destructive effect upon the living
matter of which we are composed.’! And lest it should
be supposed that it is the high organization which,
in this case, renders the body susceptible to heat, he
refers to the action of boiling water on the hen’s egg
to dissipate the notion. ‘The conclusion,’ he says,
*would seem to force itself upon us that there is
something intrinsically deleterious in the action of
boiling water upon living matter—whether this matter
be of high or of low organisation.’? Again, at another

1 Bastian, ‘Evolution,’ p 133. 2? Thid. p. 135

SPONTANEOUS GENERATION. 315

place: ‘It has been shown that the briefest’ exposure
to the influence of boiling water is destructive of all
living matter.’ !

The experiments already recorded plainly show that
there is a marked difference between the dry bacterial
matter of the air, and the wet, soft, and active bacteria
of putrefying organic liquids. The one can be luxu-
riantly bred in the saline solution, the others refuse to
be born there, while both of them are copiously de-
veloped in a sterilized turnip infusion. Inferences, as
we have already seen, founded on the deportment of
the one liquid cannot with the warrant of scientific
logic be extended to the other. But this is exactly what
the heterogenist has done, thus repeating as regards
the death-point of bacteria the error into which he
fell concerning the germs of the air. Let us boil our
muddy mineral solution with its swarming bacteria for
five minutes. In the soft succulent condition in which
they exist in the solution not one of them escapes
destruction. The same is true of the turnip infusion
if it be inoculated with the living bacteria only—the
aérial dust being carefully excluded. In both cases the
dead organisms sink to the bottom of the liquid, and
without re-inoculation no fresh organisms will arise.
But the case is entirely different when we inoculate
our turnip infusion with the desiccated germinal matter
afloat in the air.

The ‘death-point’ of bacteria is the maximum
temperature at which they can live, or the minimum
temperature at which they cease to live. If, for ex-
ample, they survive a temperature of 140°, and do not
survive a temperature of 150°, the death-point lies
somewhere between these two temperatures. Vaccine
lymph, for example, is proved by Messrs, Braidwood
and Vacher to be deprived of its power of infection by

' Bastian, ‘ Evolution,’ p. 46.

316 THE FLOATING-MATTER OF THE AIR.

brief exposure to a temperature between 140° and 150°
Fahr. This may be regarded as the death-point of the
lymph, or rather of the particles diffused in the lymph,
which constitute the real contagium. If no time, how-
ever, be named for the application of the heat, the term
‘death-point’ is a vague one. An infusion, for example,
which will resist five hours’ continuous exposure to the
boiling temperature, will succumb to five days’ exposure
to a temperature 50° Fahr. below that of boiling. The
fully developed soft bacteria of putrefying liquids are
not only killed by five minutes’ boiling, but by less
than a single minute’s boiling—indeed, they are slain
at about the same temperature as the vaccine. The
same is true of the plastic, active bacteria of the turnip
infusion.}

But, instead of choosing a putrefying liquid for
inoculation, let us prepare and employ our inoculating
substance in the following simple way :—Let a small
wisp of hay, desiccated by age, be washed in a glass of
water, and let a perfectly sterilized turnip infusion be
inoculated with the washing liquid. After three hours’
continuous boiling the infusion thus infected will often
develope luxuriant bacterial life. Precisely the same
occursif a turnip infusion be prepared in an atmosphere
well charged with desiccated hay-germs. The infusion
in this case infects itself without special inoculation,
and its subsequent resistance to sterilization is often
very great. On the Ist of March last I purposely in-
fected the air of our laboratory with the germinal dust
of a sapless kind of hay mown in 1875. Ten groups

1In my paper in the Philosophical Transactions for 1876, I
pointed out and illustrated experimentally the difference, as regards
rapidity of development, between water-germs and air-germs; the
growth from the already softened water-germs proving to be prac-
tically as rapid as from developed bacteria. This preparedness of
the germ for rapid development is associated with its preparedness
for rapid destruction.

SPONTANEOUS GENERATION, 317

of flasks were charged with turnip infusion prepared in
the infected laboratory, and were afterwards subjected
to the boiling temperature for periods varying from
15 minutes to 240 minutes. Out of the ten groups
only one was sterilized—that, namely, which had been
boiled for four hours. Every flask of the nine groups
which had been boiled for 15, 30, 45, 60, 75, 90, 105,
120, and 180 minutes, respectively, bred organisms
afterwards. The same is true of other vegetable in-
fusions. On the 28th of February last, for example, I
boiled six flasks, containing cucumber infusion prepared
in an infected atmosphere, for periods of 15, 30, 45, 60,
120, and 180 minutes. Every flask of the group sub-
sequently developed organisms. On the same day, in
the case of three flasks, the boiling was prolonged to
240, 300, and 360 minutes; and these three flasks were
completely sterilized. Animal infusions, which under
ordinary circumstances are rendered infallibly barren
by five minutes’ boiling, behave like the vegetable in-
fusions in an atmosphere infected with hay-germs. On
the 30th of March, for example, five flasks were charged
with a clear infusion of beef and boiled for 60 minutes,
120 minutes, 180 minutes, 240 minutes, and 300 minutes
respectively. Every one of them became subsequently
crowded with organisms, and the same happened to a
perfectly pellucid mutton infusion prepared at the same
time. The cases are to be numbered by hundreds in
which similar powers of resistance were manifested by
infusions of the most diverse kinds.

In the presence of such facts I would ask my
colleague whether it is necessary to dwell for a single
instant on the one-sidedness of the evidence which led
to the conclusion that all living matter has its life
destroyed by ‘the briefest exposure to the influence of
boiling water.’ An infusion proved to be barren by

318 THE FLOATING-MATTER OF THE AIR,

six months’ exposure to moteless air maintained at a
temperature of 90° Fahr., when inoculated with full-
grown active bacteria, fills itself in two days with
organisms so sensitive as to be killed by a few minutes’
exposure to a temperature much below that of boiling
water. But the extension of this result to the desic-
cated germinal matter of the air is without warrant or
justification. This is obvious without going beyond
the argument itself. But we have gone far beyond the
argument, and proved by multiplied experiment the
alleged destruction of all living matter by the briefest
exposure to the influence of boiling water to be a de-
lusion. The whole logical edifice raised upon this basis
falls therefore to the ground; and the argument that
bacteria and their germs, being destroyed at 140°, must,
if they appear after exposure to 212°, be spontaneously
generated, is, I trust, silenced for ever.

Through the precautions, variations, and repetitions
observed and executed with the view of rendering its
results secure, the separate vessels employed in this
inquiry have mounted up in two years to nearly ten
thousand.

Besides the philosophic interest attaching to the
problem of life’s origin, which will be always immense,
there are the practical interests involved in the appli-
cation of the doctrines here discussed to surgery and
medicine. The antiseptic system, at which I have
already glanced, illustrates the manner in which bene-
ficent results of the gravest moment follow in the wake
of clear theoretic insight. Surgery was once a noble
art; it is now, as well, a noble science. Prior to the
introduction of the antiseptic system, the thoughtful
surgeon could not have failed to learn empirically that
there was something in the air which often defeated the
most consummate operative skill. That something the

SPONTANEOUS GENERATION, 319

antiseptic treatment destroys or renders innocuous, At
King’s College Mr. Lister operates and dresses while a
fine shower of mixed carbolic acid and water, produced
in the simplest manner, falls upon the wound, the lint
and gauze employed in the subsequent dressing being
duly saturated with the antiseptic. At St. Bartholomew’s
Mr. Callender employs the dilute carbolic acid without
the spray ; but, as regards the real point aimed at—
the preventing of the wound from becoming a nidus
for the propagation of septic bacteria—the practice in
both hospitals is the same. Commending itself as it
does to, the scientifically trained mind, the antiseptic
system has struck deep root in Germany.

Had space allowed, it would have given me pleasure
to point out the present position of the ‘germ theory’
in reference to the phenomena of infectious disease,
distinguishing arguments based on analogy—which,
however, are terribly strong—from those based on
actual observation. I should have liked to follow up
the account I have already given! of the truly excel-
lent researches of a young and an unknown German
physician named Koch, on splenic fever, by an account
of what Pasteur has recently done with reference to the
same subject. Here we have before us a living con-
tagium of the most deadly power, which we can follow
from the beginning to the end of its life cycle.2 We
find it in the blood or spleen of a smitten animal in
the state say of short motionless rods. When these
rods are placed in a nutritive liquid on the warm stage
of the microscope, we soon see them lengthening into
filaments which lie, in some cases, side by side, forming

1‘ Wortnightly Review,’ November, 1876 ; see preceding Article on
‘ Fermentation.’

? Mallinger and Drysdale had previously shown what skill and
patience can accomplish, by their admirable observations on the life
history of the monads,

15

320 THE FLOATING-MATTER OF THE AIR.

in others graceful loops, or becoming coiled into knots
of a complexity not to be unravelled. We finally see
those filaments resolving themselves into innumerable
spores, each with death potentially housed within it,
yet not to be distinguished microscopically from the
harmless germs of Bacillus subtilis. The bacterium
of splenic fever is called Bacillus Anthracis. This
formidable organism was shown to me by M. Pasteur
in Paris last July. His recent investigations regarding
the part it plays pathologically certainly rank amongst
the most remarkable labours of that remarkable man.
Observer after observer had strayed and fallen in this
land of pitfalls, a multitude of opposing conclusions
and mutually destructive theories being the result. In
association with a younger physiological colleague, M.
Joubert, Pasteur struck in amidst the chaos, and soon
reduced it to harmony.. They proved, among other
things, that in cases where previous observers in France
had supposed themselves to be dealing solely with
splenic fever, another equally virulent factor was simul-
taneously active. Splenic fever was often overmastered
by septicemia, and results due solely to the latter had
been frequently made the ground of pathological in-
ferences regarding the character and cause of the
former. Combining duly the two factors, all the
previous irregularities disappeared, every result obtained
receiving the fullest explanation. On studying the
account of this masterly investigation, the words where-
with Pasteur himself feelingly alludes to the difficulties
and dangers of the experimenter’s art came home to
me with especial force: ‘J’ui tant de fois éprouvé que
dans cet art difficile de l’expérimentation les plus
habiles bronchent 4 chaque pas, et que l’interprétation
des faits n’est pas moins périlleuse.’!
' Comptes-Rendus, lxxxiii. p. 177.

APPENDIX.

—+<

The following Abstract of Essay IIL, taken from the Pro-
ceedings of the Royal Society for 1877, may be of use to
the reader.

For reasons which will appear in the sequel, it will be
desirable to glance, in the first place, at the results already
submitted to the Royal Society.

Portions of the autumn of 1875, and of the winter and
spring of 1875-76, were devoted to the first section of
these researches, and on the 18th of January, 1876, its
main results were communicated orally to the Royal
Society. The completed memoir was handed in to the
Society on the 6th of April: it is published in vol. 166 of
the ‘ Philosophical Transactions.’

Many of the ‘closed chambers’ employed in the
inquiry were submitted on the 13th of January to the
inspection of the Fellows. There had been over fifty of
them in all, and several of them had been used more than
once. The air in these chambers had been permitted to
free itself from floating matter by self-subsidence, no
artificial means of cleansing it being employed. Sterilized
organic liquids and infusions of the most varied kinds
freely exposed to air thus spontaneously purified were
found, when tested by the microscope, to remain absolutely
free from organisms of all kinds, and equally free from the
turbidity, scum, and mould which to the naked eye are the
infallible signs of the generation and multiplication of
such organisms.

These experiments embraced, among others, the follow-

322 APPENDIX.

ing organic liquids :—urine in its natural conditions; in-
fusions of mutton, beef, pork, hay, turnip, sole, haddock,
codfish, salmon, turbot, mullet, herring, eel, oyster,
whiting, liver, kidney, hare, rabbit, barndoor fowl,
pheasant and grouse.

The number of separate vessels containing these liquids
which were exposed to spontaneously purified air amounted
to several hundreds, and the consensus of their testimony,
in the sense just indicated, was complete.

Five minutes’ boiling was found in all cases sufficient
to sterilize the infusions. ;

When, after remaining sterile for months, the doors of
the chambers were opened so as to admit the uncleansed
air of the laboratory, the contact of such air, or, more
correctly, of the matter mechanically floating in it,
infallibly produced organisms in abundance—sometimes
exclusively Bacterial, sometimes exclusively fungoid, and
sometimes a combination of both.

Infusions of the substances above referred to were
afterwards exposed in succession to air which had been
freed of its floating matter by filtration through cotton
wool, also to air from which the floating matter had been
removed by calcination, and finally to vacua obtained by
exhausting as far as possible with an air-pump, large
receivers which had been previously filled with filtered air.

Boiled for five minutes and exposed to air thus treated,
or to vacua thus produced, none of the infusions showed sub-
sequently any alteration of colour or of transparency to the
naked eye, or to the microscope any manifestation of life.

Thus far are summed up the results obtained with
self-purified air, filtered air, calcined air, and air-pump
vacua, the liquids in all cases being exposed in open test-
tubes. Small retort-flasks, with drawn-out necks, were
afterwards resorted to. Charged with the infusions, they
were boiled in heated oil or brine, and sealed with ex-
ceeding care during ebuillition, At the Royal Society on
January 13, 1876, one hundred and thirty such flasks
were submitted to the Fellows, free alike from putrefaction

APPENDIX. 323

and from life. They embraced specimens of all the sub.
stances above mentioned and some others.

Briefly expressed, then, the evidence furnished by six
months’ assiduous work during the autumn, winter, and
spring of 1875-76, proved conclusively that in the
atmospheric conditions then existing in the laboratory of
the Royal Institution, not one of the many hundred flasks
and tubes experimented on failed to be sterilized by five
minutes’ boiling, and no countenance was given to the
notion that any of these once sterilized infusions possessed
the power of spontaneously generating life.

The investigation embodied in the memoir now sub-
mitted to the Society was opened in the summer of 1876
by a series of tentative experiments on turnip-infusions, to
which were added varying quantities of bruised or pounded
cheese. Seven different kinds of cheese were employed,
fifty-seven test-tubes being charged with the mixture and
exposed to the self-purified air of closed chambers.

The majority of these mixtures remained unchanged ; a
minority became charged with organisms, which are, in my
opinion, completely accounted for by reference to the
protective action of the cheese. In the memoir of which
this is an abstract such protective action is illustrated by
the fact that when ordinary mustard seeds were tied
together in a calico bag, they resisted the boiling tem-
perature for a considerable multiple of the time which
sufficed to kill them when no bag enveloped them. The
bag and outside seeds protected the interior ones.

Not temperature alone, but the ability to diffuse its
juices or salts, is a condition of prime importance in the
destruction of the integrity and life of a germ by boiling
water. Without diffusion a germ may withstand tem-
peratures competent to utterly destroy it where diffusion is
free. I need not remark on the imperviousness of cheese
to water, and its consequent power to prevent diffusion.

These summer experiments on turnip-cheese infusions
were, however, merely tentative, and I purpose completing
them hereafter.

324 APPENDIX.

In the autumn I resumed experiments on infusions of
hay, which had been purposely postponed. With this sub-
stance no difficulty was encountered in my first inquiry.
Boiled for five minutes, and exposed to air purified spon-
taneously, or freed from its floating matter by calcination
or filtration, hay-infusion, though employed in multiplied
experiments at various times, never showed, the least
competence to kindle into life. After months of trans-
parency, in a great number of cases, I inoculated this
infusion with specks of animal and vegetable liquids con-
taining Bacteria, and observed, twenty-four hours after-
wards, its colour lightened and its mass rendered opaqne
by the multiplication of these organisms.

But in the antumn of 1876, the substance with which
I had experimented so easily and successfully a year pre-
viously appeared to have changed its nature. The in-
fusions extracted from it bore, in some cases, not only five
minutes’ brt fifteen minutes’ boiling with impunity. On
changing the hay a different result was often obtained.
Many of the infusions extracted from samples of hay pur-
chased in the antumn of 1876 behaved exactly like those
extracted from the hay of 1875, being completely sterilized
by five minutes’ boiling.

The possible influence of age and dryness soon sug-
gested itself, and I tested the surmise to the uttermost.
Numerous and laborious experiments were executed with
hay derived from different localities ; and by this means,
in the earlier days of the inquiry, it was revealed that the
infusions which manifested this previously unobserved
resistance to sterilization were, one and all, extracted from
old hay, while the readily sterilized infusions were
extracted from new hay, the germs adhering to which had
not been subjected to long-continued desiccation.

As the inquiry proceeded the distinction between old
and new hay became more and more blurred, while pro-
longed experiment with hay of various kinds failed to
rescue the question from uncertainty. I therefore turned
to substances of a succulent nature—to fungi, cucumber,

APPENDIX. 325

melon, beetroot and artichoke, for example, whose parasitic
or epiphytic germs were unlikely to have suffered desic-
cation.

Boiled for periods varying from five to fifteen minutes
and exposed afterwards to moteless air, in numberless
experiments these infusions broke down, charging them-
selves throughout with organisms, and loading themselves,
almost in all cases, with a soapy corrugated scum.

I then fell back upon infusions whose deportment had
been previously familiar to me, and in the sterilization of
which I had never experienced any difficulty. Fish, flesh,
and vegetables were re-subjected to trial. Though the pre-
cautions taken to avoid contamination were far more
stringent than those observed in my first inquiry, and
though the interval of boiling was sometimes tripled in
duration, these infusions, in almost every instance, broke
down. Spontaneously purified air, filtered air, and calcined
air (calcined, I may add, with far greater severity than
was found necessary a year previously) failed, in almost
all cases, to protect the infusions from putrefaction.

I was sometimes cheered by a success which, at the
time of its occurrence, would seem to be the result of
increased severity in the methods of experiment. But the
success was subsequently so opposed by failure that it
finally stood out rather as an accident than as the normal
result of the inquiry.

I bad the most implicit confidence in the correctness of
my earlier experiments ; indeed incorrectness would have
led to consequences exactly opposite to those arrived at.
Errors of manipulation would have filled my tubes and
flasks with organisms, instead of leaving them transparent
and void of life. By the unsuccessful experiments about
referred to a clear issue was therefore raised :—Hither
infusions of fish, flesh and vegetables had become endowed
in 1876 with an inherent generative energy which they did
not possess in 1875, or some new contagium external to the
infusions, and of a far more obstinate character than that
of 1875, had been brought to bear upon them at the later

326 APPENDIX.

date. The scientific mind will not halt in its decision
between these two alternatives.

For my own part the gradual but irresistible ix teraction
of thought and experiment made it in the first instance
probable, and at last certain, that the atmosphere in which
I worked had become so virulently infective as to render
utterly impotent precautions against contamination and
modes of sterilization which had been found uniformly
successful in a less contaminated air. I therefore removed
from the laboratory, first to the top, and afterwards to the
basement of the Royal Institution, but found that even
here, in a multitude of cases, failure was predominant, if
not uniform. This hard discipline of defeat was needed to
render me acquainted with all the possibilities of infection
involved in the construction of my chambers and the treat.
ment of my infusions.

I finally resolved to break away from the Royal
Institution, and to seek at a distance from ita less infec-
tive atrnosphere. In Kew Gardens, thanks to the President
of the Royal Society, the requisite conditions were found.
Ichose for exposure in the Jodrell laboratory the special in-
fusions which had proved most intractable in the laboratory
of the Royal Institution. The result was that liquids which
in Albemarle Street resisted two hundred minutes’ boiling,
becoming afterwards crowded with organisms, were utterly
sterilized by five minutes’ boiling at Kew.

A second clear issue is thus placed before the Royal
Society :—Either the infusions had lost in Kew Gardens
an inherent generative energy which they possessed in our
laboratory, or the remarkable instances of life-development,
after long-continued boiling, observed in the laboratory
are to be referred to the contagium contained in its vessels
or diffused in its air.

With a view to making nearer home experiments similar
to those executed at Kew, I had a shed erected on the roof
of the Royal Institution. In this shed infusions were
prepared and introduced into new chambers of burnished
tin, which had never been permitted to enter our labora-

APPENDIX. 327

tory. After their introduction the liquids were boiled for
five minutes in an oil-bath.

The first experiment in this shed resulted in complete
failure. Not one of the infusions exposed to the moteless
air of the shed escaped putrefaction.

Either of two causes, or both of them combined, might,
from my point of view, have produced this result. First,
a flue from the laboratory was in free communication with
the atmosphere not far from the shed; secondly, and this
was the real cause of the infection, my assistants, in pre-
paring the infusions, had freely passed from the laboratory
to the shed. They had thus incautiously carried the con-
tagium by a mode of transfer known to every physician.

The infected shed was disinfected; the infusions were
again prepared, and care was taken, by the use of proper
clothes, to avoid the former causes of contamination. The
result was similar to that obtained at Kew, viz. organic
liquids which, in the laboratory, withstood two hundred
minutes’ boiling, were rendered permanently barren by
five minutes’ boiling in the shed.

A third clear issue is thus placed before us which I
should hardly think of formulating were it not for the
incredible confusion which apparently besets this subject
in the public mind. A rod thirty feet in length would
stretch from the infusions in the shed to the same in-
fusions in the laboratory. At one end of this rod the
infusions were sterilized by five minutes’ boiling, at the
other end they withstood two hundred minutes’ boiling.
As before, the choice rests between two inferences :—
Either we infer that at one end of the rod animal and
vegetable infusions possess a generative power which at
the other end they do not possess, or we are driven to
the conclusion that at the one end of the rod we have
infective and at the other end uninfective air.

The second inference is that which will be accepted by
the scientific mind. To what, then, is the inferred differ.
ence at the two ends of the rod to be ascribed? In one
obvious particular the laboratory this year differed from

328 APPENDIX.

that in which my first experiments were made. On its
floor were various bundles of old and desiccated hay, from
which, when stirred, clouds of fine dust ascended into’ the
atmosphere. This dust proved to be both fruitful and, in
the highest degree, resistant. Prior to the introduction of
the hay which produced the dust, no difficulty as regards
sterilization had ever been experienced; subsequent to its
introduction my difficulties and defeats began.

I have twice glanced at periods of boiling amounting to
two hundred minutes ; for, after long and laborious trials of
shorter periods, I advanced to longer ones, subjecting turnip,
cucumber, and other infusions to the boiling temperature
for intervals varying from five minutes to three hundred
and sixty minutes. Up to a certain point these liquids
maintained their power of developing hfe, but beyond this
point complete sterility was the result. In the preliminary
experiments bearing upon this question the point of steriliza-
tion lay between 180 and 240 minutes. Boiled for the
former period the infusions continued fruitful; boiled for
the latter period they remained permanently barren.

In these and numerous other experiments a method was
followed which had been substantially employed by Spal-
lanzani and Needham, and more recently by Wyman and
Roberts, the method having been greatly refined by the
philosopher last named. The flasks were partially filled
with the infusions, the portions unoccupied by the liquids
being taken up with ordinary unfiltered air. Now as
regards the death-point of contagia we know that in air it
may be much higher than in water, the selfsame tempera-
ture being fatal in the latter and sensibly harmless in the
former; hence the doubt whether, in my recent experi-
ments, the resistance of the contagium did not arise from
the fact of its not being surrounded by liquid water.

I changed the method, and made a long series of ex-
periments with filtered air. They were almost as unsuc-
cessful as those made with ordinary air. From time to
time I succeeded in producing complete sterility by five
minutes’ boiling; but these successes were so checked by

APPENDIX. 329

failures that, similar to other cases referred to, they finally
appeared in the light of accidents. They were, however,
by no means uninstructive, for they revealed the existence
of breaks in the prevalence of the contagium, which, under
the circumstances, might have been foreseen.

A rapid glance at the means employed to improve the
methods of experiment, and at the results of their employ-
ment, may be permitted here. Bulbs, exhausted by an
air-pump and afterwards heated almost to redness, were
filled when cool with filtered air. While being charged
with the infusions the bulbs were warmed, so as to produce
a gentle outflow of air, and their necks were sealed while
the outflow continued. It was thus sought to avoid the
contamination consequent on an indraught.

The failures resulting from this mode of experiment
greatly predominated over the successes,

Employing similar bulbs, their necks in the first instance
were drawn out at the ends to tubes of capillary fineness.
The bulbs were then filled each with one-third of an atmo-
sphere of filtered air, and, while connected with the air-pump,
were heated almost to redness. The capillary tubes were
then sealed with the lamp. The sealed ends were afterwards
broken off in the body of the liquid, two-thirds of each bulb
being thus filled with the infusion. By great care it was
found possible to re-seal the capillary tubes without remov-
ing them from the liquid. The infusions were afterwards
boiled from five to fifteen minutes.

Here also the fruitfulness of the boiled infusion was
the rule, and its barrenness the exception.

A source of discomfort clung persistently to my mind
throughout these severer experiments. I was by no means
certain that the observed development of life was not due to
germs entangled in the film of liquid adherent to the necks
and higher interior surfaces of the bulbs. This film might
have evaporated, and its germs, surrounded by air and
vapour, instead of by water, might, on this account, have
been able to withstand an ordeal to which they would have
succumbed if submerged.

330 APPENDIX.

A plan was therefore resorted to, by which the infusions
were driven by atmospheric pressure through lateral chan-
nels issuing from the centres of the bulbs. As before, each
bulb was filled with one-third of an atmosphere of filtered
air, and afterwards heated nearly to redness. When fully
charged, the infusion rose higher than the central orifice,
and no portion of the internal surface was wetted save that
against which the liquid permanently rested. The lateral
channel was then closed with a lamp without an instant’s
contact being permitted to occur between any part of the
infusion and the external air. It was thus rendered ab-
solutely certain that the contagia exposed subsequently to
the action of heat were to be sought, neither in the super-
jacent air nor on the interior surfaces of the flasks, but in
the body of the infusions themselves.

By this method I tested in the first place the substance
which, at an early stage of the inquiry, had excited my
suspicion—without reference to which the discrepancy
between the behaviour of infusions examined in the winter
of 1875-76 and those examined in the winter of 1876-77 is
inexplicable, but by reference to which the explanation of
the observed discrepancy is complete ; I mean, the old hay
which cumbered our laboratory floor.

Four hours’ continuous boiling failed to sterilize bulbs
charged with infusions of this hay. In special cases, more-
over, germs were found so indurated and resistant that
five, six, and, in one case, even eight hours’ boiling failed to
deprive them of life.

All the difficulties encountered in this long and laborious
inquiry were traced to the germs which exhibited the ex-
traordinary powers of resistance here described. They
introduced a plague into our atmosphere—the other in-
fusions, those of fresh hay included, like a smitten popula-
tion, becoming the victims of a contagium foreign to
themselves.!

It is a question of obvious interest to the scientific

1 A hard and wiry hay from Guildford, which I have no reason
to consider old, was found extremely difficult to sterilize.

APPENDIX. 331

surgeon whether those powerfully resistant germs are
amenable to the ordinary processes of disinfection. It is
perfectly certain that they resist to an extraordinary extent
the action of heat. How would they behave in the wards
of an hospital? There are, morcover, establishments
devoted to the preserving of meats and vegetables. Do
they ever experience inexplicable reverses? I think it
certain that the mere shaking of a bunch of desiccated hay
in the air of an establishment of this character might render
the ordinary process of boiling for a few minutes utterly
nugatory, thus possibly entailing serious loss. They have,
as will subsequently appear, one great safeguard in the
complete purgation of their sealed tins of air.

Keeping these germs, and the phases through which
they pass to reach the developed organism, clearly in view,
I have been able to sterilize the most obstinate infusions
encountered in this inquiry, by heating them for a small
fraction of the timeabove referred to as insufficient to sterilize
them. The fully developed Bacterium is demonstrably
killed by a temperature of 140° F. Fixing the mind’s eye
upon the germ during its passage from the hard and
resistant to the plastic and sensitive state, it will appear in
the highest degree probable that the plastic stage will be
reached by different germs in different times. Some are
more indurated than others, and require a longer immersion
to soften and germinate. For all known germs there exists
a period of incubation, during which they prepare them-
selves for emergence as the finished organisms which have
been proved so sensitive to heat. If during this period,
and well within it, the infusion be boiled for even the fraction
of a minute, the softened germs which are then approach-
ing their phase of final development will be destroyed.
Repeating the process of heating every ten or twelve hours,
before the least sensible change has occurred in the in-
fusions, each successive heating will destroy the germs then
softened, until, after a sufficient number of heatings, the
last living germ will disappear.

332 APPENDIX,

Guided by the principle here laid down, and applying
the heat discontinuonsly, infusions have been sterilized by
an aggregate period of heating, which, fifty times multi-
plied, would fail to sterilize them if applied continuously.
Four minutes in the one case can accomplish what four
hours fail to accomplish in the other.

If properly followed out, the method of sterilization
here described is infallible. A temperature, moreover, far
below the boiling-point suffices for sterilization.

Another mode of sterilization, equally certain and re-
markable, was forced upon me, so to speak, in the following
way. In a multitude of cases a thick and folded layer of
fatty scum, made up of matted Bacteria, gathered upon the
surfaces of the infusions, the liquid underneath becoming
sometimes cloudy throughout, but frequently maintaining
a transparency equal to that of distilled water. The living
scum-layer, as Pasteur has shown in other cases, appeared
to possess the power of completely intercepting the atmo-
spheric oxygen, appropriating the gas and depriving the
germs in the liquid underneath of an element necessary to
their development.

Placing the infusions in flasks, with large air-spaces
above the liquids, corking the flasks, and exposing them
for a few days to a temperature of 80° or 90° F., at the end
of this time the oxygen of the superjacent air seems com-
pletely consumed. A lighted taper plunged into the flask
is immediately extinguished. Above the scum, moreover,
the interior surfaces of the bulbs used in my experiments
were commonly moistened by the water of condensation.
Into it the Bacteria sometimes rose, forming a kind of
gauzy film to a height of an inch or more above the liquid.
In fact, wherever air was to be found, these Bacteria fol-
lowed it. It seemed a necessity of their existence. Hence
the question, What will occur when the infusions are
deprived of air ?

I was by no means entitled to rest satisfied with
inference as an answer to this question ; for Pasteur has

APPENDIX. 333

abundantly demonstrated that the process of alcoholic fer-
mentation depends on the continuance of life without air—
other organisms than Torula being also alleged to be com-
petent to live without oxygen. Experiment alone could
determine the effect of exhaustion upon the particular
organisms here under review.

Air-pump vacua were first employed, and with a con-
siderable measure of success. Life was demonstrably
enfeebled in such vacua.

Sprengel pumps were afterwards used to remove more
effectually both the air dissolved in the infusions and that
diffused in the spaces above them. The periods of ex-
haustion varied from one to eight hours, and the results of
the experiments may be thus summed up :—Could the air
he completely removed from the infusions, there is every
reason to believe that sterilization without boiling would in
most, if not in all, cases be the result. But, passing from
probabilities to certainties, it is a proved fact that in
numerous cases unboiled infusions deprived of air by five
or six hours’ action of the Sprengel pump are reduced to
permanent barrenness. In a great number of cases, more-
over, where the unboiled infusion would have become
cloudy, exposure to the boiling temperature for a single
minute sufficed completely to destroy the life already on
the point of being extinguished through defect of air.
With a single exception, I am not sure that any infusion
escaped sterilization by five minutes’ boiling after it had
been deprived of air by the Sprengel pump. These five
minutes accomplished what five hours sometimes failed to
accomplish in the presence of air.

The exception here referred to is old-hay infusion,
which, though sterilized in less than half the time needed
to kill its germs where air is present, maintained a power
of developing a feeble but distinct life after having been
boiled for a large multiple of the time found sufficient to
render infusions of mutton, beef, pork, cucumber, turnip,
beetroot, shaddock, and artichoke permanently barren.

These experiments gave me the clue to many others

334 APPENDIX,

which might have readily become subjects of permanent
misinterpretation. In the midst of a most virulently in-
fective atmosphere, where, even after some hours’ boiling,
there was no escape for infusions supplied with air, the
expulsion of the air by less than five minutes’ boiling in
properly shaped retort-flasks, and the proper sealing of
the flasks during ebullition, insured the sterility of the
infusions. P

The meaning of a former remark regarding the part
played by boiling, in establishments devoted to the pre-
serving of meats and vegetables, will be now understood.

The inertness of the germs in liquids deprived of air is
not due to a mere suspension of their powers. The germs
are killed by being deprived of oxygen. For when the
air which has been removed by the Sprengel pump is, after
some time, carefully restored to the infusion, anaccom-
panied by germs from without, there is no revival of life.
By removing the air we stifle the life which the returning
air is incompetent to restore.

These experiments on the mortality arising from a
defect of oxygen are, in a certain sense, complementary to
the beautiful results of M. Paul Bert. Applying his
method to my infusions, I find them sterilized in oxygen
possessing a pressure of ten atmospheres or more. Like
higher organisms, our Bacterial germs are poisoned by the
excess and asphyxied by the defect of oxygen.

A few short sections on Bacteria germs as distinguished
from Bacteria themselves,! and on the alleged destruction
of germs by merely drying them, on hermetic sealing, and
on the deportment of hermetically-sealed flasks exposed to
the sun of the Alps, are introduced towards the end of
the memoir.

1 By the excellent researches of Dallinger and Drysdale it has
been proved that the germs of Monads, as compared with the adult
organisms, possess 2 power of resistance to heat in the proportion
of 11 to6.

APPENDIX. 835

NOTE ON THE DEPORTMENT OF ALKALIZED
URINE.!

THE communication ‘On the Influence of Liquor Potassz
and an Elevated Temperature on the Origin and Growth
of Microphytes,’ which, at Dr. Roberts’s request, I have
had the pleasure of presenting to the Royal Society, causes
me to say earlier than I should otherwise have done that
the subject which has occupied Dr. Roberts’s attention has
also occupied mine, and that my results are identical with
his.

In some of the experiments the procedure described by
Dr. Roberts was accurately pursued, save in one particular
which has reference to temperature. Small tubes with
their ends finely drawn out were charged with a definite
amount of caustic potash, and subjected for a quarter of
an hour to a temperature of 220° Fahr. They were then
introduced into flasks containing measured quantities of
urine. The urine being boiled for five minutes, the flasks
were hermetically sealed during ebullition. They were
subsequently permitted to remain in a warm place suffi-
ciently long to prove that the urine had been perfectly
sterilized by the boiling. The flasks were then rudely
shaken, so as to break the capillary ends of the potash-
tubes and permit the liquor potasse to mingle with the
acid liquid. The urine thus neutralized was subsequently
exposed to a constant temperature of 122° Fabr., which
is pronounced by Dr. Bastian to be specially potent as
regards the generation of organisms.

Ihave not found this to be the case; for ten flasks,

1 From the Proceedings of the Royal Society, No. 176, 1876,

836 APPENDIX,

prepared as above described towards the end of last
September, remained for more than two months perfectly
sterile. I have no doubt that they would have remained
so indefinitely.

Three retorts, moreover, similar to those employed by
Dr. Bastian, and provided with potash-tubes, had fresh
urine boiled in them on the 29th of September, the retorts
being sealed during ebullition. Several days subsequently,
the potash-tubes were broken and the urine neutralized.
Subjected for more than two months to a temperature of
122° Fahr. they failed to show any signs of life.

These results are quite in accordance with those ob-
tained by Dr. Roberts. His potash-tubes, however, were
exposed to a temperature of 280° Fahr., while mine were
subjected to a temperature of 220° only.

With regard to the raising of the potash to a tempera-
ture higher than that of boiling water, M. Pasteur is in
advance both of Dr. Roberts and myself. In a communi-
cation to the French Academy, on the 17th of last July,
M. Pasteur showed that when due care is taken to add
nothing but potash (heated to redness if solid, or to 110°
C. if liquid) to sterilized urine, no life is ever developed
as a consequence of the alkalization.'

M. Pasteur has quite recently favoured me with
sketches of the simple but effectual apparatus by means
of which he has tested the conclusions of Dr. Bastian.
Since his return from his vacation at Arbois, he has care-
fully gone over this ground with results, he reports to me,
not favourable to Dr. Bastian’s views.

I may add that I have by no means confined myself to
the thirteen samples of urine here referred to. The ex-
periments have already extended to one hundred and five
instances, not one of which shows the least countenance
to the doctrine of spontaneous generation.

1 That alkaline liquids are more difficult to sterilize than acid

ones was announced by Pasteur more than fourteen years ago. 8ee
« Annales de Chimie,’ 1862, vol. Ixiv. p. 62.

APPENDIX. 337

The method of ‘ Discontinuous Heating’ was first described
in the following letter to Professor Hualey.!

Royal Institution, Feb. 14, 1877.

My pear Hoxuey,—In my ‘Preliminary Note,’ communi-
cated to the Royal Society on the 18th of January, various
infusions were referred to as manifesting an astonishing
resistance to sterilization by heat. This resistance was
traced to its source ; and I have been since informed that
you were good enough to express at the time a very
favourable opinion as to the significance and value of the
results indicated.

Tt will, I think, now iaterest you to learn that the most
obstinate of the infusions referred to in the ‘ Note’ have
been since rendered tractable by the application of very
simple means. Following up the plain suggestions of
the germ theory, I have been able, even in the midst
of a virulently infective atmosphere, to sterilize all the
infusions by a temperature lower than that of boiling
water.

It is known that the prolonged application of a low
temperature is often equivalent to the brief application of
a higher one; and you may therefore be disposed to
conclude that in the experiments here referred to I have
substituted time for intensity. This, however, is not the
case. The result depends solely upon the manner in
which the heat is applied. For example, I boil an infusion
for fifteen minutes, expose it to a temperature of 90°
Fahr., and find it twenty-four hours afterwards swarm-
ing with life. I submit a second sample of the same
infusion to a temperature lower than that of boiling
water for five minutes, and it is rendered permanently
barren.

The secret of success here ig an open one. I have
already referred to the period of latency which precedes
the clouding of infusions with visible Bacteria. During

' From the Proceedings of the Royal Society, No. 178, 1877.

338 APPENDIX.

this period the germs are being prepared for their emer-
gence into the finished organism. They reach the end of
this period of preparation successively—the period of
latency of any germ depending upon its condition as
regards dryness and induration. This, then, is my mode
of proceeding :—Before the latent period of any of the
germs has been completed (say a few hours after the pre-
paration of the infusion), I subject it for a brief interval
to a temperature which may be under that of boiling
water. Such softened and vivified germs as are on the
point of passing into active life are thereby killed; others
not yet softened remain intact. I repeat this process well
within the interval necessary for the most advanced of
those others to finish their period of latency. The number
of undestroyed germs is further diminished by this second
heating. After a number of repetitions, which varies with
the character of the germs, the infusion, however obstinate,
is completely sterilized.

The periods of heating need not exceed a fraction of
a minute in doration. Sum them up in the case of an
infusion which they have perfectly sterilized ; they amount
altogether to, say, five minutes. Boil another sample of
the same infusion continuously for fifteen or even sixty
minutes, you fail to sterilize it, although the temperature
is higher and its time of application more than tenfold
that which, discontinuously applied, infallibly produces
barrenness.

In a few weeks I hope to bring this entire subject
under the notice of the Royal Society; meanwhile, if you
think it would interest them, I should be glad if you
would communicate to the Fellows this general statement
of the most recent results of experiment.

Believe me,
Ever faithfally yours,

Joun TYNDALL.
T. H. Huxley, Esq., Sec. B.S.

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With Illustrations and Colored Plates. 12mo. Cloth, $2.50.

Huxley and Youmans’s Elements of Physiology
and Hygiene. By T. H. Huxzey and W. J. Youmana
12mo. $1.50.

For gale by all booksellers; or sent by mail, post-paid, on receipt of

aa D. APPLETON & CO., Publishers,
1. 8, & & Bonp Srruxt, New York.

CHARLES DARWIN’S WORKS.

Origin of Species by Means of Natural Selection, or the
Preservation of Favored Races in the Struggle for
Life. New and revised edition, with Additions, 12mo. Cloth,
$2.00.

Descent of Man, and Selection in Relation to Sex. With
many Illustrations. A new edition. 12mo. Cloth, $3.00.

Journal of Researches into the Natural History and Geol
ogy of the Countries visited during the Voyage of H.
M.S. Beagle round the World. A new edition. 12mo.
Cloth, $2.00.

Emotional Expressions of Man and the Lower Animals.
12mo, Cloth, $3.50.

The Variations of Animals and Plants under Domesticas=
tion. With a Preface, by Professor Asa Gray. 2 vols. Iilua-
trated. Cloth, $5.00.

Insectivorous Plants. 12mo. Cloth, $2.00.

Movements and Habits of Climbing Plants. With Ilustra.
tions. 12mo. Cloth, $1.25.

The Various Contrivances by which Orchids are Fertile
ized by Insects. Revised edition, with Illustrations, 12mo.
Cloth, $1.75.

The Effects of Cross and Self Fertilization in the Vegetae
ble Kingdom. 12mo. Cloth, $2.00.

Different Forms of Flowers on Plants of the same Species.
With Illustrations. 12mo. Cloth, $1.50.

The Power of Movement in Plants. By Cartes Darwin,
LL. D., F.R.S., assisted by Francis Darwin. With Illustrations.
12mo. Cloth, $2.00.

The Formation of Vegetable Mould, through the Action

of Worms. With Observations on their Habits, With Mlustra-
tions. 12mo. Cloth, $1.50.

Yor sale by all booksellers; or sent by mail, post-patd, on receipt of price.

New York: D, APPLETON & CO., 1,3, & 5 Bond Street.

ESSAYS ON THE FLOATING MATTER
OF THE AIR,

IN RELATION TO PUTREFACTION AND INFECTION.

By Professor JOHN TYNDALL, F.R.S.
12mo. Cloth, $1.80.

“Tyndall has lately considered what he calls ‘the floating matter of the air,’ and
has given many experiments and observations of his own, as well as those of Pasteur
and others, in regard to the germ theory of decay and disease. The volume before us
does not come down later than the summer of 1881, but it indicates clearly enough the
course that modern science has taken in regard to fermentation. putrefaction, and
contagious or epidemic diseases. In brief, this course is toward the establishment of
a distinctly vegetable or animal origin for all the develop ts of fer ion, pu-
trefaction, and contagion—this origin being found in the bacillus, the bacterium, o
other microscopic creature which reproduces itself with surprising readiness in all
possible situations where it can appear. ‘Tyndall's great instrument of observation is
not the microscope--though he makes use of that—but a concentrated beam of light,
passing t'. ‘ugh the air, the chemical solution, the infusion of hay, turnip-seed, beef-
juice, or. ..er substance, with which he may may wish to experiment, and revealing
there, or failing to reveal, the obscure infusorial life which his researches involve. He
appears to demonstrate that ‘the individual particles of the finest floating matter of
the air lie beyond the present reach of the microscope,’ while, as he adds, the con-
centrated beam of light ‘reveals them collectively, long after the microscope has
ceased to distinguish them individually.” He thus has, as he believes, ‘virtually a
new instrument, exceeding the microscope indefinitely in power.’ This will not at
first be admitted, and has in fact been denied, but the demonstratton seems to be
with Tyndall. His book will at once command attention.”"—Springfield Republican.

“To the wide-awake, common mind, a strong ray of sunlight shining through a
key-hole into the quietest and cleanest room will reveal pretty much all needed evi-
dence that most ‘good air,’ like ‘pure water,’ is very much alive, and that a clean
vacuum is not to be found. Professor Tyndall's book is a calm, patient, clear, and
thorough treatment of all the questions and conditions of nature and society involved
in this theme. The work is lucid and convincing, yet not prolix or pedantic, but pop-
ular and really enjoyable. It is worthy of patient and renewed study.”"—Philadelphia
Times.

“The matter contained in this work is not only presented in a very interesting way,
but is of great value."—Boston Journal of Commerce.

“The germ theory of disease is most intelligently presented, and indeed the whol
work is instinct with a high intellect."— Boston Commonwealth.

“In the book before us we have the minute details of hundreds of observations on
infusions exposed to optically pure air; infusions of mutton, beef, haddock, hay, turnip,
liver, hare, rabbit, grouse, pheasant, salmon, cod, etc.; infusions heated by boiling
water and by boiling oil, sometimes for a few moments and sometimes for several
hours, and, however varied the mode of procedure, the result was invariably the same,
with not even a shade of uncertainty. The fallacy of spontaneous generation and
the probability of the germ theory of disease seem to us the inference, and the only
inference, that can be drawn from the results of nearly ten thousand experiments per-
formed by Professor Tyndall within the last two years."—Pittsburg Telegraph.

For sale by all booksellers; or sent by mail, post-paid, on receipt of price,

New York: D. APPLETON & CO., 1, 3, & 5 Bond Street.

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