B10LOSY

LIBRARY

G

LECTURES ON BACTERIA

DE BARY

HENRY FROWDE

OXFORD UNIVERSITY PRESS WAREHOUSE
AMEN CORNER, E.C.

LECTURES

ON

BACTERIA

BY

A. DE BARY

PROFESSOR IN THE UNIVERSITY OF STRASSBURG

SECOND IMPROVED EDITION

AUTHORISED TRANSLATION BY

HENRY E. F. GARNSEY, MA.

Fellow of Magdalen College, Oxford

REVISED BY

ISAAC BAYLEY BALFOUR, M.A., M.D., F.R.S.

Fellow of Magdalen College and She rardian Professor of Botany
in the University of Oxford

WITH 20 WOOD-ENGRAVINGS

AT THE CLARENDON PRESS

1887

[ All rights reserved ]

BIOLOSY

LIBRARY

G

PREFACE TO THE ENGLISH
EDITION.

THIS translation of Professor De Bary's ' Vorlesungen iiber
Bacterien' has been prepared because there is at present
no book in English which gives in like manner ' a general
view of the subject ' of Bacteria, and ' sets forth the known
facts in the life of Bacteria in their connection with those
with which we are acquainted in other branches of natural
history.'

I. B. B.

OXFORD, 1887.

AUTHOR'S PREFACE.

THE present work is in the main a short abridgement of a
number of lectures, some of which were delivered in a connected
series as a University course, others as occasional and separate
addresses. The form of the lectures has been occasionally
altered to meet the difference between a written treatise and free
oral delivery accompanied by demonstrations. Some things
have been omitted and others added, especially some matters of
general importance which were not published or did not become
known to me till after the delivery of the actual course.

The lectures were an attempt to introduce an audience com-
posed of persons of very different professional pursuits, medical
and non-medical, to an acquaintance with the present state of
knowledge and opinion concerning the much discussed questions
connected with Bacteria. They had, therefore, to give such a
survey of the subject as would be intelligible to all who were
not strangers to the elements of a scientific training, and
especially to set forth the known facts in the life of the
Bacteria in their connection with those with which we are
acquainted in other branches of natural history.

A survey of the present extensive literature of the subject,
and of the almost daily additions to it, shows the existence of
many serviceable and some excellent publications, but at the
same time also of much that is mistaken and obscure. The
scientific and semi-scientific converse of the day, if I may use

viii Preface.

the expression, is greatly influenced by works of the latter kind,
and the chief reason for this, if I am not mistaken, lies in the
absence of a general view of the subject itself and of its relations
to other portions of natural history; we cannot see the wood for
the trees. An attempt to give such a view would be no mere
superfluous addition to existing works, and this consideration
was a decisive reason in the judgment of myself and of those
who gave me their encouragement for afterwards transcribing
and publishing my lectures.

The present treatise, therefore, must not be expected to be
a Bacteriology, or even to report and enumerate all the details
which may be of interest and importance ; it should rather
serve only as a guide for the direction of the student through
these details.

Many readers, devoted to the study of the Bacteria, will be
familiar with the literature or with the guides to it before they
take up this book. For the sake of those who seek to gain
some knowledge of the subject from its perusal, and also for
the purpose of naming the most important sources of informa-
tion which I have made use of along with my own investigations.
I have added a few notices of publications at the end of the
volume, and have indicated by numerals in brackets the places
in the text to which the citation marked with the same number
refers.

So much by way of introduction to this little work. I trust
that it may do something to clear up existing views on the
subject of the Bacteria, and to lead the investigation of these
organisms from its present stage of storm and pressure into the
ways of quiet fruitful labour and increase of knowledge.

The above with the omission of one sentence is the word-
ing of the preface written in July, 1885, for the first edition of
this book. The kindly reception which it met with can only

Preface. ix

have been due to the circumstance that the form in which the
subject was presented in it was the one best adapted to attain
the object proposed ; it could scarcely be that there was any-
thing new in it. Hence the form and limits of the second
edition which is now demanded are alike prescribed to me ;
it must be made as like as possible to the first. This has been
done ; the original frame is unaltered, and the old matter still
appears in it in many places. On the other hand, much pro-
gress has been made in the period which has elapsed since the
work was originally composed, and some new views have been
laid down which could not be disregarded. The new edition,
therefore, will be found to contain not only some editorial
improvements in the special descriptions, but also various
important alterations.

These observations apply also to the notes at the end of the
work, except that I have introduced somewhat more critical and
explanatory remarks than in the first edition.

A. DE BARY.

STRASSBURG, Oct., 1886.

CONTENTS.

I. — Introduction. Bacteria or Schizomycetes and Fungi. Struc-
ture of the Bacterium-cell . . . : . . . i

II. — Cell-forms, cell-unions, and cell-groupings .... 9

III. — Course of development. Endosporous and Arthrosporous

Bacteria . . . ...'*. . . 15

IV, — Species of Bacteria. Distinct species denied. The grounds
for this denial insufficient. Method of investigation.
Relationships of the Bacteria and their position in the
system 24

V.— Origin and distribution of Bacteria . . . . . 37

VI. — Vegetative processes. External conditions : temperature and
material character of the environment. Practical ap-
plication of these in cultures, in disinfection, and in
antisepsis . . . . » . ' Y • Y . 49

VII. — Relation to and effect upon the substratum. Saprophytes
and Parasites. Saprophytes as exciting decompositions
and fermentations. Characteristic qualities of Forms
exciting fermentation . . . . . . . 64

VIII.— Most important examples of Saprophytes. The nomenclature
explained. Aquatic Saprophytes: Crenothrix, Cladothrix,
Beggiatoa; other aquatic forms . . -. . .-« . 72

IX. — Saprophytes which excite fermentation. Fermentations of
urea. Nitrification. Acetous fermentation. Viscous
fermentations. Formation of lactic acid. Kefir. Bacillus
Amylobacter. Decompositions of proteid. Bacterium
Termo 83

X.— Parasitic Bacteria. The phenomena of parasitism . . 107

xii Contents.

PAGE

XI. — Harmless parasites of warm-blooded animals. Parasites of
the intestinal canal. Sarcina. Leptothrix, Micrococci,
Spirillum, Comma-bacillus of the mucous membrane of
the mouth 115

XII. — Anthrax and Fowl- cholera 122

XIII — Causal connection of parasitic Bacteria with infectious
diseases, especially in warm-blooded animals.
Introduction . . . ' .

Relapsing fever

Tuberculosis

Gonorrhoea

Asiatic Cholera '.--.... . . ... \

Traumatic infectious diseases . .
Erysipelas . . f . ; . .

Trachoma and xerosis ; pneumonia, leprosy, syphilis,

cattle-plague . . . . . ,, .. . 169

Malaria . . . . . . . .170

Typhoid fever and diphtheria . . . ' " ' ". ' - . 171
Infectious diseases in which the presence of contagium

vivum has not been demonstrated . . . . 1 74

XIV. — Diseases caused by Bacteria in the lower animals and in
plants.

Diseases of insects . . . v ..." . _ ,' . 174

Diseases of plants . -. - , . ; ::. - . . 177

Conspectus of the Literature and Notes ..'.'.. . 181
Index of Names . « . . ... . . . 191

I.

Introduction. Bacteria or Schizomycetes and Fungi.
Structure of the Bacterium-cell (1).

THE purpose of these lectures is to give some account of the
present state of our knowledge respecting the objects included
under the name of Bacteria. It is unnecessary to enlarge upon
the manifold interest attaching to these organisms at a time when
the statement urged daily on the educated public does not fall far
short of saying, that a large part of all health and disease in the
world is dependent on Bacteria. If we are therefore spared that
customary portion of the introduction to a lecture which seeks
to impress the hearer with the importance of the subject, it be-
comes the more necessary to give prominence from the first to
the reverse side of the question ; that is to say, to call special
attention to the fact, that the problem presented to us can only
be solved by quiet scientific examination from every possible
point of view of the objects under consideration; and a study of
this kind is dry rather than exciting, or to use a common ex-
pression, interesting. But this should not deter any one who
is really desirous of acquiring some knowledge of our subject.

The order of our remarks will follow the natural arrangement
.of the subject before us; and our first task therefore will be to
''enquire what Bacteria are ; in other words, to make ourselves
acquainted with their conformation, their structure, their de-
velopment, and their origin in connection with their development.
Next, we have to enquire what they do, what good and what

2 Lectures on Bacteria. [§ i.

harm they occasion, that is, we must study their vital processes
and the effects which these produce on the objects outside of
themselves.

We begin with the first question, and we will first of all bestow
a moment's consideration on the name.

Bacteria, meaning rod-shaped animalcules or plantlets, from
the rod-like form which many of them exhibit, are also termed
Fission-fungi or Schizomycetes. The two expressions are not,
strictly speaking, of the same import.

The reason of this is that the word Fungi is used in two
senses. In the one it is the name for those lower flowerless
plants which are devoid of chlorophyll, the green colouring
matter of leaves, and hence exhibit certain definite peculi-
arities in the process of their nutrition. We shall speak of
these peculiarities at greater length in succeeding lectures;
at present we will only make the preliminary observation,
that all organisms devoid of chlorophyll require already formed
organic carbon-compounds for their nutrition, and cannot obtain
the necessary supplies of carbon from the carbon dioxide which
finds access to them. The construction of organic compounds
from this substance is bound up with the presence of chlorophyll
and analogous bodies.

Fungi in this sense are therefore a group characterised by
definite physiological peculiarities the mark of which is the
absence of chlorophyll, somewhat in the same way as birds and
bats may be grouped together under the head of winged
creatures.

In the other sense, that of descriptive taxonomic natural
history, the term Fungi denotes a group of lower plant-forms
distinguished by definite characteristics of structure and develop-
ment, and recognised at once when we see a mushroom or a
mould. The members of this group are all as a matter of fact
devoid of chlorophyll, but they might contain chlorophyll and
yet belong to this group, just as a bird may have no apparatus
for flight and yet be allowed to be a bird. To these Fungi, as

§ i.] Structure of the Bacterium-cell. 3

defined by natural history and not by physiological characters
only, Bacteria are as little related in structure and development
as bats are to birds ; the relationship is even less, because there
are a few, though only a few, true Bacteria which contain chlo-
rophyll and decompose carbon dioxide, and which are therefore
not Fungi in the physiological sense.

For these reasons we shall be more strictly correct if we
speak on the present occasion of Bacteria rather than of Fission-
fungi ; but so long as we are quite clear as to the difference in
the meaning of the two words, it is a matter of no importance
which we use.

The conformation, structure, and growth of Bacteria are
extremely simple, if we put out of sight certain phenomena of
propagation and consider only the vegetative state.

Bacteria appear in the form of round or cylindrical rod-shaped,
rarely fusiform, cells of very minute size. The diameter of the
round cells or the transverse section of the cylindrical cells is in
most cases about o'ooi mm. ( = i micromillimetre = i /z) or even
less. The length of the cylindrical cells is 2-4 times the trans-
verse section, rarely more. There are only a few forms with dis-
tinctly larger dimensions. Putting aside, for later consideration,
the forms from the group of Beggiatoa, Crenothrix and their
allies, which differ to some extent in this and other respects from
the rest of the Bacteria, the greatest breadth yet observed is 4 /a,
the measurement given by Van Tieghem for the rod-shaped
cells of Bacillus crassus.

We are obliged to apply the term cells to those minute bodies,
because they grow and divide like plant-cells, and also because
all that we know of their structure agrees with the corresponding
phenomena in plant-cells. It is true that their small size does
not permit of our going at present very deeply into the minutiae
of their structure. Cell-nuclei, for instance, have not yet been
observed in them ; but this is the case in many small cells of
other plants of a low order of growth, especially Fungi, and till
recent times it was the case with respect to all fungal cells.

B 2

4 Lectures on Bacteria. [$ i.

Perseverance and constantly improving methods of research
advance our knowledge as time goes on.

The Bacterium-cell is mainly composed of a portion of
protoplasm, which in the smaller and in most also of the
larger forms appears as an entirely homogeneous translucent
substance, but in some of the larger forms it is also often finely
granular or shows a different kind of structure, which will be
further described presently. It consists, as Nencki (2) has shown
in a number of cases, chiefly of peculiar albuminoid compounds
(mycoprotein, anthrax-protein) which vary with the species, and
its behaviour, when the usual empirical reagents are applied to it,
agrees in general with that of the protoplasmic bodies of other
organisms — the yellow and brownish-yellow coloration with
solutions of iodine, and the absorption of, that is to say, the
intense staining by, preparations of carmine and anilin dyes.
Yarious specific differences occur in individual cases in the
behaviour of the protoplasm to these colouring reagents, and
supply very useful marks of distinction in certain cases which
will be mentioned again on subsequent occasions.

We have already alluded to the fact that the protoplasm of
certain Bacteria described by Engelmann and van Tieghem,
for example, Bacillus virens, v. T., is coloured by chlorophyll,
being of a uniform pale leaf-green hue. In the very large
majority of cases it is colourless ; most Bacteria, not only when
isolated under the microscope but also when collected into
masses, have a pure or dirty-white colour, and in the latter case
show various shades of tint inclining to gray or yellow, &c.,
which the practised observer may even apply to the determina-
tion of species. On the other hand, there are not a few Bacteria
which exhibit lively colours when they are associated in masses,
yellow, red, green, violet, blue, brown, &c., according to the
individual. Schroter has collected together a number of such
cases. How far these colours belong to the protoplasm itself
or to its envelope, the cell-membrane, which will be described
presently, or to both, cannot in most cases be certainly ascer-

§ i.] Structure of the Bacterium-cell. 5

tained, because the individual cell is so small that it does not by
itself show any indications of colour. In some comparatively
large forms, those, for instance, grouped together by Zopf under
the name of Beggiatoa roseo-persicina, it can be seen that the
living protoplasmic body shares at least in the coloration, which
in this case is a bright red. Some of the colouring matters in
question have been submitted to closer examination and have
even received special names, as bacterio-purpurin, &c. In their
optical qualities they show various points of resemblance to
anilin dyes, as is indicated by the above name ; but we must
not infer from this that the chemical composition is analogous.

Among other phenomena of frequent recurrence in the
structure and contents of the protoplasm the starch-reaction
claims special attention. Bacillus Amylobacter and Spirillum
amyliferum, v. T., in certain stages of their development have
this peculiarity, that a portion of their protoplasm, distinguished
from the remainder by being somewhat more highly refringent,
when treated with watery solution of iodine assumes an indigo-
blue colour like starch-grains, or speaking more exactly like
the granulose which forms a large part of their substance. The
conditions under which this phenomenon makes its appearance
and again disappears will be discussed at greater length below.
E.Hansen'sMicrococcusPasteurianus also and usually Leptothrix
buccalis show the granulose-reaction. We may also mention in
this connection the occurrence of sulphur-granules in Beggiatoa,
referring the reader to Lecture VIII for further particulars.

The protoplasmic body of the Bacteria is surrounded by a
membrane or cell-wall. This membrane in one of the species
which have been examined, Sarcina ventriculi (see Lecture XI),
possesses, as far as is at present known, the qualities of typical
plant-cellulose-membrane; it is firm and thin, and assumes
the characteristic violet colour when treated with Schulze's
solution. But in the majority of cases there is no trace of the
characteristic coloration of cellulose. In single specimens
scattered about in a fluid the membrane appears under the

6 Lee hires on Bacteria. [§ i.

microscope as a delicate line drawn round the free surface, and
forming the boundary between contiguous cells. It may even be
seen distinct from the protoplasm in the larger forms by the aid
of reagents which strongly contract the protoplasm and colour it
at the same time without affecting the membrane, for instance
alcoholic solution of iodine (see Fig. i, p\ It is plainly
shown also in the formation of spores which will be described
in Lecture III. This membrane, which lies close upon
the protoplasm, is in certain forms at least, the species of
Beggiatoa and Spirochaete for example, highly extensible and
elastic, for it is seen to follow the curves often made by the
elongated organism, and the protoplasm can alone be the active
agent in producing these. But the membrane which thus directly
covers the protoplasm is certainly in all cases only the innermost
firmer layer of a gelatinous envelope surrounding the proto-
plasmic body. This may be seen directly in not a few forms
if observed attentively under the microscope, when the cells
or small aggregations of cells lie isolated in a fluid. Large
masses of Bacteria are always more or less gelatinous or slimy
when in a sufficiently moist condition. When the cells are
dividing, the outer layers of the membrane may sometimes be
seen to swell up in succession. Hence, speaking generally, we
may say that the cells of Bacteria have gelatinous membranes,
with a thin and comparatively firm inner layer. The consistence
of the mucilage and its capability of swelling in fluids differ
in different cases, changing gradually, but this point will be
considered again presently at greater length.

The possession of gelatinous membranes of this kind is com-
mon to the Bacteria and to various other organisms of the lower
sort, of which Nostocaceae and some Sprouting and Filamentous
Fungi may be quoted as examples. In Bacteria, as in the latter
plants, the gelatinous membrane has been shown in a number
of forms which have been examined to consist of a carbohydrate
closely related to cellulose ; this is specially the case in the Bac-
terium of mother of vinegar and in Leuconostoc, the frog-spawn-

§ i.] Stricture of the Bacterium-cell. 7

bacterium of sugar factories. On the other hand, Nencki found
that the membranes of certain putrefactive Bacteria not distinctly
determined are in a great measure composed, like the proto-
plasm which they enclose, of the mycoprotein mentioned on
page 4. Lastly, a statement of Neisser (65) must also be men-
tioned in this place ; he suspects, from the behaviour of the
membrane or envelope of the Bacterium of xerosis conjunctiva
in the presence of reagents, that it contains a considerable amount
of fatty matter. Further investigation into these points is at all
events desirable. The membranes of Cladothrix and Crenothrix
which live in water are often coloured brown by the introduc-
tion of compounds of iron.

Many Bacteria are capable of free movement in fluids. They
rotate about their longitudinal axis, or they oscillate like a
pendulum and move rapidly forwards or backwards. Search
has consequently been made for organs of motion, and these
are supposed to have been found in certain very slender filiform
appendages, cilia or flagella, which are attached singly or in
pairs to the extremities of rod-shaped Bacteria. Such cilia are
present in many relatively large cells not belonging to the Bacteria,
and endowed like them with the power of free movement in fluids,
the swarm-cells, for example, and swarm-spores of many Algae
and some Fungi. In these cases the cilia oscillate rapidly as
long as the movement continues, causing rotation round the
longitudinal axis, and may consequently be considered to be
the active organs of motion. In the swarm-cells of the Algae
they are processes, projections as it were, from the surface of
the protoplasmic body, and belong therefore to the protoplasm.
When the protoplasm is surrounded by a membrane, the cilia
pass out through openings in the membrane. But no such
characteristic structural conditions have been observed in the
Bacteria. Delicate thread-like processes have certainly been
observed occasionally at the points above-mentioned in coloured
specimens which have been exposed to desiccation. That they
are really there and not, or at least not always, in the imagina-

8 Lectures on Bacteria. [§ i.

tion of the observer only, is proved by the fact that they
appear in photographs. But in an overwhelming majority of
cases no cilia can be seen, though the Bacteria are capable of
independent movement and are examined with the best optical
aids after being killed and coloured. Where they are found,
they are as van Tieghem rightly says, not processes of the
protoplasmic body, but belong to the membrane, as is shown
by their behaviour with reagents, and must therefore be con-
sidered to be thread-like extensions of the soft gelatinous
membrane-layers. They have accordingly nothing in common
with the cilia of swarm-spores of the Algae, and cannot therefore
be regarded as organs of motion, since it was only from the
analogy of the cilia in the Algae that this function was inferred.
Such is the state of the case at least in the great majority of
species. Whether there are any exceptional cases must be deter-
mined by further investigation. It should be added, that among
lower organisms there are some comparatively large forms,
the Oscillatorieae, for example, the near relatives according to
our present knowledge of the Bacteria — a point to be further
considered below — which show similar movements, though no
cilia or other distinct organs of motion have been observed in
them. It follows that analogy does not require the discovery
of cilia in the Bacteria.

Vegetating Bacterium-cells multiply by successive division,
each cell forming two daughter-cells. When a cell has reached
a certain size, a fine transverse line makes its appearance in it,
dividing the cell into two equal parts. This line is subse-
quently shown by its gelatinous swelling to be the commence-
ment of a cell-membrane. This agrees with the phenomena
observed in the divisions of larger plant-cells, and there is
nothing to prevent our assuming that the details of the process
of division, which the minuteness of the object makes it impos-
sible to observe directly, are the same in both cases.

It must be acknowledged that the transverse wall which
appears as the cell divides is often so delicate as easily

§ ii.] Cell-forms. 9

to escape observation, and becomes visible only under the influ-
ence of reagents which give a deep colour to the protoplasm
and make it shrink, especially alcoholic solution of iodine.
This must not be forgotten in determining the length of cells.

The successive bipartitions are either all in the same direction,
and the transverse walls are therefore parallel ; or more rarely
the walls lie in two or three directions in space, so that they
successively cut one another, and may actually cross at a right
angle.

II.

Cell-forms, cell-unions, and cell-groupings.

SINGLE Bacterium-cells, the simple structure of which has been
considered in the preceding chapter, may appear in very various
forms, the variety depending partly on their own shape and on
that of their simplest aggregations, partly on whether they are
united into larger aggregations or not, and on the peculiar
characters of these aggregations.

i. The shape of the individual cells and their simplest
genetic combinations give rise to the distinction into round-
celled, and straight or spirally twisted rod-like forms. A billiard-
ball, a lead pencil, and a cork-screw, so exactly illustrate these
three chief forms, that no one requires for his instruction in
this case the costly models which are offered for sale. The
figures on subsequent pages, which will be examined more
closely in later lectures, will for the present give a sufficiently
clear idea of the matter.

These forms have received a variety of names in the course
of the development of our knowledge. The round forms are
at present most commonly known as Cocci (Figs. 3, 4), and are
spoken of as Micrococci or Macrococci according to their size,
or as Diplococci when they still remain united in pairs after a
bipartition ; earlier writers called them monads, a name which
they applied to a variety of heterogeneous objects.

io Lectures on Bacteria. -[$ IT.

The straight rod-forms (Figs, i, 2) have received the special
name of rods, Bacteria, from the earlier writers. Short or long
rods and other terms are obvious designations for subordinate
peculiarities of shape, but have no other value.

The screw or cork-screw forms are termed Spirilla, Spiro-
chaetae. Those which are only slightly curved, that is, which
form a portion only of a turn of the screw, being intermediate
between the two preceding categories, have been called by Cohn
Vibriones in accordance with the nomenclature of older authors.
It is well that we should understand clearly that these and other
names, which will be mentioned presently, are only used to define
the shapes of the organisms. It would indeed be better to give
them proper names expressive of their outward appearance,
and to use terms like sphere, screw ; and it is to be hoped
too that the jargon which prevails at present, especially
in medical literature, will gradually be replaced by a rational
terminology.

The cocci and rod-forms are sometimes liable to a peculiar
deviation from their ordinary shape ; single cells, lying between
other cells which remain true to one of the typical forms
described above, swell into broadly fusiform or spherical or oval
vesicles several times larger than the typical cells. This has been
observed in species of Bacillus, Cladothrix, &c., and with special
frequency in the Micrococcus of mother of vinegar. There is
some ground for assuming, though further proof is required,
that these swollen forms are the products of diseased develop-
ment, indications of retrogression and involution, and they were
therefore termed by Nageli and Buchner involution-forms (see
Fig. io).

2. According to the nature of the union or want of union of
the cells, we must first of all distinguish between the forms in
which genetic union and arrangement is maintained after succes-
sive bipartitions, and those in which it is severed or displaced.

When the cells continue united together in the connected
sequence of the divisions we have —

§ IL] Cell-unions, Cell-groupings. 1 1

a. The cells arranged in rows in the direction of the succes-
sive divisions. From their thread-like form these cell-rows
(Fig. 2, &c.) are termed filaments in accordance with the
traditional terminology; a strange confusion of ideas led to
their being also called pseudo-filaments, objects which look like,
but are not real, filaments.

It is obvious after the foregoing remarks, first, that these
filaments must be of different shape according as the individual
cells are round or of some other form ; secondly, that the
length of the filaments, measured by the number of cells, may
be very various. It may be said specially of the rod-like and
spiral forms, that the cells usually remain united into short
rows in such a manner that the rod or spiral is actually
composed of more than one cell, and then after a definite
increase of the entire length and of the number of the segment-
cells is divided into two at the oldest points of division. The
words Leptothrix, Mycothrix, and others designate the longer
filamentous forms.

b. Cells united together and arranged genetically in a simple
surface, or as a body of three dimensions, are of less frequent
occurrence, as has been already said ; Zopf s Bacterium meris-
mopoedioides may be given as an example of the former kind,
of the latter the cube-shaped cell-packets of Sarcina ventriculi
(see Fig. 14).

By the side of these phenomena of genetic union and variously
combined with them appears a series of groupings, as they may
be briefly termed, which owe their character to a great extent to
the mass, cohesion, and other specific qualities of the gelatinous
membranes as these are formed, and next and in combination
with these, to their own very various specific peculiarities, which
cannot, as a rule, be shortly defined ; some explanation of the
latter, though unfortunately only an imperfect one, will be given
further on when we are considering vital processes. The nature
also, and especially the state of aggregation of the substratum,
may in certain circumstances have an influence on the grouping.

12 Lectures on Bacteria. [§ n.

Thinness of the gelatinous membranes and a high degree of
capacity for swelling reaching to deliquescence will cause the
separation of cells or of the simplest cell-unions from one
another when growing in a fluid. Thick cell-membranes, and
a narrowly limited capacity for swelling in the gelatinous sub-
stance, will keep the cells united together in compact gelatinous
masses in the same fluid. These, which are the extreme con-
ditions, are actually found in nature, and all kinds of intermediate
states also occur. The firmer gelatinous masses (see Fig. 3)
are called by the old name Palmella, or by the more recent
name now commonly used, Zoogloea. The less sharply denned
Zoogloeae, as they may be shortly described, may naturally be
termed swarms. It depends on their specific gravity whether a
Zoogloea or a swarm will float on the surface or sink to the
bottom of the same fluid, while their general outline and the
grouping of the separate aggregates which compose them will
be fashioned in accordance with their further specific qualities.

To illustrate this point in passing by a few examples, —
let us take three flasks containing a similar 8-10 per cent,
solution of grape-sugar and extract of meat in water. In one
flask the fluid is pretty uniformly clouded with the short motile
rods of Bacillus Amylobacter. In the second the surface of
the slightly clouded fluid is covered with a thick wrinkled scum,
dry on the upper surface, which is formed by Bacillus subtilis,
the so-called hay-bacillus. In the third the filaments of Bacillus
Anthracis, the Bacillus of anthrax which in other respects re-
sembles B. subtilis, form a flocculent deposit at the bottom of
the clear fluid. We can scarcely call this deposit by the name
of Zoogloea, we may perhaps call it a swarm. The hay-
bacillus-scum is properly a Zoogloea with a special characteristic
form. Formations more or less like it are found often enough
in fluids containing decomposable organic bodies. Highly
characteristic Zoogloeae developed in a fluid are the frog-spawn-
Bacterium of sugar-factories and the Bacterium of kefir. The
former is a round-celled organism, Leuconostoc, with a thick

§ ii.] Cell-groupings. 1 3

compact gelatinous envelope which may fill entire vats with a
substance looking like frogs' spawn, and which will be con-
sidered again in a later lecture ; the term kefir-grains is applied
to the bodies employed by the inhabitants of the Caucasus in
the preparation from milk of a sourish beverage rich in car-
bonic acid. The kefir-grains are in the fresh living state white
bodies, usually of irregularly roundish form, equal to or ex-
ceeding a walnut in size. They have their surface crisped with
blunt projections and furrowed like a cauliflower ; they are of a
firm toughly gelatinous consistence, becoming cartilaginous,
brittle, and of a yellow colour when dried, and are chiefly com-
posed of a rod-shaped Bacterium. The small rods are for the
most part united together into filaments, which are closely
interwoven in countless zig-zags and firmly connected together
by their tough gelatinous membranes. It must also be observed,
that the Bacterium-filaments are not the only constituents of the
granules ; numerous groups of a Sprouting Fungus like the
yeast-fungus of beer are enclosed between them, especially in
the periphery, living and growing in common with the Bacterium,
but in much smaller quantity, and taking only a passive part in
the formation of Zoogloeae.

If Bacteria grow not in fluids but on some solid substance
which is only wet or moist, the grouping into Zoogloeae is a
frequent phenomenon even in those forms which separate
from one another in larger amounts of fluid owing to the
deliquescence of their gelatinous envelopes. The more limited
supply of water on the merely damp substratum is not
sufficient to make this gelatinous substance swell up to the
point of deliquescence. On decaying potatoes, turnips, and
similar substances we may often see small lumps of gelatinous
matter of a white or yellowish tint or of some other shade of
colour, and composed of these aggregations of Bacteria. These
lumps deliquesce in water. We have a special instance of the
kind in the often-described occurrence of the blood-portent,
Micrococcus prodigiosus (Monas prodigiosa of Ehrenberg), pro-

14 Lectures on Bacteria. [§ n.

ducing on substances rich in starch, such as dressed potatoes,
bread, rice, or wafers, moist blood-red spots which sometimes
spread rapidly and widely. Their colour has given rise to a
variety of superstitious notions when they have appeared
unexpectedly on objects of household use. They consist of
one of the chromogenous Bacteria which have been already
mentioned.

It was stated above that the grouping of different forms is
different in the same fluid, and in like manner the conformation
of the Zoogloeae on solid substances shows manifold variation
of forms which differ in other respects also.

These various facts connected with the grouping are them-
selves calculated to afford very valuable marks for character-
ising and distinguishing forms, the more valuable indeed in
proportion to the difficulty oftentimes of discriminating in-
dividual cells of such minute size under the microscope. It is
precisely in the phenomena of grouping that specific peculiarities
of conformation best display themselves, being collected together,
as it were, in larger quantity; these characters must indeed
be present in the single cell, but, with the means at present
at our disposal, it is difficult or even impossible to recognise
them there. But there is nothing peculiar in this. There
are many cells of gigantic size in comparison with the Bacteria
and highly differentiated, of which we cannot say with cer-
tainty when we see them by themselves whether they belong
to a lily or a tulip. But in their natural connection or grouping
some of them form a lily, others a tulip, and by this we know
that they are different.

§ in.] Endosporous Bacteria. 1 5

III.

Course of development. Endosporous and Arthro-
sporous Bacteria.

THE different conformations and groupings described in the
preceding lectures indicate primarily nothing more than de-
finite forms of one phenomenon marked in each case by a
distinct name, such as present themselves at any moment of
observation, and without reference to their origin or future
destination. They are forms of the vegetative development,
growth-forms as they may be shortly termed, and correspond
to those which in the higher plants are designated by the words
tree, shrub, bulbous plant, and the like. Forms which are
determined only by their conformation correspond indeed only
to separate members of a particular growth, such as woody
stem, tendril, tuber, bulb, &c.

If we wish to know the significance of a tendril or a bulb in
the chain of phenomena, or indeed that of any other form of
living creature, we must answer the above questions of its
origin and destination, or, to use the customary form of words,
we must learn the course of its development. For every form
of living being taken at any one moment of time, though it
may be present in millions of specimens, is only a member of a
chain of periodic movements which coincide with a regular
alternation of forms. If therefore we wish for a more intimate
acquaintance with Bacteria, we must proceed to enquire into
their course of development.

As far as our present knowledge goes, this development is
not quite the same in all cases. We must distinguish two
groups, one of which contains the Endosporous, the other the
Arthrosporous Bacteria.

The former group consists of a number of straight rod-
forms which will here receive the special name of Bacillus, and
a few screw-twisted Spirilla. The phenomena, so far as they

16

Lectures on Bacteria.

[$

are known, are essentially the same in both, and they have now
to be described in detail in the case of Bacillus. See Fig. i.

The Bacilli in the highest state of vegetative development are
rod-shaped or shortly cylindrical cells with the characters already
described, which either remain isolated or are united together into
unicellular rods or longer filaments ; they are motile or motion-
less, and display active growth and division (Fig. i, a—c],
Both growth and division at length come to an end, and then
begins the formation of peculiar organs of reproduction — spores.
This process begins at the point to which it has been followed
furthest back with the appearance of a comparatively very minute
point-like granule in the protoplasm of a hitherto vegetative
cell. This granule increases in volume and soon presents the

appearance of an elon-
gated or round, highly
refringent, sharply-defined
body, which attains its
ultimate size rapidly, some-
times in a few hours, and
is then the mature spore
(Fig. i, d-f}. The spore
always remains smaller
than its mother-cell, the
protoplasm and other con-
tents of which disappear
with the growth of the
spore, being doubtless
consumed for its benefit, until at length the spore is seen sus-
pended in a pellucid substance inside the delicate membrane
of the mother-cell (Fig. i, r, h^.

Fig. i. Bacillus Megaterium. a outline sketch of a chain of rods in
active vegetation and motion, b pair of rods in active vegetation and
motion, p a 4-celled rod in this stage after treatment with alcoholic solution
of iodine, c 5-celled rod in the first stage of preparation for forming spores.
d-f successive states of a spore-forming pair of rods, d about 2 o'clock

fin.] Endosporous Bacteria. 17

The details of these processes disclose sundry variations of
diagnostic value, especially in connection with the shape. In
Bacillus Megaterium, B. Anthracis, B. subtilis, for example, the
sporogenous cell does not differ in shape from the vegetative
cell, but in the two latter the mature spore is much shorter ; in
B. Anthracis it is slightly narrower, in B. subtilis often rather
broader than the mother-cell, in B. Megaterium it is a little
shorter but much narrower than the comparatively short
mother-cell (cf. Figs, i and 2).

In other species the spores are much smaller in every
direction than the mother- cell, and the latter is distinguished
from the cylindrical vegetative cell before or during the form-
ation of the spore by swelling into a permanent fusiform or
ovoid shape, either over the entire area of the cell or at the spot
where the spore lies, and which is then usually at one ex-
tremity of the cell. In the latter case, and also when cells that
are still cylindrical are attached on one side to a mother-cell
which has swollen up all over, the forms are produced which
were once known as capitate Bacteria, cylindrical Bacteria
with a capitate sporogenous swelling at the extremity. Ex-
amples of this kind are Bacillus Amylobacter (Fig. 13), B.
Ulna, and some others.

In Bacillus Amylobacter and Spirillum amyliferum, v. Tiegh.,
the appearance of the spore is preceded by the formation of
granulose described above, and the spot where the spore

p.m., e about one hour later, /one hour later than e. The spores in /were
mature by evening ; no others were formed ; the one apparently commenced
in the third upper cell of d and e disappeared ; the cells in / which did
not contain spores were dead by 9 p.m. r a four-celled rod with ripe
spores, g-1 five-celled rod with three ri;e spores placed in a nutrient
solution after drying for several days, at 12.30 p.m.; gz the same speci-
men about 1.30 p.m. ; g* about 4 p.m. h^ two dried spores with the mem-
brane of the mother-cell placed in a nutrient solution, about 11.45 a.m.;
hz the same specimen about 12.30 p.m. i, k, I later stages of germination
explained in the text on p. 2 1 . m rod dividing transversely, grown from a
spore placed eight hours before in a nutrient solution, a magnified 250
times ; the other figures 600 times.

C

1 8 Lectures on Bacteria. [$ in.

begins to be formed is marked by the absence of granulose.
This spot looks in solution of iodine like a notch of a pale
yellowish colour, occupying one extremity of the rod which
elsewhere tends to be blue, and is moreover distinguished by
its lower power of refraction even before the use of a reagent.
As the spore grows in size the granulose disappears. Accord-
ing to Prazmowski the granulose is not always present before
the formation of the spore, even in Bacillus Amylobacter. In
other Bacilli, the three, for example, just previously named, it
has never been observed ; their protoplasm either remains un-
changed before spore-formation, or at most becomes a little
less transparent and in larger forms more evidently finely
granular.

A mother-cell, so far as can be positively stated, never pro-
duces more than a single spore. This can be determined with
certainty in almost all cases, and the few accounts which have
been given of the formation of two spores in a single cell are
doubtful, being unaccompanied by any guarantee that the
boundaries of adjoining cells have not been overlooked or
errors of other kinds admitted. I must, however, add that an
exception to the prevailing rule has recently come under my
own observation in the case of a species nearly allied to Bacillus
Amylobacter (see Lecture IX), which usually follows the rule,
but does also sometimes contain two spores in a cell which has
swollen and become broadly fusiform. I have not yet succeeded
in observing the further development of the twin spores.

In cultures formation of spores usually takes place when
other growth comes to an end because the substratum is no
longer adapted to maintain it, being either exhausted, as we
are in the habit of saying, or impregnated with the products
of decomposition which are unfavourable to vegetative develop-
ment. Formation of spores then spreads rapidly through the
larger number of the cells and through the special aggregations,
if the particular form is present in abundance. Some of these
it is true do not produce spores, in some the process begins

$ in.] Endosporous Bacteria. 19

but is not completed. All cells which do not take part in
the normal formation of spores ultimately die and are de-
composed, if they are not transferred in good time to a fresh
substratum.

In other Bacilli, as B. Amylobacter, the procedure is dif-
ferent. Here spore-formation begins in single cells and spreads
by degrees to more and more of them, while a number of other
cells continue to vegetate and divide. We cannot therefore
regard the unsuitableness of the substratum to the vegetative
process as the cause which generally determines the formation
of spores.

By spores are usually meant such cells as are delimited
from a plant to develope again under favourable conditions
into a new vegetating plant. The commencement of this
latter process is termed germination. The bodies to which we
have here given the name of spores are so called because their
behaviour corresponds to that of germinating spores. As soon
as they are fully grown, that is, as soon as they are ripe, the
membrane of the mother-cell dissolves gradually or swells, and
the spores are thus set at liberty, retaining the characters
which have been already described; that is, they are round,
ovoid, or rod-shaped, according to the species, rarely of some
other shape, with a dark outline and usually colourless, but
with a peculiar bluish glistening appearance ; according to Cohn
the spore of Bacillus erythrosporus is tinged with red. Round
the dark outline may often be perceived a very pale and
evidently soft gelatinous envelope, which either covers the
spore uniformly all round, or is thicker at the two extremities
and drawn out into processes.

Germination shows that the spore is a cell surrounded by a
thin but very firm membrane, defined by the dark outline inside
the gelatinous envelope. Germination begins when the ripe
spore is subjected to the conditions favourable to the vege-
tation of the species, supply of water, suitable nutriment, and
favourable temperature. As it begins the spore loses its high

c 2

20

Lectures on Bacteria.

[f "I.

©

Vi

l?

refringent power, its lustre and dark outline ; it assumes the ap-
pearance of a vegetative cell, and grows at the same time to the
size and shape of the vegetative cell from
which it sprang. With the completion
of this process movement begins in the
motile species, and this is followed by
the growth, division, and grouping which
have been described above as occur-
ring in the vegetative stages, and which
at length come to an end with a fresh
formation of spores. In many cases
a few hours only intervene between the
first observable commencement of ger-
mination and active vegetative growth.
See above, Fig. i, h-m.

With the first increase in size a mem-
brane is often seen to split and rise from
off the surface of the growing cell, being
evidently lifted from off it by a swelling
gelatinous outer layer surrounding the new
membrane of the cell. The rent through
the membrane is in the direction of
the length, or across the middle, accord-
ing to the species. The former is the
case according to Prazmowski in Bacillus Amylobacter, and it
occurs also in other species. The latter has been observed in

Fig. 2. A Bacillus Anthracis. Two filaments partly in an advanced
stage of spore- formation ; above them two ripe spores escaped from the
cells. From a culture on a microscope-slide in a solution of meat-extract.
The spores are drawn a little too narrow ; they are nearly as broad as the
breadth of the mother-cell. B Bacillus subtilis. I fragments of filaments
with ripe spores. 2 commencement of germination of spore ; the outer wall
torn transversely. 3 young rod projecting from the spore in the usual
transverse position. 4 germ-rods bent into the shape of a horse-shoe, one
afterwards with one extremity released. 5 germ-rods already grown to a
considerable size but with both extremities still fixed in the spore-membrane.
All magnified 600 times.

Fig. 2.

$in.] Endosporous Bacteria. 21

B. Megaterium (Fig. i) and B. subtilis (Fig. 2, B)] the trans-
verse rent either extends quite across, so that half the membrane
is placed like a cap on each extremity of the cell, or the halves
remain attached on one side, so that the growing cell must
emerge from a gaping cleft (Fig. i , h-f). The ruptured mem-
brane is usually delicate and pale. In B. subtilis only it retains
at first the lustre and dark outline of the spore before ger-
mination, and hence it is probable that these phenomena have
their origin in the membrane. Sooner or later the membrane
thus torn from the cell swells and disappears. It may be owing
to the very early period at which the swelling sets in that
sometimes, as, for example, in B. Megaterium and B. Amylo-
bacter, the removal of the membrane is not perceptible in one
germinating spore, while it is clearly seen in others, and that in
other species, as in B. Anthracis, no removal of the membrane
takes place at all.

The longitudinal growth of the first cell in germination has
always the same direction in space as the longitudinal axis of the
spore or spore-mother-cell. This is the case also in Bacillus
subtilis, which appears at first sight to behave differently in this
respect. In this species the first rod-shaped germ-cell usually
emerges from the open transverse rent in the spore-membrane
in such a manner that its longitudinal axis crosses that of the
spore at a right angle, but this is not caused by a corresponding
divergence of the longitudinal growth, but by the circumstance
that when the germ-cell has attained a certain length it bends
through about 90°, and thus projects on one side at a right
angle from the rent in the membrane. The bending of the
germ-cell is evidently caused by the resistance offered to the
elongation of the cell by the spore-membrane, which in this
species is highly elastic and is always ruptured on one side.
When growth is very rapid the two extremities of the young
rod may remain fixed in the membrane, and in that case the
middle portion projects in a curve from the aperture. It is not
till a later period, when the rods have begun to divide and

22 Lectures on Bacteria. [§ in.

separate into daughter-rods, that the latter straighten themselves
out.

Endogenous spore-formation, as it has now been described,
that is, formation of spores taking place inside the previously
vegetative cell, sharply distinguishes the endosporous forms from
the rest of the Bacteria, which we have termed arthrosporous.
The name is intended to indicate the fact, that in these forms
members of an aggregation or of a series of united generations
of vegetative cells separating from the rest assume the character
of spores immediately without previous endogenous rejuvenes-
cence, that is, they may become the origins of new vegetative
generations. In a number of the forms comprised in this divi-
sion, a more or less distinct morphological difference may be
observed between vegetative cells and spores; in others, as
far as we know at present, no such distinction is to be found.

Simple examples of the former kind are supplied by Leuco-
nostoc mentioned above and by Bacterium Zopfii, Kurth. The
former (Fig. 3) consists, according to van Tieghem's descrip-
tion, of curved bead-like rows of small round cells with firm
gelatinous coats united together in large numbers into Zoogloeae
(Fig. 3, a, b}. A large portion of the cells dies at the end of the
vegetative period when the nutrient substratum is exhausted. On
the other hand single cells irregularly distributed in the rows
become somewhat larger than the rest, acquire a more distinct
outline, that is, become thicker-walled, and their protoplasm
grows darker (Fig. 3, c). They at length become free by the
deliquescence of the gelatinous envelopes, and may claim the
name of spores, because when placed in a fresh nutrient solution
they develope into new rows of beads like those of the mother-
plant (Fig. 3, d-h).

Bacterium Zopfii was originally found by Kurth in the intes-
tinal canal of fowls, and then cultivated partly in gelatine partly
in suitable watery solutions. In the fresh substratum the Bac-
terium vegetates at first in the rod-form. In the gelatine the
rods continue united together into large filaments often twisted

1 III.]

A rthrosporous Bacteria.

into a coil ; in the fluid short and motionless filaments are
formed only at a temperature of more than 35° C. ; at 20° C. the
filaments separate into motile rods. At the close of their vege-
tation when the substratum is exhausted, the rods fall asunder

Fig. 3-

into short roundish cells, and these again may be termed spores
since in a fresh substratum they develope into new rods or
filaments.

Though their course of development is more complex yet the
phenomena observed in Crenothrix, Cladothrix, and Beggiatoa,
if ZopPs description is correct, closely resemble those just de-
scribed. They will be noticed again below in Lecture VIII.

Fig. 3. Leuconostoc mesenterioides, Cienkowski. a sketch of a Zoogloea.
b section through a full-grown Zoogloea just before the commencement of
spore-formation, c filaments with spores from an older specimen.
d isolated ripe spores, e-i successive products of germination of spores
sown in a nutrient solution ; sequence of development according to the
letters. In e the two lower specimens show the fragments of the ruptured
spore-membrane on the outer surface of the gelatinous envelope indicated by
dark strokes, i portion of a gelatinous body from h broken up into short
members, which have been separated from one another by pressure. After van
Tieghem (Ann. d. sc. nat. ser. 6, vii). a natural size, b-i magn. 520 times.

24 Lectures on Bacteria. [$ iv.

Examples of the other and simpler kind of arthrosporous forms
are to be found, according to our present knowledge, in the
forms described under the name of Micrococcus
(Fig. 4). Each vegetative cell may at any moment
begin to form a new series of vegetative cells ; there
is no distinction between specifically reproductive
F'1S- 4- and vegetative cells.

The entire distinction between endosporous and arthro-
sporous Bacteria is required by the present state of our know-
ledge. It remains to be seen whether and to what extent it will
be maintained. Our knowledge is at present still so incomplete
that we must on the one hand regard the discovery of endo-
genous formation of spores as possible or probable in forms
where they are hitherto unknown, even in the simplest Micro-
cocci, and I say this to prevent all misunderstanding; and on
the other hand we cannot say that facts will not come to light
in course of time which will do away with any sharp separation
between the two divisions.

IV.

Species of Bacteria. Distinct species denied. The
grounds for this denial insufficient. Method of in-
vestigation. Relationships of the Bacteria and their
position in the system.

HAVING now made ourselves acquainted with the course of
development in Bacteria in its main features, we proceed to
consider the much-debated question whether there are specifi-
cally distinct forms, species of Bacteria, as these terms
are used in descriptive natural history, and how many such
species can be determined. Species are determined by the
course of development. By the term species we mean the sum

Fig. 4. Micrococcus Ureae, Cohn, from putrifying urine. Single cells
and cells united in rows (= Streptococcus). Magn. noo times.

5 iv.] The question of species. 25

total of the separate individuals and generations which, during
the time afforded for observation, exhibit the same periodically
repeated course of development within certain empirically deter-
mined limits of variation. We judge of the course of develop-
ment by the forms which make their appearance in it one after
another. These are the marks by which we recognise and dis-
tinguish species. In the higher plants and animals we are
in the habit of taking the marks chiefly from a single section of
the development, namely, from the one in which they are most
distinctly shown. We distinguish birds better by their feathers
than, for instance, by their eggs. This abbreviated method of
distinguishing is convenient, wherever one section of the de-
velopment is so pregnant as to make the consideration of the
rest unnecessary. But this is not always the case. The simpler
the forms of an organism are, the larger must be the portions
of development requisite for characterising and distinguishing it,
and the demand is still greater when we have to compare the
entire course of the development of the species, to use the same
figure, from the ovum of the first to the ovum of the next gene-
ration. We are pleased if we succeed in this way in finding any
single mark to serve our purpose, but we must not be too con-
fident of finding one.

Experience has taught us that different species may behave
very differently in respect of the forms which make their appear-
ance successively in their course of development. In some the
same forms constantly recur one after another with comparatively
small individual variations. These may be termed monomorphic
species. Most of the common higher plants and animals are
examples of this, and also many of the lower and simpler kinds.
They can be readily distinguished after a little experience even
by single portions from the general development. We can re-
cognise a horse-chestnut, for example, by each individual leaf
plucked from the tree.

Other species are pleomorphic and may appear in very
unlike forms even in the same segments of the development,

26 Lectures on Bacteria. [§ iv.

partly from the effect of external causes which are known and
may be varied at pleasure in our experiments, partly from
internal causes which cannot at present be analysed. The
white mulberry-tree, for example, in contrast to the horse-
chestnut just mentioned produces foliage-leaves very unlike each
other and with no certain rule of succession, some simply cor-
date, others deeply notched and lobed. We should not recog-
nise the species by a leaf of the latter kind, if we had before
only happened to have seen the cordate leaves. This occurs
frequently and to a still greater extent in the lower plants,
though they need by no means belong, like the Bacteria, to the
simplest and smallest forms. Many of the larger Fungi, for ex-
ample, the forms of Mucor,and green Algae, such as Hydrodictyon
and the remarkably pleomorphous Botrydium granulatum, exhibit
phenomena of this kind in a very striking manner, especially
when it further happens, as it often does happen in similar
plants, that the successive members of the development do
not continue in prolonged connection with each other, like the
leaves of the mulberry, but separate and vegetate apart from
one another. In this case if we happen to find the objects
separate and alone, and are accustomed from our experience
of the chestnut always to judge of a species by the individual
form, we fall into mistakes such as the history of botanical study
can supply in great abundance. But if we observe how each
form developes and how it originated, we perceive that they
have all the same course, the same origin, and the same return
to similar beginnings, or as we may say, conclusions of the
development.

The pleomorphous species therefore differ from the relatively
monomorphous species only in the greater number of forms
and in the greater amount of differentiation in the course of
development; the qualities of the species are apportioned in
equal measure in the one as in the other.

As regards then the species of Bacteria two views have been
promulgated, which in their extreme form differ much from one

$ iv.] The question of species. 2 7

another. According to the one view their case is the same as
that of all organisms other than Bacteria, that is, of all other
plants and animals ; like these they are distinguished into
species. This was accepted as a matter of course by the earlier
observers from the first discovery of the Bacteria by Leeuwen-
hoek (3), to the more careful and extended observations of these
organisms which was undertaken by Ferdinand Cohn (4) at the
beginning of the period from 1860 to 1870. Cohn, following
in the steps of his predecessors, especially Ehrenberg (5), en-
deavoured to give a general view and classification of the forms
which had become known to himself and others. It was im-
portant to arrange the material in hand and waiting further ela-
boration in some provisional manner, and to do this it was
either allowable or necessary to start from the assumption,
which certainly required to be proved, that a species was always
characterised by a definite form, as is the case with the above-
mentioned comparatively monomorphous kinds. The species
were therefore distinguished by their shape and growth-form, with
some help from their effects on the substratum, and then further
classified. The names Coccus, Spirillum, Spirochaete, &c., applied
above to growth-forms corresponding to such terms as tree and
shrub, were used as names for definite natural genera like birch,
chestnut, &c. ; such genera we may accordingly therefore term
form-genera. Whether these form-genera and form-species did
or did not really coincide in all points with natural genera and
real natural species, was expressly left undecided by Cohn and
reserved for further investigation.

Cohn's view as expressed in his provisional classification was
opposed by other writers, who went so far as to deny that there
were any species of Bacteria. They considered that the ob-
served forms proceeded alternately from one another, the one
being convertible into the other with a change in the conditions
of life, and that this change might be accompanied by a corre-
sponding change in the effects on the substratum, though this
point does not, strictly speaking, belong to the subject which we

28 Lectures on Bacteria. [$ iv.

are considering. Full expression was given to this view by
Billroth (6) in 1874 in a lengthy publication, in which he includes
all the forms which he had examined, and they were many and
various, in one species which he names Coccobacteria septica.
N'ageli (7) and his school have supported the same views since
1877. Nageli indeed expresses his opinion on the one hand
with circumspection and reserve, saying that he finds no necessity
for separating the thousands of Bacterium-forms which have come
under his observation even into two species, but that it would be
rash to speak decidedly on a subject that is so imperfectly ex-
plored. On the other hand he goes so far as to say : If my view
is correct, the same species in the course of generations assumes
a variety of morphologically and physiologically dissimilar forms
one after another, which in the course of years and decades
of years at one time turn milk sour, at another give rise to
butyric acid in sauerkraut, or to ropiness in wine, or to putrefac-
tion in albumen, or decompose urine, or impart a red stain to
food-material containing starch, or produce typhus, relapsing
fever, cholera, or malarial fever.

In presence of this statement of opinion our practical interests
require that we should obtain a decided answer to the question
of species which we are here considering, for it certainly is not
a matter of indifference in medical practice, for example,
whether a Bacterium which is everywhere present in sour milk
or in other objects of food, but without being injurious to health,
is capable or not of being changed at any moment into a form
which produces typhus or cholera. The scientific interest cer-
tainly demands that the question should be set at rest.

It may safely be maintained that continued investigation has
at length arrived at a decision and it is this, that there is no
difference as regards the existence of species and their deter-
mination between this and any other portion of the domain of
Natural History.

Species may be distinguished provided we follow the course
of development with sufficient attention. Some which are

$ iv.] The question of species. 29

familiar to us through the researches of Brefeld, van Tieghem,
Koch, and Prazmowski are comparatively monomorphous ; they
make their appearance in the vegetative segments of their de-
velopment as a rule in the same forms as regards their shape,
growth and grouping. Others show a greater amount of
variation in these respects; they display the phenomena of
pleomorphy in varying degrees. Among the endosporous
Bacilli described above Bacillus Megaterium is a particularly
good example of monomorphy. A motile rod is developed from
the spore and gives rise as it grows to successive similar gene-
rations of rods, until these at length proceed to the formation of
fresh spores (Fig. i).

Bacillus subtilis when growing normally in a fluid differs to
some extent from B. Megaterium; successive generations of
rods moving about in the fluid proceed from the germinating
spores, but the later generations which proceed from them re-
main united into long filaments and are without motion, being
grouped together and forming on the surface the Zoogloea-
membrane mentioned on page 12. In this state they then form
fresh spores. Here therefore we have a small amount of
pleomorphy, two, or reckoning the spores, three distinct forms,
and in a sequence also which is regularly repeated from one
spore-generation to another. Moreover the special conditions
of shape and size always remain the same within certain limits
of variation, for variations in the direction indicated certainly
occur in this case as they do everywhere in the organic world.
Stunted forms may also be met with. I have for instance re-
peatedly observed some of the rods in a group of Bacillus
Megaterium, in circumstances unfavourable to its nutrition, sepa-
rate into its cells which were themselves already short, and these
cells round themselves off and in this way represent what may
be termed Cocci. Other unusual forms also made their appear-
ance with the Cocci. There was scarcely any or no formation
of spores. Under improved food-conditions these stunted forms
reverted to the normal state.

30 Lectures on Bacteria. [^ iv.

The arthrosporous species, Crenothrix and Beggiatoa, which
have been mentioned above, are particularly striking examples
of pleomorphous species, if the accounts of them which we
possess are correct (see Lecture VIII). But it is in these very
forms that the course of development, as we have already pointed
out, has not been so completely followed out and so clearly ex-
plained as to exclude the possibility, that the apparently irregular
pleomorphism is due in these cases to the admixture sometimes
of several less pleomorphous species. And even if we accept very
extreme statements with regard to Bacteria, it is nevertheless
true that the most pleomorphous Bacteria show a very high
degree of uniformity when compared with the lower plants
mentioned on page 26, such as Botrydium, Hydrodictyon, and
many others.

Any one not familiar with the subjects and investigations in
question will be inclined to ask how there can be such a pro-
found difference of opinion as that between the negation and
affirmation of the existence of species in Bacteria. The answer
is, that the difference has its origin in the differences and to
some extent in the mistakes in the method of investigation. I
do not use the word method here in the customary sense of
manual skill and practical contrivances in investigation, but to
express the course of procedure in examining and judging of
the observed phenomena.

Species, as is acknowledged and as has been already pointed
out above, can only be determined and recognised in and
through the course of development, and this consists in the suc-
cessive development of forms, one from another. The forms
which appear later in the series proceed from the earlier forms,
as parts of them, and are therefore at every moment in un-
broken continuity with them, even when subsequently separated
from them. The proof that they all belong to one and the
same course of development can only therefore be established
by proving this continuity. The attempt to establish it in any
other way, for example, by ever so careful observation of the

$ iv.] The qitestion of species. 3 1

forms which make their appearance one after another at the
same spot, or by the construction of a hypothetical series of de-
velopments by the most exact and ingenious comparison of
these forms, involves a logical fallacy. We distinguish, for in-
stance, a species of wheat by its seed, its stem and leaves, its
flowers and fruits, and we know that these proceed alternately
from one another ; but the latter fact we know only by ob-
serving that the one of these members arises as part of one of
the others, and by observing also how this happens. This is
the only reason why we consider the grain of wheat to belong
to the wheat-plant, whether it is attached to it or has fallen to
the ground or lies thrashed out on the floor of the granary.
That the stem with the leaves belongs to the grain we know by
observing its origin as part of the grain, not because we have
seen wheat-plants growing where wheat was sown ; weeds may
grow at the same spot along with the wheat.

This mode of viewing the matter sounds trivial ; its truth will
seem obvious to every one, and rightly so ; and yet it cannot be
too often repeated, for the logic which it is intended to illustrate
is being constantly disregarded, and a mass of confusion has
been the result of this neglect. This may be shown by means
of the very example which we have chosen, for less than fifty
years ago it was maintained that all sorts of weeds were pro-
duced from the seed of the wheat-plant, and people (8) in other
respects well-educated and intelligent believed that this was
possible, because these weeds sprang up in the spots where
wheat had been sown. But whoever examines at the right place
finds that either wheat or nothing grows from the wheat-grain,
that the weed springs only from the seed of the species of
weed which may happen to be present, and that where
the weed grows up instead of or with the wheat, its seed has
found its way by some means to the place where the wheat
was sown.

Notions and mistakes like these in the case of the wheat-
plant have appeared again and again in connection with smaller

32 Lectures on Bacteria. [$ iv.

organisms, such as Algae and Fungi, both those of the larger
kinds and the microscopically minute. The separate species
were imperfectly known, and different ones were brought into
genetic connection with one another, because observation of
continuity was omitted or imperfectly made, and in its place was
substituted the observation of the succession in time of forms
at the same spot, or the comparison of them as they made their
appearance there together.

The smaller and simpler the forms, the greater certainly is
the difficulty of satisfying our logical demand, and the greater
the attention which must be paid to it. In small forms consist-
ing of isolated cells of no very marked shape, such as some of
the lower Fungi and the Bacteria, we must observe carefully
whether the sowing contains the germs of a single species or of
several mixed together. The latter is very frequently the case,
as experience shows. Various species often occur together and
mixed with one another at the spots from which the material
for the observation was obtained ; during the investigation forms
not desired, ' unbidden guests/ may find their way with par-
ticles of dust into the material, and even when we are dealing
with apparently quite pure material, a small quantity of micro-
scopic weeds, as we may say in this case also, may be mingled
with it.

If every thing in the mixture grows at an equal rate, the
different species may be kept distinct with comparative ease, and
the character of the mixture is clearly understood. But the state
of things may be different from this, and experience shows that
it often is different. The one species develops vigorously under
the existing conditions, the other feebly or not at all ; the more
successful species gains the upper hand of the less successful,
dispossessing it and even entirely destroying it. Further ex-
amination shows that in some cases a weed has grown up in
place of the wheat. This may very easily happen. We shall
see further on that some Bacteria, for example, double the num-
ber of their cells under favourable conditions in less than an

$ iv.] The question of species. 33

hour. Those to which the conditions are unfavourable may be
seen, if a single specimen is watched continuously, to be dis-
solved and to disappear entirely in a few hours. By the com-
bination of phenomena of this kind the character of any given
mixture may be totally changed in a short space of time.

It is obvious that difficulties such as these do not invalidate
our postulate, but on the contrary bring it out into sharper
relief. Those who altogether deny the existence of species in
Bacteria, with Billroth and Nageli at their head, have in fact
never undertaken a direct observation of continuity of develop-
ment, and they are therefore not justified in denying their exist-
ence. Billroth has accurately examined and compared the
forms, but has never continuously followed and checked the
changes in a preparation or culture ; the observation has been
interrupted by intervals of sufficient length to allow of various
things happening unobserved. Nageli, as far as can be gathered
from his publications, has not closely examined the forms at all,
but grounds his conclusions, even when they are morphological,
on non-morphological observations with respect to phenomena
of decomposition on the great scale. One instance of this mode
of dealing with the subject may be mentioned. Nageli remarks
that milk which has not been boiled turns sour when left standing
for a time, but that boiled milk becomes bitter (9). He admits
that the sourness is due to the presence of a Bacterium. He
considers the bitterness to be the result of a change in the
action of the same Bacterium caused by the boiling — a ' trans-
formation of the definite ferment-nature of a single Fungus into
a ferment of another kind.' Here it is assumed that a single
Bacterium-species is present in the unboiled milk ; the question
is not asked whether there may not perhaps be several species in
it, some of which predominate before, the others after the boil-
ing, and whether the different changes in the milk may not be
thus explained. But Hueppe's more recent researches have
shown that such is really the true state of the case (10). Of the
various Bacteria-forms present in the unboiled milk, Micrococcus

34 Lectures on Bacteria. [$ iv.

lacticus is at first most active at a low temperature, and turns the
milk sour by the formation of lactic acid ; it is killed by boiling,
but the spores of Bacillus Amylobacter, the Bacillus of butyric
acid, which is also present in the milk retain their vitality, and
this Bacillus causes the decompositions in boiled milk which
give it a bitter taste.

Another instance of the same kind is the statement ema-
nating from Nageli's laboratory, that the hay-bacillus, Bacillus
subtilis, is identical with Bacillus Anthracis, the Bacillus of
anthrax. The two species are very like each other, and Buch-
ner's observations certainly contain some true remarks about
them, which will be discussed in Lecture XII. But the most
striking characteristic of B. subtilis is the often-described ger-
mination of its spores, the growing out of the germ-cell from
the transverse fissure of the spore-membrane at right angles to
the longitudinal axis of the spore. The Bacillus of anthrax
does not exhibit this phenomenon, as Buchner himself tells us.
But due regard has nowhere been paid to these differences, so
that it is still doubtful whether Buchner has examined B. subtilis
at all. In this case too the morphological statement is without
certain foundation and justification.

The increased attention bestowed by observers on this subject,
beginning with the wheat-plant and going down through various
larger forms of the lower plants to Bacteria, has done away
one after another with the erroneous notions indicated, and led
to the general adoption of the view above explained, that ques-
tions of species are essentially alike throughout the series of
organisms. In the case of the Bacteria much still remains to
be done ; our knowledge of these is yet only in its infancy.

I say that increased attention is leading to this result. I
should wish at the same time to point out once more the con-
ditions which have been and which are of the first importance.
As might be expected, the aids to investigation, apparatus, tech-
nical methods, reagents, &c., have been improved. To deter-
mine the questions which we are at present considering, minute

$ iv.] The question of species. 35

organisms have to be isolated and unceasingly watched in order
to see what proceeds from the single individual, if it developes.
This end can only be obtained by means of cultures which can
be followed with exactness under the microscope. A spore or
rod in the preparation must be permanently fixed under the
microscope, and the phenomena of its growth must be observed
without interruption. This is done by help of the moist
chamber, a contrivance in which the microscopic object pro-
tected from desiccation can be observed continuously under con-
ditions favourable to vegetation. There are several varieties of
apparatus of this description, which have their advantages and
disadvantages according to the special case and also to the
habits of the observer, but we must not enter into a detailed
description of them here.

Fluids are usually employed as the medium in which the ob-
ject is placed for microscopic observation and for culture, on
account of their transparency. Living and especially moving
objects readily change their position in a fluid and become
mixed together. A method which greatly assists the fixing of
an object where continuity of observation is required, consists in
the use of a transparent medium which allows of the conditions
necessary to vegetation, and is soft but not fluid, so that dis-
placement of the objects and disturbance of the observation are
more or less perfectly avoided. Such media are gelatine and
similar substances, especially the gelatinous substance known
in commerce as agar-agar and prepared from sea-weeds of
the Indian and Chinese seas. Gelatine, as I understand, was
first employed by Vittadini in 1852 in the culture of micro-
scopic Fungi (11), and has been frequently used since that time,
especially by Brefeld. Klebs more recently in 1873 (12) re-
commends it specially for the cultivation of Bacteria ; cultures
of these organisms have been conducted in recent times in a
gelatinous substratum, especially by Koch.

Having thus glanced at the morphology and the history of the
development of Bacteria, we have still to enquire what is their

D 2

36 Lectures on Bacteria. [§ iv.

position in the organic world and their natural affinity to other orga-
nisms. The question is of only secondary interest to us on the
present occasion, and must not therefore be examined at any length.

If we compare the structure and development of Bacteria with
those of other known creatures, as we must do to answer the
above question, the arthrosporous Bacteria are seen to agree
entirely in all essential points with the members of the plant-
group of Nostocaceae in the wider sense of the word ; only
the Nostocaceae are furnished with chlorophyll in conjunction
with another blue or violet colouring matter which is soluble
in water, and are thus distinguished from the Bacteria which
contain no chlorophyll. There is no reason why the arthro-
sporous Bacteria should not be termed Nostocaceae which
are devoid of chlorophyll. Structure, growth, occasional for-
mation of Zoogloeae, more or less constant motility, especially
developed in the Oscillatorieae, a division of the Nostoca-
ceae, are the same in the two groups, so that apart from the
absence of chlorophyll there is no greater difference between
them than between the separate species of either of the groups.
This may be illustrated by the case of Leuconostoc described
on page 22. The name indicates that the plant entirely re-
sembles in all respects the bluish-green species of the genus
Nostoc which live in water and on moist soil, only it is colour-
less and white. To this may be added, that most of the
Nostocaceae attain to considerably larger dimensions than the
Bacteria in their cells and in the aggregations of their cells, and
that the members of the group which resemble the Bacteria are
related to other forms of a more varied and higher differentia-
tion and conformation.

The Bacteria which we have distinguished as endosporous
entirely resemble the arthrosporous Bacteria in every respect ex-
cept the peculiar formation of spores, and resemble no other
known organisms. We must therefore place them next to the
arthrosporous division, at least for the present and in accord-
ance with our present knowledge.

$ v.] Origin and distribution. 37

Hence the Bacteria have been arranged in one group with
the Nostocaceae, and this group has received the name of
Fission-plants or Schizophytes ; the Nostocaceae which contain
chlorophyll are Fission-algae, those which have no chlorophyll
are Fission-fungi.

The entire group of the Schizophytes is somewhat isolated in
the general system ; a closer association with other groups can-
not be established at present, and it would lead us too far away
from our more immediate subject to enter further into the con-
jectures which may be formed about them. So much however
is beyond doubt, that most Schizophytes, the Nostocaceae
especially, have all the characteristics of simple plants. They
show a very slight approximation to the Fungi, in the sense in
which that term is used in the natural system, as has been
already stated in the Introduction. We can only say therefore
that the Bacteria, together with the rest of the Schizophytes, are
a group of simple plants of a low order.

The old observers regarded them as belonging to the animal
kingdom and to the group of Infusorial Animalcules, chiefly on
the ground of their motility and in the absence of the basis re-
quired for a more exact comparison. At present there is no
reason for separating them from the vegetable kingdom, though
it is merely a matter of convention in the case of these simple
organisms where and how we should draw the line between the
vegetable and animal kingdoms.

V.

Origin and distribution of Bacteria.

WE commenced our survey of the mode of life of the Bacteria
by explaining in what manner and from whence they make their
way to the spots where we find them.

If we adhere to the general result of the foregoing con-
siderations, namely, that Bacteria are like other vegetable growths,

38 Lectures on Bacteria. [§ v.

we may at once assume that their origin is the same as that
of other plants, that is, that the Bacteria existing at any given
time have sprung from beginnings which proceeded from in-
dividuals of the same species, and experience shows that this
is really the case. These beginnings may be spores or any
other cells capable of life; we shall here usually call them
germs.

The germs of living beings, especially plants, are extra-
ordinarily numerous. They may be said to cover the surface
of the earth and the bottom of the waters with an infinite
profusion of mingled forms. The number of plants observed
in the developed state gives no idea or only a very imperfect
idea of this fact, because a much larger number of germs is in
all cases produced from a single plant than can arrive at their
full development in the space at their command, which is in
fact always limited. The smaller the organisms are, the greater
advantages they enjoy as a general rule caeteris paribus for the
production and distribution of their germs, for it is so much
easier for them to find space and a sufficient quantity of food for
their development and for the production of new germs; the
mechanical conditions for the transport of the germs from place
to place are also more favourable in proportion as the volume
and mass are diminished. For these reasons the number and
distribution of the germs of lower microscopic organisms, espe-
cially in the vegetable world, must seem astonishingly great to
any one who is unprepared for the facts. If spring-water is
allowed to stand in a glass, it becomes green in time from the
growth of small Algae, whose germs were present in the water
before it was placed in the glass or have been carried there with
particles of dust. If a small piece of moistened bread is placed
in the water a growth of mould soon makes its appearance, pro-
ceeding from germs of Mould-fungi. Some time since I made
researches with a different object into the Saprolegnieae, a
group of rather large Fungi consisting of about two dozen
well-known species, which grow in water on the bodies of

$ v.] Origin and distribution. 39

dead animals, and it was found that germs of one or several
species of this single group were present in every handful of
mud from the bottom of every sheet of water from the sea-level
to a height of 2000 metres. The actual presence of the germs
may be shown in all these cases by microscopic and experi-
mental examination, to the conduct of which we will recur
presently.

As these facts again would lead us to expect, among micro-
scopic growths some are rare and some are common, some
have a limited and some a very extensive area of distribution.
The principle must be the same with these as with the higher
and larger organisms ; climatic and other external causes must
have a similar effect on the distribution, though for the reason
stated above that effect is generally less powerful than in larger
and more pretentious forms. The researches into this subject
are not yet extensive enough to permit of the production of
many details. But we know, for example, that a small Fungus,
scarcely visible to the naked eye, Laboulbenia Muscae, which
vegetates on the surface of the bodies of living house-flies in
Vienna, and which appears to be common in southern Europe,
does not occur in the middle and west of Europe ; at all events
after careful search it has not yet been found. Instances
of the reverse kind are more numerous. Our common species
of moulds, Penicillium glaucum, for example, and Eurotium,
are spread over all parts of the world and all climates, and the
same is the case with other small Fungi and Algae.

In this point also Bacteria are only special instances of the
series of phenomena which have been shown above to occur
as a rule in small organisms. Our knowledge of the several
species, as appears from preceding lectures, is too imperfect to
enable us to make precise statements with respect to the larger
number of them ; at the same time we know that some species
are comparatively rare, such as Micrococcus prodigiosus and
Bacillus Megaterium, while others, like B. subtilis, B. Amy-
lobacter, and Micrococcus Ureae, occur in almost every situation

4O Lectures on Bacteria. [§ v.

in which they find the conditions of vegetation, which are them-
selves of very common occurrence. We shall make acquaint-
ance with other illustrative instances in subsequent special
discussions. Dispensing with an exact determination of the
species in every case, we shall be perfectly safe in declaring,
as the result of direct observations, that the vital germs of
Bacteria are scattered abroad with such profusion in earth, air,
dust, and water, that their appearance at all spots where they
find the conditions* necessary for vegetation is more than
sufficiently explained.

The way to prove this, and at the same time to determine
approximatively the number of germs within a given space, is ob-
viously the same in the case of the germs of Bacteria as in that
of other lower organisms, Fungi and others; both necessarily
come under our observation at the same time, when they are
present. It consists first of all and simply in microscopical
examination. But in this method we encounter considerable
difficulties. Sometimes the germs are not present in every
smallest spot ; they must be sought for, and this is at all times a
troublesome process, especially when it is intended to count them.
Various devices may it is true be applied to lighten this labour.
Pasteur (13), for example, employed an ingenious contrivance
for finding germs in the air in the form of a suction-apparatus,
an aspirator, which drew in the air through a tube stopped with
a dense plug of gun-cotton. The plug allows the air to pass,
while the solid substances in suspension in the air and the
germs therefore with them are caught on or in the plug. The
quantity of air passing through the apparatus within a given
time can be easily determined. The gun-cotton is soluble in
ether, and by taking advantage of this property the germs which
have been intercepted in the plug may be obtained suspended
in a clear solution, and collected within a narrow space for ex-
amination and even for counting.

But in this process the germs are very liable to be killed by
the ether, and even in ordinary microscopical examination it is

$ v.] Origin and distribution. 41

impossible to be quite certain whether we are dealing with dead
or with living objects. Yet it is a matter of the first importance
to determine whether germs capable of development are present
or not, and this would require further and very complex modes
of procedure.

Hence various other methods have been tried with the object
of making the investigation easier and more trustworthy in both
directions. It was Koch who at length cracked the egg, like
Columbus. Starting from the empirical fact that gelatine, com-
bined with other nutrient substances easily prepared and in a
state of solution, is a very favourable substratum for the develop-
ment of most Fungi that are not strictly parasitic, and also
of Bacteria, he distributes quantities of the substances intended
for examination, earth, fluids, &c., in properly prepared gelatine,
liquefying at a temperature of about 30° C., and then makes the
gelatine stiffen by lowering the temperature. The quantities
may be exactly determined. Each germ is fixed in the
stiffened mass and so developes, and the products of the
development are at least at first also fixed and not liable to
displacement in the medium. If the transparent gelatine is
spread in a thin layer on glass slides at the commencement of
the investigation, the germs and the products of their develop-
ment can be found with certainty with the microscope, and if
necessary be counted. If the object is to examine the air, the
best plan is to draw it in slowly by means of an aspirator
through glass tubes, coated inside with a layer of gelatine. If
the stream is properly regulated, the greater part at least of the
germs which are mixed with the air sink downwards and are
caught in the gelatine, where they may then undergo further
development. If experiments of this kind are properly con-
ducted and disturbing impurities excluded, distinct groups of
Bacteria, Fungi, &c., will be found after a few days in the
gelatine. Each group originates in a germ, or in some cases in
an assemblage of germs, which made .its way to the particular
spot at the commencement of the experiment, as may often

42 Lectures on Bacteria. [§ v.

be easily ascertained by direct observation. It is obvious that
the purpose under consideration can be most certainly and most
simply effected in the way which has just been described. The
result certainly can never be more than approximatively exact,
because the nature of the process does not ensure that all the
germs capable of development which find their way to the
gelatine in the apparatus do in any given case actually develope,
or in the case of air-suction that all the germs without exception
are always actually caught. No other method which has not
this fault in an equal or even greater degree and without the
advantage of fixing the germ has up to the present time been
devised, nor is it easy to imagine one that would be practicable.
It may be added here that Koch's method has the further
advantage of making the sorting and selection of Bacteria for
isolated culture comparatively easy. Each of the groups derived
from a single germ in the experiments above described must
contain a single species without admixture. To obtain a
quantity of this species for a pure culture we have only to remove
a sample from the group with the needle. To sort a mixed mass
of Bacteria requires simply the spreading small quantities of it
over a large amount of gelatine, and thus isolating germs capable
of development. The groups formed from these germs supply
pure species-material. Various other experiments have been
tried with the same objects and on the same principles, but with
less perfect arrangements and methods ; we must not, however,
enter here into a more detailed account of them. The most
elaborate are those instituted by Miquel and continued from
year to year in the meteorological observatory at Montsouris,
near Paris, intended especially to ascertain the distribution of
germs in the air and in water (15).

All researches hitherto conducted have given the general
result described above, and a further one which might have
been expected beforehand, namely, that the number of germs
capable of development v.aries, other conditions being the same,
with the place, the time of year, the weather, and other circum-

§ v.] Origin and distribution. 43

stances. To give some idea of the approximate numbers it may
be added, that the number of germs in the air caught on glass
plates in a mixture of glycerine and grape-sugar in the aspirator,
Fungi and Bacteria capable of development and in some cases
dead being taken together, varied in the garden of Montsouris,
in a single series of observations, from between 0-7 to 3-9 in
December and to 43-3 in July in a litre of air.

The most exact air-determinations have been recently carried
out by Hesse with the aspirator and gelatine-process. These
showed the presence of germs capable of development in a litre
of air, as follows :

In Sick-ward No. i, with 17 beds, Bacteria 2-40, — Moulds 0-4.
» » 2, „ 18 „ „ n-o, „ i-o.
Cattle-stall for experimental pur-
poses belonging to the Na-
tional Office of Health : (a) „ 58-0, „ 3-0.

W » 232'°> » 28'°-

The air out of doors in Berlin was found to contain o- 1-0-5

germs per litre, of which about half were Fungi and half
Bacteria.

Miquel obtained thirty-five germs per cubic centimetre in
rain-water caught as it fell, sixty-two in river-water from the
Vanne; in that from the Seine above Paris 1400, below
Paris 3200.

We have no numerical determinations of the number of germs
present in the soil; but we can produce growths of Fungi and
Bacteria from every small pinch of soil taken from the surface
of the ground. In lower strata, according to some preliminary
researches made by Koch (14) in winter, the number of germs
capable of development diminishes rapidly.

A special interest attaches to the question of the presence of
germs in and on sound living organisms. That they must remain
hanging in profusion to the surface of such organisms is obvious
from the preceding statements, and is proved by every investiga-
tion. They can penetrate into the interior of the higher forms of

44 Lectures on Bacteria. [$ v.

plants through the open slits in the epidermis, the stomata, which
lead to the system of intercellular passages. It is probable that this
actually takes place, but it is not yet quite certain and requires
further investigation. The respiratory and alimentary canals in
healthy, especially warm-blooded, animals are constantly acces-
sible places for the entrance of germs with air, meat and drink,
and it is these parts, especially the mouth and the intestinal
canal, both in man and other warm-blooded animals, which are
as a matter of fact always a well-stocked garden of vegetating
Bacteria. They may also make their way into the glands which
are in communication with these canals through their excretory
ducts. Researches into their occurrence in the blood of healthy
living warm-blooded animals give different results. Hensen,
Billroth, and other observers maintain their presence there. Very
careful investigations by Pasteur, Meissner (13), Koch, Zahn,
and others give a negative result; the affirmative result may
therefore be due to disturbances and errors in the experiment.
But this conclusion is not unavoidable, for a series of experi-
ments by Klebs (12) have placed it beyond doubt that both
states may occur, and why they may occur. Klebs examined
the blood of some dogs, and partly with a negative result. But
in the case of one dog the result was affirmative, the fact being
that putrefactive Bacteria had been injected into the blood of
this animal some time before on the occasion of some other
experiments ; it had sickened with them but had quite recovered
long before the date of the investigation of which we are now
speaking. It cannot be doubted that in this case germs capable
of development but actually dormant had remained from the
first experiment in the animal's blood, and we may conclude
generally that Bacteria germs may be present in healthy blood,
if they have once made their way into it through a wound or in
some other way.

The result of the above facts is to show the wide distribution
and great abundance of Bacteria-germs, though their species
are not at present clearly discriminated. They show also on

$ v.] Origin and distribution. 45

the other hand that it would be an exaggeration to suppose
that these bodies are everywhere present, that is, in every
minutest space. Even Pasteur's earlier and famous researches
show the inequality of the distribution by extreme examples.
This may be briefly illustrated by the following account. A
small quantity of germ-free nutrient fluid, very favourable for the
development of lower organisms, was introduced into small
narrow-necked phials of 1-200 ccm. content ; the air was
withdrawn from the phials and the narrow neck hermetically
closed. Subsequently the closed neck was reopened by in-
tentional fracture of its extremity; air rapidly poured in, and
as soon as this had taken place the neck was once more closed.
From 1-200 ccm. of air were thus hermetically inclosed in the
phial. The germs which they contained were at liberty to develope
in the nutrient fluid, which, to use a short expression, remains
unaltered if no germs are present. Of ten such phials filled with
air in the court-yard of the Paris Observatory not one remained
unaltered ; nine out of ten filled in the cellar of the Observatory,
which was almost entirely free from dust, and nineteen out of
twenty filled at the Montanvert near Chamonix were unaltered.

The views here expressed with regard to the origin of
Bacteria, and especially the fundamental axiom, that they are
produced without exception from germs springing from species
of the same name, have not been arrived at without trouble or
without opposition, and the latter has not entirely ceased even
at the present day. We must not pass by the view of the
opponents without at least a brief consideration. It may be
concisely stated thus : Bacteria may be formed at any moment
from parts of other organisms, living or dead ; but it is allowed
that they may afterwards multiply by their own growth and also
produce their own germs.

This view is a survival from the old doctrine of original
production without parents, spontaneous or equivocal genera-
tion. Plants or animals are often known to appear in numbers
in places where they had never been seen before, and the super-

46 Lectitres on Bacteria. [§ v.

ficial observer is led to assume in such cases that they owe their
origin to other bodies present at the particular place before their
appearance there, no matter what these bodies may be, and not
to germs formed from similar parents. Such views were not
unnatural in ancient times. Virgil's (16) account of the pro-
duction of a swarm of bees from the buried entrails of a steer
furnishes an obvious illustration, and shows how utterly defective
were the observation and reasoning which admitted of such
notions. With a closer observation of nature it became evident
in one case after another that the appearance of the particular
organisms invariably commenced with germs which were the
product of parents of the same kind, and that the point not
observed was how these germs found their way to the place of
observation. Generation without parents was step by step driven
into a corner. The process began with large and coarse objects
like the maggots of flies which appear in carrion, not by spon-
taneous generation, but produced from the ova of flies which
have been deposited in it. And as the adherents of the old
doctrine were driven back on smaller objects, such as moulds,
the lowest forms of animal life and the like, their refutation
followed step by step with equal success in these domains also.
Microscopic and improved experimental methods by turns
sharpened the weapons. Thus we find ourselves face to face
with the fact that the adherents of generation without parents,
at least during the last hundred years, seek for support to their
doctrine always in the minutest and at the time the most inac-
cessible objects. The view has never been entirely given up, and
for two good reasons. First, because an opinion once expressed
or put into print, be it what it may, never totally disappears ; the
second and much better reason is, that we must necessarily assume
that organisms were certainly once produced without germs and
without parents ; the possibility that this may happen again at
any time must be allowed, and to prove that this does happen and
to show where and how it happens would be highly interesting,
and a really worthy subject for the efforts of the enquirer.

$ v.] Origin and distribution. 47

Bacteria rank with the smallest organisms at present known
to us, with the least accessible and the most imperfectly investi-
gated. It is true that the question of actual spontaneous gene-
ration has been in all essential points decided in the same way
in their case as in that of other organisms, by the beautiful
researches conducted by Pasteur twenty-five years ago at the
instance of the Academy of Paris, and intended to test the
doctrine in question in connection with the smallest and least
accessible creatures; and every pure and trustworthy investi-
gation has confirmed Pasteur's results. Nevertheless there are
writers who still hold to the doctrine and who seek for fresh
arguments in support of it. A comprehensive theory in this
direction is contained in Be*champ's doctrine of Microzymes (17)
published twenty years ago. The term Microzyme was applied
by him to minute form-elements, such as occur generally
in the shape of granules in the protoplasm of animals and
plants, and are doubtless formed in them as parts of their
substance. If these particles of matter are set free by any
cause, especially after the death of the parent, they are supposed
to undergo a further process of independent development and
to become partly Bacteria, partly also small Sprouting Fungi.
They not only outlive the organism which produces them, but
enjoy a very prolonged existence extending over geological
periods. Close scrutiny of the accounts given by Be'champ in
a volume of almost a thousand pages shows no sharp dis-
crimination of forms, and no sign that the continuity of the
development has been strictly followed, and yet this is a point
of the very first importance. The whole matter therefore is
without any certain foundation, and is no longer a subject for
discussion.

A. Wigand (18) has quite recently published a preliminary
communication, in which he arrives at the same results as
Bechamp as regards the question before us. Small portions
of living or dead organisms, the latter not being Bacteria, are
said to separate from them under definite conditions and to

48 Lectures on Bacteria. [$ v.

develope into Bacteria. The course of the observations, from
which this conclusion is drawn, is in most cases not stated
with sufficient exactness to allow of our forming a judgment
upon them. Still one observation is mentioned which it was
admissible and desirable to have repeated and tested. Wigand
states, for the removal ' of all doubt about spontaneous forma-
tion of Bacteria in the protoplasm of cells/ that motile Bacteria
are found in the living healthy cells of the leaf of Trianea bogo-
tensis and in those of the hairs of Labiatae. My attention had
been directed to the matter from another quarter before I
proceeded to examine into this remarkable statement. Trianea
is a South American water-plant, which floats in the manner of
our Frogbit (Hydrocharis). If living tissue from the fresh
healthy leaf is placed under the microscope, we shall really see
in many cells the prettiest representations of the appearance of
Bacteria, small slender rods, isolated or attached together in
short rows and actively following the movements of the proto-
plasm and other cell-contents. An excellent representation, as
I said, or model. But a drop of dilute muriatic acid destroys
the illusion. The acid at once dissolves the rods in Trianea,
which it would not do if they were really Bacteria ; they are
simply small crystals of calcium oxalate, which often occur in
vegetable cells and in the form of rods. Of the same kind are
the much less beautiful rods in the young hairs of the leaf of
Galeobdolon luteum and Salvia glutinosa, and so also in other
Labiatae or lipped-flowered plants. The case is full of instruction,
as showing how a preconceived opinion may lead even good and
intelligent observers into the greatest absurdities. I should not
otherwise have mentioned it, and I do not think it necessary to
go any further into similar matters. Such things at all events
are not calculated to weaken the proposition, that according to
the observations which actually lie before us even the smallest
organisms spring only from germs produced from ancestors of
the same kind ; and to this we must hold fast in spite of what-
ever may be thought possible or desirable.

vi.] Vegetative processes. 49

VI.

Vegetative processes. External conditions : tempera-
ture and material character of the environment. Prac-
tical application of these in cultures, in disinfection,
and in antisepsis.

IN passing on to the consideration of processes of vegetation,
we must first of all remember that agreement in structure and
development between Bacteria and other lower organisms neces-
sarily implies also an agreement in the chief phenomena and
chief conditions of vegetative life. In fact we have simply to
do with special cases of phenomena which are of general occur-
rence in all living organisms, and which do not differ more from
those to be met with in other plants than these do from one
another. It is specially true of the Bacteria which do not
contain chlorophyll, that their vegetative process agrees essen-
tially with that of other vegetable cells which do not contain
chlorophyll, both those which belong to the higher plants, and
more particularly those belonging to the Fungi. It is to the
investigation of the Fungi, which are more easily studied, that we
owe much of the advance that has been made in our knowledge
of the Bacteria. It is perhaps scarcely necessary to observe
that differences prevail from one case to another among Bacteria
also as regards the phenomena and conditions of vegetation,
analogous with those in the allied groups.

Our present object, however, is not to give a complete account
of everything belonging to the vegetative process, but only to
call attention to the points most worthy of notice in connection
with the subject of these lectures. The conditions of tempera-
ture and the material character of the environment are chiefly
to be considered.

Every process of vegetation is dependent on the temperature
of the surrounding medium ; it finds its limits within certain
extreme degrees of heat, and its greatest activity at a fixed

E

50 Lectures on Bacteria. [§ vi.

temperature between these extremes. The cardinal points of
temperature are accordingly distinguished as minimum, maxi-
mum, and optimum.

Transgression of the limits leads at first to a cessation of the
particular process going on at the time ; other processes may
possibly persist. If the raising or lowering of the temperature
beyond the maximum or minimum point of vegetation reaches
certain extreme degrees, life is destroyed, in other words the
death-point is attained.

In all these respects considerable variations occur in confor-
mity with every one's daily experience, according to the species,
the state of development, and the character of the environment.

The limits of temperature in the growth and multiplication of
cells are the points which have been chiefly examined in the
case of the Bacteria ; it being assumed with some reason that
the rest of the vegetative processes, other conditions remaining
the same, run proportionally with the growth.

It appears from the data before us that non-parasitic species,
if well and properly nourished, have a tolerably wide range and
a high optimum of growth-temperature. The former lies in
Bacillus subtilis, for example, according to Brefeld (19), between
6°C. and 50° C., the optimum being at about 30° C. Bac-
terium Termo, Cohn grows between 5° C. and 40° C., while
its optimum is 30-35° C. (Eidam 20). Bacillus Amylobacter,
according to Fitz (21), has its optimum in solution of glycerine
at 40° C., its maximum at 45° C. The minimum of growth,
according to present accounts, in Bacillus Anthracis in cultures
in gelatine, on potatoes, &c., is at i5°C., the maximum at
43° C., the optimum at 20-25° C. As a parasite in the blood
of rodents it grows at about 4° C. ; at least, not less vigorously
than in the optimum just given for specimens under culture. In
the Spirillum of Asiatic cholera, according to van Ermengen
(see Lecture XIII), the minimum is reached at 8°C., the
optimum at 37° C., the maximum at 40° C.

That the species which are more strictly adapted for a para-

§ vi.] Conditions of vegetation. Temperature. 5 1

sitic life in warm-blooded animals have a higher maximum and
optimum is probable beforehand, and has been proved by Koch
(60) in the case of the Bacillus of tubercle, in which the limits
of temperature were found to be from 28° to 42° C., and its
optimum 3 7-3 8° C.

The optimum temperature for the formation of spores in
endosporous Bacilli, as far as can be ascertained, approaches
that of growth. The temperatures for the germination of the
endogenetic spores are higher, at least in the case of the op-
timum, being 30-34° C., for instance, in Bacillus subtilis, which
however also germinates in the temperature of a room which
is somewhere about 20° C. B. Anthracis does not germinate,
as far as our experience goes, at 20° C. ; the minimum given
for this species is 35-3 7° C., the optimum can scarcely be much
higher. Other species, as B. Megaterium, grow and germinate
quite well at a temperature of about 20° C.

Transgression of the limits of temperature of vegetation in
the downward direction without destruction to life is possible in
the case at least of a large number of Bacteria, and to such an
extent that in view of the phenomena which are known to occur
we may even say that there are no limits. Frisch (22) found
the power of development in the forms which he examined, and
in their vegetative cells, unaffected when they were frozen in a
fluid at a temperature of — no°C. and afterwards thawed
again. Bacillus Anthracis is one of the forms which behave in
this manner; in the case of other species the point remains
undecided, but it is probable that in some of them the lower
death-temperature is higher than this.

The upper death-temperature, so far as is at present known,
is about the same for the vegetative cells of the majority of
forms, as for most other vegetable cells, 50-60° C. Similar
figures are true also for the spores of arthrosporous forms,
though this point requires further investigation. Exceptional
cases will be mentioned further on. On the other hand, the
endogenetic spores of the Bacilli are capable of enduring

E 2

52 Lectures on Bacteria. [$ vi.

extreme high temperatures. Most of them continue capable of
germination after being heated in a fluid up to ioo°C. ; some
will bear 105° C., uo°C., and as much as i3o°C.

These are all general rules and are not affected by the modi-
fications and exceptions which occur in different cases, and
which in part depend on the species and individual, other con-
ditions remaining the same, in part also are found in the same
species, being then dependent on the external conditions, such
especially as the length of the time during which they are heated,
dried, or soaked, and in the latter case on the nature of the
surrounding fluid.

There are first of all species which develope vigorously at a
temperature considerably above 50° C. Cohn and Miquel supply
instances of this, but the best is that of a Bacillus described by
van Tieghem (23), which grows and forms spores in a neutral nu-
trient solution at a temperature of 74°C.; growth ceases at 77°C.

The Bacilli obtained by Duclaux (24, 25) from cheese, and
named by him Tyrothrix, are instructive examples on all the
points above-mentioned. The vegetative cells of T. tenuis
cultivated in a neutral fluid were only killed at a temperature of
90-95° C., in a slightly alkaline fluid they bear a temperature
of over ioo°C., while the ripe spores remain capable of germin-
ation when subjected to a temperature of 115° C. in a similar
fluid. The most favourable temperature for vegetation in this
species is 25-35° C. T. filiformis in the vegetative state will
bear a temperature of ioo°C. in milk, but is killed in the space
of a minute in an acid fluid at the same temperature. The
spores of this species are uninjured at a temperature of i2o°C.
in milk, but are killed at less than 110° C. in gelatine. Duclaux
gives similar accounts of other species. The vegetative cells also
of Bacillus Anthracis are said by Buchner (28, p. 229) to continue
capable of infection when heated for an hour and a half in
neutral and slightly acid fluids up to a temperature of 75-80° C.
Brefeld (19) found all the spores of Bacillus subtilis in a nutrient
solution kept for a quarter of an hour at a temperature of

$ vi.] Conditions of vegetation. Moisture. 5 3

ioo°C. capable of germination; if they remained in it at the
same temperature for half an hour the majority still germinated,
if for one hour a smaller number; none retained their vital
power after a space of three hours. The spores were killed in
fifteen minutes at a temperature of 105° C., in ten minutes at
107° C., in five minutes at no°C.

Fitz (21) found that the spores of his Bacillus butylicus
(B. Amylobacter) bear a temperature of 100° C.for a time vary-
ing from three to twenty minutes, according to the fluid in
which they happen to be. But if the time of exposure is pro-
longed, temperatures under ioo°C. are sufficient to kill them,
80° C. for example, when they are kept seven to eleven hours
in glycerine solution.

Spores, at least, are proof against still higher degrees of dry
heat ; those of Bacillus Anthracis, B. subtilis, and others con-
tinued capable of development in Koch's experiments (14, p. 305)
in a chamber heated up to 123° C.

Among the conditions connected with the nature of the en-
vironment, the requisite supply of water must be mentioned first
in this case as in that of all living cells. Withdrawal of water
to the point of air-dryness not only stops the process of vege-
tation but kills vegetative cells, at least in a number of cases,
in a very short time, those of Bacterium Termo, Cohn, and B.
Zopfii, for example, in seven days. But here, too, the effect
varies in different cases ; Micrococcus prodigiosus, for instance,
continues alive and capable of development for months in a
state of desiccation.

The resistance of spores to desiccation is greater than that of
vegetative cells. The spores of the arthrosporous Bacterium
Zopfii withstand it for seventeen to twenty-six days; those of
the endosporous Bacilli on the average certainly a year, those of
Bacillus subtilis, according to Brefeld, at least three years.
Here, too, limits and modifications will arise according to other
internal and external causes, but air-dry cells can hardly be
expected to retain their vitality for centuries.

54 Lectures on Bacteria. [§ vi.

Oxygen is not equally necessary in all cases. Two extreme
cases are distinguished in Pasteur's terminology as aerobia
and anaerobia. The first require an abundance of air con-
taining oxygen, as well as a good supply of nutrient sub-
stances for luxuriant vegetation and growth ; of this kind are
Micrococcus aceti, Bacillus subtilis, B. Anthracis, and Koch's
Spirillum of cholera. The other kind does well on good food
without oxygen ; free access of air reduces their vegetation to a
minimum or to zero, as for example in Bacillus Amylobacter.

Intermediate cases, however, are found between the two
extremes, as is well shown by Engelmann's beautiful example
which will be referred to again presently ; and according to the
investigations of Nencki, Nageli, and others, Bacteria which
excite fermentation, like the Sprouting Fungi which give rise to
alcoholic fermentation, grow luxuriantly without oxygen, when
they are in a suitable fluid capable of fermentation with them.
If these forms are placed in a less favourable nutrient fluid in
which they cannot incite fermentation, they will not grow with-
out a supply of oxygen.

Oxygen may impede and even destroy vegetation even in the
case of aerobiotic forms if it takes place under high pressure.
Bacillus Anthracis, for example, remained alive for fourteen days
in oxygen under a pressure of fifteen atmospheres, but was dead
in a few months' time. Duclaux contends that the germs even
of aerobiotic forms, when withdrawn from the conditions re-
quired for growth, lose their power of development more quickly
under the continued effect of atmospheric oxygen than when
oxygen is excluded. The facts on which this view is founded
are in themselves remarkable. In some glass bottles which had
been used in Pasteur's researches about 1860, and had been
kept hermetically sealed with their contents decomposed by
Bacteria, the germs of these Bacteria were found thoroughly
capable of development after twenty-one and twenty-two years.
Plugs of cotton-wool full of germs of all kinds, which had been
kept dry and protected from dust during the same time, but not

$ vi.] Conditions of vegetation. Oxygen. 55

from contact with the air, did not contain a single living germ. A
few similar plugs which were only six years old contained germs
still capable of development. Duclaux' interpretation of these
facts may be correct, but it requires further proof, since we are
dealing with matters in which many other things besides the
supply of oxygen may have been unequal. Above all things it
is necessary in these questions that experiment should be made,
not with collective Bacteria, that is, with mixed masses which are
possibly or certainly undetermined, but always with a single
definite species.

Oxygen is taken up as material for respiration or breathing,
oxygen-breathing, to use a more precise term, carbon-dioxide
being at the same time given off. Water, except in some cases
which will be mentioned presently, serves as the agent and
medium of the chemical processes of the metabolism. Neither
of these bodies is properly a nutrient substance, that is, a sub-
stance from which carbon-compounds, the constructive material
for growth and cell-formation, are produced.

With respect to the true nutrient substances which therefore
supply building-material we must assume in the case of the few
green Bacteria, if they really contain chlorophyll, that accord-
ing to the analogy of all other plants containing chlorophyll,
they assimilate carbon as their food and give off oxygen.
Engelmann (26) has ascertained that a small portion of oxygen
is given off by his Bacterium chlorinum, and this supports the
assumption, while the employment of water also as a food-
material in the case of these forms, as in all other plants con-
taining chlorophyll, would also be probable.

The Bacteria containing no chlorophyll, which are by far the
greater number and almost the only ones which concern us
at present, require, like all cells and organisms that are devoid
of chlorophyll, carbon-compounds previously formed else-
where for the supply of their carbon, and do not assimilate
carbon-dioxide. The nitrogenous food-material may be furnished
both by previously formed organic and also by inorganic sub-

56 Lectures on Bacteria. [§ vi.

stances, compounds of nitric acid or still better of ammonia.
In addition to these a small supply quantitatively and quali-
tatively is required, as in other plants, of soluble constituents of
the ash.

It does not fall within the scope of these lectures to go more
deeply into the consideration of the value of the several com-
pounds as food-material; on this point the special literature,
especially Nageli's publications (27, 28), should be consulted.
It is sufficient for our general guidance and for practical pur-
poses to observe that according to Nageli's investigations a
number of moulds and Sprouting Fungi as well as Bacteria also
can find their food in solutions which contain nitrogenous and
non-nitrogenous nutrient substances in the following compounds
or combinations, the several solutions being arranged and
numbered in descending order according to their nutritiveness : —
i. Proteid (peptone) and sugar. 2. Leucin and sugar. 3.
Ammonium tartrate or sal-ammoniac and sugar. 4. Proteid
(peptone). 5. Leucin. 6. Ammonium tartrate or ammonium
succinate, or asparagin. 7. Ammonium acetate.

But we must not seek to determine or judge of the optimum
of feeding - quality for all species or forms of Bacteria from
this table. The above scale is not even true for all moulds,
though it was first drawn up from the study of one of that group,
Penicillium glaucum. The requirements in the way of food of
single definite species of Bacterium have as yet been little studied,
and much needs more exact investigation. A number of prac-
tical experiences, which will be partly noticed further on under
the particular examples, point already to the great multiplicity
of the actual relationships which have to be taken into account.

Besides the amount of suitable food-material contained in the
substratum, other chemical qualities in it are also of importance
to the vegetative process in Bacteria. It is an old experience
that most of these organisms^ in contrast to the reverse be-
haviour of Sprouting Fungi and moulds, flourish best, other
conditions being the same, in a medium with a neutral or

§ vi.] Conditions of vegetation. Food. 57

slightly alkaline or at most with a slightly acid reaction ; should
the reaction be strongly acid, vegetative processes are hindered
or wholly stopped. According to Brefeld (19) the development
of Bacillus subtilis, for example, is impeded, if 0-05 per cent, of
sulphuric or tartaric acid or 0*2 per cent, of lactic or butyric
acid is added to a good nutrient solution. But this, too, is
only a rule which has its exceptions ; the Bacterium of kefir
vegetates well, and, as far as our experience goes, best in milk
which has been rendered strongly acid by lactic and even acetic
acid ; the Micrococcus of vinegar vegetates in the same way in
an acid fluid.

Other soluble bodies also impede or destroy the vegetative
process when mixed with the food-material. This is of course
the case with substances which always act as poisons upon living
cells, such as corrosive sublimate, iodine, &c., when present in
sufficient quantity. But other bodies have a similar at least re-
tarding poisonous effect on Bacteria. Fitz, for instance, found
that the vegetation of his Bacillus of butyl-alcohol in a solution
of glycerine and under conditions otherwise most favourable was
impeded by the addition of 2-7-3-3 per cent, by weight of ethyl-
alcohol, o'9-i*o5 per cent, of butyl-alcohol, or o'i per cent, of
butyric acid. Since these prejudicial compounds are often
formed by the vegetative process itself, the latter may even be
stopped by the accumulation of its own products, as, for instance,
in lactic acid fermentation in sugars by the accumulation of
lactic acid ; if this is fixed, as by addition of chalk or zinc-
white, the vegetation of the Bacterium which causes the fer-
mentation continues. These phenomena are also found mutatis
mutandis, in other plants beside Bacteria, especially in Fungi,
and they vary in the individuals of different species. That
which disturbs one species may be of advantage to others, and
hence a change in the composition of the substratum may
favour the supplanting of one species by another, which was
previously perhaps present in the very smallest quantity. In
such a case the first species has prepared the ground for the

58 Lectiires on Bacteria. [§ vi.

others by its vegetative process and its products. This must
always be kept in mind in judging of processes on the large
scale ; attention to it supplies the explanation of a number of
phenomena which are at first sight puzzling.

The influence of other agencies besides those which have
been mentioned on the vegetation of Bacteria cannot in general
be disputed, but in the present state of our knowledge it is of so
subordinate importance, that a very short notice of it will be
sufficient on this occasion. The dependence of carbon-as-
similation upon the rays of light in the forms which contain
chlorophyll follows of necessity from what we know of the
function of chlorophyll. With respect to other effects of light
we have only some uncertain statements by Zopf on the pro-
bable promotion of the growth of Beggiatoa roseo-persicina by
illumination, and an investigation by Engelmann (29) into the
dependence on the rays of light of the movements of a form
which, though named Bacterium photometricum, is possibly, to
judge by the illustrations, not a Bacterium at all. Influence of
light has not been proved in the case of the majority of Bacteria.
The effects of electricity have been recently investigated by Cohn
and Mendelssohn (30), and may be gathered from their paper.

The dependence on the conditions of vegetation which we
have been considering is true of all stages and phases of the
normal vegetative process, not excepting its first beginnings, the
germination of the spores. Of this it must be specially remarked
that it occurs, as far as is at present known, only in a nutrient
substratum favourable to the vegetation of the species. This
agrees with the corresponding behaviour of some spores of Fungi,
those for example of Mucorini. It does not agree with that of
most other spores or with the seeds of flowering plants, which
germinate, or at least can germinate, without nutrient substances,
provided they are supplied with water, oxygen, and the necessary
warmth.

It has been already stated above on page 19, that in some
cases, as in Bacillus Amylobacter, spore -formaf ion takes place

§ vi.] External conditions of vegetation. 59

even while vegetation and growth are going on in a portion of the
vegetative cells, and therefore while the conditions of vegetation
are still in operation. In other and especially in the endo-
sporous species it is true to say, that the formation of spores
begins when the substratum is exhausted, that is, has become
unsuitable for the vegetation of the species. Whether the latter
condition is really due in every case to a consumption of the
requisite nutrient substances or to an accumulation of checking
products of decomposition, or whether the formation of spores is
induced in this case as in others by internal causes when the
vegetation has reached a definite height, are all questions which
require more precise investigation, though they may perhaps be
of only subordinate practical importance.

Vegetation proceeds with great rapidity in most Bacteria
under the co-operation of the most favourable conditions.
Brefeld determined in the case of Bacillus subtilis, that with a
good supply of food and oxygen, and a temperature of 30° C., a
rod divides once in every thirty minutes, which means that it
doubles its length every thirty minutes, the thickness remaining
the same, and then separates transversely into two equal parts.
The process goes on more slowly in proportion as the condi-
tions recede from the optimum. If we assume that the increase
directly observed in the way here described is accompanied
by a corresponding increase in the mass, especially of the
dry substance, an assumption which is not strictly proved
but from the indications before us is certainly approximatively
correct, then we have growth to double the former size in the
full sense of the expression once in every thirty minutes.
Similar results are arrived at from observations on many other
species, as Bacillus Anthracis, B. Megaterium, &c. But here,
too, there are exceptions. The Bacterium of kefir, for example,
in the cases which I examined, required more than three weeks
for growing to about twice its weight, more than 500 times the
period observed in Bacillus subtilis. I am not able to say
whether the conditions were absolutely the most favourable ; at

60 Lectures on Bacteria. [§ vi.

all events, they were those in which the kefir-organism grows best
according to our present knowledge, namely, in milk at an air-
temperature of 1 5-20° C., and with a supply of atmospheric air.

The movements also of the Bacteria, as well as their growth
and germination, are directly dependent on the conditions of
vegetation in the species and forms which are capable of inde-
pendent movement. The occurrence and the direction of the
motion are specially determined by the influence of nutrient
substances, and of oxygen. If a form of this kind, Bacillus
subtilis for instance, in the vegetative condition in which it is
capable of movement is placed in a drop of nutrient solution on
a slide under a cover-glass, the motile rods are seen to collect
at once round the margin of the cover-glass where the oxygen
of the air has free access. The comparatively few which remain
behind in the centre of the drop, and are there cut off from the
atmospheric oxygen, become slower in their movements and
finally lose them altogether. Aerobiotic forms enclosed in a
drop of water in which there is no free oxygen along with
Algae containing chlorophyll at first remain motionless. But
as soon as the cells containing chlorophyll are induced to give
off oxygen under the influence of light, the Bacteria begin to
move actively, as Engelmann (31) has shown, and the movement
is directed towards the spots where the oxygen is being given
off. Here the Bacteria collect, and they may therefore be used
as an extremely delicate reagent for the detection of quantities
of oxygen of almost inconceivable minuteness. The frequent
grouping of aerobiotic forms into films or membranes on the
surface of fluids is no doubt partly due to the influence in
question determining the direction of the movement.

While the above-mentioned forms approach as near as pos-
sible to the source of the atmospheric oxygen, there are others
which, as Engelmann (26) found in the case of a Spirillum,
always remain at a certain distance from it, the distance
diminishing as the amount of free oxygen diminishes in the air
which finds access to the Bacteria. This observation proves the

$ vi.] Culture of Bacteria. 61

existence of intermediate cases, mentioned above, between ex-
treme aerobia and anaerobia.

Pfeffer (32) has further shown that chemical stimuli, exerted
by other bodies in a state of solution, may influence cells which
have the power of locomotion and organisms of very various
kinds, hastening and determining the direction of their move-
ment, and that the Bacteria supply special instances of this
general phenomenon. The chemical bodies which have this
effect on the Bacteria are those which were spoken of before as
their nutrient substances. The direction of the movement is
due, as Pfeffer shows, to diffusion-currents by the introduction of
the solutions on one side, the axis of rotation of the cells being in
the same direction as the currents and the movement in space
in the opposite direction. Other conditions remaining the same
the effect varies according to the quality of the body in solution
and the concentration of the solution, and it must be particularly
observed that it is not every diffusion-current that influences the
direction of movement, but only the current from solutions
determined in each case by the species of Bacterium. These
facts explain a phenomenon which has been frequently observed,
namely, that swarms of Bacteria assemble in water round solid
bodies, such as dead parts of plants, pieces of flesh and the like,
which gradually give off soluble nutrient substances.

The practical application of these remarks on the conditions
and phenomena of vegetation in conjunction with the ascertained
facts respecting germs and their dissemination are in the main
obvious, if the important points and conditions in each case are
kept clearly in mind. We require always a certain amount of
positive knowledge and careful consideration of the object which
we desire to attain and can really attain in a particular way. The
practical remarks therefore may, for the present, be summed up
in a very few words.

First, with respect to the culture of Bacteria, there is but
little to be said. Pure extracts of animal and plant-substances,
the meat-extracts sold in the shops, broths, the juice of

62 Lectures on Bacteria. [§ vi.

fruits, neutralised, if necessary, and dissolved in not too con-
centrated (about 10 per cent.) watery solutions or in gelatine,
are, as a rule and in accordance with general experience, good
nutrient substrata ; the special choice must be made by experi-
ment in each case. Fresh urine has been repeatedly used with
success by French observers. The serum of blood has been
found to be a very suitable substance, and is almost the only
one that can be used in the cultivation of some parasitic forms,
especially if made stiff by being heated up to 60-70° C. after the
mode of proceeding described by Koch.

Among the very first requisites are the securing the purity of
the species under cultivation, the absence of unintentional ad-
mixtures, on which point some practical hints were given in a
former lecture (pp. 34 and 41), and the perfect control of the
continued purity of the cultures. The possibility of different
species displacing each other has been already discussed (p. 32).

To obtain purity of a culture as well as for other practical
purposes, it is often necessary to effect the entire destruction or
death of germs present in it. In the conduct of cultures there
is the special risk of these germs adhering to the apparatus to
be employed, vessels, nutrient substances, &c., and they must
be killed in order to provide for the purity of the culture. This
process of destruction is known as sterilisation, an expression
introduced by the school of Pasteur.

Bodies poisonous to protoplasm, such as acids, corrosive sub-
limate, &c., if sufficiently concentrated will usually effect the de-
sired result, where the object is only to destroy, of course on the
one condition that they are able to force their way into the proto-
plasm which is to be killed. This is the case in most poisons
but not in all. Absolute alcohol is a poison which is imme-
diately fatal to protoplasm, and it must therefore kill the proto-
plasm of endosporous Bacilli, if it reaches them. Nevertheless,
the spores of Bacillus Anthracis, as Pasteur discovered, and no
doubt also those of other endosporous species retain their vitality
after lying several weeks in absolute alcohol. If the same ex-

J vi.] Culture of Bacteria. Sterilisation. 63

periment is made with sound ripe seeds of the ordinary garden
cress, Lepidium sativum, the same result is obtained ; they ger-
minate if they are taken from the alcohol after four weeks' time,
and washed and sown. The spores of the Bacillus and the
seeds of the cress agree in being enveloped all round in a gela-
tinous membrane into which the alcohol cannot penetrate, and
thus the protoplasm, which in the cress-germ would otherwise
be certainly killed at once, remains unattacked.

But the application of poisons to cultures for purposes of
sterilisation is attended with great inconveniences in all the many
cases in which they must be got rid of again that they may do no
injury to the culture itself. New impurities may be introduced in
the process of washing the vessels and the rest of the apparatus.

Hence much the most practical mode of sterilisation consists
in. the application of extremely high temperatures, which must
exceed ioo°C., if the object is to kill any spores that may pos-
sibly be present; in dry vessels it is best to raise it to 120-
150° C. In the sterilising of fluids a heat of even 100° C. may not
always be possible for practical reasons, as, for example, when it
is necessary to avoid the coagulation of the albuminous sub-
stances dissolved in the fluid. Since most vegetating cells are
killed by a temperature of 50-60° C., the plan suggested by
Tyndall (33) is the most effective ; the fluid is allowed to stand
till whatever germs it contains begin to grow; if it is then
heated to 60-70° C. and the process repeated at an interval of
two days, the fluid will be in most cases free from Bacteria,
always presupposing of course that the plug which closes the
vessel is compact and clean.

Lastly, in practical life all that is usually required is to
render harmless any germs that may be present by preventing
their further development, whether they continue capable of it
or not. Here, too, complete destruction would be best and
most desirable ; but the use of most poisons in the state of con-
centration which is most certainly fatal, or that of a certainly
fatal degree of heat, would also ordinarily lead to the destruc-

64 Lectures on Bacteria. [jj vii.

tion of the objects intended to be protected from the Bacteria.
We must therefore be content with what is within our reach.

If, as there is no reason to doubt, the favourable results of the
application of disinfectants at the present day, the splendid
results of antisepsis in surgery, are due to the protection obtained
against destructive Bacteria, there can be at the same time little
doubt that this protection, partly due to the absence of germs
through the increase of cleanliness consequent on these modes
of procedure, is chiefly secured by staying the development of
the germs and in a much less degree by their destruction. The
elaborate experiments of Koch (14, p. 234) show that of the
various disinfecting and antiseptic agents in the proper state of
concentration or dilution, only corrosive sublimate, chlorine and
bromine have the effect of killing the germs. Bodies like
salicylic, carbolic, and other acids in the suitable state of
dilution, and powdered cane-sugar can only be supposed to have
the desired effect by stopping the growth of the Bacteria. It
wou^d be highly important to enquire more closely into the
specific sensibilities which may exist in the different species of
Bacteria. The behaviour of a Micrococcus of ulcer or erysipelas
in the presence of antiseptics may possibly be different from that
of Bacillus Anthracis, which has been the chief subject of Koch's
study.

VII.

Relation to and effect upon the substratum. Sapro-
phytes and Parasites. Saprophytes as exciting
decompositions and fermentations. Characteristic
qualities of Forms exciting fermentation.

THE vegetative process in organisms, which use organic com-
pounds for their food, must necessarily effect changes in the
substratum from which this food is withdrawn. To these
changes are added other effects, more closely connected with
the process of respiration, which lead to profound transforma-
tions in the organic substratum.

§ vii.] Relation to the substratum. Saprophytes. 65

This is especially the case with organisms whose mode of life
is of the kind described and therefore with all that do not
contain chlorophyll, Infusoria and Fungi as well as Bacteria.
Fungi, especially in the narrower use of the word, Sprouting
Fungi, moulds, &c. being comparatively easy to examine, have
supplied the best and most numerous conclusions with respect
to the phenomena in question, and we shall often have to make
use of them as examples in the following remarks.

The interest attaching to the Bacteria which are devoid of
chlorophyll rests chiefly on their effects on their substratum, and
after the foregoing introduction we must proceed to consider
these organisms, and endeavour to give a clear idea of them
by calling attention to the most important known examples.

Organisms not containing chlorophyll are separated into two
primary divisions, according as the organic substratum is a
living or a dead body. Those which have their habitat on or
in living fellow-creatures, and derive their sustenance from them
are termed parasites ; the others which live on dead bodies are
known as saprophytes. Different species are in fact differently
adapted to one or the other mode of vegetation; some are
known both as parasites and saprophytes, others only in one
or the other character.

We shall subsequently have to go more deeply into these
distinctions and gradations, especially in the case of parasites.
This brief mention of them is sufficient for the present.

The particular account of these forms will be simpler and
more intelligible if it begins with saprophytes. The organic
compounds present in bodies inhabited by saprophytes are split
up into simpler substances; in extreme cases total oxidation,
rotting, takes place with the decomposition of non-nitro-
genous carbon-compounds into the final products of carbon
dioxide and water ; in other cases we have partial oxidations,
not proceeding so far as the final products of combustion,
' oxidation-fermentations,' as for example in acetous fermenta-
tion— that is, the formation of acetic acid by the oxidation of

F

66 Lectures on Bacteria. [§ vn.

ethyl-alcohol. Reductions are of rarer occurrence, as in the
splitting of sulphates by Beggiatoa, which will be described
presently. The last to be mentioned are the splittings which
end in other than simple products of oxidation and are included
under the general term of fermentations ; of these the best-
known example in every respect is the alcoholic fermentation,
which is the splitting of the different sugars into ethyl-alcohol
and carbonic acid. If these splittings are accompanied with a
development of offensive gas, especially in compounds containing
nitrogen, the term putrefaction is used, an expression rather
popular and expressive than strictly and scientifically defined.

It is no part of our subject to enter further into the chemical
nature of these processes, the purely chemical and physical
sides of the theories of fermentation. With regard to the
general history of these theories also, we shall only observe
that it has been an established scientific truth since about the
year 1860, that the entire series of phenomena of rotting
and fermentation above mentioned are the results of processes
of life and vegetation in certain lower organisms, especially
Fungi and Bacteria. To Pasteur belongs the entire credit of
having placed this vitalistic theory of fermentation on a firm
basis, in opposition to other views which acknowledged no
causal relations at all between it and living organisms or causal
relations of a different kind, and of having extended it to all
phenomena of a similar kind. It is true that the same
vitalistic theory has been distinctly expressed in the case of
alcoholic fermentation since the time of Cagniard-Latour (1828)
and Schwann (1837), but it never obtained general accep-
tation.

The vegetative process of living organisms is then the direct
cause of fermentations ; there is no fermentation if the organisms
are destroyed. Organisms of this kind are therefore termed
fermentation-exciters, ferment-organisms, or simply ferments
in the terminology of the school of Pasteur. In that of Nageli
they are known as yeast, and according as the ferment-organism

§ viz.] Relation to the substratum. Fermentation. 67

is a Sprouting Fungus, a Fission-fungus, that is a Bacterium, or
a Filamentous Fungus, it is shortly termed Sprouting Yeast,
Fission Yeast, or Filamentous Yeast. The French system of
terminology limits the application of the French word levure,
which had originally the same meaning as the German Hefe and
English yeast, to the Sprouting Fungi which excite fermentation.
It is essential to the understanding of the literature to observe
that the German Hefe, English yeast, is used in quite different
senses ; it must be added also, that the same word is applied not
only to the ferment- organism simply, or to the particular form
of Sprouting Fungus which excites fermentation, but also to all
forms of Sprouting Fungi whether they excite fermentation or
not, thus often causing very needless confusion.

We shall speak again presently of the different meanings of
the word ferment.

Since the vegetation of organisms sets up fermentation, the
substratum in which the fermentation is to take place must
contain all the nutrient substances necessary for the process of
vegetation. A pure saccharine solution, for example, does not
ferment if a small quantity of fermentation-exciting Fungi or
Bacteria also in a pure state is introduced into it. The sugar, as
we have seen, is a good nutrient material for these organisms.
But it only supplies the necessary amount of carbon, the elements
of water, and free oxygen, and is therefore imperfect as food. It
is only when the compounds which supply the nitrogen men-
tioned above and the ash-constituents are added to the solution
that it is rendered capable of fermentation, and fermentation
commences as soon as the conditions favourable to vegetation
are secured. Bodies which in the natural course of things or
when artificially prepared have finished fermenting, such as
must or brewers' mash, are proper food for ferment-
organisms.

In every process of fermentation there is first of all a growth,
a multiplication of the exciting organism at the expense of the
fermenting substance. This can be seen by direct observation

F 2

68 Lectures on Bacteria. [$ vn.

when the smallest possible quantity of the organism is intro-
duced in the beginning, and its weight exactly determined.
The rest of the substratum is split up into the products of
fermentation in consequence of the processes of decomposition
which are connected with the vegetation, and which, as has
been already said, cannot be further considered here. The
best-known example of the kind is the alcoholic fermentation
of sugar by the Sprouting Fungus of beer-yeast, Saccharomyces
Cerevisiae, though it certainly does not strictly belong to the
subject-matter of these lectures. Pasteur states that in a suitable
solution about 1*25 per cent, of sugar was used for the formation
of yeast-substance, 4-5 for that of succinic acid and glycerine,
the remainder, 94-95 per cent., was broken up into alcohol and
carbonic acid.

This example shows that the process of decomposition is
complex, and does not simply consist in the breaking up of all
the sugar into carbonic acid and alcohol. But these, in point
of quantity and from their importance to human requirements,
are the most prominent products of the fermentation in ques-
tion. Accordingly, we distinguish in this and all other cases
primary and secondary products of fermentations, and we name
the particular process of fermentation from some characteristic
primary product.

It is known that the nature of the fermentations set up by
Bacteria is in general analogous with that of the case just men-
tioned. But in most of them the splitting-process is at present
less exactly understood, and in many only the primary products
are qualitatively known. Among these carbonic acid constantly
makes its appearance, as in Saccharomyces. Further remarks
will appear below along with special examples. At present we
will only briefly call attention to the colouring matters which
are observed not unfrequently in fermentations with Bacteria ;
they were noticed before on page 4, and have given rise to the
expression pigment-fermentations.

Some, but not all, ferment-organisms give off into the fluid

$ vii.] Relation to the substratum* Enzymes. 69

medium dissolved substances, which in the very minute quantity
in which they are excreted are able to give rise to other changes
in the substratum than those which belong directly to the
process of fermentation. Analogous products with analogous
effects are often obtained from other sources also, for instance
in Fungi which do not excite fermentation, and on certain
organs or in the cells of higher organisms, even of plants
containing chlorophyll. The Fungus of beer-yeast, for example,
Saccharomyces Cerevisiae, excretes a substance which inverts
cane-sugar in solution, as the phrase is, that is by absorbing
water splits it into glucose and laevulose (grape-sugar and fruit-
sugar). By means of a similar excretion Bacillus Amylobacter
breaks up cellulose into products soluble in water. The
cells of germinating seeds produce a body, diastase, which
breaks up starch-granules into dextrin and maltose. Substances
of this kind are known as enzymes or unformed or unorganised
ferments, in German terminology simply ferments. The ter-
minology of the French schools consistently carried out, especially
by Duclaux, terms them generally diastases, and then for the
separate cases invents special words, all having the same ending,
as amylase, saccharase (' sucrase'!), casease, and so on, reserving
the word ferment, as we have learned, for the living ferment-
organisms themselves. Enzymes, as has been already intimated,
are either unorganised bodies or bodies with a definite form,
soluble in water, and are all allied as regards chemical character
to the proteid compounds. They can with proper manage-
ment be separated from the organisms which produce them
without putting an end to their activity. Their characteristic
mark as a rule is the power which they possess of causing
chemical changes, chemical separations, without passing them-
selves into the final products of these changes and so losing
their active powers. Their effects are specifically different in
every case, and they are accordingly distinguished, as in the
examples cited, into inverting, sugar-forming, and other enzymes,
to which may be added those that, like the pepsin of the gastric

70 Lectures on Bacteria. [§ vn.

juice of animals, convert albuminous bodies with absorption
of water into easily soluble peptones, peptonising enzymes.

After what has now been said it scarcely requires to be
pointed out that every organism which sets up fermentation or de-
composition displays a specific activity in the directions indicated,
and it may be also a specific formation of enzymes. In the
same saccharine solution one species excites alcoholic fer-
mentation, another lactic acid or butyric acid fermentation, and
so on. Again, the same fermentation, according to the primary
products, may also be produced by dissimilar species under
otherwise similar conditions, though in unequal quantitative
amount. Alcoholic fermentation, for example, is excited in
saccharine solutions by several species of Saccharomyces, and
also by certain species of the group of Mucorini. The same
species can also set up different decompositions in different sub-
strata. The vinegar-bacterium oxidises the alcohol in a dilute
solution, and converts it into acetic acid and this into carbonic
acid and water when the alcohol is exhausted. The Saccharo-
myces of beer-yeast changes grape-sugar by fermentation
directly into carbonic acid and alcohol ; cane-sugar does not
ferment, but is first ' inverted ' by the above-mentioned enzyme,
and the ' invert-sugar ' formed of glucose and laevulose ferments
as it arises.

The Bacillus of butyl-alcohol of Fitz (Bacillus Amylobacter,
see Lecture IX) vegetates in nutrient solutions of milk-sugar,
erythrite, ammonium tartrate, salts of lactic acid, malic acid,
tartaric acid, &c., without exciting characteristic fermentations
in them ; it produces fermentation in glycerine, mannite, and
cane-sugar, with carbonic acid, butyric acid, and butyl-alcohol
as the primary products, and small amounts of lactic and other
acids as secondary products, the quantities of the primary pro-
ducts varying much according to the nature of the substratum.
The relative quantities of butyric acid, for example, under similar
conditions of fermentation, are 17-4 in the case of glycerine,
35-4 in that of mannit'e, and 42-5 in that of cane-sugar.

§ viz.] Relation to the substratum. Enzymes. 71

Many similar examples are to be found in works on fermen-
tation.

The production of enzymes may also vary in the same form
according to the quality of the substratum. Wortmann (34) found
in the case of a Bacterium which he does not further determine,
that it excretes a starch-dissolving enzyme, and dissolves starch
if carbon is presented to it in the form of starch-grains only.
If the carbon is offered it in the form of a carbohydrate
which is readily soluble in water, such as sugar, or of tartaric
acid, the starch-grains which are offered to it at the same time
remain untouched. Similar facts are recorded of Bacillus
Amylobacter, which, according to van Tieghem, when fed with
glucose, leaves the cellulose which is presented to it at the same
time untouched, but decomposes it and takes it in as food if no
source of more readily assimilable carbon is available.

Lastly, the definite activity of a particular species in the way
of fermentation or decomposition may be reduced to zero by a
change in the external conditions within the limits of vegetation,
even when the quality of the nutrient material remains the same.
Examples of this are furnished by the Mucorini already men-
tioned in passing, by the different species of Saccharomyces,
and by Bacillus Amylobacter and other Bacteria. Bacillus
Amylobacter, according to Fitz, loses the power of causing fer-
mentation, without losing that of vegetation, when exposed to a
high temperature, for instance, after the spores are boiled from
1-3 minutes in a solution of grape-sugar, or after being heated
for 7 hours up to 80° C. ; the same effect is produced if it is
cultivated during many generations with a copious supply of
oxygen in a nutrient solution, in which it is unable to excite
fermentation. The Mucorini present themselves in very dif-
ferent forms according to the change of conditions, though the
form is quite fixed in each particular case. Such a change of
form does not occur in Saccharomyces and the Bacteria which
have been more thoroughly examined as to this point, or only
to an inconsiderable degree. That external conditions of every

72 Lectures on Bacteria. [§ vm.

kind should have some influence on the form of Bacteria is a
legitimate a priori assumption, and may be directly observed
from the facts stated on page 29. It is therefore highly
probable, though further distinct proof is required, that the
change of form of strongly pleomorphous Bacteria (see pp. 25-6)
is to a large extent determined by changes in the external
conditions of vegetation.

In the natural course of things the processes of development
and decomposition of which we have been speaking, seldom if
ever go on their way purely and smoothly from beginning to
end. Many of the organisms in question are so numerous that
their germs find their way simultaneously or in rapid succession
into a nutrient solution or other decomposable substratum. In
that case they either develope simultaneously and the effects of
their decomposing action appear side by side ; or some find a
favourable substratum at first, but changing its character by their
vegetation, which is thereby impeded, they thus prepare a highly
favourable substratum for other forms ; in this way various de-
velopments and decompositions make their appearance, one
after another, in the same substratum.

Examples of such combinations and successions of products
of fermentation and decomposition are found everywhere in the
natural course of things, and in matters connected with domestic
economy. There is less need for me to dwell on them here,
because many of them will have to be noticed in the succeeding
descriptions of the several species.

VIII.

Most important examples of Saprophytes. The nomen-
clature explained. Aquatic Saprophytes : Crenothrix,
Cladothrix, Beggiatoa; other aquatic forms.

IN proceeding now to the special consideration of a few
saprophytic Bacteria, three remarks must first be made. First,

.] Examples of 'Saprophytes. Nomenclature. 73

we cannot attempt to give an account of all the phenomena
which have been described. We confine ourselves to such as
are at present best known, and are at the same time of more
general interest. It is to be presumed that many more will
have to be added to these in the course of time, and that various
changes will have to be made in the views at present enter-
tained. We are still very much in the position of beginners as
regards our knowledge of these matters and our investigations.
Secondly, we do not propose to go any further into the details
of the chemical processes attending the work of decomposition ;
we are chiefly concerned with the morphological and biological
points of view. Thirdly, we must keep clearly in mind that our
knowledge of the morphology and biology of the Bacteria is at
present very imperfect, or at least very unequally developed.
So much is this the case, that we are not yet in a position to
attempt a consistent classification and nomenclature on the
principles of systematic botany. What at present seems like
such a classification is only a temporary expedient. In such a
case the only thing to be done is to agree upon a provisional
arrangement and nomenclature for the time being. We will
therefore, first of all, adhere to the primary division into endo-
sporous and non-endosporous or arthrosporous forms proposed
in Lecture III. Single better-known groups in these two
divisions may and must then be constituted genera, and receive
names capable of being precisely defined. We limit the use of
the name Bacillus, and apply it to all endosporous forms and
species with rod-like vegetative cells and cell-unions of the
first order. Single arthrosporous forms, such as Beggiatoa,
Cladothrix, Leuconostoc, Sarcina and others, may be separated
from the rest and distinguished by characters which will be de-
scribed presently. There still remain a number of forms, in
respect of which we are reduced to superficial distinctions of
shape, and their ultimate classification must therefore be deferred.
Among these the spiral forms may be included under the name
Spirillum. Some of these, according to van Tieghem, belong

74

Lectures on Bacteria.

vm-

to the endosporous division ; others appear to be arthrosporous,
while there is a third group in which the point is not yet ascer-
tained, but appearances are in favour of their being kept together,

as at present, under the same
genus. The rod-forms which
are not known to be endo-
sporous may all be termed
Bacterium, and the coccus-
forms (page 9) Micrococcus.
It is obvious that no sharp
line of distinction can be
drawn between Micrococci
and short rod-shaped Bac-
teria, but it is convenient
and customary to distinguish
them. The species too, which
are at present distinguished,
require care in their deter-
mination. Some of them are
certainly known to be fully
and clearly distinct ; of others
this cannot be said, and
their present names in all
probability include two or
more species which have
yet to be studied severally.
Thus it seems to me quite
certain that more than one distinct species has been described

Fig. 5. Crenothrix Kiihniana, Rabenhorst. n group of young filaments
attached below, a, b older filaments ; at the upper end of b single cells are
issuing from the opened sheath, c broad filament with flatly disk-shaped
cells in its upper portion, which are divided in basipetal succession along
the length of the filament into minute round spore-cells ; the spores are
issuing from the uppermost extremity of the open sheath, d, c spores
developing into young filaments. After Zopf. n magn. 450, a, b 540,
d, e 600 times.

$ viii.] Aquatic Saprophytes. Crenothrix. 75

under the name of Bacillus subtilis. Such collective names — col-
lective species, as we may shortly say — have occurred in all
branches of natural history and have been gradually dis-
entangled ; here, too, they will ultimately be cleared up. We
have only to keep an eye upon them, and not be induced by
names to adopt premature conclusions respecting them (35).

We will now proceed to give some examples.

The comparatively large arthrosporous forms, which are
described under the names of Crenothrix, Cladothrix, and
Beggiatoa, are found often in injurious, or at least in very dis-
agreeable quantities, in waters containing organic substances in
solution (36).

i. Crenothrix Kiihniana, Rabenhorst (Fig. 5), in the most highly
differentiated stage of its development, forms filaments, accord-
ing to Zopf, 1-6 p. thick and about i cm. long, attached at one
end to fixed bodies, entirely unbranched, straight or less often
slightly spirally twisted. The filament consists of a row of
cylindrical cells, which are half to about one and a half
times as long as broad. The outer layers of their lateral
walls coalesce and form a delicate sheath surrounding the whole
filament, which is colourless when young, but at a later period
is often coloured from yellowish to dark brown or brownish
green by salts of iron. The filaments not unfrequently break up
transversely into pieces, which float free in the water and collect
into flocculent masses. The segments of the filaments may pass
by repeated bipartitions into the form of isodiametric cells which
then round themselves off. In this way the cells of thicker
filaments first take the shape of flattish disks, and then divide
one or more times in the longitudinal direction of the filament
into small roundish cells (b, c}. These ultimately escape from
the sheath, either because the sheath swells up along its whole
length, or because it swells up and opens at the apex only and
allows the small cells to escape at that point ; the cells are either
passive and are thrust forth by the continued growth in length
of the lower portions of the filament, or have a slow movement

76 Lectures on Bacteria. [§ vm.

of their own. These minute cells may be called Cocci from their
form, or spores on account of their capability of further de-
velopment, for when cultivated in bog-water they develope into
new filaments resembling the parent-filaments (d, e). ' On the
other hand they may retain the Coccus-form and multiply, pro-
ducing at the same time a large quantity of jelly, and in this
state they form Zoogloeae, which vary in size from microscopical
minuteness to more than i cm. in diameter. They also occa-
sionally pass, according to Zopf, into the motile condition, and
back again into the resting-state. The Zoogloeae are at first
without colour, but like the sheaths of the filaments they gradu-
ally become coloured by deposition of iron. The Cocci also
may ultimately develope from the Zoogloea-state into the fila-
ments as at first described. The external conditions for these
formations are not certainly understood.

Crenothrix Kiihniana is found in every kind of water, even in
the water of the soil as far as twenty metres below the surface.
It may become a formidable nuisance in water-pipes, drain-
pipes, and the like, in which its tufts of filaments and its Zoo-
gloeae increase to such an extent as to form dense gelatinous
masses stopping up the passages; in reservoirs it may form
slimy layers several feet in depth. The water is thus ren-
dered unfit for drinking and for various technical uses, though
no direct injury to human health has been traced to the Creno-
thrix. We do not know that any other processes of decom-
position are caused by Crenothrix.

2. Cladothrix dichotoma, Cohn is of still more frequent occur-
rence than Crenothrix, especially in dirty water, such as the
outflow from manufactories and from similar sources, and also
in streams (Fig. 6). It often forms extensive films of flocculent
matter of a grayish white colour floating near the edge of the
water. Its delicate filaments, ensheathed as in the preceding
species, are chiefly distinguished from those of Crenothrix in
the full-grown state by being branched. Branching is effected
by any single cell of a filament bending one of its extremities

§ viii.] Aquatic Saprophytes. Cladothrix. 77

laterally out of the line of the rest, and then growing on in the di-
vergent direction and dividing transversely.
The divergent branch forms an acute angle
with the primary filament, and in relation
to the point of attachment or base of the
latter the angle is usually open upwards,
seldom the reverse. This form of branch-
ing, which is of common occurrence in the
Nostocaceae, in Scytonema, for example,
and Calothrix, has been termed false
branching, because the part which the
individual cells take in it, morphologically
speaking, is not the same as in most
of the other lower plants which have
filaments formed of a single row of cells ;
it is false only in this sense, and is really
a peculiar mode of branching.

Whatever else is known of the structure
and development of Cladothrix, especially
since Zopfs researches, so far agrees
with the accounts given of Crenothrix,
that only a few remarkable particulars
need be touched upon here; Zopfs
monograph should be consulted. First
of all it is not perhaps superfluous to re-
mark that Cladothrix also receives a de-

Fig. 6.

posit of iron oxide in the sheaths of its filaments, and becomes

Fig. 6. Cladothrix dichotoma, Cohn. a extremity of a live filament, which
grew originally in the direction r— p. The branches n, n have been formed
by lateral divergence and subsequent growth of segment-cells in the new
direction. The construction of the filament out of cylindrical segment-cells
is clearly shown at the apex of the branches ; elsewhere it is recognisable
only by the aid of reagents, b portion of a filament showing the segmen-
tation and the sheath ; the latter is empty in its upper half, except
where one cylindrical cell remains fixed in it. Magn. 600 times, but made
a little too broad in the drawing.

78 Lee hires on Bacteria. [$ vm.

coloured accordingly. The often striking accumulations
of ochre-coloured slime-masses in springs and small streams
which contain iron, the filamentous constituents of which are
known by the old name of Leptothrix ochracea, Kiitzing,
consist, according to Zopf, of this iron-containing Cladothrix.

The filaments multiply by the abscision and further growth
of portions, which form longer or shorter rods according to
their size — a mode also very common among the allied Nos-
tocaceae — and also, according to Zopf, by means of spores or
' Cocci/ that is, short rounded cells, which issue from the sheath
and develope into filaments.

The filaments, or single branches of them, instead of retaining
the usual tolerably straight form, may become spiral with more
or less narrow or open coils, and these spiral forms also may
break up transversely into separate pieces.

Both the longer and the shorter abscised rod-shaped and
spiral portions of filaments, and the round spores and Cocci
also, not unfrequently become motile, the longer ones
creeping or gliding with a slow movement, the short forms
displaying an active swarming motion, such as is described on
page 7.

Lastly, the four forms, the filamentous, the rod-like, the spiral,
and the coccoid, whether mixed together or separate from one
another, may remain united by a jelly into Zoogloeae, which
sometimes appear as bodies of considerable size with shrub-
like branching. The short forms may again become motile,
and swarm out of a Zoogloea; but they may also develope
again into the filamentous form, the typical form from which we
set out ; this has certainly not been directly observed in the case
of the spiral rods.

If all these statements are correct, Cladothrix supplies the
most complete example of a pleomorphous course of develop-
ment.

No more is known of injurious properties and decomposing
power in Cladothrix than in Crenothrix.

$ viii.] Aquatic Saprophytes. Beggiatoa. 79

3. The species of Beggiatoa (Fig. 7) agree closely, according
to Zopf, with Crenothrix and Cladothrix in their pleomorphous
course of development. Straight and spiral filaments, abscised
straight and spiral rod-like portions of filaments, the latter pro-
vided with cilia and described under the name of Ophidomonas
(d), round Cocci or spores (e-k) and Zoogloea-aggregates of
these, make their appearance in just the same alternation as in
the two preceding genera, rods, Spirilla, and Cocci having in many
cases a swarming motion. The distinction between them and the
species of Crenothrix and Cladothrix lies chiefly in the presence
of sulphur in their structure, and in the motility of the filaments
which, like those of Crenothrix, are never branched.

Beggiatoa alba, Vaucher, the most common species, has
colourless filaments, attached when quite intact to solid bodies
but easily breaking off from them and thus set free, and varying
in thickness from i to 5 p. The filaments consist of cells of
more or less elongate cylindrical to flat disk-like form, the latter
occurring especially in the thicker specimens. They have no
distinct sheath clothing the row of cells ; moreover, while the pro-
toplasm of Crenothrix and Cladothrix is uniformly clouded or
finely granular, in Beggiatoa alba it has disseminated through its
substance comparatively thick round highly refringent grains,
with a dark contour therefore, and composed of sulphur, as
Cramer has shown. Similar sulphur-grains are also present in
the non-filamentous states or forms assigned here by Zopf.
Their number is not the same in different filaments ; in some
filaments (c) but few are to be seen, and in parts of them
they may even be entirely wanting. In most filaments they are
present in large numbers, so large sometimes that they en-
tirely conceal the structure of the thread, which looks like a
rod having its uniformly clouded protoplasm traversed by a
dense mass of granules with a black outline. It is only by the
use of reagents which largely withdraw the water of the cells
that it is possible to distinguish them (£).

Again, the filaments usually exhibit active movements, such as

8o Lectures on Bacteria. [$ vm.

are known in the green Oscillatorieae, which have been noticed
already several times, and which are undoubtedly the near allies
containing chlorophyll of the species of Beggiatoa and of the
arthrosporous Bacteria. The movements consist in progression
in the line of the axis of the filament in one direction, or in
opposite directions alternately, together with rotation in a path
which forms the outline of a very pointed cone, or of a
double cone such as is described in the case of rod-shaped
Bacteria. These movements, when hastily observed, appear
to be gliding in a forward direction, while the ends of
the filaments swing hither and thither in the manner of a
pendulum. Sometimes also the filaments become curved, and
then often straighten themselves again with a jerk, showing their
great flexibility throughout their entire length.

Several other species of Beggiatoa are known : B. roseo-per-
sicina, distinguished by its rose-red to violet colour, and also
said to be pleomorphous, its Zoogloeae, according to Zopf,
being Cohn's Clathrocystis roseo-persicina ; B. mirabilis, Cohn,
known only in the filamentous form, a gigantic species 20-30 /A
in thickness; B. arachnoidea, Roth, and some others. Apart
from the differences indicated, all these agree with B. alba in the
characteristic marks, especially in the presence of sulphur-grains.

B. alba is one of the most common inhabitants of our waters.
It is found in the water of marshes, in the waters that flow
from manufactories, in hot sulphur-springs, and in these places
often in company with Cladothrix, and in the sea on shallow
coasts. B. roseo-persicina is less common in these localities ;
the other species mentioned above are known only as coming
from the sea. The species of Beggiatoa live on the decompos-
ing remains of organised bodies, especially plants; they are,
therefore, chiefly found at the bottom of water, where such objects
accumulate. They form there, when largely developed, slimy
membranous coverings or films of flocculent matter, which are
either white in colour or vary from rose to brown-violet, as in
B. roseo-persicina.

viii.] Aquatic Saprophytes. Beggiatoa. 81

The species of Beggiatoa are said to have the peculiar power
of reducing the sulphates contained in the waters which they
inhabit, especially sodium sulphate and gypsum, setting free the
sulphur and sulphuretted hydrogen. That the living protoplasm
is the seat of this process is shown by the appearance in it
of the sulphur-grains. The form-
ation of sulphuretted hydrogen
causes first the precipitation of iron
sulphide in the slime inhabited
by Beggiatoa, which is thereby
turned black, and then the presence
of sulphuretted hydrogen, either
dissolved in the water or set
free by evaporation, gives rise to
the well - known odour, and may
have a noxious effect on the
animals inhabiting the water. The
' white ' ground in the Bay of Kiel,
for example, covered by species
of Beggiatoa, is also called the
' dead ' ground, because it is
avoided by fishes, though not by
all animals (37). These plants
therefore play a peculiar and
important part in the economy of FiS- 7-

nature and of mankind. According to the statements of some

Fig. 7. Beggiatoa alba, Vaucher. a portion of a stout living filament.
b fragment of the same after treatment with alcoholic solution of iodine show-
ing the segmentation into cells, c a very thin living filament from the same
preparation as a. d motile spiral form (Ophidomonas). e-h formation of
spores ('Cocci') by successive division of the segment-cells of a stout filament
(e). The lumen of each spore is nearly filled up by a grain of sulphur. Inf
the division has advanced further than in e. g breaking up of the filament
into groups of spores, h the spores isolated. *, k spores appearing to
germinate ( ), in a state of motion, a-c magn. 600 times, but drawn a
little too large, </ 540 times, e-k 900 times, d-k after Zopf.

82 Lectures on Bacteria. [$ vm.

observers, they share this part with other plants which are green
and are related to the Oscillatorieae and Ulothricheae (25, p. 769).
The forms which have now been described are the largest,
but by no means the only, representatives of the aquatic Bac-
terium-flora.

The Spirilla which live in bog-water are remarkable forms,
and may be briefly illustrated here by two examples. Spirillum
Undula, Cohn (Fig. 8, A), forms small spirally-twisted rods of about
i p. in thickness. The width of the spiral in dead specimens is
about 3 ft, three times therefore the diameter of the cell, the height

of a turn of the spiral 5-6 n
(4-5 ^ according to Cohn).
Each individual is usually
formed of from ii to 2

„ turns only of the spiral ;

•p. 8 when it has reached this

length it divides transverse-
ly in the middle into two. According to Cohn 3 turns of the
spiral are only rarely attained. The rod consists of segment-
cells, which, as far as can be determined, are immediately after
division about as long as a half turn ; they separate from one
another as soon as they are of this size (a\ or after longer
growth.

Spirillum tenue, Cohn (Fig. 8, J5), is more slender and more
closely twisted than S. Undula, and has several connected turns
of the spiral, usually 3, 4, or 6. The length of each of the
segment-cells which compose the spiral is at the time of division,
as far as I was able to determine, about half a turn, the same
therefore as in S. Undula.

No other phenomena of development than growth and division
of the rods have been perceived in these two species, even during
a cultivation of some months' duration; they both remain

Fig. 8. A Spirillum Undula, Cohn ; at a separation into two segment-
cells. B Spirillum tenue, Cohn; three specimens of different lengths.
Magn. 600-700 times.

§ ix.] Aquatic Saprophytes. Spirillum. 83

constant in their forms and distinctions. They are often found
by themselves in the waters of bogs ; when 'they occur in large
quantities, and comparatively unmixed with other species, they
form dense swarms which, in S. Undula especially, are of a
beautiful dark reddish-brown colour. Single live rods are,
under the microscope, colourless and homogeneous. When
killed and treated with colouring reagents (iodine, anilin-dyes),
they exhibit a remarkable separation in the case of both species
into short irregular transverse zones of alternately darker and
lighter colour — a phenomenon which must not be confounded
with the transverse segmentation into distinct cells mentioned
above. Finally, both species are distinguished by the extreme
vivacity of their movements, and dart like meteors, says Cohn,
across the field of vision, the slender Spirillum tenue affording
in this way a very elegant display.

Many other forms of the kinds previously described, and
among them of endosporous Bacilli, might be mentioned as
living in water. We still desiderate such investigation of these
forms as would enable us to give a more exact account of them
and of the decompositions which they may effect ; the scattered
particulars which are known of them have no interest for us on
the present occasion. Of the germs of Bacteria which may be
found even in the purest waters when exposed to the air and
to dust I have already spoken in the fifth Lecture.

IX.

Saprophytes which, excite fermentation. Fermentations
of urea. Nitrification. Acetous fermentation. Vis-
cous fermentations. Formation of lactic acid. Kefir.
Bacillus Amylobacter. Decompositions of proteid.
Bacterium Termo.

WE have now to consider saprophytic forms which are known
to be the causes of distinct processes of decomposition or
fermentation, and as examples of more general interest we select

6 2

84 Lectures on Bacteria. [$ ix.

for closer examination the Micrococcus of urea, the nitrifying
Bacteria, the mother of vinegar, the Bacteria of lactic acid-
fermentation, of butyric acid-fermentation, and of the viscous
fermentation of carbohydrates and other bodies, and, lastly, the
Bacteria of the decompositions of proteids.

i. The normal urine of men and carnivorous animals if kept
exposed to the air acquires an alkaline and ammoniacal smell '
in place of the acid reaction present in it when fresh. The
cause of this is, that the urea takes in water and is converted
into ammonium carbonate. The originally clear fluid becomes
clouded by the presence, as examination shows, of a number of
lower organisms, among which there may be a variety of Fungi
and Bacteria. Pasteur first proved that one of these Bacteria,
Micrococcus Ureae, Cohn, was the exciting cause of this process
of fermentation in urea (38 ; 25, p. 697), by showing that the
Micrococcus, if grown pure and cultivated in a pure nutrient
solution containing urea, causes the same decomposition in it
as in urine.

The Micrococcus (Fig. 9) consists of small round cells about
0-8 p in diameter, which usually, though not in-
variably, remain connected together in rows often
of more than 12 cells. These rows are in many
cases curved and bent in an undulating manner,
and are often ultimately wound into coils or small
g' 9* Zoogloeae as they may be termed, in which the cells
appear to be irregularly heaped together. At the first beginning
of a culture the cells, according to von Jacksch, are cylindrical,
though not very much longer than they are broad ; they retain
this shape for some time, firmly united together in genetic
connection, forming therefore rod-like rows of short cylindrical
cells, and afterwards become rounded off. We may therefore, if we
please, speak of a ' rod-form/ but we shall not gain in clearness
by so doing. No distinct spores have been observed in this

Fig. 9. Micrococcus Ureae, Cohn, from decomposing urine. Cells
separate or united in rows ( = Streptococcus). Magn. noo times.

§ ix.] Fermentation of urine. Nitrification. 85

Micrococcus. Leube has recently demonstrated the existence
of four quite distinct species of Bacteria, in addition to the
Micrococcus just described, producing the same effects.

Micrococcus Ureae, as we learn from experiment, requires a
supply of oxygen for its vegetation. It can hardly therefore
be the cause of the alkalisation of the urine inside the bladder,
which has been observed in some affections of the bladder and
is supposed to be an effect of it, for the oxygen required is not
present. But numbers of small Bacteria are found in urine in
this diseased alkaline condition, and it must be assumed that
having found their way spontaneously or forcibly, as for instance
by means of the catheter, through the urethra into the bladder
they are the exciting cause of the decomposition in question.
It must accordingly be further assumed, that other species which
are anaerobiotic have the power of producing fermentation in
urine, or processes similar to it. Leube's species appear from
the accounts given of them not to be anaerobiotic. Miquel
(15, vol. for 1882) has in fact discovered a very delicate rod-
form occurring in dust, which he names Bacillus Ureae and
which vegetates anaerobiotically, converting urea into ammo-
nium carbonate in the same way as Micrococcus Ureae.

We learn from van Tieghem that hippuric acid is converted
into benzoic acid and glycocol in the urine of herbivorous
animals by a Micrococcus, which is perhaps identical with
Micrococcus Ureae, but requires further investigation.

2. In connection with the forms which change urine into
ammoniacal compounds, we may now turn to the consideration
of nitrification, the oxidation of compounds of ammonium into
nitrates, such as occurs on a large scale in the formation of
saltpetre, in so far as this also is due, according to the observa-
tions of Schlossing and Miintz (25, p. 708 ; 39), to the vegeta-
tion of small Bacteria. The phenomenon occurs in moist soil
penetrated by air and containing compounds of ammonium with
small quantities of organic matter and basic substances, for
example, salts of calcium. It may be induced artificially in

86 Lectures on Bacteria. [§ ix.

nutrient solutions containing compounds of ammonium, if a
small quantity of soil is added at a suitable temperature, the
optimum being 37° C., and with constant access of air.

Thus the formation of saltpetre is a result of the vegetation
of Bacteria ; it ceases when these are killed ; it also commences
when these Bacteria, artificially reared, are placed by themselves
without soil in the proper nutrient solution. From this we must
conclude that we have here an oxidation produced by the Bacteria
which are widely diffused in the superficial layers of a moist soil.

The morphology of these Bacteria is not yet clearly ascertained.
According to the above-named writers, the individual organism
is a very small delicate Micrococcus, somewhat resembling
M. aceti, and van Tieghem, in his text-book, has named it
M. nitrificans. But the appearance assumed by this form is not
clear from the descriptions, and Duclaux speaks of a mixture of
different forms. The importance of the processes calls for a
more exact study of them, that is, of the question, whether nitrifi-
cation is the exclusive function of a distinct species, or of several
species and their combinations.

3. Acetous fermentation (25, p. 504; 40, 41,42). If an acid
nutrient solution containing a small percentage of alcohol is
exposed to the air at a temperature of about 30-40° C., vinegar
is formed in it, that is, the alcohol is oxidised into acetic acid.
The fluid is at the same time more or less clouded, and its sur-
face covered with a thin colourless membrane. This membrane
consists in most pure cases of mother of vinegar, Micrococcus
aceti, Bacterium aceti (Arthrobacterium aceti ; Mycoderma aceti
in Pasteur's earlier nomenclature). Pasteur showed twenty-
five years ago that this Bacterium lives and grows on the organic
and mineral substances contained in the solution, and absorbing
oxygen from the air oxidises the alcohol into acetic acid. The
exact proof was obtained by adding 4 per cent, of alcohol and
1-2 per cent, of acetic acid to pure nutrient solutions of the
kind described on pages 61 and 67, and then introducing into
the liquid an infinitesimal quantity of membrane of mother of

§ ix.] Acetous fermentation. 87

vinegar. In the proper temperature, and with free access of
atmospheric air, the mother of vinegar developes into the mem-
brane described above, and as this takes place the alcohol in
solution is converted into acetic acid.

The various methods used in the arts for the preparation of
vinegar, into the details of which we do not here enter, are cul-
tures of Micrococcus aceti at the proper temperature, and with
exposure to the air under regulations which vary in each par-
ticular case. The mixtures from which the vinegar is to be
prepared — beer, wine, &c., with addition of previously formed
vinegar, have the essential characters of nutrient solutions as
described above. The vinegar of commerce is a diluted solution
of acetic acid, and contains a larger or smaller number of the
Micrococcus aceti. Germs of this organism are also diffused
elsewhere, and in particular are never wanting in the vessels
used for the preparation and storing of alcoholic fluids. When
these turn acid, owing to careless management, it is in part at
least owing to the activity of the Micrococcus. M. aceti, like
M. Ureae, is as far as we know at present an arthrosporous
Bacterium, and resembles the latter in shape (Fig. 10). It con-
sists usually, and always in the normal vegetating stage, of
cylindrical cells, which are not much longer than broad, and
have a transverse diameter of about o-8-i /*. The cells multiply
by the usual process of transverse division, and often remain
united together in rows forming long filaments ; in older cultures
they are often thrust out of the filament but are held together
by jelly. With this short-celled Micrococcus-form cell-rows
often occur, in which some cells are in the form of long rods,
others not only several times longer than broad, but also fusiform
and so swollen in a bladder-like manner that their greatest
breadth may be more than four times the diameter of the ordinary
cells. No one would suppose these inflated cells to belong to
the small ones, if they did not usually occur with them, either
singly or several together, as members of the same genetic rows
and connected with them by a variety of intermediate forms.

88 Lectures on Bacteria. [§ ix.

Cases of this kind have been observed also in other Bacteria ;
these are the cells with which we made acquaintance before on
page 10 under Nageli's name of involution-forms. Whether they
are really retrograde states, as this name would express, or
diseased forms, I shall not undertake to say in the case of
the Micrococcus aceti. They certainly do not appear at all in
some cultures, or only one by one, while in others they are ex-
traordinarily numerous, and in the latter case I could never find
that they gave the 'impression of being incapable of further
development.' Positive statements, however, are at present no
more possible respecting their significance in the history of
development than they are respecting the conditions of their
presence or absence.

A Micrococcus has been found by E. Chr. Hansen, and named
by him M. Pasteurianus, which behaves in every respect in
the same way as M. aceti, except that its cells
throughout the successive generations show the
blue reaction of starch with iodine (see page 5),
while the ordinary M. aceti is coloured yellow
by that reagent. This fact shows at once that
M. aceti although certainly the usual is not the
only vinegar-forming species. In fact the power
of producing acetic acid has been observed in
some other Bacteria, which are, however, comparatively unim-
portant to us for our present purpose.

Micrococcus aceti has the power not only of producing but
also of destroying vinegar. When it has oxidised all the alcohol
of a fluid into acetic acid, it may continue to develope, as
Pasteur showed, and by a further process of oxidation convert
the acetic acid into carbonic acid and water, the final products
of all decomposition.

Fig. 10. Micrococcus aceti (mother of vinegar) ; roundish cells, single
and united in rows, also rows of elongated rod-like and fusiform or swollen
flask-shaped members ; the latter from a culture at a temperature of 40° C.
Magn. 600 times.

§ ix.] Viscous fermentation. 89

It does not strictly belong to our subject, but it is perhaps
not superfluous to remark that every white membrane which
makes its appearance spontaneously on the surface of a fluid
suitable for forming vinegar is not necessarily mother of vinegar.
The white and ultimately wrinkled film which usually forms on
beer or wine, is a well-known object, and to the naked eye looks
so like the membrane of vinegar as to be often mistaken for it.
But under the microscope it is distinguished from it by being
formed from a comparatively large Sprouting Fungus, Saccharo-
myces Mycoderma, which has no direct connection with the
formation of vinegar. On the contrary, it converts alcohol and
other bodies in solution by oxidation into carbonic acid and
water. Indirectly it may, indeed, in this way promote the for-
mation of vinegar by destroying any excessive amount of alcohol
and acid which would impede the development of the Micro-
coccus aceti, and so providing it with a substratum favourable
to its vegetation.

4. We now come to a series of examples of phenomena of
fermentation and decomposition produced by Bacteria in the
sugars and in the allied carbohydrates. When in the following
remarks we speak simply of saccharine solutions, it is always to
be understood that they contain also the constituents required
for nutrient solutions.

We must first of all say a word or two respecting the so-called
viscous fermentations (25, p. 572, 43, 44). The juices of plants
which contain sugar, such as onion and beet, when extracted
by crushing often assume a sticky viscous character, and produce
carbonic acid and in many cases also mannite. Organisms
also, to be described presently, make their appearance as a
sediment in the viscous mass. If a small portion of the sub-
stance is introduced into a suitable solution of cane-sugar which
was before free from germs, the same viscidity is caused in it
as the organisms develope. These must therefore be regarded
as the causes of the change. The organisms in question are,
according to Pasteur, of two kinds. The first is a Micrococcus

90 Lectures on Bacteria. [$ ix.

very like M. Ureae and forming rows of bead-like cells ; by itself
it produces viscidity and mannite in the cane-sugar solution with
separation of carbonic acid. Secondly, cells of irregular shape
and somewhat larger size than those of the Saccharomyces of
beer-yeast (see page 98), and with morphological peculiarities,
which the descriptions which we have of them do not at all
clearly explain ; these cells are at all events not Bacteria, and
are said to cause viscidity only and to form no mannite in the
cane-sugar solution. The viscous substance itself, of which we
are here speaking, is stated to be a carbohydrate with the for-
mula of cellulose (C6H10O5).

From these data, which it is true are still very imperfect, it
must be acknowledged that the disengaged carbonic acid and the
mannite are products of fermentation ; but the viscous substance
itself is more probably to be placed in the category of muci-
lagino-gelatinous cell-membranes, which are so common in Bac-
teria and Fungi and which we have already observed so often
in connection with the Zoogloeae ; it is therefore not a product
of the fermentation of the nutrient solution, but of the assimi-
lation of the organism which excites the fermentation.

This view is distinctly supported by the history of the
development and vegetation of Leuconostoc mesenterioides, the
frog- spawn-bacterium of sugar-manufactories, examined by Cien-
kowski and van Tieghem, which has the power of converting
large casks of the juice of the sugar-beet in a short space of
time into a mucilagino-gelatinous mass and thus of causing
considerable loss. Durin saw a wooden vat containing fifty
hectolitres of a 10 per cent, solution of molasses become filled
with a compact Leuconostoc-jelly in less than twelve hours. The
development of Leuconostoc was mentioned above on page 2 2 as
an example of an arthrosporous course of development, but a
more detailed description of it must now be given. See Fig. n.

The round spore-cell (d) germinates in a nutrient solution,
and appears at first to be surrounded by a gelatinous envelope
several times thicker than the spore itself (e). Then a simple

§ ix.] Viscous fermentation. Leuconostoc. 91

filiform row of isodiametric cells is formed by the growth and
successive transverse division of the protoplasmic body, and the
envelope follows the longitudinal growth of the cells, forming a
thick, rounded, cylindrical sheath of the consistence of firm gela-
tine round the filament. The transverse walls also of the filament
in its young state are gelatinous, appearing as broad pellucid
partitions between the protoplasmic bodies and being continued
into the sheath on the outside (f-i}. The partitions disappear
in older filaments and the protoplasmic bodies are in contact

Fig. ii.

with one another (b). As the single filament developed from
a spore increases in length it forms successively stronger curva-
tures, which lay themselves in loops round each other and round

Fig. ii. Leuconostoc mesenterioides, Cienkowski. a sketch of a Zoogloea.
b section through a full-grown Zoogloea before the commencement of spore-
formation, c filament with spores from an older specimen, d isolated ripe
spores, e-i successive products of germination of the spores sown in a
nutrient solution. Order of development according to the letters. In e the
two lower specimens show fragments of the ruptured spore-membrane on
the outer surface of the gelatinous envelope indicated by dark strokes.
i portion of the gelatinous body from h divided into short members, and
with the members separated from one another by pressure, a natural size,
other figures magn. 520 times. After van Tieghem in Ann. d. Sc. nat.
ser. 6, VII.

92 Lectures on Bacteria. [$ ix.

other filaments. Growth is also accompanied with separation
of the originally elongated gelatinous filaments into shorter
transverse sections, which are always surrounded by the sheath
and remain firmly attached to one another (*). Closely twisted
coils are thus produced of the size of or larger than a hazel-nut
(a), forming the compact gelatinous bodies mentioned above
which accumulate and fill the casks. Sections through older gela-
tinous bodies appear to be divided from the edges of the sheaths
into chambers in which the curved cell-rows lie (6). When the
development is completed, and the nutrient solution exhausted,
the gelatinous sheaths deliquesce, the cell-rows separate, and
most of the cells die. But previously to this single cells, not
occurring in any particular order in the row, develope into
distinct spores, becoming a little larger than the rest, and sur-
rounding themselves with a firm non-gelatinous membrane, the
outer coat of the spore (c). It was from these spores that we
set out in the description ; but every living portion of a filament
that from any cause becomes separated from the connection
may develope into a new gelatinous body. The vegetating
protoplasmic bodies are, according to van Tieghem, 0-8-1-2 /M
in thickness, the sheaths 6-20 /n, the spores 1*8-2 //.

In the germination of the spore the gelatinous sheath origi-
nates (e) as a newly formed inner layer of the cell-wall, or by the
considerable increase in thickness of a pre-existing inner layer ;
the outer coat of the spore then bursts into pieces. This shows
decisively that the sheath is a product of assimilation, a growing
part of the growing filament. The gelatinous substance has
the same chemical composition as the mucilage of viscous fer-
mentation. The material for its formation is of course supplied
by the sugar of the solution. In van Tieghem's cultures
of Leuconostoc in a solution of glucose, air being admitted
and the fluid prevented from becoming strongly acid, about
40 per cent, of the sugar which disappeared was expended
in the formation of the Leuconostoc itself; the greater part of
the remainder was converted by combustion into carbonic acid

§ ix.] Lactic acid-fermentation. 93

and water without any sensible development of gas. The culti-
vation of Leuconostoc in solution of cane-sugar soon resulted in
the splitting (inversion) of the sugar into glucose and laevulose,
and for this reason it is so highly detrimental to the fabrication
of cane-sugar ; the sugar then disappears as in the first experi-
ment, the glucose first, and about 40-45 per cent, of the sugar
which disappears is expended in the formation of the Leuconostoc.

A similar formation of mucilage to that of the viscous
fermentation of saccharine solutions, is seen in the ropiness
of beer and wine, in which condition they are capable of
being drawn out into filaments. These phenomena also are
accompanied, or doubtless caused, by the formation of Micro-
cocci united together in rows, and the slime may very well have
the same origin and morphological significance as the jelly of
Leuconostoc. It may be observed in passing that other so-
called ailments of beer and wines are caused by Bacteria, but
we cannot enter into any further description of them here1.

5. The old method of inducing ordinary lactic acid fermen-
tation (25, 45) of the different kinds of sugar is by adding sour
milk or cheese to a fermentable solution and keeping it exposed
to the air at a temperature of 40-50° C. Calcium carbonate
or zinc-white must also be added in order to throw down the
lactic acid as it is disengaged, because the fermentation ceases
as soon as the acid content of the fluid exceeds a certain
amount.

Pasteur first showed that a particular Bacterium, and others
perhaps along with it, was introduced with the cheese or sour
milk, and that it vegetates in the fluid, especially in the sediment
at the bottom, and acts as a ferment. It appears in the form
of minute cylindrical cells, which immediately after division are
scarcely half as long again as they are broad, and average o'5 p.
in thickness. After each division they usually soon separate
from one another, rarely remaining united, and forming short

1 See Pasteur, Etudes sur le vin, Paris, 1866, and Etudes sur la biere,
Paris, 1872.

94 Lectures on Bacteria. [$ ix.

rows ; portions of the transverse partition- walls are plainly seen
and are indicated by a slight constriction. They have no power
of independent movement. In form, therefore, this species resem-
bles the Bacterium of vinegar and may be called Micrococcus
lacticus, as has been done by van Tieghem. Hueppe, however,
states that there is a formation of spores, if I understand him
aright, after the endosporous type. If this is confirmed, the
Bacterium of lactic acid is a very small Bacillus in our use of
the term, and must be so named.

It is evident that this Micrococcus or Bacillus is always
present in milk, not of course when it comes from the udder,
but as soon as it is in use. The germs of the organism are
diffused to such an extent in the cattle-stalls and in the vessels
of the dairy that it never fails to be developed. This is why
milk turns sour, because the Bacterium excites lactic acid-
fermentation of the sugar contained in the milk; and when
the acidification has reached a certain point, the lactic acid
causes the homogeneous gelatinous coagulation of the casein,
which is characteristic of good buttermilk.

Further physiological peculiarities of this Bacterium have been
described in detail in Hueppe's careful treatise, and should be
studied there.

In the Bacillus or Micrococcus lacticus which has now been
described we have made acquaintance with a very widely diffused
and active lactic acid-ferment, but it is by no means the only
one. On the contrary, the number of species of Bacteria which
form lactic acid in saccharine solutions or in milk appears to
be more than usually large. Hueppe alone mentions five, and
all Micrococci ; one of these is known to us as M. prodigiosus of
the blood-portent mentioned on page 14. Two others Hueppe
discovered to be the exciting cause of the lactic acid which
occurs in the human mouth, while he found the Bacillus first
described only occasionally in the mouth. We still wait for
closer investigation into most of these forms, and into their
operation as ferments. It is, however, already plain that on all,

J ix.] Kefir. 95

or almost all, occasions on which lactic acid makes its appear-
ance in considerable quantities we may expect to find a ferment-
organism, and indeed a Bacterium which produces it, but this
need not always be the one form, described above as that of
ordinary acidification of milk. It is well to call particular
attention to this point on account of the wide diffusion of lactic
acid, for example in human food, whether this be purposely
made sour, -as in ' sauerkraut ' and the like, or is a case in which
the turning sour indicates decomposition, as in soured vegetables
or beer, so far as the effect in the latter case is not due to the
presence of acetic acid.

6. This will be the best place to recur briefly to the Bac-
terium of kefir mentioned above on page 13, which is connected
with an interesting change in milk. It was discovered by E. Kern
in 1882 (46). Kefir or kephir is the name of a drink, a fluid
effervescing kind of sour milk containing a certain amount of
alcohol, which the inhabitants of the upper Caucasus prepare
from the milk of cows, goats, or sheep, and therefore not to be
confounded with the koumiss obtained by the Nomads of the
Steppe originally from mares' milk, with which we are not at
present concerned. The drink is prepared by adding to the
milk the bodies described above as a beautiful example of
Zoogloeae, which bear the name of kefir-grains. The Cauca-
sians make use in this process of leathern bottles to hold the
milk, the more polished European employs less objectionable
glass vessels. The recipe followed by the latter is mainly as follows.

Living and thoroughly moistened kefir-grains are added to
fresh milk in the proportion of i volume of the grains to about
6-7 volumes of milk. The mixture is exposed to the air for
twenty-four hours at the ordinary temperature of a room, pro-
tected from dust by a loose covering only, and is frequently
shaken. At the end of twenty-four hours the milk is poured
off from the grains, which may be employed again for a fresh
preparation. The milk itself, which we will term ferment-milk,
is then mixed with twice the quantity of fresh milk, put into

96 Lectures on Bacteria. [$ ix.

bottles well corked and frequently shaken. The bottled sour
milk, which is more or less highly effervescent, is fit to drink
in one or more days. It has the somewhat acid taste indicated
by its name, and contains an amount of carbonic acid varying
according to the temperature and the duration of the fermenta-
tion, but sometimes sufficient to burst the bottles or drive out
the corks, and, as has been already said, a certain amount of
alcohol, which in the cases examined in Germany was less than
i per cent, but according to other accounts may be 1-2 per cent.

The changes in the milk which produce the drink here de-
scribed are brought about by the combined activity of at least
three ferment-organisms. The kefir-grains, as has been already
stated (page 13), consist chiefly of the gelatinous filamentous
Bacterium which has been named by Kern Dispora caucasica ;
intermixed with this organism and enclosed in the tough Zoo-
gloea are numerous groups of a Sprouting Fungus, a Saccharo-
myces, resembling the yeast-plant of beer; thirdly, there is
the ordinary Bacterium of lactic acid, which partly adheres to
the grains in company with some unimportant Fungi and other
impurities, and partly is introduced each time with the fresh
milk.

We know at least enough of the ferment-effects of these
organisms or of their near allies to enable us to form a probable
idea of the course of the changes which have been described.
The acidification is caused by the conversion of a portion of the
milk-sugar into lactic acid by the Bacterium of that acid. The
alcoholic fermentation, that is, the formation of alcohol and of a
large part at least of the carbonic acid, is indebted for its
material to another portion of the milk-sugar, and for its exist-
ence to the fermenting power of the Sprouting Fungus. The
kefir-grain, like its constituent the Sprouting Fungus working by
itself, gives rise to alcoholic fermentation in a nutrient solution
of grape-sugar, though of a less active kind than that caused
by the Sprouting Fungus of beer-yeast. But alcoholic fermenta-
tion is produced in milk-sugar as such neither by Sprouting

I ix.] Kefir. 97

Fungi with which we are acquainted, nor, as experiment has
shown, by those of which we are speaking. To make this
fermentation possible, the sugar must first be inverted, split
into fermentable kinds of sugar. According to Nageli(9, p. 12),
the formation of an enzyme which inverts milk-sugar is a
general phenomenon in Bacteria, and Hueppe has shown that
it is probable in the case of his Bacillus of lactic acid in par-
ticular; the inversion required in this case to enable the
Sprouting Fungus to set up alcoholic fermentation is the work
therefore of the Bacillus of lactic acid, or of the Bacterium of
the Zoogloea, or of both.

Lastly, it is to be observed that the kefir is in the fluid state.
Coagulation of the casein does indeed take place, but either it is
from the first not in the homogeneous gelatinous form of
ordinary sour milk but in small lumps and flakes suspended in
serum, or the gelatinous coagulations which are sometimes
present at first are soon partially dissolved. It is evident then
that the casein, which has already been coagulated, is partially
liquefied (peptonised). This must be ascribed to the enzyme
formed by the Bacterium of the Zoogloea, because according to
our present knowledge the Bacterium of lactic acid has no power
to peptonise casein or otherwise liquefy it.

This view, which corresponds in all important points with
Hueppe's brief communication on the subject, is in accordance
with the remarkable fact that the ferment-milk, by means of
which the kefir is prepared, contains a large number of actively
growing cells of a Sprouting Fungus and of Bacteria of lactic
acid, but no Bacteria of the Zoogloea, or only small and doubt-
ful quantities of them. The grains as a rule strictly retain
these, while they part with the sprouting cells to the milk. There
is obviously no objection to the supposition that enzymes pro-
duced from the grains pass over into the ferment-milk and co-
operate with it.

In this way, as I have said, we may explain the formation of
kefir, and I gave this account of it in the first edition of

H

98 Lectures on Bacteria. [§ ix.

this work while calling attention to the want of precise
investigation.

But A. Levy, of Hagenau, has recently discovered that the
effervescing alcoholic kefir may be obtained without any
kefir-grains, but simply by shaking the milk with sufficient
violence while it is turning sour. A trial convinced me of the
correctness of this statement. The kefir obtained by shaking
was not perceptibly different in taste or other qualities from the
kefir of the grains, and the determination of the alcohol, kindly
made for me by Professor Schmiedeberg, gave i per cent,
in some specimens of the former kind and 0-4 per cent, in
one of the latter ; sour milk not shaken contained no trace of
alcohol or only a doubtful one. Our former explanation there-
fore must be abandoned, and there is no other ready at present
to take its place; but the case is full of instruction for our
warning.

Turning now for a moment to the life-history of the kefir-

grains, we may briefly remark
with respect to the Saccharo-
myces, that it grows in the
sprout-form observed in the
Saccharomyces of beer-yeast,
partly forming groups or nests
inside or on the surface of
the grains, partly separating
from them and entering the
Fi&' I2- surrounding fluid. It is on

an average smaller and narrower than Saccharomyces Cere-
visiae, but some idea of its form may be gathered from a figure
here reproduced of that Fungus which it very closely resembles
(Fig. 12). Of the Bacterium, of which the grains chiefly consist,
I believe that we also know only the vegetative development.

Fig. 12. Saccharomyces Cerevisiae. a cells before sprouting, b-d
sproutings in fermenting saccharine solution (sequence of development
according to the letters). Magn. 390 times.

$ ix.] Kefir. Bacilhis Amylobacter. 99

It appears, as has been already said, in the form of small slender
rods united into filaments, which are closely interwoven and held
together in Zoogloeae by means of a jelly.

The source of the grains has not been traced further back
than the leather milk-bottles of the mountaineers ; their place of
birth is still unknown. They come to us in the dry state, and
are kept in this manner in the Caucasus also. They must be
dried quickly, and the best plan is to dry them in the sun.
Much of the dry imported material is dead when it comes, as
far as my experience goes. The softened living grain grows
slowly in the milk, as we have already seen (page 59), with
uniform increase in size and multiplication of all its parts.
This growth is accompanied by the separation from time to time
of single lobes of different sizes from the whole, and thus the
number of the grains increases. From isolated observations I
regard it as possible that Dispora-cells sometimes issue from a
grain, and may then develope into kefir-grains, but this is not
certain. Distinct formation of spores has not yet been observed.
Kern it is true has not only described such a formation, but
named the Bacterium of kefir Dispora, because two spores are
formed each time in a rod, one at each end. After repeated
observation I have never seen anything of the kind, though I
have very often seen figures which answer to Kern's represent-
ations, and which are due to the circumstance that a rod or
portion of a filament is curved and its middle portion lying
horizontally is seen in its length, but one or both of its
extremities which bend away from the horizontal plane are
viewed in cross-profile. It is by such appearances that Kern
has allowed himself to be misled. If we allow the name
Dispora to be used provisionally, it must not be forgotten that
the character which it is intended to express does not really
exist.

7. We will close the series of examples of the Bacteria which
excite characteristic fermentations in non-nitrogenous com-
pounds by the consideration of a species of Bacterium which is

H 2

ioo Lectures on Bacteria. [§ ix.

one of the most widely diffused, and most important and varied
in its powers of decomposition, the Bacillus of butyric acid,
known as B. Amylobacter, van Tieghem, B. butyricus, Clostri-
dium butyricum, Prazmowski (22, 47, 48), and by some other
names. I think that I ought also to refer Bacillus butylicus of
Fitz to this species, though it must be remembered that this
species as at present established may perhaps be divided into
several on further investigation.

Bacillus Amylobacter (Fig. 1 3) is nearly i p. in thickness, and
vegetates in the form of slender cylindrical rods united at
most into short rows, and usually in a state of active movement.
It is easy to characterise morphologically, because the sporo-
genous cells swell out till each becomes
fusiform and then produce inside the part
which is most enlarged an elongate ovoid
spore with rounded ends and sometimes
slightly bent, surrounded with a broad

0 ^ i 1 I S gelatinous envelope, and much shorter and

1 m j B usually much narrower than the swollen part

of the cell in which it is formed. It is also
distinguished by the starch-reaction or
granulose-reaction described on page 18,
which is usually manifested by the cells
before the spores are formed, and by its
habit, since it does not usually aggregate
and form distinct membranes or larger Zoogloeae, and at the
period of spore-formation often appears in the form of the motile
rods with capitate end, which were likewise noticed on a former
occasion (see page 17). Otherwise Bacillus Amylobacter is very
morphous; the most different special forms of sporogenous

Fig. 13. Bacillus Amylobacter. Motile rods, some cylindrical and
without spores, some swollen into various special shapes and with spore-
formation in the swelling, s mature spore with broad gelatinous envelope
and isolated by the deliquescence of their mother-cells. Magn. 600 times,
with the exception of s which is more highly magnified.

§ ix.] Bacilhis Amylobacter. 101

cells make their appearance irregularly mixed up together and
connected with one another, as Fig. 13 shows.

In its mode of life, Bacillus Amylobacter is a type of Pasteur's
anaerobia (page 54), though the possibility of its vegetating
in the presence of oxygen is not excluded. Living in this
manner it is first of all the chief promoter of butyric acid-
fermentations of sugars, that is, of fermentations in which
butyric acid is the primary product and is accompanied by other
products which vary greatly according to the special material,
as is shown by the researches of Fitz. It may also be assumed
that it is this species which causes butyric acid-fermentation
in lactates, though an objection brought by Fitz against this
view has not yet been quite removed. In this special cha-
racter of the ferment of butyric acid B. Amylobacter plays
an important part in human economy, whether as the cause of
fermentation in acid articles of vegetable food which in this case
rapidly rot, or of the butyric acid-fermentation which is essential
to the ripening of cheese.

Bacillus Amylobacter is also a specially active agent, as van
Tieghem has shown, in the decomposition of decaying parts of
plants by destroying the cellulose of the cell-membrane. It
does not attack all cell-membranes, not for example suberised
membranes, those of bast-fibres, of submerged water-plants, of
Mosses and many Fungi ; on the other hand, the membranes of
fleshy and juicy tissues, as in leaves, herbaceous stems, cortex,
tubers of land-plants, and softer kinds of wood, are especially
liable to its attacks. In all these cases it first of all decomposes
the cellulose into dextrin and glucose by means of a diastatic
enzyme which it disengages, and these then undergo the
butyric acid-fermentation. Most starch - grains escape its
attacks, but paste and soluble starch are very liable to them.
Hence the maceration and destruction of parts of plants that
are kept wet are to a great extent the work of this Bacillus,
alike in cases which involve the economical processes of mankind,
such as the maceration and rotting in water of hemp, flax, and

IO2 Lectures on Bacteria. [§ ix.

other textile plants, in order to obtain the fibres, and in such as
the wet-rot of bad potatoes according to Reinke and Berthold.
Van Tieghem is inclined to attribute to Bacillus Amylobacter a
prominent part in the nutrition of ruminant animals, since it
vegetates in their stomachs and splits up the cellulose of their
food into soluble products of decomposition capable of re-
sorption.

Van Tieghem has also shown or made it probable that this
Bacillus has been an active destroyer of cellulose at least since
the period of the coal-measures. Fossil plants silicified in a
more or less advanced state of maceration, show in their sec-
tions the same progression in the destruction of the cell-wall
which is observed in macerated plants of the present day, and
also the silicified remains of a Bacterium, which he identifies
with B. Amylobacter.

The active powers of fermentation and decomposition of this
Bacillus are not confined to the non-nitrogenous bodies just
enumerated, as is shown by the investigations of Fitz, which
have been before briefly mentioned. The details of these in-
vestigations will be found in the works already cited. The
behaviour of this Bacillus to proteids will be noticed presently.

Though there can be no doubt that much the larger number
of fermentations producing butyric acid are caused by Bacillus
Amylobacter, yet it cannot be said to be the exciting cause of
all fermentations which have butyric acid for their primary pro-
duct. On the contrary, Fitz describes a large round chain-
forming Micrococcus and a short non-endosporous rod-shaped
Bacterium, as ferments producing butyric acid in calcium
lactate and in some sugars. His former statement, that
Bacillus subtilis forms butyric acid by fermentation from starch-
paste, and that this fermentation is a very advantageous method
of procuring butyric acid, must be founded on a confusion of
forms. The typical B. subtilis of Brefeld and Prazmowski can-
not be the species intended, for Prazmowski distinctly states that
it does not excite fermentation of any kind in starch-paste.

§ ix.] Decomposition of proteid. 103

Vandevelde's observation (49) that B. subtilis certainly gives
rise to slight fermentation in meat-extract, glycerine, and grape-
sugar, after the oxygen is consumed, with special production of
butyric acid, can hardly be taken into consideration, for he
speaks of very small amounts produced from fermentation,
while Fitz states that the amount of butyric acid produced is
very large.

In the absence of more precise morphological observations,
the species of the Bacillus subtilis of Fitz's starch-fermentation
must for the present remain undetermined. In connection with
this question I will here briefly repeat the remark made on
page 74, that there are certainly several saprophytic and endo-
sporous species of Bacteria, which are very like Bacillus subtilis,
and have no doubt been frequently confounded with it. Nothing
certain can at present be stated with regard to their effects as
ferments. The B. subtilis of Brefeld and Prazmowski, the only
form to which I give the name, is clearly distinguished from
them by the assemblage of characters described in former lec-
tures, and by the mode of germination (page 21), as well as by
their collecting on the surface of the nutrient fluid into
membranes which are folded in wrinkles, and consist of
filaments disposed in parallel zigzags and ultimately forming
spores, and by the ellipsoid comparatively broad spores them-
selves.

8. If we examine in conclusion the decompositions which occur
in proteid compounds and in glue, we shall first of all see no
reason to doubt that all of them, and especially those which are
accompanied by the development of gas and are usually known
as processes of putrefaction, are the work of Bacteria. The
data which we possess show that the processes in these decom-
positions and the participation of the different species of Bac-
teria in them are, as might be expected, extremely multifarious.
The work of distinguishing between the species of Bacteria con-
cerned and their specific modes of operation is still in its
infancy.

1O4 Lectures on Bacteria. [§ ix.

A point of great importance to notice here is the liquefaction
of the gelatine which occurs in cultures of some Bacteria, for
example Bacillus subtilis and B. Megaterium, but not in all.

And here the many-sided Bacillus Amylobacter must again
be mentioned. According to the researches of Fitz and Hueppe,
this Bacillus decomposes the casein of milk in the following
manner : the casein first coagulates as when rennet is employed,
the effect being produced by the enzyme disengaged by the
Bacillus ; it then becomes liquid and is converted into peptone,
and then into further and simpler products of decomposition,
among which leucin, tyrosin, and ultimately ammonia, have
been ascertained. The fluid meanwhile acquires a more or
less pronounced bitter taste. Similar if not identical effects
on the casein of milk were observed by Duclaux to pro-
ceed from the Bacilli which he names Tyrothrix (see page 52),
the greater part of which must also morphologically approach
near to B. Amylobacter. Tyrothrix tenuis, for example, first
produced the coagulation of rennet, then liquefaction, and after
that formation of leucin, tyrosin, ammonium valerianate, and
ammonium carbonate. There can be no doubt that these
changes, and others connected with them, are the essential part
of the phenomena which constitute the process of ripening of
the cheese prepared from .the coagulated milk, the above-named
Bacteria, with some others, being contained in the cheese, and
being procurable from k for the purpose of examination.

Bienstock (50) has recently submitted the Bacteria of human
faeces to careful examination, and found that in those of adults,
besides other forms which are unimportant in reference to the
processes in question, there is always a particular Bacillus
present, which he regards as the specific cause of putrefaction
not only of the bodies contained in the faeces, but of those
which contain albumin and fibrin. This Bacillus in a pure
culture is able of itself to separate albumin or fibrin into the
successive products of decomposition which have been ascer-
tained in other cases of putrefaction up to the latest and final

fix.] Decomposition of proteid. 105

products, carbonic acid, water, and ammonia. If allowed to
operate on one of the series of decomposition-products already
prepared, tyrosin for example, it carries on the decomposition
in the order of succession of the regular products of putrefaction.
None of the other Bacteria examined by Bienstock produced these
effects. Neither casein nor artificially prepared alkaline albumi-
nates were rendered putrid by Bienstock's Bacillus; casein is
even said to remain entirely unaltered ; in accordance with this
the Bacillus itself and the specific decomposition with the
characteristic faecal smell are wanting in the intestine of
sucking children.

As regards the morphological characters of this Bacillus of
the decomposition of proteid, it appears from the descriptions of
Bienstock that it is endosporous, and resembles B. Amylo-
bacter in shape at least at the time of formation of spores, and
like it forms the motile rods with capitate end (see page 1 7)
which Bienstock compares with drumsticks. It is, however,
smaller than B. Amylobacter, and even than B. subtilis. It is
scarcely possible to form a clear idea of the course of develop-
ment of this form from the investigations and descriptions which
we possess, and we must wait for further enquiry into this point.

We must also wait to see whether the monopoly of putre-
faction claimed for the drumstick Bacillus will be confirmed.
This, with all due acknowledgment of the results as reported, is
scarcely probable when we call to mind our experience of other
processes of decomposition. I will not bring forward other
accounts which have been given as arguments against the ex-
clusive character of Bienstock's Bacillus, because precise dis-
criminations of form are too recent to set aside the objection,
that this Bacillus may be present though unrecognised where
some other form is said to have been found, and may be the
really active agent.

But it is necessary, at least, to refer in this place to these
other statements, inasmuch as the view pretty generally enter-
tained is that Bacterium Termo is the usual exciting cause of

io6 Lectures on Bacteria. [§ ix.

putrefaction. Cohn expresses this opinion in the most decided
manner when he says that he has arrived at the conviction, that
Bacterium Termo is the ferment of putrefaction in the same
sense as beer-yeast is the ferment of alcoholic fermentation, that
no putrefaction begins without B. Termo, or proceeds without
its multiplication, and that B. Termo is the primary exciting
cause of putrefaction, the true saprogenous ferment. Although
we cannot now maintain these propositions in their full extent,
and although the expression putrefaction is employed in them
without any precise determination of the processes of decom-
position and of the putrefying substance, yet on the one hand
there can be no doubt that the expression includes what is
commonly understood by the putrefaction of proteids, such
as meat, and on the other hand Bacterium Termo must,
at least, be a very constant attendant of such processes. It is
advisable, therefore, just to enquire what B. Termo actually is,
all the more since modern bacteriology itself scarcely ever uses
this old name. There is some ground for this, since it is
scarcely possible to make out with certainty what it was that
Dujardin, Ehrenberg, and others thirty years ago intended by
this name. What Cohn on the contrary described as B. Termo
in 1872 is an object as distinct as it is of frequent occurrence.
It is obtained by allowing the seeds, for instance, of leguminous
plants to rot in water, and then preparing a culture by introduc-
ing a drop of the putrid liquid into the solution known as
Cohn's nutrient solution for Bacteria1. The transference of a
drop of the solution thus infected several times in succession to
some fresh solution, sufficiently secures the purity of the culture.
The microscopic indication of the presence of Bacterium Termo
consists in the solution becoming more and more milky during
the first days of the culture, and then forming a greenish layer
on the surface, in which the form in question is collected in

1 Cohn's normal solution, as given by Eidam in Cohn's Beitr. i. 3,
p. 210, consists of potassium phosphate I gr., magnesium sulphate I gr.,
neutral ammonium tartrate 2 gr., potassium chloride o-i gr., water, 200 gr.

§ x.] Bacterium Termo. Parasitic Bacteria. 107

extraordinary large quantities. Isolation by cultivation in gela-
tine is not possible, because the gelatine is at once liquefied by
the rapid multiplication of the Bacteria.

Microscopic examination reveals a number of minute rod-like
cells, according to Cohn's measurement about 1-5 /-tin length,
and becoming one-half or one-third of that amount in breadth,
engaged in active bipartition, and thus frequently united in pairs,
but scarcely ever forming long rows; in this they resemble Micro-
coccus lacticus, but are distinguished from it by their somewhat
larger dimensions, and especially by the very active independent
movement of the individuals suspended in the fluid. The move-
ment is often a peculiar backward movement in different direc-
tions. Zoogloeae are ultimately formed on the surface of
the fluid in the form of greenish slimy films or lumps, in
which the cells lie motionless. The alternation of these two
states was clearly described by Cohn as long ago as 1853.
Formation of spores in the characteristic manner has not been
observed in B. Termo, and it must therefore be classed for the
present with arthrosporous forms. I have said thus much in
order to commend the old B. Termo to renewed observation ;
time will show how much will be left of it and its reputation as
the exciting cause of putrefaction. I leave these sentences as
they were originally written, only adding that Hauser has since
shown that Cohn's Bacterium Termo is a collective species, and
has resolved it into three kinds ; but a closer comparison of
these has still to be made (51). I now conclude with it the series
of examples of saprophytic Bacteria.

X.

Parasitic Bacteria. The phenomena of parasitism.

WE now pass on to the second category of Bacteria, distin-
guished above on page 65 by their parasitic mode of life.

The term parasite is applied in biology to the living creatures

io8 Lectures on Bacteria. [$ x.

which take up their abode on or in other living creatures, and
feed on the substance of their bodies. The animal or plant
which supplies food and lodging to a parasite is termed its
host. Parasites are known in very different divisions of the
animal and vegetable kingdoms, and many of them are well and
certainly understood. I need only mention intestinal worms on
the one hand, and on the -other the long series of true Fungi
which are parasitic especially on plants. Our experience of
these forms, which are comparatively easy to examine, teaches
us that the adaptations to the parasitic mode of life are extra-
ordinarily complex and present an extreme variety of gradations
between one case and another, that is between one species and
another, and that these are dependent on the one hand upon
the more or less strict requirements of the parasitic mode of
life, and on the other upon the mutual relations between parasite
and host.

To attempt to go at all at length into the above relations,
would lead us here much too far into details. But we must call
attention for our present guidance to one or two of the most
important points.

As regards the nature of the parasitism, we have first the case
which is farthest removed from the life of saprophytes, that of
obligate parasites, which by the provisions of their nature can
only complete the course of their development in the parasitic
and not in the saprophytic mode of life. To take an example
from amongst those with which we are best acquainted, this is
true strictly and excluding all deviation into saprophytism of .the
Entozoa, such as tapeworms and Trichinae ; among Fungi, of
those which live inside plants and have been termed rusts
(Uredineae). These organisms as a matter of fact live only in-
side their living hosts and feed on them. It is quite conceivable
that the conditions necessary for their development may arise
or be artificially produced outside the living host, and it would
certainly be an instructive experiment to grow a tapeworm from
the ovum in a nutrient solution ; but this has never been actually

§ x.] Parasitism. 109

done, and no instance of the kind is to be found in nature. In
these cases the parasitism is obligate and indeed strictly obligate.

I add the word strictly, because there is a modification of
obligate parasitism, in which a parasitic mode of life is necessary
for the completion of the entire course of the development, and
is often the only one which actually occurs, while at the same time
saprophytism may take its place, at least in certain stages of the
development. No example of this kind occurs to me at this
moment from the animal kingdom, but there are some to be
found. Among the Fungi there are a number of species of the
genus Cordyceps which inhabit insects, especially caterpillars,
and in which this adaptation occurs in a marked manner. The
germ-tubes developed from spores on the caterpillar penetrate
into the insect, spreading luxuriantly in it, and at length killing
it, and after its death they fill the whole of its body with mycelial
tissue. From this tissue, if the conditions are favourable for
vegetation, large Fungus-bodies are produced, several inches in
length, which are the stromata of the Fungus, and produce spores
(ascospores). These go through the same course of development,
if they also find their way to a suitable living insect. But if this
does not happen, the spores have the power of germinating on
a dead organic substance, for instance in a nutrient solution,
and their germ-tubes may develope there into Fungus-plants.
But these plants do not produce the characteristic stromata just
mentioned. They form different spores from those produced
in the stromata, and these spores may also develope in the
saprophytic mode of life ; but if they find their way to the
proper insect-host, they can recommence the course of develop-
ment which reaches its highest point in the formation of stro-
mata as described above. Here then we have parasites
which are able to complete a certain portion of the course of
their development while living as saprophytes, though without
reaching its highest point, namely the formation of stromata ;
they may be shortly termed facultative saprophytes.

Thirdly, there are also facultative parasites. These are

no Lectures on Bacteria. [§ x.

species which are able to develope as perfectly, or at least
nearly as perfectly, in the saprophytic as in the parasitic mode
of life. The ' or ' shows at once that there are gradations also
within this category, and these are, as might be expected,
of such a kind that some plants find the conditions more favour-
able in the parasitic, others in the saprophytic mode of life,
while others again show no difference in this respect. There
are many instances of these modifications of facultative para-
sitism among the Fungi, and we shall soon make acquaintance
with similar instances in the Bacteria.

The mutual relations in each case between parasite and host,
the dependence of the one on the other, the benefit or injury
which the one receives from the other, are independent of these
strict requirements of parasitism which vary in each separate
case. In cases like that of the Trichinae, for example, we are in
the habit of speaking of this relation as one-sided, as one in
which the parasite derives its entire means of subsistence from
the living host, while the host receives nothing but harm from
the parasite through the necessary withdrawal of its substance
and other manifold chemical and mechanical disturbances which
it suffers. States of disturbance of the normal existence of a
living being, the normal requiring to be determined in each case
by experience, are known as diseases ; the parasites of which
we are speaking cause these states and are therefore injurious
to health, the exciting causes of disease. Further, the parasite
by means of its germs, spores, ova, or whatever other name is
given to its organs of propagation, may be transferred from the
host which has been made ill by it to others in which it will
also produce disease. The maladies caused by parasites are
therefore transferable from host to host, they are, to use the
common expression, infectious.

But these cases, in which the parasite is injurious to health
and the injury is all on one side, are only one extreme among
those that are known. There are others in which the two
organisms live in common with equal advantage to both, and

§ x.] Parasitism. 1 1 1

there is every possible gradation again between these extremes.
Lastly, there are cases in which a parasite lives in a host with-
out either injuring or sensibly profiting by it, at most deriving
its food from the refuse of the metabolism of the host. In
extreme cases of this kind, which obviously lie on the border-
line of the phenomena of true parasitism, we use the expression
lodger-parasites.

Further, there is a fact more or less known to the experience
of every one, which holds good of all the categories of parasites
distinguishable according to the points of view here indicated,
namely that a parasitic species may make choice as we should
say between the hosts which it occupies, that is, attacks one host
and thrives perfectly well in or on it, while it either refuses
others altogether or at least grows less vigorously in them. In
these respects also there is every conceivable gradation. First,
as regards the choice of the host-species by a parasitic species ;
one extreme is marked by the narrowest one-sidedness. For
instance, a strictly obligate and very well marked parasitic
Fungus, Laboulbenia Muscae, mentioned on page 39, grows
exclusively on the house-fly and on no other insect, at least
according to our present investigations. Other Fungi and
other parasites besides the Fungi are not so one-sided in their
choice, since they attack a larger number of host-species, but
those only as a rule which belong to a narrow cycle of affinity,
a genus, family, &c. Thus, for example, some of the species of
Cordyceps mentioned above, grow in the larvae of a great
variety of butterflies and other insects. But it sometimes
happens that single host-species within such a cycle of affinity
remain excluded from the choice for reasons of which we are
ignorant. Lastly, we are acquainted with obligate and faculta-
tive parasites which are able to complete their development
equally well in hosts of the most different cycles of affinity.
I need only mention Trichina spiralis once more, which thrives
well in rodents, swine, men, and other animals. Examples in
plenty may also be drawn from the Fungi ; but among them

H2 Lectures on Bacteria. [f x.

also strange exceptions occur within a cycle of preference, some
host-species being spared by the parasites without any definable
reason. To name only one instance, a Fungus named Phyto-
phthora omnivora from its catholicity of taste attacks the most
heterogeneous plants, species of Oenothera and other herbs and
garden-flowers, Sempervivum, the beech, &c. ; on the other
hand it never attacks the potato-plant, which its nearest relative
Phytophthora infestans prefers.

It is at present scarcely possible to give an exact account of
the physiological causes of these preferences, but it is at the
same time obvious that they depend essentially on chemical and
physical qualities and distinctions.

If then there is a choice between one species and another,
there must be a similar choice to a certain extent between indi-
viduals of the species, for the differences between the several
species are the same in kind, though not in degree, as those
between individuals of one and the same species ; the latter are
less than the former, and are therefore also less pronounced,
being sometimes scarcely or not at all perceivable ; gradations
between the different cases which we meet with everywhere are
also not wanting here.

If we describe these phenomena which run through the whole
of the long series of parasites in the reverse way, that is to say,
not with reference to the parasite but to the host, then we say
that the host is differently suited, disposed, or predisposed, ac-
cording to the species and individual for the attack of a parasite.
We may speak of predisposition on the part of a species, or
individual, or in different states, stages of development, or ages
of an individual. Of these individual predispositions it may be
further specially observed that they must, no less than all others,
as a general rule, have their foundation in each case in the
chemical, physical, and anatomical constitution. It may be
shown for example in the case of certain Fungi of the genera
Pythium, Sclerotinia, and others which live in plants, that indi-
viduals of the same host-species have unequal susceptibility to

} x.] Parasitism. 113

the attacks of the parasite, and unequal power of resisting them
according to the relative amount of water which they contain.
Since in these cases youngerplants have more water than the older,
a predisposition dependent on age is also indicated accordingly.

In cases where the parasite causes a disturbance, which we call
sickness, of what by experience is regarded as the normal vege-
tation of the host, if the predisposition is individual we speak
usually of a sickly predisposition. This may be correct, in
so far as the predisposition to the attack of the parasite may
be connected with deviations from the state which is from ex-
perience termed the sound state. But it need not always be
correct, for there is no reason at all why the disposition for the
attack of the parasite should in every case indicate a condition,
which must be called sickly even when there is no parasite
present. The above-mentioned example of the predisposition
varying with the age is a sufficient proof of this. Here we must
distinguish between one case and another, and care is required
in determining each individual case.

An example may help to make this still more plain ; it is that
of a case which is comparatively very accurately known. The
common garden-cress, Lepidium sativum, is often attacked by
a parasitic Fungus of comparatively large size, Cystopus can-
didus. In consequence of this it shows considerable degene-
ration, swellings, curvatures of the stem, and often also of the
fruits, and on these parts and on the leaves white spots and
pustules subsequently turning to dust, which are formed by the
sporogenous organs of the Cystopus, and give the entire phe-
nomenon the name of the white rust in cress. This is a case of
disease, and so striking that every one notices it at once with the
naked eye. Now we find in a bed of cress at about flowering
time a certain number of rusty plants, two for example or
twenty. They are in the middle of the other hundred or
thousand plants, and these are healthy and free from the Fungus
and continue so till the period of vegetation is at an end. This
is the case, though the Cystopus forms countless spores in the

i

H4 Lectures on Bacteria. [§ x.

white rust-pustules, and the spores are dispersed as dust and
are at once capable of germination, finding the necessary con-
ditions for their further development in the bed of cress, and
are the instruments by which the white rust-disease is emi-
nently infectious. Nevertheless those hundred or thousand
plants are not infected. All that has been hitherto said is strictly
correct, and if we limit our view to this, we shall see in the
phenomena which have been described a conspicuous case of
individual difference in predisposition; a case too perhaps, if
we judge hastily, of sickly predisposition in the plants attacked,
for they do become sick and the others do not. And yet
this is not the true account of the matter. Every healthy
cress-plant is equally liable to the attacks of the Cystopus and
to the rust-disease which it causes, only the liability is confined
to a certain stage of the development, and ceases once for all
when that stage is past. The germinating cress-plant in effect,
first unfolds two small three-lobed leaves, the seed-leaves or
cotyledons. When it has grown a little further and formed
more foliage-leaves, the cotyledons wither and drop off. It
appears then, that the germ-tubes of the Fungus of white rust find
their way into all the cotyledons and are able to develope there,
and if this development has once begun, the Fungus establishes
itself at once in the tissue into which it has penetrated, and
grows on in and with the growing plant, and produces the
disease. The germ-tubes of Cystopus may indeed make their
way for a short distance into all the other parts of the plant, but
are unable to establish themselves inside it and continue their
development. The plant is for the future safe from the attacks
of the parasite as soon as the cotyledons have fallen off. The
two or the twenty rusted plants in the bed are the ones in which
the Fungus attacked the cotyledons in good time; if it had
attacked the thousand others in equally good time, all would
have been rusted. They continued healthy, because they were
not infected in the stage in which they were open to infection,
that is, predisposed.

§ XL] Harmless Parasites. 115

It follows necessarily from what has been said with respect to
the variety of gradations in the mutual relations of host and
parasite, that the progress and issue of the disease must also
show manifold gradations, varying with the species on both
sides, and in a less degree with the individuals. The very
general occurrence of Trichinae, tapeworms, the itch and other
diseases bring them so much under the notice of all, that this
brief notice of them here will be sufficient.

XI.

Harmless parasites of warm-blooded animals. Parasites
of the intestinal canal. Sarcina. Leptothrix, Micro-
cocci, Spirillum, Comma -bacillus of the mucous
membrane of the mouth.

IT seemed to me expedient to give the foregoing short review
of the phenomena of parasitism and of its consequences, because
all that we know of parasitic Bacteria are only special cases of
the main phenomena which occur everywhere ; and this is
equally true of all our suppositions concerning them. The
understanding of these matters will therefore be materially aided
by resting on old and long-known phenomena.

In passing now to the consideration of important examples
of parasitic Bacteria, it will be advisable to speak first and
chiefly of the parasites of warm-blooded animals, including
mankind, and afterwards to say a few words on those of other
animals, and of plants.

In the former class it will best suit our purpose to distinguish
the species which are the exciting causes of disease from those
which are less injurious or altogether harmless ; and first a few
words respecting the latter kind.

The digestive canal and the breathing passages, the former
especially, are a favourite habitat of lower organisms, Fungi and
Bacteria, putting the various kinds of worms out of considera-
tion. A large number of Fungi make use of the intestinal canal

I 2

Ii6 Lectures on Bacteria. [$ xi.

as a regular, if not in most cases an absolutely indispensable
thoroughfare, since when introduced with the food they find a
home and nourishment in it for the first stages of their develop-
ment, and then complete it on the voided faeces. This is shown
by the abundant and remarkable Fungus-flora of dung.

It is known that many forms of Bacteria occur in large
numbers in the contents of the intestinal canal. A more
thorough sifting and sorting of most of the species has yet to be
undertaken. In the human intestine Nothnagel has distinguished
Bacillus subtilis, B. Amylobacter, and other not clearly defined
forms, and Bienstock (50) his drum-stick Bacillus. Kurth found
his Bacterium Zopfii in the intestine of fowls (see page 22). To
these examples must be added the constant, and according to
van Tieghem (see page 102), the essential presence of Bacillus
Amylobacter in the stomachs of ruminants (52).

The acid of the gastric juice may prevent the appearance of
most of the Bacteria in the normal contents of the stomach (in
the rennet-stomach in ruminants). Koch's researches into
anthrax, to be noticed again presently, have even shown that
Bacillus Anthracis in the vegetative states is killed by the gastric
juice, and only its spores maintain their vitality. This may be
the case with some other species, and it may be of some import-
ance that a kind of sorting thus takes place in the normal
stomach, by means of which some only of the Bacteria intro-
duced with the food reach the intestinal canal in the living state.

That the gastric juice has not always an injurious effect, but
that here too there is a difference between one case and another,
is shown by the researches of Miller and W. de Bary (52). We
are acquainted with one species, the well-known Sarcina ven-
triculi (Fig. 14), which thrives particularly well in the human
stomach. This species forms packets in the shape of almost
perfect cubes of roundish cells arranged in regular layers
parallel with the surfaces of the cube, and kept firmly united by
tough gelatinous membranes. Comparison shows plainly that
the packets are formed in the manner which can be directly

§ XL] Sarcina. 117

observed in the case of other very similar species (see Fig. 15),
namely, from a single round initial cell by successive divisions
formed in three directions. The packets separate as they
grow into daughter-packets, each of which contains the progeny
of one of the cells of previous orders of division, and as this pro-
cess is repeated the packets multiply. Nothing further is known
of the history of the development of Sarcina.

Sarcina ventriculi is at present known only from the human
stomach and intestinal canal. In diseases, especially enlarge-
ments, of the stomach, it is often found in incredible quantities.

/ffl

a Z c d

Fig. 14. Fig. 15.

Yet no causal connection has been ascertained between its
occurrence and distinct phenomena of disease, and other con-
ditions being the same it may be present in profusion or
sparingly, or be absent ; its absence indeed is the rule in much
the larger number of stomachs, diseased as well as healthy. The
causes of all this are unknown ; nor can we tell whence it finds
its way into the stomach. Its occurrence outside the stomach

Fig. 14. Sarcina ventriculi, Goodsir. Large-celled form just taken from
the contents of the stomach of a patient and imbedded in soft gelatine ; a
comparatively small and cube-shaped packet. View of one surface only ; but
other surfaces project below and to the right beyond the edge of the first.
In the surface depicted the cells with double contour-lines are rightly
focussed ; those with single contour- lines are not in the right focus but lying
at a lower level. Magn. 600 times.

Fig. 15. Sarcina minuta, de Bary, in gelatine on a microscopic slide.
a-d successive states of the same specimen, observed as a double pair of
round cells, a about 4, b about 6, c about 9, and d at 10 o'clock in the
afternoon. In c the tetrads are still formed of a single layer, in d a division
has taken place in each cell in the plane of the paper ; each tetrad de-
velopes into an 8-celled cube-shaped packet, /a 32-celled pocket. See
note 53.

1 1 8 Lectures on Bacteria. [$ xi.

and intestine, excepting of course in the evacuations, has not
been observed with any certainty, and the attempts to cultivate
it have, up to the present time, been without success in all cases
offering clear results.

It is true that we are acquainted with a number of forms or
species, in which the cubical packets are so like those of Sarcina
ventriculi that they must be placed alongside of it as closely
allied forms. These occur both outside living organisms, as
saprophytes, and also in the bodies of living animals, and
among them of men. That they are not very widely diffused
is evident from the fact that the reported cases of their occur-
rence are always solitary ones.

Saprophytic forms of Sarcina have been found casually, that
is without having been introduced intentionally, by Cohn and
Pasteur on all kinds of nutrient solutions, by Schroter on boiled
potatoes, by myself on acetified beer, on coagulated milk, and
elsewhere. In these instances the yellow forms (Sarcina lutea,
S. flava) have repeatedly been observed (53).

Sarcina-forms inhabiting the bodies of living animals are
described as obtained from the bladder (S. Welckeri), the lung,
the mouth, and other cavities of the body, even from the blood
of the human subject, and from the cavities and the intestinal
canal of other warm-blooded animals.

These forms, the saprophytic as well as the parasitic, are, so
far as the statements before us enable us to judge, without
doubt clearly distinct from Sarcina ventriculi. Unfortunately
many accounts are so defective, so very much restricted, one
might say, to the word Sarcina, that it is impossible to determine
their identity. The fact moreover which was noticed in the
case of Sarcina ventriculi is also true of the parasitic forms ;
their occurrence, as far as our knowledge goes, has not been
shown to be in causal connection with distinctly morbid pheno-
mena, and they must for the present be regarded as simply
lodger-parasites (53).

Many kinds of Bacteria are observed in the mucous mem-

XL] Bacteria of mucous membrane of mouth. 119

brane of the mouth and nose. With regard to the latter this
assertion favours the supposition that Bacteria are uniformly
present in that catarrh of early summer which goes by the
name of hay-fever. I can bear out this statement myself
as a sufferer from this disagreeable malady, though I must
add that Bacteria are also present during the 10-11 months
of the year that are free from hay-fever. I found them to
be small, short rods resembling those of Bacterium Termo.
Whether specifically different forms are present, or predominate
at different times, has not been ascertained.

We are better acquainted with the abundant growth of Bac-
teria in the mucous membrane of the mouth. They occur in
greatest profusion on the gums and
between and on the teeth, in a more
scattered manner, but still in con-
siderable numbers on the rest of
the surface of the mouth and in the
discharged saliva. A specimen of
mucus scraped from a tooth is seen e
to be chiefly composed of a form
known by the old name of Lep-
tothrix buccalis, Robin (Fig. 1 6, a).
It consists of long straight filaments
glued together into dense bundles,
brittle and readily separating into

Fig. 1 6.

pieces transversely, and of unequal thickness ; larger filaments

Fig. 1 6. Bacteria from mucus of the teeth, a Leptothrix buccalis, Robin ;
filaments or portions of filaments of different thickness, b a portion of a
filament after treatment with alcoholic solution of iodine showing the
segmentation distinctly, c portion of a filament much narrowed at one
end, without treatment with reagents and showing segmentation distinctly.
d Lewis' comma-bacillus, that is, a short-celled Spirillum, e Spirochaete
Cohnii, Winter (Spirochaete of mucus of the teeth, Cohn, Beitr. i. 2, p. 180,
and ii. p. 421). m Micrococcus-heaps. All the figures are of specimens from
the same preparation, e and b after staining, the rest fresh from the mouth.
Magn. 600 times, with the exception of <$, which is more highly magnified.

1 20 Lectures on Bacteria. [$ xi.

are over i fi in the transverse diameter, others only half that
thickness. The length also of the members (cells) is unequal,
in some cases not exceeding the transverse diameter, in others
several times greater. The filaments, especially those with
short and thick cells, often show the reaction of granulose
(page 5), but different portions of the same filament may assume
alternately a blue and yellow colour with iodine. Rasmussen
(54) claims to have distinguished three separate forms of Lep-
tothrix buccalis by aid of cultivation. I cannot say whether
this is rightly done or not, for Rasmussen's work is only known
to me at second hand.

Secondly, the masses of Leptothrix often contain round Cocci,
which are sometimes irregularly rolled up into dense gelatinous
heaps, and like the Leptothrix-forms are without the power of
motion (Fig. 1 6, m).

Thirdly, a Spirillum-form is commonly found with the others,
showing itself rather in single specimens and in the fluid sur-
rounding the Leptothrix-masses after addition of water ; this is
Spirochaete Cohnii, Winter (S. buccalis or S. dentium), and
consists of filaments of extreme tenuity without evident trans-
verse divisions, spirally twisted into 3-6 or more steep
and often irregular coils, flexible and either exhibiting a slow
twisting movement or else without motion (Fig. 16, e).

Lastly, one more form is often though not always observed
with the others, a thin short rod-shaped Bacterium, bent like
a bow, and described first by Miller and then by Lewis (55)
as the comma-bacillus of the mucus of the mouth (Fig. 16, </);
in a fluid it usually exhibits an active hopping movement.

It may be assumed beforehand as certain, that besides these
forms other saprophytic Bacteria must also occur in the mucus
of the mouth. Miller, according to recent communications, has
found twenty-five such organisms. Hueppe speaks of two
Micrococci which produce lactic acid as coming from the human
mouth (see page 94). But other forms do not appear to be
developed in any abundance in healthy individuals. It may be

§ XL] Bacteria of tooth-caries. 121

said perhaps that their invasion is hindered by the presence
of the characteristic dwellers in the mouth mentioned above.

I repeat that I would have these latter spoken of at present
only as forms which are actually present side by side, nor will
I enter further into the question how far they stand in genetic
relation to one another. From the impression which they give
us and from present investigations it seems to be highly probable
that we have before us several distinct social species.

The dwellers in the digestive and respiratory passages which
have now been described, together with other near allies found
in mammals are, so far as our knowledge goes, almost without
exception harmless guests, lodger-parasites only, those which
live in the mouth being perhaps even useful as protectors
against an invasion of destructive ferment-forms. Certain forms
however are disagreeable exceptions, inasmuch as they cause
caries, the disease in which the teeth become hollow. Every
hollow tooth is penetrated throughout by Bacteria, and different
forms or species occur in different cases ; Miller (55), after ex-
amining hundreds of teeth, has distinguished five of these forms.
He has also shown by very thorough investigation that one of
them, a Micrococcus, forms lactic acid in a substratum contain-
ing sugar or starch. The salts of calcium in the substance of
the tooth are dissolved by the excreted acid, and the Bacterium
is thus enabled to force its way into the tooth ; as more and
more of the calcium is withdrawn the Bacterium passes into
the tubuli of the dentine of the tooth, and ultimately spreads
through and destroys the tooth. It can scarcely be doubted
that Miller's/our other species produce the same effects.

122 Lectures on Bacteria. [§ xn.

XII.
Anthrax and Fowl-cholera.

LEPTOTHRIX buccalis, as the exciting cause of caries in the
teeth, carries us on to those parasites in warm-blooded animals
which produce disease.

The best way to obtain a clear idea of these organisms, their
manner of life, and their effects will be to examine first of all
some comparatively well-known examples.

Let us take first the disease known as anthrax, charbon, sang
de rate and its exciting cause, Bacillus Anthracis (56).

Bacillus Anthracis has already been repeatedly brought be-
fore our notice. Its description will therefore only be briefly
recapitulated here, and its figure reproduced (Figs. 17, 18). It
consists of cylindrical cells about 1-1-5 /u ^n thickness, and 3-4
times that length. In the blood of animals these cells are usually
connected together into long straight rods (Fig. 17, c), which
appear homogeneous till they are carefully examined, that is, do
not distinctly show segmentation into individual members. When
grown in a dead substratum the rods develope into very long
filaments, which appear sharply bent in several places, and form
curvatures and loops ; they also separate at the points of flexure
into rod-shaped pieces, and are usually collected in large numbers
into bundles or sheaves and twisted round one another (Fig. 1 7, a).
The rods and filaments are without the power of locomotion,
except in special cases, which will be noticed below. The
formation and germination of the spores take place in the
manner described in Lecture III in the case of the endosporous
Bacilli; in germination the spores merely grow in length
(Fig. 1 7, b} without throwing off any distinct spore-membrane,
and the young germ-rod often exhibits a slow oscillating move-
ment. The ripe spore is broadly ellipsoidal, as broad as its
mother-cell which retains its cylindrical shape but much shorter,
and lies very nearly in the middle of the mother-cell till it is
set at liberty by the swelling of the membrane.

§ XII.]

Anthrax.

123

Bacillus Anthracis is distinguished under the microscope by
the absence of independent motion and by the form of its ger-
mination from B. subtilis, which is very much like it in almost
all respects, except that it is usually more slender and is not
parasitic. To these must be added in
ordinary cases the macroscopic dis-
tinction, that B. Anthracis at the
highest point of its development forms
a floccose sediment in nutrient solu-
tions, while B. subtilis forms the dry
membrane on the surface mentioned
on page 12. Some exceptional phe-
nomena will be noticed further on.

Anthrax chiefly attacks mammals,
and among these the most liable to
it are herbivorous animals, especially
rodents and ruminants ; of the species
which have been observed, domestic
mice, guinea-pigs, rabbits, sheep, and
horned cattle are the most susceptible
in the order of naming. The next in
the degree of liability are omnivorous
animals, and among them men ; then
come the carnivores, and among these cats, for instance, are
more frequently attacked than dogs. Birds also are said to be
susceptible to the disease, though this has been disputed ; Gibier
found that frogs, and Metschnikoff that lizards (Lacerta viridis)
were susceptible when they were kept at about the temperature
of the bodies of warm-blooded animals. We will pass over

Fig. 17. Bacillus Anthracis. a portion of a group of vigorously growing
filaments ; the segmentation into cells is not visible, but has nevertheless
taken place, b three successive stages of a germinating spore ; close by is
a ripe spore s before germination, c rod from the blood of an infected
guinea-pig some hours after the death of the animal, after treatment with
distilled water, a and b from cultures on microscope-slides in solution of
extract of meat. Magn. 600-700 times.

Fig. 1 7.

124

Lectures on Bacteria.

[I xii.

f

2

disputed points on the present occasion, leaving them to be
examined in the special literature of the subject (56), and con-
fine ourselves to cases which have been
certainly ascertained, especially those in
mammals. Susceptibility to infection varies
with the species, as appears from what
has been already said ; within the limits
of the species it varies according to race
and age, and with the individual.

Anthrax is a widely-spread form of
disease; at the same time it is matter of
long experience, that it appears with un-
usual frequency in certain districts, and
that these anthrax-districts are especially
dangerous to herds of cattle, and are there-
fore dreaded by breeders.

The clinical aspect of the disease is
different in different species of animals ;
in larger ones it is said to run a com-
paratively slow course, being accompanied
with violent fever, &c., and in most cases
but not always ends in death. Mice and
guinea-pigs succumbed to the disease
almost without exception in the cases ob-
served, but without showing any particularly striking symptoms

Fig. 1 8.

Fig. 1 8. A Bacillus Anthracis. Two filaments partly in an advanced stage
of spore-formation ; above them two ripe spores escaped from the cells. From
a culture on a microscope-slide in a solution of meat-extract. The spores
are drawn a little too narrow ; they are nearly as broad as the breadth of
the mother-cell. B Bacillus subtilis. 1 fragments of filaments with ripe
spores. 2 commencement of germination of spore ; the outer wall torn trans-
versely. 3 young rod projecting from the spore in the usual transverse
position. 4 germ-rods bent into the shape of a horse-shoe, one subsequently
with one extremity released. 5 germ-rods already grown to a considerable
size, but with both extremities still fixed in the spore membrane. All
magn. 600 times.

§ xii.] Anthrax. 125

up to the moment of death. In many instances I observed
guinea-pigs lively and eager for food, till they all at once (about
forty-eight hours after infection) collapsed and died after a short
struggle.

If a diseased animal is examined a little before or immediately
after death, the vegetative rods of Bacillus Anthracis (Fig. 17, c)
are found in its blood. In larger animals, such as horned
cattle, their numbers appear from the accounts before us to vary
in every case. I say appear for reasons to be given presently.
But they are always found in the capillaries of the internal
organs, at least in the spleen. Koch states that they are not
numerous in the blood of rabbits and mice, but are all the more
numerous in the lymphatic glands and in the spleen. In guinea-
pigs, the animals which I have myself chiefly examined, the
entire mass of the blood is permeated by the rods ; the smallest
drop of blood, scarcely visible to the naked eye, taken from a
slight puncture in the ear, or toe, or elsewhere, contains them ;
they are present in enormous numbers in the small vessels and
capillaries of the liver, kidneys, spleen, and other organs. The
same state of things continues for some time also after death ;
at a later period, when the first rigidity of death is passed away
it often changes visibly, and it is possible to obtain considerable
quantities of blood from the large blood-vessels, or from the
heart of the animal without discovering a single rod in them.
The rods are there but they are inclosed, often in large numbers,
in the clots of fibrin, which it may be said in passing will supply
the purest material for the culture of the Bacillus. It is quite
possible that in the cases in which few rods were observed, the
reason was, that those which were inclosed in the clots of fibrin
were overlooked when the dead animal was examined after the
coagulation of the blood ; this is a point to be remembered in
connection with the statements mentioned above, that the Bacilli
are present sometimes in larger sometimes in smaller quantities.

The rods were first seen by Rayer in 1850, and next by
Pollender, independently of Rayer, in 1855. The causal con-

126 Lectures on Bacteria. [§ xn.

nection between the Bacillus to which the rods belong and the
disease known as anthrax was first distinctly pointed out by
Davaine in 1863, and this view of the matter, though it has been
opposed on various grounds, is now accepted. It has been
distinctly proved that the disease makes its appearance only
when the Bacillus has found its way into the blood, and that the
artificial introduction of the Bacillus into the blood results in
the characteristic infection, the sickening of the animal. The
infection follows if the living Bacillus is introduced directly
into the blood by intentional inoculation, anthrax by inocula-
tion, or unintentionally through wounds of the skin, anthrax
by wounds, or through the uninjured mucous membrane of the
intestinal canal, intestinal anthrax. It is effected both by means
of living rods, and by spores, the latter then germinating in
the blood or in the intestine. In both cases it is a matter
of indifference whether the matter used for infection is obtained
direct from a diseased animal or from a culture, such as will
be described presently, which has been kept free from every
trace of any product of animal disease. The Bacillus, when
it has died of itself or been killed, is incapable of producing
the infection.

When once the Bacillus has found its way into the blood of
an animal capable of the infection, it grows and multiplies in the
rod-form and spreads partly by its own growth, partly by the
movement of the blood which carries the rods along with it in
the manner described above. In proportion as this takes place,
the sickness increases till at length death supervenes. The
minutest possible quantity of the living Bacillus is sufficient to
set these processes going. A guinea-pig, for example, dies with
the symptoms which have been described in forty-eight hours
after a quantity of spores or rods, too small to be visible with a
pocket-lense, is introduced into the skin on the point of a needle
by a puncture too slight to draw blood.

Anthrax by inoculation and anthrax by a wound are alike
caused by the introduction of both spores and living rods.

$ xii.] Anthrax. 127

Intestinal anthrax on the contrary is actually produced only
by the introduction of spores into the body, as has been proved
by Koch and his colleagues. In the natural course of things
the Bacillus can only reach the mucous membrane of the
intestine from the mouth, that is, when it is swallowed with
food. It has then to pass through the stomach, and here the rods
lose their efficiency, doubtless from the effects of the acid gastric
juice ; whether they are actually killed by it I am not prepared
to say. The spores, on the contrary, pass unaltered through
the stomach ; they find the conditions favourable to germination
in the contents of the intestine, and the rods developed in
germination make their way into the mucous membrane of
the intestine, especially through the lymph-follicles and Peyer's
patches; from there the way is open through the capillary
vessels in the mucous membrane to the passages of the
blood.

It appears from the investigations of the above-named ob-
servers that animals which chew the cud are liable to be infected
in this way from the intestine. The experiments were made
with sheep. Experience also with horned cattle not purposely
infected seems to show by its agreement with these experiments
that the latter animals also are liable to this mode of infection.
It gives also the important practical result, that the cases of
anthrax which occur in them spontaneously, that is not inten-
tionally produced for experiments' sake, are chiefly of the
intestinal form, and are caused therefore by taking in the spores
of the Bacillus with the food.

Other animals are less susceptible of infection from the intes-
tine; yet some attempts made to procure it succeeded in the
case of guinea-pigs, rabbits, and mice ; they were all unsuccessful
with rats, fowls, and pigeons.

After all these experiences the first question is, whence do
the spores come from which enter the animal ? They are not
formed either in the living animal or in the unopened carcase,
for there vegetative development only takes place. But it was

128 Lectures on Bacteria. [$ xn.

shown in a former Lecture that the Bacillus can not only
germinate and vegetate luxuriantly outside the body of the
animal, but that it forms its spores, in great profusion if the
conditions are favourable, only outside the animal. The con-
ditions for this non-parasitic development are the same as the
general conditions given above for saprophytes. A supply of
oxygen is required for perfect development ; the optimum tem-
perature for the formation of spores is 20-25° C. A great variety
of organic bodies can serve as nutrient material, as experiments
show, not only such as are of animal origin, for instance, por-
tions of an animal that has died of anthrax, or the often bloody
evacuations of diseased animals, or the meat-extract-solution in
which the culture of the Bacillus was first accomplished (see
page 12), but also many different parts of plants if they are not too
acid, such as potatoes, turnips, seeds, &c. On the moist surface
of such objects the Bacillus grows and forms extensive mem-
branous coverings, which at the close of their vegetation produce
countless spores.

Thus it is evident that the Bacillus of anthrax belongs to the
class of facultative parasites, as described on pages 109,110. It is
above all a saprophyte, for it is not only able to prolong its exist-
ence in the saprophytic mode of life, but it requires it in order to
attain to the highest phase of its development, the formation of
spores. On the other hand it is capable of parasitism, since it
finds its way into the proper host, and there acts as the exciting
cause of disease in the manner which has just been described.

The phenomena attending the appearance of anthrax are now
completely explained in all essential points from the mode of
life of the Bacillus, if we take its existence for granted in the
same sense as that of any other animal or vegetable species.
The fact that anthrax when spontaneous usually appears in the
intestinal form, shows according to the knowledge which we
have acquired of it, that it passes in the spore-form from the
saprophytic into the parasitic state, and that the route which it
takes must be the same as that which serves for the food taken

§ XIL] Anthrax. 129

in by the animal. The starting-points in this migration must
then be the places where the fodder is produced, meadows,
grazing-grounds, &c. It is obvious that the Bacillus finds
opportunity for its vegetation, and in the heat of the summer
season the requisite temperature for forming its spores, on the
dead organic bodies which are always to be found in these
localities, and that when it has once established itself it can pass
the winter there (see above, page 51), and thus remain from year
to year in readiness to establish itself in a suitable host.

It is more difficult to say precisely why certain localities
are the favourite homes of anthrax whilst others are free from
it. Koch has shown some ground for thinking that the
preference may be connected with conditions of moisture and
inundation, so far as these affect the vegetation and diffusion
of the Bacillus. I have not the requisite material for forming
a decided opinion. It follows from what has been before said
that the Bacillus is not obliged to return from its existence
as a parasite and from the body of the attacked or dead
animal to saprophytic vegetation in the infected places ; as it is
not obliged to pass through the state of parasitism, it can, as we
learn from cultures, live as a saprophyte through an unlimited
number of generations. On the other hand experience as cer-
tainly shows that it can return from the sick or dead animal to
the life of saprophytism, for it remains in the animal long after
its death and continues alive and capable of growth, and it can
in fact return to the ground and to the condition of a sapro-
phyte with the bloody .dejecta, which, as we are told, larger
animals void in a severe attack of anthrax, or with the decom-
posing carcases and the substances flowing out therefrom, which
are excellent food for them.

The Bacillus can at the same time also be transported as a
parasite from one place to another, and the spots on which sick
animals fall down or their dead bodies are buried may become
the abodes of the disease, as experience has long since shown.
For the same reason a locality may possibly continue perma-

K

130 Lectures on Bacteria. [§ xn.

nently infected. If no herds of cattle visit them, small animals,
the rodents especially, which are so susceptible of the disease,
may ensure the introduction and conservation of the Bacilli.
But these circumstances are, as was said, not directly necessary
for the existence of the Bacillus and of the risk of anthrax, not-
withstanding the importance which has been attributed to some
of the conditions connected with them.

To complete this review of the subject we may remark in
conclusion, that the Bacillus and its effects appear to be trans-
ferable as might be expected from one living animal to another,
and the disease is propagated by this transmission. This infec-
tion belongs of course to the category above distinguished, of
anthrax as produced by inoculation or by a wound. It can
only be brought about by means of vegetating rods, because
these alone are present in the living animal, and the rods, as we
saw, must be conveyed directly into the blood of the living
animal, to be capable of further development. And now the
conditions of infection have been sufficiently indicated for
our purpose. A possibly exaggerated importance has been
ascribed to stinging flies and gnats as agents of infection,
since these insects, when they have sucked blood from an
animal which contains Bacilli and then puncture a healthy
animal for the same purpose, may easily effect a true inoculation
of the disease.

The Bacillus of anthrax in the character of a parasite pro-
duces in the animals and in the cases which have been described
injurious effects, which may be provisionally compared to those
of a poison, and may therefore be termed poisonous and
virulent.

This virulence may be gradually attenuated till it ceases to be
dangerous even in the case of that most susceptible of all the
animals experimented on, the domestic mouse. Pasteur has
shown that this takes place when the Bacillus is cultivated in a
neutral nutrient solution, meat-broth, especially chicken-broth
with a plentiful supply of oxygen at a temperature of 42-43° C.

§ XIL] Anthrax. 131

Toussaint and Chauveau obtained the same results at a higher
temperature. A culture of this kind ends in the death of the
Bacillus, which ensues, according to Pasteur's account, in about
a month or a little more than a month. Till this time the
Bacillus vegetates without change in its morphological charac-
ters, except that the formation of spores is delayed or altogether
stopped. That it never takes place is denied by Koch, Gaffky,
and Loffler on the ground of direct observation. If the Bacillus
is transferred to a fresh culture at any time before death has
supervened, it will develope in the normal manner, and even
produce normal spores at the proper temperature. If the tem-
perature continues to be raised, complete attenuation results in a
shorter time ; a few days are required at a temperature of 45° C.,
a few hours at one of 47° C., a few minutes at one of 50-53° C.
The three Berlin observers found that there was a considerable
difference between 42° and 43° C. in the time required for total
attenuation in correspondence with the temperature-differences
of tenths of a degree, the process being accelerated as the
temperature rose.

It follows that if the Bacillus is cultivated at a temperature
between 42° and 43° C., we obtain material which will be harm-
less to animals in the order of their susceptibility to infection,
for instance to rabbits first, after them to guinea-pigs, and lastly
to mice ; fluctuations will naturally occur according to indi-
vidual susceptibility, age, and other circumstances.

It has been already stated that the Bacilli are capable of
further vegetation after passing through every degree of atten-
uation of their virulence before reaching the stage of actual
loss of vitality. If their cultivation is continued under optimum
conditions they grow in their normal shape and form normal
spores, but the successive generations, even when produced
from spores, nevertheless retain as a rule the degree of attenua-
tion of the first generation; some kill mice for example and
are harmless in the case of guinea-pigs, others do not affect the
health of mice. Cultures of the latter quality were continued

K 2

132 Lectures on Bacteria. [$ xn.

during two years by Koch, Gaffky, and Loffler without any
change or any return to virulence.

The behaviour of Bacilli which have been rapidly attenuated
at 4 7-50° C. and at still higher temperatures is different; they
recover their virulence when cultivated under the most favourable
conditions.

It is true that a return from the attenuated to the virulent
condition is not altogether excluded, even in forms which have
been slowly attenuated. Pasteur affirms that if matter, which is
not fatal to full-grown guinea-pigs but kills young individuals
a day or two old, is taken from one of the latter and used to
inoculate other guinea-pigs successively older, a degree of viru-
lence is ultimately attained sufficient to kill old animals. Koch
and his colleagues have not found these statements confirmed by
their results, and though their experiments were somewhat differ-
ently arranged, yet they seem to show that no such fixed rule ob-
tains in this matter as might be gathered from Pasteur's account.
On the other hand the same observers have distinctly proved
that there is a return to increased virulence in individual and
not very similar cases.

Lastly, they have also proved that cases of the reverse kind
occur, in which the virulence of a culture suddenly diminishes
of its own accord, that is without any ascertained external cause;
spores from material which killed rabbits and guinea-pigs pro-
duced eight weeks later a generation which did not injure these
animals but was still fatal to mice. To this class of phenomena
belongs perhaps an observation recently communicated by
Prazmoswki, according to which a pure culture of Bacillus
Anthracis in a nutrient solution entirely lost its virulence with-
out apparent cause. I have myself seen the same or a similar
case. Buchner's investigation, which bears on this point, will
be noticed presently.

I have already observed that the form of the Bacillus remains
unchanged in the virulent and attenuated states. In the main
points this is always the case, though some modifications have

§ xii.] Anthrax. 133

been observed. Thus it is stated by Koch and his colleagues
that the Bacillus which is only strong enough to kill mice
fills the capillaries, especially of the lungs, in the form of
long filaments, which may often be followed continuously from
the capillaries into the larger microscopic vessels, while the
more virulent Bacillus is usually present in the capillaries in the
form of short rods.

In Prazmowski's observation the difference between the viru-
lent and attenuated forms was, that the rods of the latter kind
were motile during several generations, though their motion was
slow and dragging in comparison, for example, with that of the
hay-bacillus, and that they not only form flakes at the bottom
of the nutrient solution which is clear above them, but also rise
in it and make it turbid, and form on its surface ' thickish dirty-
white films of a slimy consistence.' Exactly the same appear-
ance has been observed by myself in meat-extract-solution;
there the rods even up to the time of forming their spores were
much less united into long filaments than in the virulent forms,
and in the surface-films they lay in every direction, and were
densely and irregularly compacted together into a felted mass.
This mode of grouping is in appearance so unlike that of the
common Bacillus, that we are naturally led to assume that we
are dealing with a form very like Bacillus Anthracis, but yet
specifically distinct from it, which has not allowed the latter to
thrive in the solution, the Bacillus perhaps of Koch's malignant
oedema ; but the harmlessness of this form, even in the case of
small rodents, is against this assumption.

Buchner undoubtedly observed the same phenomenon, when
he grew Bacillus Anthracis through several generations in nu-
trient solutions composed of i per cent, of meat-extract, with or
without the addition of sugar and peptone, and at a temperature
of 35-3 7° C., and kept the cultures in constant movement by
help of a rocking-apparatus in order to secure the largest
possible supply of oxygen. The products of the cultivation
gradually assumed the characters of Prazmowski's modified form.

1 34 Lectures on Bacteria. [§ xii.

Since this form in its want of virulence, its formation of super-
ficial films, and its power of independent movement is more
like the hay-bacillus, B. subtilis, than the virulent form, Buch-
ner maintained that the virulent B. Anthracis had been entirely
changed by cultivation into the harmless B. subtilis, and the
matter excited much attention, since there was here apparently
an evident case of the conversion of a species held to be distinct
into another. But, as was shown on page 34, he has not yet
proved his point. Buchner certainly tried the reverse process
also, and endeavoured to convert the harmless B. subtilis into
the virulent B. Anthracis by cultivating successive generations
of it in various solutions containing albumen, which I must not
enumerate here. The results obtained were for the most part
distinctly negative, and the few which were said to be positive
are open to so many objections, that without insisting on strict
morphological proof we must consider them as quite uncertain.
Here too the morphological proof has been omitted. It is quite
possible that the usually harmless B. subtilis may by breeding be
endowed with an exceptional virulence ; but its specific character
would no more be affected by this, than is that of B. Anthracis
by its attenuations, nor would the fact that the latter is the
ordinary exciting cause of anthrax be rendered at all doubtful.

Pasteur and Toussaint, led by experience derived from other
sources which will be noticed again presently, have attempted
with success to use the attenuated Bacillus of anthrax for pro-
tective inoculation against the virulent Bacillus. If an animal is
inoculated with the Bacillus attenuated to the degree requisite
for it, that is for that species, it either does not sicken or it
sickens slightly and recovers from the disease. It resists then
infection with less attenuated Bacillus, and at the next inocula-
tion it resists the Bacillus which possesses the highest degree of
virulence. The certainty of these results, and their special im-
portance at the same time in reference to the practical art of
the breeder, is differently appreciated in different quarters;
Koch especially and his colleagues have brought forward well-

§ XIL] Anthrax. 135

grounded objections to the praises bestowed on the school of
Pasteur. We cannot enter further in this place into these prac-
tical questions. The fact, however, of the frequent success of
protective inoculation is well established, and is abundantly con-
firmed even by those who are opposed to the exaggerated
estimate of its practical importance. We record it therefore as
a phenomenon of high scientific interest.

Having now become acquainted with these phenomena relative
to Bacillus Anthracis and the disease which it produces, let us
enquire how the injurious effects of the virulent Bacillus are
brought about, and how the attenuation of the virulence and the
operation of protective inoculation just described are to be
explained.

In the present state of our knowledge we shall succeed in
answering these questions best if we begin with the second. To
prevent misunderstanding I will say beforehand most distinctly,
that we can at present only make an attempt to answer these
and all other questions, and must wait for our answers to be
confirmed or amended by future investigation.

We begin therefore with the question of the explanation of
protective inoculation, and we may formulate it a little differently
and extend it by asking how it is that an animal is or becomes
unsusceptible to, safe from the attacks of the injurious parasite.
Metschnikoff has lately published some investigations which, if
confirmed, bring us a step nearer to the understanding of this
phenomenon. I report them because they seem to be trust-
worthy ; I have not been able to repeat them myself.

We know that the blood of vertebrate animals contains red
blood-corpuscles suspended in the fluid blood-plasma, and be-
sides these colourless or white blood-corpuscles or blood-cells
in considerably smaller quantity. The lower animals have no
red blood-corpuscles, only the colourless blood-cells, which are
uncoloured nucleated protoplasmic bodies. They possess a
variety of remarkable qualities, but at present we are chiefly
concerned with the fact that, like many other protoplasmic

136 Lectures on Bacteria. [$ xn.

bodies of similar structure, they are subject during their life to
constant changes of shape in their soft viscid substance, ex-
hibiting undulatory movements of their outline and alternate
protrusion and retraction of processes (see Fig. 19). These
amoeboid movements, as they are called, are combined with the
power of taking up and absorbing solid bodies, or oil-drops, or
similar objects into their soft substance. If the foreign body
comes into contact with the surface of the amoeboid cell, the
latter puts out processes which embrace it, and gradually close
over it as the waves close over a drowning animal, so that it
lies at last inside the soft cell-substance. It may be cast out
again at some future time, but it may also suffer decomposition
inside the cell, be killed, and disappear.

In connection with these well-known facts, and also with the
observation made by him in the case of a disease in some small
crustaceans caused by the invasion of a peculiar Sprouting
Fungus, that the cells of the Fungus were absorbed by the colour-
less blood-cells of the animal and decomposed in it, that there
was a struggle, so to say, between the parasitic Fungus and
the amoeboid cells of the animal, Metschnikoff investigated
the behaviour of the colourless blood-cells of the vertebrate
animals to the Bacillus of anthrax. He found that the virulent
rods when introduced by inoculation into an animal liable to
take the fever, such as a rodent, were absorbed by the blood-
cells only in exceptional instances. They were readily absorbed
by the blood-cells of animals not liable to the disease, as frogs
and lizards, when the temperature was not artificially raised
(Fig. 1 9), and then disappeared inside the cells. The same thing
happened when susceptible animals were inoculated with Bacillus
Anthracis which had been attenuated to the harmless state.
Chauveau had already stated that the attenuated Bacilli pass into
the lungs and liver of the animal and there disappear. From all
these data we must assume with Metschnikoff that the Bacillus is
harmless because it is absorbed and destroyed by the blood-cells,
and injurious because this does not happen ; or at least that it

§ XIL] Anthrax. 137

becomes harmless if the destruction by the blood-cells takes
place more rapidly and to a greater extent than the growth and
multiplication of the Bacillus, the converse being also true.

If these ideas are correct, and a normally virulent Bacillus
is harmless after protective
inoculation and in the absence
of this is still virulent, we are
driven to the further assump-
tion that the protective inocu-
lation produces this result by
giving the blood-cells the
power which they did not be-
fore possess of absorbing and

destroying virulent Bacilli. We have no distinct investigations
into this point for our guidance, but if we once more accept
the views set forth above we must almost necessarily assume
that by the actual absorption of less virulent Bacilli the
blood-cells of an animal successively acquire the power of
absorbing and destroying the more virulent, which would not
have been taken up without this preparation.

The security of an animal from infection by a dangerous
parasite which has found its way into its blood, or the suscepti-
bility to it, would accordingly depend on the reaction of the
blood-cells on the parasite ; and it would be possible to alter
their power of reaction by gradually accustoming them as it
were to a succession of more and more virulent individuals.
In this way we obtain a partial explanation of the effects of
protective inoculation with material of increasing virulence.

But now there is the further question, why are virulent Bacilli
scarcely ever taken up by the blood-cells of an unprepared
animal, while the attenuated ones are readily absorbed ? Since

Fig. 19. a blood-cell of a frog in the act of engulphing a rod of Bacillus
Anthracis, observed in the living state in a drop of aqueous humour, b the
same a few minutes later; the shape of the cell is changed and the bacillus
is completely engulphed. After Metschnikoff. Highly magnified.

138 Lectures on Bacteria. [§ xn.

we find no morphological or anatomical differences in the con-
curring parts in cases which differ furthest from one another,
we can only assume that the cause of the difference in behaviour
lies in material differences, differences in the chemical be-
haviour of the two objects. And since we are dealing on the
one hand with portions of an animal which, as far as we can
perceive, is not essentially altered in its collective properties, and
on the other hand with a Bacillus which has its properties which
are in this case the subject of direct observation essentially
altered by attenuation, it follows that the changes in the chemi-
cal qualities must chiefly be on the side of the Bacillus. Nor is
this at all inconsistent with the phenomena of protective inocu-
lation, the accustoming the blood-cells, as was said, to the
absorption of a succession of Bacilli each more virulent than the
preceding one. On the contrary we know that other amoeboid
protoplasmic bodies which absorb solid substances, for example
the plasmodia of the Myxomycetes, do become habituated to
contact with and probably also to the absorption of bodies with
certain chemical qualities, though at first they hastily withdraw
from contact with them ; and without further arguments there
is good reason for attributing the same power to the blood-
cells, because they agree with plasmodia in all other qualities
which have any bearing on this point.

No precise account can at present be given of the nature of
the chemical differences between virulent and attenuated Bacilli,
and what can be said about it will be mentioned presently.
The proximate cause of the attenuation by Pasteur's method
is to. be sought not in the effect of oxygen but in the
heightened temperature ; this has been shown convincingly
by Chauveau and by Koch and his colleagues, who call
attention to the fact that the degree and permanence of the
attenuation and also the time required for attaining it are di-
rectly dependent, other conditions being the same, on the tem-
perature and even on small variations of temperature. We know
nothing at present respecting the causes of the attenuations

§ XII.]

Anthrax. 139

obtained by other methods than that of Pasteur and of the
possible return of virulence.

If we proceed in the next place to enquire how the parasite
causes disease, we find that it is not possible to give a decisive
answer ; still there are some definite facts and analogies leading
to a conception of the matter which approaches very near to
probability. The first fact is the appearance of the carbuncle
of anthrax in human subjects infected by inoculation or
through a wound. At the spot where the infection has taken
place there appears at first a violent local inflammation of the
skin, and it is not till 2-3 days later that the general symptoms
supervene. The inflammation is specifically different from
other violent inflammations of the skin, just as the local symptoms
produced by a definite poison with peculiar effects differ from
others which are caused by some other poison or by other
causes. This, it appears to me, excludes the view sometimes
expressed, that the Bacillus becomes the exciting cause of
disease by giving rise to merely mechanical disturbances, or
simply by withdrawing the oxygen from the living blood in
which it vegetates ; it is much more probable that the effect of
the Bacillus is peculiar to itself, the result of a specific poison.
If this is conceded, then the poison must issue, be excreted
from the Bacillus, for it could have no effect if it remained in
it. This agrees with MetschnikofFs observation that the same
blood-cells readily absorb the Bacillus if it is not virulent, while
if it is virulent it is virtually not absorbed. There must be
something in the virulent Bacilli which there is not in the
others, and it is probable, as was shown above, that this some-
thing possesses distinct chemical properties, and it must be on
the outside of or at least at the surface of the body of the Bacillus,
for if it were only in the inside there would be no reaction
with the blood-cells upon their coming into contact with the
Bacillus.

We know nothing of the real nature of the poison which is
thus supposed to be excreted by the Bacillus. Attempts to

140 Lectures on Bacteria. [J xn.

isolate it have been hitherto ineffectual. If the Bacilli in the
blood of an infected animal are separated from the fluid of the
blood by nitration through porous earthenware, the fluid when
injected does not produce anthrax. In these negative results
lies the gap in the foregoing line of argument. If we still stand
by our previous assumption, it follows that the poison is ex-
creted and is operative in very minute absolute quantities, or
merely that it decomposes rapidly outside the living blood and
loses its efficiency, or both of these suppositions are true.

The analogies, which may be brought forward in support of
the assumption here made that a poison excreted by the Bacillus
is the exciting cause of the disease, are drawn partly from the
fact that bodies which in extremely small quantities exert a
virulent poisonous effect, the poisons of dead flesh, ptomaines, are
produced by other Bacteria, though it is true out of dead organic
substances, partly and chiefly from Pasteur's observations on
fowl-cholera, a disease running a parallel course to that of
anthrax and caused by a parasitic Bacterium, of which we will
now proceed to give an account.

But before doing so I have one more remark to make on the
attenuation of virulence. If we consider that Bacillus Anthracis
is a distinct species, it seems highly remarkable according to our
usual experience that it should have a poisonous effect at one
time and not at another. Yet similar phenomena are not
altogether rare. It will be sufficient to mention one example,
that of the sweet and bitter almond to which attention was first
called by Nageli, if I am not mistaken, in connection with the
subject which we are considering. The bitter almond is
poisonous from the amount of amygdalin which it contains,
though it is not very dangerous to human beings ; the sweet
almond contains no amygdalin and is not poisonous. The
sweet almond tree does not differ specifically from the bitter ; a
tree with bitter seeds may be produced from a sweet seed ; bitter
and sweet seeds may even be borne on the same tree in flowers
and fruits not morphologically distinguishable from each other.

§ xii.] Fowl-cholera. 141

We do not at all know the origin or cause of this difference, and
the instance cannot therefore help us to an actual explanation
of the phenomenon before us ; it only shows that we are not
dealing with a peculiarity confined to Bacteria or to a single
Bacterium, but with a special case of a not uncommon series of
phenomena.

Fowl-cholera or fowl-plague (57) is the name given to
a disease which attacks domestic poultry, and which shows
a similar behaviour to that of anthrax in the points with which
we are at present concerned. We learn from Pasteur's researches
that it occurs in fowls in an acute and in a chronic form.
Characteristic symptoms of the former are a state of profound
torpor or stupefaction ; the bird sits with closed eyes and staring
feathers perfectly still and taking no notice of anything about it ;
this is followed by diarrhoea produced by inflammation and ulcer-
ation of the intestinal canal. Dissection also discloses abscesses
in different organs, fatty degeneration of the muscles, and other
symptoms. Death usually takes place in from 2-2 1 days, recovery
being rare. The chronic form shows similar symptoms but
with less violence, in some cases only local abscesses ; these may
continue for many weeks and the bird often recovers.

Dissection shows the presence of large numbers of a small
Micrococcus in the blood and abscesses, and on the intestinal
mucous membrane of the sick birds, and of those that have
died of the disease, really therefore in all parts of the body.
The cells of the Micrococcus, according to Kitt, are round,
from 0-3 to 0-5 /x in size, often united in pairs, and sometimes
also grouped together in larger numbers. The Micrococcus
has no power of locomotion, and no distinct spores have been
observed.

The Micrococcus of fowl-cholera may be grown outside the
living bird ; according to Kitt on the usual media of cultivation,
gelatine, blood-serum, potatoes; according to Pasteur it de-
velopes with especial luxuriance in neutralised chicken-broth. A
supply of oxygen is necessary for its vegetation. It sinks to the

142 Lectures on Bacteria. [§ xn.

bottom of Pasteur's culture-fluid when vegetation has ceased
and the nutrient-material is exhausted, and will remain there
alive and capable of renewed vegetation in a suitable substratum
for about eight months if the air has access to it, for a longer time
if air is excluded, as in hermetically sealed flasks.

If the Micrococcus is taken fresh from a sick or dead bird
or from its excrements, or from an artificial culture abso-
lutely free from any diseased part of the bird, and introduced
into a healthy bird, the minutest possible quantity of it, ex-
hibiting ordinary growth and multiplication, will reproduce the
disease. Infection is obtained by inoculation in or beneath
the skin, and by introduction of the Micrococcus with the
food into the digestive canal. Pasteur succeeded in com-
municating the disease by inoculation to mammals as well as
to birds ; rabbits thus inoculated died ; in the case of guinea-
pigs abscesses only formed at the place of inoculation, and
these contained a large quantity of the Micrococcus, but
they did not spread and ultimately healed. Kitt has extended
these experiments with similar results to mice and sheep and to
a horse.

Enough has been said to show that in this Bacillus, as in that
of anthrax, we have a facultative parasite specifically capable of
causing disease ; but its history and manner of life, especially
as regards the saprophytic sections of its development are not as
well known to us as those of Bacillus Anthracis.

Pasteur further discovered that the Micrococcus loses to some
extent its power of infection when it is kept some time exposed
to the air ; the number of successful inoculations and the se-
verity of the attack caused by them diminish with the age of the
matter used in inoculation. The cases mentioned before of
slighter attacks of the disease ending in recovery are chiefly
cases of inoculation of this kind. We may say therefore in
words which have been used before that age produces an
attenuation of the power of infection or virulence of the
Micrococcus.

§ xii.] Fowl-cholera. 143

Individual birds, which had recovered from the disease,
were generally but not always found to be no longer susceptible
to virulent infection, to be secure against a fresh attack, and
on this Pasteur founded the ideas with regard to protective
inoculation and his method of employing it which he proceeded
to extend to anthrax also.

When the fluid of a fresh culture in broth was separated by
filtration from the Micrococcus, which cannot be done by filtra-
tion through paper, for the Bacteria invariably pass with it through
the paper, but can be managed by means of filtration through
porous earthenware, the fluid was not in a condition to produce
the disease in the perfect form, not even when all the consti-
tuents contained in solution in 120 grammes of it were injected
into the blood of a fowl. But one characteristic symptom of
the disease, the stupor, was produced; the birds were sleepy
and as if stupefied after infection, continuing in this state about
four hours, and then returning to their normal state of health.

The observation, if established, shows that in this case a nar-
cotic poison separable from the Bacterium was actually disengaged
from it, and this is the reason why the fowl-cholera is especially
instructive in judging of the effects of parasites of this kind in
the production of disease. That the effect of the poison in these
experiments was comparatively slight and transitory, is to be
explained by the small amount of it in the fluid, and by the fact
that like other poisons it is either decomposed in the infected
fowl or is withdrawn from it with the normal secretions. The
case is different when the poisonous organism itself is present in
the fowl, apart from the circumstance that the conditions are
then probably more favourable for the formation of the poison.
While the poison is being perhaps constantly decomposed within
the fowl or is being removed with the normal secretions, it is
constantly being produced by the parasite, and what has been
removed is replaced ; thus the symptoms of the disease neces-
sarily become more permanent and more severe, and ultimately
also more complicated. Further complications also arising from

144 Lectures on Bacteria. [$ xm.

the more strictly mechanical effects of the parasite are of course
not impossible.

XIII.

Causal connection of parasitic Bacteria with infectious
diseases, especially in warm-blooded animals. Intro-
duction. Relapsing fever. Tuberculosis. Gonorrhoea.
Cholera. Traumatic infectious diseases. Erysipelas.
Trachoma. Pneumonia. Leprosy. Syphilis. Cattle-
plague. Malaria. Typhoid fever. Diphtheria. In-
fectious diseases in which the presence of conta-
gium vivum has not been demonstrated.

i. I SHOULD have wished to have added to the foregoing
two examples of facultative parasites which cause disease, one
example at least of a strictly obligate parasite, but I am unable
to find even one which is sufficiently well known to allow a
detailed account to be given of it. All that can be produced on
this point will therefore be included in the following summary,
which is intended to contain in a few words the most important
part of the knowledge which we at present possess of the nature
of Bacteria as the exciting causes of infectious diseases in warm-
blooded animals, and especially in man (58).

By the term infectious diseases we mean all those forms of
disease which are only found where they are conveyed from a
sick person to a healthy one so far as the particular disease is
concerned, or the origin of which is confined to localities of a
particular character. The former kind are known as contagious
diseases, such as scarlet fever, measles, small-pox ; the latter, of
which malarial fever is the best known example, are termed
miasmatic diseases. If the two conditions are combined, we may
speak of miasmo-contagious disease and that in two senses ; we
may mean firstly that a disease may be caught in certain localities,
or by infection from person to person independently of locality
of miasmatic character, or secondly that a disease is indeed

§ xiii.] Causal connection with infectious disease. 145

contagious, but requires the existence of previous miasmatic
infection in the person who is to take it. It should be ob-
served also, that up to recent times the term infectious disease
was only used when the exciting cause of infection, the con-
tagium or miasma, was only imperfectly understood. If disease
was caused by known parasites, such as lice or entozoa, trans-
ferable from one person to another or only to be procured in
certain localities with special characters, it was not called in-
fectious but parasitic.

It was natural that some ideas should be entertained respect-
ing the general qualities of the unknown and invisible contagia
and miasmata, and it was assumed, not without reason, that
they were special particles of matter which were efficacious for
infection in a state of the most minute subdivision and in the
most infinitesimal quantities.

The qualities of living beings were for a long time ascribed
by some observers to these infectious particles or contagia, as
we may now usually call them, and first of all in the period of
history from which we have received the terms 'contagium
vivum ' or ' animatum/ then used in a somewhat obscure and
indefinite sense. The traditional expression contagium vivum
received a more precise meaning in 1840 from Henle, who in his
' Pathologischen Untersuchungen ' showed clearly and distinctly
that the contagia till then invisible must be regarded as living
organisms, and gave his reasons for this view. His argument may
be briefly stated in the following manner. The contagia have
the power, possessed as far as we know by living creatures only,
of growing under favourable conditions, and of multiplying at
the expense of some other substance than their own and
therefore of assimilating that substance. The quantity, certainly
minute, of the contagium which communicates infection to
any one who pays a hasty visit to a person suffering from an
infectious disease, has the power of multiplying enormously in
the body of the infected person, for the latter is able to give the
infection to an unlimited number of healthy but susceptible

146 Lectures on Bacteria. [I xm.

persons, and therefore to part again for an unlimited number of
times with the same minute portion of contagium which he
himself received. But if we are forced to recognise the charac-
teristic qualities of living beings in these contagia, there is no
good reason why we should not regard them as real living
beings, parasites. For the only general distinction between
their mode of appearance and operation and that of parasites is,
that the parasites with which we are acquainted have been seen
and the contagia have not. That this may be due to imperfect
observation is shown by the experiments on the itch in 1840,
in which the contagium, the itch-mite, though almost visible
without magnifying power, was long at least misunderstood.
It was only a short time before that the microscopic Fungus,
Achorion, which causes favus, was unexpectedly discovered, as
well as the Fungus which gives rise to the infectious disease in
the caterpillar of the silkworm known as muscardine. Other and
similar cases occurred at a later time, and among them that of
the discovery of the Trichinae between 1850 and 1860, a very
remarkable instance of a contagious parasite long overlooked.
Henle repeated his statements in 1853 in his 'Rationelle Patho-
logic/ but for reasons which it is not our business to examine
here, his views on animal pathology met with little attention or
approval.

It was in connection with plant-pathology that Henle's views
were first destined to further development, and obtained a firmer
footing. It is true that the botanists who occupied themselves
with the diseases of plants knew nothing of Henle's pathological
writings, but made independent efforts to carry on some first
attempts which had been made with distinguished success in
the beginning of the century. But they did in fact strike upon
the path indicated by Henle, and the constant advance made
after, about the year 1850, resulted not only in the tracing back
of all infectious diseases in plants to parasites as their exciting
cause, but in proving that most of the diseases of plants are due
to parasitic infection. It may now certainly be admitted that

$xm.] Causal connection with infectious disease. 147

the task was comparatively easy in the vegetable kingdom, partly
because the structure of plants makes them more accessible to
research, partly because most of the parasites which infect them
are true Fungi, and considerably larger than most of the con-
tagia of animal bodies.

From this time observers in the domain of animal pathology,
partly influenced, more or less, by these discoveries in botany,
and partly in consequence of the revival of the vitalistic theory
of fermentation by Pasteur about the year 1860, returned to'
Henle's vitalistic theory of contagion. Henle himself, in the
exposition of his views, had already indicated the points of
comparison between his own theory and the theory of fermenta-
tion founded at that time by Cagniard-Latour and Schwann.

Under the influence, as he expressly says, of Pasteur's
writings, Davaine recalled to mind the little rods first seen by
his teacher, Rayer, in the blood of an animal suffering from
anthrax, and actually discovered in them the exciting cause of
the disease, which may be taken as a type of an infectious
disease both contagious and miasmatic also, in so far as it
originates, as has been said, in anthrax-districts. This was, in
1863, a very important confirmation of Henle's theory, inasmuch
as a very small parasite, not very easy of observation at that
time, was recognised as a contagium. It was some time before
much further advance was made. Rather the too great zeal of
inexperienced observers, especially excited by the cholera-epi-
demic of 1866, led to a so-called searching for parasites, barren
of all but mischievous results, which was the more calculated to
repel more earnest observers because for a time it attracted
some measure of applause. These are things which are now
long passed away and require no further notice.

Since about the year 1870 more general attention has been
again directed to these questions. The number of publications
discussing or bearing upon them is rapidly increasing, and we
cannot follow them here in detail. Prominent among them, as
new and especially suggestive attempts to deal with the subject,

L 2

148 Lectures on Bacteria. [$ XIIT.

are Conn's and Billroth's works already mentioned (1, 6), and
those of von Recklinghausen and Klebs on the more specially
pathological side ; it is the merit of Klebs more particularly to
have clearly indicated not only the nature of the problem as
conceived by Henle, whom he expressly follows, but also the
details of the ways and methods to be adopted for its solution,
and to have pursued them himself, though sometimes perhaps
with more zeal than discretion. Pasteur and his school pursued
the same course independently. Thus questions and experi-
ments were framed and knowledge acquired with constantly
increasing precision and results. The latest advance to be
recorded begins with the participation of Robert Koch in the
work of research since 1876. He may claim to have gone
forward as a highly intelligent observer on the paths marked
out by his predecessors without precipitancy, and with careful
use of all improvements in morphological investigation and in
microscopical and experimental methods. Hence he was the
first to obtain clear results in cases which up to that time had
always been disputed, as is shown by our account in a former
lecture of the aetiology of anthrax, the final settlement of which
is due to his investigations ; he has also shown what must be
done to ensure progress in researches of this kind.

The result of all these efforts is the same as that which was
arrived at in plant-pathology thirty years before. Firstly, it is
certain that in a number of cases the contagium is a micro-
scopic parasite, and that certain diseases, the infectious nature
of which was formerly denied or was doubtful, are infectious
diseases of this kind. Secondly, the same conclusion is rendered
at least highly probable in other cases. Thirdly, there remains
a very considerable number of diseases in which the parasite
has been sought for, but has either not yet been found, or its
existence is doubtful.

Further, it has been proved that, with some exceptions,
especially of skin-diseases and similar affections in which true
Fungi of a relatively large size are concerned, by far the most

f XIIL] Causal connection with infectious disease. 149

important parasites of contagion in warm-blooded animals
hitherto certainly determined are Bacteria.

We may note as consequences of what has now been said,
firstly, that Henle's doctrine has become a widely-accepted
dogma. There is no objection to this, if we put in the place of
belief that intelligent personal conviction which is distinctly
directed toward a particular view, but does not lose sight of the
possibility that it may some day be corrected or altered. That
the parasite required by the theory has not yet been found is no
reason for abandoning it, for the parasite may very easily have
been overlooked, owing to its extreme minuteness, or its power
of refraction, or because the observer has not learnt the right
place or time to look for it. When Henle founded his doctrine
in 1840, the Bacillus of anthrax had never been seen; the
Trichinae had been seen, but no one suspected that they were
the cause of disease.

The second result is that at present in almost every doubtful
or questionable case, it is only for Bacteria that search is made.
This is wrong in principle ; it may be practically right to search
for such forms as present experience shows are the most likely
to be found. But it should be remembered that organisms of
another kind may make their appearance unexpectedly, about
which we at present perhaps know very little. It is not so long
ago, that we knew very little about Bacteria and expected them
as little. That this is not idle talk is shown by some surprising
experiences recorded in connection with plant-pathology and by
the history of pe'brine which will be noticed presently.

Thirdly, if belief is stronger than the critical faculty, there is
great danger of concluding at once from the presence of a Bac-
terium that it is the exciting cause of disease for which we may
be seeking. From what we learnt in Lecture V on the wide
diffusion of Bacteria possessing full powers of development it
will at once be seen that Bacteria may be developed in a diseased
body before or after death, and that a particular form may be
present as a characteristic feature and even constantly and exclu-

150 Lectures on Bacteria. [} xm.

sively in a particular disease, and therefore have high diagnostic
value, without being the contagium which causes the disease.
To make sure of this it is absolutely necessary to experiment with
pure material and to obtain a clear positive result ; there must
therefore be a pure separation of the parasite to be examined
from all admixtures, a pure infection of the proper subject for
experiment with pure matter, and the strictest control and
criticism of the result. The example of anthrax described above
will illustrate these rules. Without successful experimentation
there is always a gap in the proof which cannot be filled up by
other arguments, however well adapted they may be to serve as
the foundation of a personal conviction. It is true that the latter
may persist in spite of defective experimental proof. A parasite,
as has been before explained, does not thrive, or does not thrive
equally well in every host-species; it can attack and cause
disease in one and not in another. The experiment therefore in
the case in question may give no positive result, because the
right, that is the susceptible, species of warm-blooded animal was
not employed. This point must be specially attended to in the
case of infectious diseases which attack human beings chiefly.
We cannot or must not experiment freely with human beings,
but must trust in the main to experiment on other warm-blooded
animals, and this may be the only reason why that in certain
cases, some of which will be noticed further on, the results of
experiment have as yet remained doubtful or negative.

Enough has been said to give inexperienced persons an idea
beforehand of the reasons why we may have to speak here of
doubtful cases and doubtful statements.

We will now proceed to a consideration of the facts. Our
object, as was said before, is to bring forward whatever is most
important in connection with the Bacteria which are the exciting
causes of disease. A minute discussion of the diseases them-
selves does not fall within the plan of these lectures, and must
be sought in medical publications.

Whatever peculiarity there may be in each individual case, we

§ xiii.] Relapsing fever. 151

are constantly confronted in dealing with the main points of our
subject with similar facts and questions to those which were
considered at some length in connection with anthrax and fowl-
cholera ; they form part of the great series of facts and questions
relating to parasitism, of which it was attempted to give a con-
cise review in Lecture X.

With this brief reference to these previous expositions we now
proceed to consider a few comparatively well-known cases.

2. Relapsing fever, febris recurrens (59), is a disease which is
widely spread in Asia and Africa, is endemic in Russian Poland
and Ireland, and sometimes finds its way into other countries
of Europe. It is communicated directly from the body of one
person to another or through the intervention of articles of daily
use. In 5-7 days after infection violent fever sets in with other
symptoms which need not be described here, and usually lasts
another 5-7 days, and is then followed by a period of absence
of fever for about the same number of days. Then comes a
relapse into the fever state, and the same alternation may be
repeated several times, usually with a favourable ending.

During the attack a slender Spirillum, resembling Spirochaete
Cohnii (Fig. 16, <?), sometimes 40/11 in length and exhibiting
active movements, is found in abundance in the blood of the
patient which is often of a dark-red colour; discovered by
Obermeier in 1873 it was named after him Spirochaete Ober-
meieri ; it disappears during the interval when there is no fever.

The disease is conveyed to men and monkeys when they are
inoculated with the blood of a fever-patient containing Spiro-
chaete. Blood taken during the interval of freedom from fever
and therefore free from the Spirochaete does not produce the
disorder after inoculation. Experiments in the inoculation of
other animals were always without result. Attempts to cultivate
the Spirochaete outside the body of the animal have not as yet
been successful.

From these facts it may properly be assumed that the Spiro-
chaete is the contagium of relapsing fever, though we are still

152 Lectures on Bacteria. [§ xm.

very imperfectly acquainted with its life-history, for we have
no certain information as to its place of sojourn during the in-
tervals of the fever, the form and mode of its conveyance from
one person to another, the formation of spores if any, or other
resting states.

3. One of the most important results of the researches into
the Bacteria which are the exciting causes of disease is the dis-
covery of the contagium of tuberculosis, the Bacillus of tubercle
long since rendered familiar to us by Koch's publications (60).
Tuberculosis has received its name from the formation of new
substance or the degeneration by which it is characterised, and
which appear in the form of small knots or tubercles in the
tissue of the organs. The formation of tubercle is best known
in the lungs as pulmonary-tuberculosis, pulmonary consumption,
but it may occur in any organ and the lymphatic glands are
particularly subject to it.

Tuberculosis attacks warm-blooded animals of every species
as well as man, and especially our ordinary domestic animals
and those used for experiments. The tuberculosis of horned
cattle is known by the name of pearly disease, bovine tuberculosis.
Different species show different degrees of susceptibility ; the
field-mouse is highly susceptible to infection, the domestic mouse
only slightly. The primary anatomical changes in the formation
of tubercle are in all cases the same. The succeeding ones and
the general character of the disease may be very dissimilar.

In tubercle, at least in the fresh state, Koch and simulta-
neously with him Baumgarten demonstrated the presence of a
characteristic rod-shaped Bacillus. According to these observers
it is always there, though in very unequal quantities in different
cases. It passes into the ejected matter, the sputum of pulmo-
nary tuberculosis, and may be found in it. With due care it may
be kept pure and be cultivated pure through repeated generations
on stiffened blood-serum or in infusion of meat.

Tubercular matter containing Bacilli, or still better the purely
cultivated Bacillus, introduced beneath the skin of susceptible

§ xiii.] Bacillus of tubercle. 153

animals or injected into a blood-vessel or into a cavity of the
body, or pure Bacillus-material inhaled in a state of fine division
suspended in water, resulted in the formation of tubercle with
its consequences in every case without exception — Koch
experimented on 217 individuals of susceptible species of
animals (rabbits, guinea-pigs, cats, field-mice), besides animals
used in control-experiments and individuals of less susceptible
species — and the Bacillus was in every case found in the tuber-
cles. In every case also the place where the tubercle appeared,
its frequency and distribution, and the line of distribution through
the body answered the expectations founded on the mode of
infection and the spot where the infecting matter was applied.
These results, still further strengthened by control-experiments,
established the infectious nature of tuberculosis, and the conta-
gious character of the Bacillus, which had indeed been previously
concluded on other grounds.

Such observations on the Bacillus itself as have been published
leave much to be desired as regards its morphology. Observers
have been generally satisfied with proving its presence, and the
proof has been rendered easy by its peculiar behaviour with
aniline colouring matters. In contrast to the great majority of
other known Bacteria, it slowly and with difficulty takes in alka-
line solution of methylene blue or saturated solution of methyl-
violet, absorbing them only in the space of several hours or
after being heated, but it obstinately retains the colour it has
acquired, while other Bacteria are quickly decolorised by certain
reagents, for example, dilute nitric acid. By this peculiarity
in their behaviour as well as by their shape and size, the Bacilli
are comparatively easy to recognise and distinguish from other
species. . In form they are slender rods which are sometimes
curved or bent at an angle, and reach a length of i'5-3'5/*.
Neither in the natural nor in the coloured state can transverse
septation as a rule be observed. Endogenetic spores are found
in them, both in cultures and in the body and sputa of diseased
animals ; these according to Koch's brief account must answer

154 Lectures on Bacteria. [§ xm.

to the spores of endosporous Bacilli, but no further description
is given of them. Judging from the figures of sporogenous speci-
mens, and assuming that this species does not differ altogether
in behaviour from other endosporous Bacteria (see page 15),
the rods must be segmented in the same way as those of Bacillus
Megaterium described above, for they are represented with 4-6
spores standing close in a row one above another, as in Fig. i, r.
If our assumption and the account given is correct, each of these
spores must lie in a short segment-cell. This agrees with the
fact, that in coloured preparations the rods are sometimes found
divided by narrow hyaline transverse septa into a series of seg-
ments not longer than broad, such as Zopf figures in his third
edition. To call these segments Cocci is only playing with words.
If young vegetating rods are divided into long segments, this is
another point of agreement with Bacillus Megaterium. After
this description I abstain from giving a figure of this species ; a
drawing of what has been at present seen would represent a
simple or interrupted black stroke. In Fig. i, <$-_/" and r corre-
spond with our present knowledge of the form of the Bacillus of
tubercle, except that the length of the rods in the latter species
is on an average not greater than the breadth of those of Bacillus
Megaterium in the figure.

The living rods, according to Koch, are not motile. When
grown on stiffened blood-serum they do not liquefy it, but
remain on the surface, and there even when developed in com-
parative abundance they form thin dry scales of small extension,
which are shown under the microscope to consist of sinuously
curved swarms and bundles of single rods.

The Bacillus of tubercle grows slowly as compared with most
other Bacteria, and in this respect resembles the Bacterium of
kefir. In cultures on serum 10-15 days elapse before growth
can be detected by the unaided eye. The result of an inocula-
tion is not apparent in less than 2-8 weeks.

The attempts to cultivate this species outside the living animal
on any other nutrient substrata than those above-mentioned

§ xiii.] Bacillus of tubercle. 155

have not been successful ; the cardinal points for the tempera-
tures of vegetation are those given on page 51.

The Bacillus of tubercle offers a somewhat high degree of
resistance to injurious influences from without, and is thus able
to preserve its powers of infection. It can bear temperatures
approaching the boiling point, though it is soon killed if it is
heated in a thoroughly moist condition. It was not affected by
desiccation during a period of 186 days, or by being kept in
putrefying sputum for 43 days. The experiments on its powers
of resistance have chiefly been made with sputum containing the
Bacilli. No attempt has been made to determine precisely how
far these powers of endurance are confined to the spores or
belong also to the vegetative rods, but our experience in other
cases would lead us to suppose that they belong chiefly to the
spores.

These facts taken together give a satisfactory explanation of
the appearance of tuberculosis as the result of infection with the
Bacillus. Every one knows how widely spread the disease is,
even if we think only of pulmonary tuberculosis ; a seventh part
on an average of the deaths of human beings are caused by this
form of the disease. The Bacillus is generally present, capable
of development and in a virulent condition, in the excretions of
those suffering from tuberculosis. The expectorations of con-
sumptive persons often during months and years must be espe-
cially but by no means exclusively taken into account in this
connection. The Bacillus was absent from 44 only of the 982
specimens of sputa examined by Gaffky. It is clear that the
Bacillus is communicated in large numbers to these excretions,
and that when they dry up, it must be disseminated with the
dust and in other ways. There is therefore abundant oppor-
tunity for infection in the ordinary intercourse of human beings.
We need not enter more minutely into this point, and to discuss
the mode in which the Bacillus spreads in the body which has
once become infected would also lead us too far into medical
details. That a good deal depends on the susceptibility of the

156 Lectures on Bacteria. [§ xm.

subject to be infected to the results of infection is shown by the
fact, that in sick-rooms and institutions in which consumptive
patients remain the year through, it is not every one who is suc-
cessfully infected with tuberculosis. This fact is in accordance
with the general knowledge which we possess of individual or
specific differences in susceptibility to the attacks of parasites.

The foregoing facts and views are not affected by the state-
ments of Malassez and Vignal, who describe a form of tuber-
culosis with a copious growth of Micrococcus, which they call
'tuberculose zoogloique,' and in which they sometimes found
the Bacillus and sometimes not. Supposing these accounts to
be correct, we must assume with the clear results of Koch's in-
vestigations before us that there is either some complication
here, or that we are dealing with some disease resembling
ordinary tuberculosis but different from it in so far as it is caused
by a different parasite.

4. Gonorrhoeal affections (61). These are inflammations
of the mucous membrane of the urethra and of the conjunc-
tiva of the eye accompanied by suppuration and occurring
in the human species. Purulent conjunctivitis in new-born
children, ophthalmia neonatorum, may certainly be classed
with them.

One of the characteristic peculiarities of these maladies is that
they are highly infectious, and it has long been known that in-
fection is due to the purulent secretion of the patient. The
infection of healthy human eyes takes place, as Hirschberg says,
with the certainty of a physical experiment. With the same
certainty there is found in the infectious matter a large Micro-
coccus, which was discovered by Neisser and named by him
Gonococcus (Fig. 20), chiefly appearing to be attached to the
surface of the epithelial and pus-cells, according to recent
observations really penetrating a slight distance into the body
of the cells, less often lying between them. It should be added
that the number of the cells beset with the Gonococcus is always
relatively small and varies from case to case.

f xiii.] Gonorrhoeal affections. 157

The cells of the Gonococcus are roundish in shape and of
some size, about 0-8 /* in diameter, often attached together in
pairs corresponding to their partitions, separated in the full-grown
state by a hyaline gelatinous intervening substance, and often
distributed in large numbers and at tolerably regular distances
on the surface of the pus-cells. It is un-
certain whether this superficial arrangement
is due to successive partitions taking place
alternately in two directions, or to a cor-
responding displacement with the partition
always in the same direction ; I see nothing Fig. 20.

in the observed facts to compel us to adopt the first as-
sumption.

Gonococcus is not found in other inflammations of the
mucous membranes in question, and other Bacteria do not give
rise to the phenomena of gonorrhoea. These facts make it
probable with the aid of analogy that the infectious nature of
the gonorrhoeic secretion is due to the presence of the Coccus,
that this is the active contagium.

Warm-blooded animals other than man are, as far we know,
either not susceptible to gonorrhoeic infection or take it with
difficulty ; a very large majority of the experiments on animals
with the secretion from the eye were unsuccessful.

Cultures of Micrococcus Gonococcus outside the living
patient seldom succeed. Yet some are said to have been suc-
cessful, those for example of Hausmann from the secretion from
the eye of an infant on stiffened blood-serum, and those of
Bockhardt and Bumm from the secretion from the urethra ;

Fig. 20. Micrococcus Gonococcus, Neisser. From the secretion from
the conjunctiva of a child treated for Ophthalmia neonatorum. Four
pus-cells with Micrococcus attached, from a preparation coloured with
methyl-violet. The pale-coloured pus-cells with their nuclei are faintly
shown in the drawing in order to make the Micrococcus more apparent.
n outline of an isolated cell of Micrococcus and of a pair of cells formed by
bipartition. Magn. 600 times, with the exception of n, which is more
highly magnified.

158 Lectures on Bacteria. [$ xm.

the careful observations of the latter author leave no room for
doubt. The introduction of the Coccus from a pure culture
into the eye of a new-born rabbit by Hausmann, and into the
eye and urethra of a human subject by Bockhardt and Bumm,
communicated the infection. It appears from Bumm's obser-
vations on the conjunctiva of the human eye, that the Micro-
coccus penetrates between the epithelial cells into the papillary
body of the mucous membrane, multiplies and spreads in these
spots and later also in the purulent secretion, and is ultimately
stopped in its further advance and got rid of by regeneration of
the epithelium and secretion of pus. The case examined by
Bockhardt showed more complicated phenomena. Bumm's
excellent monograph should be consulted for the details.

I have put together relapsing fever, tuberculosis, and gonor-
rhoea, different as they are from one another, because if we
once put the doubts and the gaps in our knowledge on one side,
and take probability for certainty, they supply us with examples
of actual obligate parasitic Bacteria.

Spirochaete Obermeieri is, as far as we at present know,
strictly obligate, inasmuch as it can only be conveyed from one
person to another without digression into saprophytism, and is
confined to men and apes.

The Bacillus of tubercle and Gonococcus may certainly be
cultivated as saprophytes, a facultative saprophytism cannot be
denied them. But this character can scarcely be taken into
consideration in their case ; not in that of the Bacillus of tubercle,
as Koch urges, because the conditions of its vegetation as a
saprophyte are of such a kind and so limited, that they will
scarcely ever be found except in an apparatus contrived for the
special purpose, nor yet in that of Gonococcus for similar
reasons. This follows at once from our experience in
general, and it follows further that the resisting power of
the Gonococcus is very small, and its dissemination for the
purpose of infection, as for example in dust after desiccation,
is not worth consideration. Gonorrhoeic affections are scarcely

§ XIIL] Asiatic cholera. 159

less common than tuberculosis ; their secretions are scattered
about and the Gonococcus with them. If the Gonococcus were
capable of saprophytic vegetation under ordinary natural con-
ditions, it is hardly to be supposed that infection would not
sometimes take place in some other way than from one person
to another. This, however, notwithstanding some quite doubtful
and isolated accounts, is not the case.

5. Asiatic cholera (75) may now be very fairly reckoned
among the comparatively well-known infectious diseases, which
we are at present considering. As early as the beginning of
the year 1850, Pacini believed that he had found a contagium
vivum of this disorder in the Bacteria, or Vibrios as he terms
them, which he observed in the intestinal canal and its evacua-
tions. Some time after (1867) Klob examined the contents of
the intestinal canal, and the evacuations of patients suffering
from Asiatic cholera, and likewise found Bacteria present in
them in considerable quantities ; and starting with the assump-
tion that these organisms are instruments of decomposition, he
showed it to be probable that these Bacteria set up the disease
in the intestinal canal, and spread it from thence to other parts
of the body. Our knowledge of the Bacteria had not then
reached the point at which attempts could be made to dis-
tinguish more precisely between the various forms found in the
intestine and in the dejecta and to separate them from one
another. The absurd notion, entertained in other quarters be-
tween the years 1860 and 1870, of referring the cholera-con-
tagium, Bacteria included, to ordinary moulds and hypothetical
parasites of the rice-plant, and the fact that Bacteria apparently
quite similar to those of Klob were found in the intestinal canal
of persons who were not suffering from cholera, had the effect
of withdrawing attention once more from these and other efforts
to discover the contagium vivum of this disease. In India,
the perennial home of the pestilence, the researches conducted
at a later time by English physicians gave no certain and positive
results.

160 Lectures on Bacteria. [§ xiu.

Our knowledge of the Bacteria and of the real existence of
contagia viva was in a much more advanced state, when the
outbreak of the epidemic in Egypt in 1883 led to a fresh re-
sumption of the question. R. Koch, the most experienced
investigator of the subject, pursued his enquiries in Egypt and
in India, and there became acquainted with a distinctly marked
Bacterium-form which is found in the intestinal canal in fresh
cholera-cases, and was once observed also in a water-tank in a
cholera-district. This Bacterium he suspected to be the specific
contagium or miasma of the Indian pestilence ; we will for the
present call it a Spirillum.

According to the facts as at present known, there can scarcely
be a doubt that Koch's Spirillum is really the contagium vivum
of Asiatic cholera. First of all, its constant presence — for we
may call it constant — in the small intestine or in the evacuations
of cholera-patients is acknowledged by all observers, even by
those who do not accept Koch's views. It is sometimes found
almost as in the state of a pure culture in the mucus of the in-
testine in bodies examined immediately after death ; under other
circumstances certainly it is less pure and abundant. In the
exceptional cases in which it was not found, either strict search
was confessedly not made, or it may have been overlooked or
have actually disappeared, especially at an advanced stage of the
disease, and therefore have once been present. Koch's Spirillum
has never been found either in the intestinal canal or in any
other part of the body in any disease except Asiatic cholera.

The Spirillum of cholera can readily be cultivated pure as a
saprophyte, as will be noticed again further on. Attempts to
inoculate animals with pure living material of this kind gave at
first only negative or in the most favourable case uncertain
results, and this is especially true with regard to the experiments
in which it was sought to convey infection with the food. It was
found that the Spirilla were killed by the acid gastric juice, or
were rendered inoperative by some other causes. But a change
in the mode of conducting the experiment led to a positive result.

$xm.] Asiatic cholera. 161

Nicati and Rietsch and van Ermengem avoided the passage of
the stomach and introduced the Spirillum by injection directly
into the small intestine. In van Ermengem's experiments the
Spirillum, which had been cultivated in meat-broth or serum,
was injected into the duodenum of some guinea-pigs, eleven in
number, in small quantities, — a single drop or a much smaller
portion of the fluid. Of the eleven, one died soon after the
operation, nine in two to six days after infection ; the eleventh,
which had received ' about one-fiftieth of a drop/ recovered after
a short illness.

The phenomena of the disease and the state of things as
shown by dissection corresponded, according to van Ermen-
gem's account, in all essential particulars with those of Asiatic
cholera, making the necessary allowance for the difference
between the human being and a guinea-pig. The Spirillum
vegetated abundantly in every case in the intestine of the infected
animal, either pure or mixed with other Bacteria. A drop of
fluid containing the Spirillum from the intestine of the animal,
communicated the same form of disease to sound animals when
injected into their duodenum. Lastly, when fluids containing
other Bacteria were injected into the duodenum as a test-
experiment, no cholera-symptoms appeared, and usually no dis-
turbance of the ordinary health.

I have here put these experiments in the front place, because
they could be most simply and briefly described. Other ob-
servers, Koch especially and Doyen, obtained the same positive
result by introducing the Spirilla with food after the acidity of
the contents of the stomach had been neutralised by an alkaline
fluid, and further by increasing the predisposition of the animals
for the infection by administering opium and alcohol, in accord-
ance with an observation of Koch's. I must limit myself here
to these few remarks in proof of the success of the attempts to
communicate the infection, and refer to the special literature for
further details.

It appears from the accounts which we possess that the

M

1 62 Lectures on Bacteria. [§ xm.

Spirillum of cholera vegetates invariably in the intestine of
the patient, both in the mucus of the intestine and also, according
to some observers, penetrating into the tissue of the mucous
membrane. Neither it nor any other Bacteria are found in other
organs of those who have died of the disease, according to Koch
and most other observers. But Doyen attests its presence in
kidneys and liver, and van Ermengem found it in the blood-
channel of three of the animals in his experiment before or
immediately after death.

On the strength of the observation that the Spirillum occurs
only in the intestinal canal, Koch's view is very generally thought
to be highly probable, that it produces a very powerful poison
there, and that it is this poison which being absorbed from
the intestine causes the severe general symptoms of cholera.
If it should be proved that the Spirillum is carried through the
body with the flow of blood, this assumption must at least receive
some modification, and in any case it still requires more distinct
proof.

As regards its shape, Koch's cholera-contagium appears,
when its segmentation is most perfect, in the form of spirally-
twisted rods or filaments, closely resembling the Spirilla
figured on page 82, and of very unequal length and number of
spirals. The filament is about 0-5 \i in thickness, but it is not
possible to give the exact measurement ; the width of the turns
of the spiral is about the same as the thickness of the filament,
or less ; the steepness of the individual turns varies. The fila-
ment is composed of segments or segment-cells, which are about
as long as a half-turn of the spiral, and each of them, therefore,
is a more or less curved rod. A separation of the segments
from one another does actually and as a rule take place soon
after every division, if the Spirillum is actively vegetating in
a gelatinous nutrient substratum (gelatine, agar) or on the
mucous membrane of the intestine ; in these places, therefore,
the Bacterium takes the form of crooked rods, which are either
single or united together into short rows; the shape of these

$ XIIL] Asiatic cholera. 163

rods was naturally compared by Koch to that of a comma, and
he therefore called them comma-rods, comma-bacilli. In good
nutrient solutions, such as meat-broth, and in old gelatine
cultures, the segments more frequently remain united together
into long unbroken and apparently unsegmented spirals. In
both forms the Spirillum has the power of movement, the single
rods being more active than the longer spiral filaments, especially
when they have grown in old gelatine- cultures.

Hueppe has observed in old cultures a further phenomenon,
which must be termed spore-formation, — the formation in fact
of arthrospores. The spiral filaments, beginning at intercalary
spots, divide for a certain distance into spherical segments,
which are a little thicker than the vegetating cells, are more
highly refringent, and are separated or held together by thinner
gelatinous envelopes. In this form they do not divide, but if
supplied with fresh nutriment they may at a later period
develope again into comma-rods, and by so doing they justify
their claim to be called spores. Spores of this kind appear to
have been seen, but not rightly understood, by former ob-
servers. They are quite distinct from the formations described
by Ferran. These are to be seen when spiral filaments in old
cultures swell up irregularly and shapelessly, or form round
bladders at their extremities, and then, as later observers have
unanimously declared, die off and disappear. They are con-
nected, therefore, simply with the retrogressive or involution-
forms common among Bacteria, and noticed above on page 10.
Ferran's sensational descriptions of these objects are inconceiv-
able to every sensible man with any pretension to a scientific
education. They have no other significance than that of a
warning example of the follies a man may commit, when he is
bent on making faulty observations seem important to himself
and others by the use of names and technical expressions which
he does not understand.

With respect to the biological characters of the Spirillum of
cholera, it is no longer needful from the accounts which we

M 2

164 Lectures on Bacteria. [$ xm.

have of it to refer expressly to its facultative saprophytism. Its
saprophytic vegetation requires an abundant supply of oxygen.
If cultivated with this upon a suitable moist substratum it
developes rapidly and copiously, taking the place of any com-
petitors it may encounter ; but after some days the energy of its
growth rapidly diminishes, perhaps in consequence of the dis-
turbing influence of its own decomposition-products. These
phenomena were most strikingly exhibited in cultures on moist
linen, which was selected for practical reasons. The optimum
temperature for vegetation is, as was stated above on page 50,
that of the body of a warm-blooded animal, about 37° C., but
20-25° C. is sufficient for good development. Death ensues
without fail in a fluid heated to 50-55° C. The Spirillum is
not killed by being cooled to or below the freezing point, even
if this temperature is maintained some hours. Perfect desic-
cation kills the vegetating Spirillum in less than twenty-four
hours ; the arthrosporous Spirilla on the contrary, according to
Hueppe's direct observation, continue capable of germination
for four weeks after desiccation. On the other hand, as it is a
matter of observation that new vigorously vegetating generations
may proceed from desiccated cultures after a longer period than
this, and for almost ten months, Hueppe suspects, on good
though not quite conclusive grounds, that the new growths
always spring from arthrosporous Spirilla, and that these are
the specifically resistent resting states of the Bacterium of
cholera. I have already said all that is here necessary con-
cerning the food-requirements of the Spirillum, and on the
unfavourable or even fatal effect upon it of the acid reaction of
the substratum.

The phenomena in the life of the Spirillum, which have now
been described, supply the needful explanation of the chief facts of
experience in connection with cholera as an infectious disease,
especially its claim to be indigenous in India, its introduction
into other countries and parts of the globe, and the chief points
in the history of its diffusion there. It is true that something

$ xiii.] Asiatic cholera. 165

still remains unexplained ; for instance, the immunity enjoyed
by certain localities, the fact that an epidemic of the disease in
Europe ceases entirely after the lapse of a certain time, and
some other points. But it is no objection to well-established
explanations, either here or in any other domain of human
knowledge, that this or that point is still unexplained.

Other objections, current certainly till quite recent times, were
aimed directly at the real character of Koch's Spirillum as the
specific contagium of cholera. So far as they rested on the
failure of attempts to communicate the infection with the pure
Spirillum, they are set aside by the positive results now before
us of similar attempts, supposing these to be trustworthy. On
the other hand, they denied that Koch's organism was present
exclusively in cases of Asiatic cholera. Finkler and Prior dis-
covered a Spirillum extremely like it in the affection of the bowels
known as indigenous cholera, cholera nostras. Lewis and, after
him, Klein pointed to the comma-spirillum of the mucus of
the mouth (see page 120 and Fig. 1 6, d), which is common in
healthy human beings, and when seen in single specimens is also
so like Koch's Spirillum that it might be considered to be identical.
But further investigation has now removed all doubt concerning
certain trustworthy distinctions, which come to light especially in
cultures on a large scale, between these and other similar forms
which cannot be enumerated here and Koch's organism; all
attempts even to cultivate Lewis' Spirillum from the mouth as a
saprophyte have as yet been attended with no positive result.
Whether Finkler's and Prior's Spirillum may be the specific
exciting cause of some other disease than Asiatic cholera cannot
be considered here.

The most thorough-going objection, however, is that brought
forward by Emmerich and supported by H. Buchner; these
observers maintain that another than Koch's Bacterium is the
specific contagium of cholera — a short non-motile rod-bac-
terium, which figures in literature under the provisional name
of the Naples Bacillus.

1 66 Lectures on Bacteria. [$ xm.

Emmerich found his Bacterium in the gelatine- cultures which
he employed in the examination of the bodies of persons who
had died of cholera in Naples; fresh bits of the wall of the
intestine, of the kidneys, and of other internal organs, together
with blood from persons who had died of the disease or who
were suffering from it, were placed with every precaution in the
nutrient gelatine. The presence of the Bacterium in the above
organs was concluded from the results of the culture ; it grew in
the culture, but it was not directly proved to have been present
in the organs. The result of researches undertaken a year later
in Palermo was, that no Bacterium could be shown to be present
in the internal organs, liver, spleen, kidneys, or in the heart's
blood in the majority of acute cholera-cases, nor was it found in
the viscid exudation of the peritoneal cavity. In one case only
was the Naples Bacillus obtained by culture from the liver of a
patient. But it was now found in most cases in abundance in
the contents of the stomach and intestine, though it must be
added that there was some doubt as to the identity of the forms,
and the decision on this point is reserved for further study.
Moreover, the Naples Bacillus was obtained plentifully in most
cases from the bronchial tubes and lungs. On the other hand,
Emmerich and Buchner both bear witness to the practically
constant presence of Koch's Spirillum in the intestine in the
cases which they examined.

Emmerich also experimented on animals by inoculating them
with pure material of his Bacillus, and obtained in this way
positive results, the sickening with indubitable cholera-symptoms.
But symptoms of this kind appear, as Virchow pointed out at
the second Berlin Conference on cholera, when animals are
inoculated with the most various kinds of substances which are
putrid or contain Bacteria ; they cannot therefore by themselves
be regarded as decisive. It is true that this objection may also
be made to the positive results mentioned above of infection with
Koch's Spirillum. But all reported observations and results of
experiment, the observations even of Koch's opponents, do at

§ xiu.] Traiimatic infectious diseases. 167

present agree in attesting the significance of his Bacillus as the
specific contagium of cholera. Emmerich's results from Naples
and Palermo, on the other hand, are not consistent with those
of any other observer or with themselves; this detracts from
the value of his experimental results in view of Virchow's
observations. From the material before us the unprejudiced
critic cannot, in my judgment, find any valid objection to the
views of Koch and his school.

6. Among the diseases due to the action of Bacteria must be
reckoned also traumatic infectious diseases, with their great
variety of characteristic symptoms, affections also incident to
child-bearing, and others connected with the formation of groups
of ulcers, of abscesses of the skin and of the internal organs, of
local skin-abscesses, boils, and ulcers, as well as more serious
maladies (62). In these affections Bacteria-forms are found on
the infected surfaces of the wounds, in pus, &c., and in all but a
few cases, which for some special reasons are of an exceptional
nature ; and the eminent success of the antiseptic treatment of
wounds introduced by Lister, the object of which is to pre-
vent the approach of the organisms which set up decompo-
sition, and to render them harmless, is an indirect proof
according to our present views that these forms, as promoters
of decomposition, are in causal connection with the affections in
question.

This connection may be of two kinds. The contagium may
cause local suppuration, formation of abscesses, &c., at the spot
where it is found, either remaining in the wound which received
it, or passing from it into the blood and with the blood into
remote organs ; or else unorganised poisonous bodies, ptomaines
(see page 1 40), or similar substances are formed at the points of
infection, as products of the vegetation of the contagium, and are
then distributed in the blood and conveyed into the body, pro-
ducing symptoms of poisoning in it. It is also conceivable that
these two fundamentally distinct processes may occur in com-
bination.

1 68 Lectures on Bacteria. [§ xm.

This subject can only be thus briefly noticed here; the details
will be found in the extensive medical literature on the subject
with which I am myself only imperfectly acquainted. I have
chiefly followed Rosenbach's work, cited in note 62, on the con-
tagia of traumatic infectious diseases. I will only add one
remark, that a very noteworthy series of recent experiments are
now offered for our study, in which inflammation, it is true, but
no suppuration was caused by the application of the strongest
chemical irritants of very different kinds, when the co-operation of
Bacteria was excluded; Passet has however raised objections
to the universal application of this principle.

As regards the Bacteria themselves of which we are speaking,
several kinds have been observed. Rosenbach alone speaks of
four different Bacilli or at least rod-forms, and especially of
Micrococci, three kinds of which are common ; the others need
not be noticed here. The individual Micrococci cannot be
certainly distinguished under the microscope ; they are minute
round bodies with a swarming movement only, and show no
distinct formation of spores; but they are known from one
another by their appearance when grouped together, and by the
form and colour in which they show themselves in cultures on
the large scale on the surface of agar-jelly. One genus which
Billroth has named Streptococcus, has its cells united together
in rows, in the manner of Micrococcus Ureae (see page 84). In
the others the cells separate from the rows after division, and
form aggregations which Ogston has compared with a bunch
of grapes, and he has expressed the resemblance by the name
Staphylococcus. One species of Staphylococcus forms orange-
yellow, another white gelatinous expansions like the thallus of a
Lichen on agar-jelly, and they are therefore known as Staphy-
lococcus aureus and S. albus. If removed from abscesses and
collections of pus and isolated in a pure culture, each of
these Micrococci retains its characteristics unchanged ; some-
times only one species occurs in these products of disease,
sometimes the two are found together ; from the accounts before

§ xiii.] Erysipelas. Trachoma. 169

us it would seem that Streptococcus and Staphylococcus aureus
are the most common and the most destructive kinds. Rosen-
bach obtained positive results from inoculations and injections
of pure culture-material obtained from men in several experi-
ments on animals, that is, the introduction of the parasite caused
fresh abscesses, though, if I rightly understand the accounts,
large quantities of matter were employed in inoculation.

The above Bacilli and Micrococci are facultative parasites,
and may be cultivated as saprophytes without difficulty and in
abundance. No details are known with respect to their diffusion
as saprophytes in nature, but experience of a more general kind
makes it probable that these formidable foes exist everywhere,
and especially in places of human resort; Passet has in fact
found two of them (Staphylococcus aureus and S. albus) in
dish-water and in putrid meat.

7. The Micrococcus which makes its way into the lymphatic
ducts of the skin and is the contagium of erysipelas (63) is
closely allied in respect of its shape and facultative parasitism
to the forms of the preceding section, and is in effect a chain-
forming Streptococcus. We owe our earlier knowledge of this
organism to von Recklinghausen and Lukomski. Fehleisen
has recently grown it in a pure state, and his inoculations with
it were successful. The unpleasant though not dangerous
affection of the skin of the hands, known as erythema migrans
or finger-erysipelas, to which those are liable who have to
handle raw meat, has been referred by Rosenbach to a Micro-
coccus (62).

8. A distinct species of Micrococcus, capable of cultivation
and of being conveyed by inoculation with production of the
characteristic disease is according to Sattler's investigation (64)
the contagium of trachoma, the granulose inflammation of the
conjunctiva of the human eye. It may be added that another
disease of the conjunctiva of the eye, xerosis conjunctivae, is
attributed to a small rod-bacterium as its exciting cause (65).

A Micrococcus forming short rows of cells in thick broad

1 70 Lectures on Bacteria. [$ xm.

gelatinous envelopes, and capable of cultivation in its character-
istic form on gelatine, is said by Friedlander to have a strictly
specific effect as the contagium of acute fibrinous pneumonia
(66).

A specifically distinct Bacillus, nearly allied in every respect to
the Bacillus of tubercle, has been proved by Hansen's and
Neisser's investigations to be the exciting cause of leprosy in the
human species. The Bacillus discovered by Lustgarten, and
supposed to be the contagium of syphilis, is still a subject of
dispute (67). Other species of Bacilli, or at least of rod-forms,
approaching in their mode of life the Bacillus of anthrax, have
moreover been discovered, and many of them carefully studied
as the contagia of a series of diseases in the lower animals, such
as Koch's mouse-septicaemia, Koch and Gaffky's malignant
oedema (68), glanders (69), symptomatic anthrax (70), ery-
sipelas in pigs (71), and Loffler's diphtheria in pigeons and in
calves (74).

9. The type of miasmatic infectious diseases is malaria,
intermittent fever with its kindred states (72). The infection is
confined to certain localities with a marshy soil and stagnant
water, and is not usually conveyed from one person to another.
It is natural to assume therefore, in accordance with other well-
known cases, that of anthrax for example, that an organism is
present in the soil and in the water of the malaria-district, and
that it causes the infection. Klebs and Tommasi Crudeli have
consequently examined specimens of soil and water from localities
where malaria abounds, and have found Bacteria in them in pro-
fusion, one especially, a rod-shaped species which forms filaments
and which theyname Bacillus Malariae. Theyproduced symptoms
of malarial fever, swelling of the spleen and intermittent fever in
different animals by injecting the Bacillus from these specimens
of the soil as well as from cultures. Cuboni and Marchiafava,
Lanzi, Perroncito, Cect, and Ziehl have found Bacteria in blood
taken from the skin, veins, and spleen of persons suffering from
intermittent fever, especially in the cold stage of the attack.

§ xiii.] Malaria. Typhoid fever. 171

Cuboni and Marchiafava have obtained in animals, into which
they had injected the blood of persons suffering from inter-
mittent fever, symptoms which they considered to be those of
malaria-infection. I am not in a position to say how far these
symptoms observed in animals after infection may, or ought to
be regarded as sure signs of the presence of malarial fever.

On the other hand it is obvious that the injection of some
cubic centimetres of fluid containing particles of soil or of a
Bacillus-culture does not really correspond to an ordinary in-
fection, in which a very minute portion of the contagium is in
every case absorbed, introduced by inoculation or inhaled.
And with respect to the descriptions given in the different pub-
lications of the Bacteria which were examined, we cannot be
sure whether one species of Bacterium was present in each case
or more than one, or whether the forms which one observer saw
in the blood were the same or of the same species as those
which others grew from soil-specimens. It therefore does not
seem to me that we have before us any precise determination of
the nature of the contagium or miasma vivum of malaria, but
that the question has now to be really attacked on the basis of
the former laborious investigations and with careful sifting of
their results. That these remarks, which appeared in the first
German edition of this book, were not without good foundation
is shown by the latest reports, especially those of Marchiafava
and Celli, in which it is stated that the contagium of malaria
is not a Bacterium, but a small amoeboid organism which
penetrates into the red blood-corpuscles. We must hope for
clear and decisive investigations into this organism.

10. Our knowledge concerning the causal connection between
Bacteria or parasites generally, and typhoid fever and diphtheria
in men is also at present uncertain, notwithstanding Gaffky's
and Loftier' s model investigations.

Typhoid fever is a distinctly miasmatic infectious disease,
which may sometimes become contagious. Causal relations
between its appearance and certain localities and the use of

172 Lectures on Bacteria. [§ xm.

impure water have long been clearly established. It is natural,
therefore, as in the previous case, to suppose that a facultative
parasite is the proximate cause of the disease. As early as 1871
von Recklinghausen found Bacteria, and especially colonies of
Micrococcus, in the bodies of those who had died of this fever.
Later investigations, given at length in Gaffky's publication (73),
have resulted in reports of the occurrence of Bacteria and Fungi
which do not always agree with one another. Gaffky has recently
undertaken a thorough investigation of the subject, and has found
in the internal organs, the mesenteric glands, spleen, liver, and
kidneys of persons who have died of typhoid fever, as an almost
constant phenomenon — in twenty-six out of twenty-eight cases, —
a well- characterised endosporous Bacillus, and always the same
kind. This species grows in characteristic form and abundantly
on gelatine and blood-serum, and on potatoes exposed to the air.
Gaffky, whose work should be consulted, states that in shape
it is not unlike Bacillus Amylobacter (see page 100), but con-
siderably smaller in size; each rod is about 2-5^ in length, and
the breadth is about one-third of the length. Contrary to the
expectations which were justified by the unfailing and character-
istic presence of the Bacteria in the bodies of the dead, Gaffky's
extensive experiments in the infection of animals, and among
them of monkeys, gave wholly negative results. The question
of cause must therefore be considered to be at present undecided.
How far more recent accounts of successful experiments of this
kind will avail to alter this judgment I am not yet able to deter-
mine. It has also not yet been proved that the Bacilli of typhoid
fever occur spontaneously outside the organism, especially in
the water for drinking and for domestic use which is connected
with epidemics of the fever.

ii. We are indebted to Loffler (74) for extended and careful
investigations into the nature of diphtheria. His work contains
a detailed discussion of the statements of his predecessors, and
should therefore be consulted. One well-known and character-
istic symptom of diphtheria in the human subject is the forma-

$ xiii.] Diphtheria. 173

tion of the white lining on the mucous membrane of the throat,
especially on the tonsils, and it has been proved that by means
of this lining the disease can be communicated to a healthy person.
Enquiry was accordingly directed to this substance, and it was
found to contain, along with a variety of accidental matters, first
of all enormous accumulations of Micrococci, and secondly, small
rods in many of the cases which were examined, but not in all of
them, as was at first maintained by Klebs.

Loftier having ascertained the presence of these organisms
subjected them to pure culture, and made experimental trial of
their efficacy in the production of disease.

The Micrococcus in a pure culture forms chains which are
very like those of erysipelas. It forces its way from the diphtheritic
lining on the mucous membrane into the tissues of a person
suffering from the disease, and passes through the lymph-vessels
into the most dissimilar internal organs, where it forms nests.
It behaved in a similar manner when introduced in the pure
state into animals by inoculation, and produced some forms of
disease, but did not give rise to the symptoms characteristic of
diphtheria. We may therefore ascribe to this Micrococcus the
power of producing morbid complications, but we cannot accept
it as the specific contagium of diphtheria.

The rods thrive well on blood-serum, but are difficult of
cultivation in other substrata. They are about as long as those
of the Bacillus of tubercle and twice as thick, and are otherwise
distinguished from this species by marks which cannot be fully
described here. They are found collected together in heaps in
the lining of the diphtheritic mucous membrane, in the layers
beneath the surface. They have not been observed in the in-
ternal organs of sick persons. Introduced by inoculation into
animals of the kinds usually employed for experiment, they
produced symptoms very like those of diphtheria. LorBer there-
fore considers that the rods are the contagium of diphtheria in
the human subject, though he is careful to draw attention to the
objections to this conclusion.

1 74 Lectures on Bacteria. [$ xiv.

12. In conclusion we must not omit to remark, that in a
large number of infectious diseases, and these too of the most
common occurrence, no one has as yet succeeded in discovering
a distinct Bacterium or any other microscopic parasite as the
cause of the particular disease, or the supposed discovery of
such organisms is quite untrustworthy. This is true of diarrhoea,
of typhus fever, of yellow fever, of whooping-cough, and of
acute exanthemata of the skin, such as scarlet fever, measles,
and small-pox in men and equivalent diseases in other animals.
We practise vaccination, as is well known, as a protection
against small-pox, and Pasteur applies his famous method for
attenuating the contagium of hydrophobia, for protective inocu-
lation and for curing the infected, but the organism which may
possibly be the real contagium has hitherto at least escaped
observation. It is not really necessary to repeat that Henle's
postulates remain unchanged as against these negative results
in the search for the contagium vivum.

XIV.

Diseases caused by Bacteria in the lower animals
and in plants.

i. THERE is reason for assuming that Bacteria play a more
important part as disease-producing parasites in cold-blooded
as well as in warm-blooded animals, than is at present ascer-
tained. What we do know at present is chiefly connected with
insects (76).

The foul brood in bees, which may in a short time destroy
the hives of a whole district, is the work of an (endosporous)
Bacillus, B. melittophthorus, Cohn, in all probability the same
species as B. alvei, which has been carefully studied by Cheshire
and Cheyne.

The disease in silkworms known as flacherie is caused,

$ xiv.] Diseases in lower animals. 175

according to Pasteur, by a Bacillus and by a chain-forming
Micrococcus, M. Bombycis, Cohn, which resembles M. Ureae
(see page 84) ; these organisms are introduced with the food, and
by decomposing it in the intestinal canal give rise first of all to
derangement of the digestion, and then to the death of the insect,
which first becomes inert, without appetite, and flabby, and soon
succumbs to the disease. Its dead body is soft and soon turns
a dark and dirty brown, putrefactive Bacteria make their ap-
pearance in it and it dissolves for the most part into discoloured
stinking matter.

A number of other contagious and epidemic diseases in cater-
pillars of Lepidoptera have been recently referred by S. A. Forbes
to the attacks of certain forms of Micrococcus and Bacillus.

There are two diseases among silkworms very distinct from
the flacherie, which is the prevalent one at the present time,
namely, muscardine or calcino, and the spotted disease or
pe'brine. Muscardine, known since the last century, was very
destructive to the silkworm-culture in Europe during the first
years of the present century, but is said to have almost entirely
disappeared since 1855, while it continues to be of frequent
occurrence among the caterpillars living in the wild state. It is
caused, as has been fully shown, by a Fungus, and does not
therefore belong to our present subject.

Pebrine (gattine, petechia, maladie des corpuscules) has been
a known form of disease for some hundreds of years, and com-
mitted great ravages in Europe between 1850 and 1875. It
received the name of spotted disease from the dark spots on
the skin which make their appearance in the insect as it becomes
dull and inert, and which are caused by the presence of a micro-
scopic parasite, Panhistophyton ovatum, Lebert, Nosema Bom-
bycis, Nageli. The parasite is known under the form of small
colourless, highly refringent bodies of irregularly ellipsoid
shape, and not more than 0-4 /z in length, once termed the Cor-
nalian bodies, which appear in our preparations either singly,
or in pairs, or several connected together, and occur in all organs

176 Lectures on Bacteria. [$ xiv.

of the creature, and not in the caterpillar only, but also in the
butterfly and even in the eggs, from which they may find their
way again into the young caterpillar. They are also found in
enormous quantities, filling the entire insect. Pasteur especially
has shown that these bodies belong to a parasite, which
penetrates into the insect, and multiplying at its expense pro-
duce the disease. If they are introduced with the food into the
intestinal canal of a healthy caterpillar, they are subsequently
found to have penetrated into the wall of the intestine, at first
one by one, afterwards in greater numbers, and to have spread
from thence into the other organs.

The same or similar bodies have been found by different
observers in sundry other insects and articulated animals.

It would appear from this brief description that the Cornalian
bodies resemble a small Bacterium, and specially a Micro-
coccus, and they have been regarded as such by many observers.
Nageli calls attention in his first communication to their relation-
ship to Micrococcus aceti. This view rested on the similarity
of form, and specially on the observation that they were frequently
united together in pairs, since this fact was regarded as an indi-
cation of their multiplication by successive bipartition. Their
bipartition was not directly observed at that time nor has it been
observed subsequently, and it is obvious that union in pairs may
be brought about in other ways. There was therefore experi-
mental proof that the bodies did multiply, but how they multi-
plied was not known. Then Cornalia, Leydig, Balbiani, and
also Pasteur put forward another view in opposition to the theory
that the bodies were Micrococci; they supposed them to be
totally distinct from Micrococcus and Bacterium, and to be
Psorospermiae, that is, states of peculiar low organisms,
Sporozoa or Sarcosporidia. Metschnikoff has recently and
distinctly confirmed this view; he states briefly that the
parasite of pe*brine consists of protoplasmic bodies having the
power of amoeboid movement, after the manner, that is, of the
colourless blood-cells described on page 135, and subsequently

§ xiv.] Diseases in lower animals and in plants. 177

becoming lobed, and that the Cornalian bodies are produced in
them by endogenous formation. It follows from analogy with
other better-known Sporozoa, that the Cornalian bodies would
be spores, and that their germination gives rise to the amoeboid
protoplasmic bodies in which fresh spores are formed in large
numbers. The extreme delicacy of such amoeboid protoplasmic
bodies as these sufficiently explains why it was so long before
they were clearly made out, especially when they had penetrated
into and were enclosed in the tissue of the insect's body which
is also protoplasmic.

Hence the parasite of pe*brine must also be excluded from
consideration in a treatise on Bacteria; nor would so much
have been said about it here, if it did not serve to show in a
very instructive manner, not only that very minute parasites
which are not Bacteria are the contagium in infectious diseases
in animals, but that we may be dealing with organisms of a quite
different kind, conformation, and mode of life from Bacteria,
even when the figures before us are very like Bacteria and are
easily mistaken for them.

2. Lastly, parasitic Bacteria do not often appear, according
to our present experience, as the'contagia of diseases in plants (77).
Most contagia of the many infectious diseases in plants belong
to other groups of animals and plants, the larger number to the
Fungi proper, as was observed on pages 146, 147.

Among cases of the kind we may mention first the yellow
disease studied by Wakker, which destroys hyacinth-plants.
Wakker found that the most characteristic symptom in this
disease is the appearance of a rod-shaped Bacterium, 2-5 //, long
and a fourth or half as broad, which aggregates into slimy yellow
masses filling the vessels and tissue of the vascular bundles
in the bulb-scales during the time when vegetation is dormant.
At flowering time these masses ascend also into the leaves,
where they are not confined to the vascular bundles, but make
their way from them into the intercellular passages and into the
cells of the parenchyma, stopping up the passages and destroying

178 Lectures on Bacteria. [§ xiv.

the cells, and ultimately emerging through the bursting epi-
dermis. Attempts to communicate the disease by inoculation
have not yet been successful, nor has the life-history of the
Bacterium been at present thoroughly worked out.

J. Burrill, of Urbana, in the state of Illinois, describes a
disease in pear-trees and apple-trees, known by the indefinite
name of 'blight/ and attributes it to the attack of a
Bacterium, a rather elongated Micrococcus, M. amylovorus,
Burr., the cells of which are about i /z in length. The disease,
which destroys the bark, is at first narrowly localised, but may
spread and form a ring round the branch or stem which it
attacks, and may then prove fatal to it. Burrill found that the
Micrococcus had penetrated into the cells of the diseased part,
and that as it developed the normal contents of the cells,
especially the starch, disappeared, while ' carbonic acid, hydrogen
and butyric acid' were formed. Numerous attempts at inoculation
by introducing the Micrococcus into small incisions or punc-
tures in the bark of healthy pear-trees and apple-trees resulted
in the communication of the disease. Arthur has confirmed
Burrill's observations and given further proof that his Micro-
coccus is a facultative parasite, producing effects peculiar to
the species. This disease of pear-trees, as far as I am aware,
is either unknown in Europe, or has not been investigated.

From some very brief statements of Burrill it would appear
that diseases caused by Bacteria also occur in the peach-tree,
the Italian poplar, and the American aspen.

Prillieux gives a short description of a change which some-
times takes place in grains of wheat ; this change which is recog-
nised by the rose-red colour which it produces, advances part
passu with the development of a Micrococcus, which destroys
the starch-grains, the glutinous contents of the peripheral cell-
layers, and to some extent the cell-membranes as well. Dis-
organising operations of the Micrococcus are thus distinctly
disclosed. Its real significance as an exciting cause of disease
cannot be certainly determined from the few published state-

§ xiv.] Diseases in plants. 1 79

ments, it may perhaps only play a secondary part as a saprophyte
in consequence of injuries produced by other causes.

The latter supposition is partly founded on the phenomenon
of wet rot in potatoes, which has been closely examined by
Reinke and Berthold. It appears from the observations of
these authors, that the proximate cause of the phenomenon is
the development of Bacteria ; Bacillus Amylobacter is shown by
the descriptions to be present, and perhaps some other forms.
The wet rot usually attacks tubers which have been previously
sickly, that is, have been partly destroyed by a purely parasitic
Fungus, Phytophthora infestans. The rot does indeed attack
the tissue which had been spared by the Fungus and is still
alive, but it nevertheless is only a secondary phenomenon. At
the same time the rot appears in potatoes which have not suffered
from Phytophthora, though this is exceptional ; and the above-
mentioned observers succeeded in producing wet rot in healthy
potato-tubers by inoculating them with their Bacteria. This
agrees with a recent experiment of van Tieghem, who succeeded
in entirely destroying living tubers by the introduction of Bacillus
Amylobacter into their inner substance, and by keeping them
at the same time at the high temperature of 30° C. The same
results were obtained with the seeds of beans, stems of Cacti, &c.
In other words, these facts show that saprophytic Bacteria may
also, under special conditions, attack the tissues of living plants
as facultative parasites, produce disease in them and destroy
them. But this only confirms what was said above, that Bacteria
are not objects of great importance as contagia of diseases
affecting plants.

N 2

CONSPECTUS OF THE LITERATURE
AND NOTES.

1. FOR the general literature of the Bacteria see de Bary, Comparative
Morphology and Biology of the Fungi, Mycetozoa, and Bacteria, Clarendon
Press, 1887, and W. Zopf, Die Spaltpilze, 3rd edition, Breslau, 1884. —
The works of Pasteur, F. Cohn, v. Nageli, van Tieghem, R. Koch, Brefeld,
A. Prazmowski, Fitz, must be specially mentioned here as laying generally
the foundations of our knowledge ; they are cited in the works above-named,
and some of them again below. — Duclaux, Chimie biologique, Paris, 1883,
gives an elegant account of the views and methods of the French school,
and especially of the school of Pasteur ; F. Hueppe, Die Methoden d.
Bacterienforschung (3rd ed., 1886), gives hints for the conduct of investigation
according to the method perfected especially by R. Koch. — Writers on
General Morphology and Classification are F. Hueppe, Die Form en d.
Bacterien. &c., Wiesbaden, 1886; J. Schroter in the Kryptogamenflora v.
Schlesien, ed. F. Cohn, Bd. Ill, 2 Lieferung, pp. 136-172. This work gives
a good classification and description of most known forms ; it reached me
while the present work was in the press, and it was hardly possible for me
to make any use of it. — Of the many general Text-books of Bacteria of
recent date may be mentioned : C. Fliigge, Fermente u. Mikroparasiten, in
v. Pettenkofer and v. Ziemssen, Handb. d. Hygieine (the second edition
with the title, Die Mikroorganismen, Leipsic, 1886, came out while this
work was being printed) ; E. M. Crookshank, Introduction to practical
Bacteriology, London, 1886; and a copious Text-book of the Bacteria of
Disease, by Cornil et Babes, Les Bacteries et leur role dans 1'anatomie et
1'histologie pathologiques des maladies infectieuses, 2nd ed., Paris, 1886.
With these may be coupled the Jahresbericht u. d. Fortschritte d. Lehre v.
d. pathogenen Mikroorganismen of P. Baumgarten, Erster Jahrg. 1885,
Braunschweig, 1886, of which I have made frequent use, and to which
I here refer the reader once for all for the more recent special literature.

2. Nencki u. Schaffer, Journ. f. pract. Chemie, Neue Folge, XX. —
Nencki, Berichte d. D. Chem. Ges. Jahrg. XVII, p. 2605.

3. Leeuwenhoek, Experimenta et contemplationes, Delft, 1695, especially
p. 42, on Bacteria- forms from saliva.

4. F. Cohn, Unters. ii. Bacterien, in Beitr. z. Biologic d. Pfl., continued
since 1872 (I, Heft 2, p. 127).

1 82 Lectures on Bacteria.

5. C. G. Ehrenberg, Die Infusionsthiere als vollk. Organismen, Berlin, 1838.

6. Billroth, Coccobacteria septica, Berlin, 1874.

7. v. Nageli, Die niederen Pilze, Munch en, 1877.

8. Hornschuch in Flora, Regensburg, 1848.

9. v. Nageli, Niedere Pilze, 1877, p. 21.

10. F. Hueppe, Unters. ii. d. Zersetzgn. d. Milch., in Mittheil. aus d. K.
Gesundheitsamt, II, 1884.

11. C. Vittadini, Delia natura del calcino, in Giorn. Istitut. Lombardo,
III (1852).

12. E. Klebs, Beitr. z. Kenntn. d. Mikrokokken, in Arch. f. exp. Patho-
logic, I (1873).

13. Pasteur, Examen de la doctrine des generations spontanees in Ann.
de Chimie, ser. 3, LXIV. See also Ann. d. sc. nat., Zoologie, ser. 4, XVI.
— Rosenbach has given an account of Meissner's excellent researches in
Deutsche Zeitschr. f. Chirurgie, XIII, p. 344. For more recent works and
discussions, see in Baumgarten's Jahresber.

14. R. Koch in Mittheil. aus d. K. Gesundheitsamt, I, p. 32. See also
Hesse, in the same publication, II, 182.

15. Annuaire de 1'observatoire de Montsouris, since 1877, and especially
since 1879.

16. Virgil, Georgics, IV, 281.

17. A. Bechamp, Les Microzymas dans leurs rapports avec 1'heterogenie,
1'histiogenie, la physiologic et la pathologic, Paris, 1882. In this volume
Bechamp has brought together the views successively entertained by him
and published in the Comptes rendus of the Paris Academy.

18. A. Wigand, Entstehung u. Fermentwirkung d. Bacterien, Marburg,
1884.

19. O. Brefeld, Botan. Untersuch. ii. Schimmelpilze, IV.

20. E. Eidam in Cohn's Beitr. z. Biol. d. Pflanzen, I, Heft 3, p. 208.

21. A. Fitz in Ber. d. Deutsch. Chem. Ges., nine papers in the years
1876-84.

22. Frisch in Sitzungsber. d. Wien. Acad., Mai, 1877.

23. P. van Tieghem in Bull, de la Soc. Bot. de France, XXVIII (1881),

P- 35-

24. E. Duclaux, Etudes sur le lait, in Ann. de Tlnstit. Nat. Agronomique,
No. 5, Paris (1882), pp. 22-138.

25. E. Duclaux, Chimie biolog., in Encyclop. Chimique, publiee par M.
Fremy, IX, Paris, 1883.

26. W. Engelmann in Bot. Ztg., 1882, p. 321.

27. v. Nageli, Ernahrung d. niederen Pilze, in Sitzungsber. d. Miinchener
Acad., Juli, 1879.

28. v. Nageli, Unters. ii. niedere Pilze, in Unters. aus d. Pflanzenphysiol.
Inst. z. Munchen, Miinchen, 1882.

29. W. Engelmann, Bacterium photometricum, in Unters. aus d. Physiol.
Laboratorium z. Utrecht, 1882.

Literature and Notes. 183

30. Cohn u. Mendelssohn in Beitr. z. Biol. d. Pflanzen, III.

31. W. Engelmann in Bot. Ztg., 1881, p. 441.

32. W. Pfeffer, in Unters. a. d. Bot. Inst. z. Tubingen, I, Heft 3.

33. J. Tyndall in Phil. Trans, of the Royal Soc., London, 166 (1876),
167 (1877). The latter paper especially contains the statements with respect
to fractionating sterilisation.

34. J. Wortmann in Zeitschr. f. physiol. Chemie, VI, p. 287.

35. I still keep to the classification and nomenclature founded on Cohn's
divisions. It is better to treat what is imperfect as imperfect than to give it
the appearance of being perfect, and so cheat oneself and the beginner into
belief in a state of things which does not really exist. This might also be
said in criticism of some of the most recent attempts at improvement, but
further discussion of these would be out of place here. We have not yet
accomplished that which is an indispensable condition for any real advance
in classification, namely, a tolerably continuous morphological examination
of the individual species, — I do not mean of all existing species, but only of
such as at present pass for being ' described,' — whether collective or ' bad '
species. Such an examination might be made with the material which we
at present possess, but this has not yet been done.

36. W. Zopf, Zur Morphol. d. Spaltpflanzen, Leipsic, 1882 ;— Id., Entwick-
lungsgeschichtl. Unters. ii. Crenothrix polyspora, die Ursache d. Berliner
wassercalamitat, Berlin, 1879 ; — Id. in Monatsber. d. Berliner Acad.,
Marz 10, 1881.

37. E. Warming, Om nogle ved Danmarks Kyster levende Bacterier, in
Vidensk. Meddelelser fra d. naturhist. Forening, Kjobenhavn, 1875. — A.
Engler, Die Pilzvegetation d. weissen od. todten Grundes d. Kieler Bucht,
in Ber. d. Commiss. z. Erforschung d. deutschen Meere, IV.

38. P. van Tieghem, Sur la fermentation ammoniacale, in Compt. rend.
LVIII (1864), p. 211. — v. Jacksch in Zeitschr. f. physiolog. Chemie, V
(1881), p. 395. — Leube, Ueber d. ammoniakal. Harngahrung. in Virchow's
Archiv, C, p. 540.

39. Schlossing u. Miintz in Compt. rend. LXXXIV, p. 301 ; LXXXIX,
pp. 91, 1074.

40. Pasteur in Compt. rend. LIV, p. 265 ; LV, p. 28 ; — Id., Etudes sur
le vinaigre, Paris, 1868.

41. v. Nageli, Theorie d. Gahrung, Miinchen, 1879.

42. E. C. Hansen, Beitr. z. Kenntn. d. Organismen welche, in Bier u.
Bierwiirze leben, in Meddelelser fra Carlsberg Laboratoriet, I, Kopenhagen,
1882.

43. Pasteur in Compt. rend. LII, p. 344.

44. P. van Tieghem, Leuconostoc, in Ann. d. sc. nat. ser. 6, VII.

45. F. Hueppe, Unters. ii. d. Zersetzung d. Milch durch Mikroorganismen,
in Mittheil. a. d. k. Reichsgesundheitsamt, II, 309, with a full account of
the history and literature.

46. E. Kern, Ueber ein Milchferment aus dem Kaukasus, in Bot. Ztg.,

1 84

Lectures on Bacteria.

1882, p. 264, and in Bullet, de la Soc. Imper. d. Nat. de Moscou, 1881.— See
also F. Hueppe, Ueber Zersetzungen d. Milch, &c., in Borner's Deutscher
med. Wochenschrift, 1884, No- 48.— W. Podwyssotzki (Sohn), Kefyr, kau-
kasisches Gahrungsferment u. Getrank, &c., translated from the Russian of
the 3rd Edition by Moritz Schulz, St. Petersbg., 1884.— W. N. Dimitrijew,
Kefir oder Kapir, echtes Kumyiss aus Kuhmilch, translated from the
German by E. Rothmann, St. Petersbg., 1884. — Alexander Levy, Die wahre
Natur des Kefir, in Deutsche medicinal Zeitung, 1886, p. 783. Levy's
manner of proceeding is to add one part of ordinary sour milk to 8-10
parts of cold boiled milk, and then to shake the mixture at a temperature of
about I2°C.

47. P. van Tieghem, Sur le Bacillus Amylobacter, &c., in Bull. Soc. Bot.
de France, XXIV (1877), p. 128 ; — Id., Sur la fermentation de la cellulose,
in Bull. Soc. Bot. de France, XXVI (1879), p. 25.

48. A. Prazmowski, Untersuch. ii. Entwicklungsgesch. u. Fermentwirkung
einiger Bacterien-Arten, Leipzig, 1880.

49. Vandevelde, Studien z. Chemie d. Bacillus subtilis, in Zeitschr. f.
physiolog. Chemie, VIII, 367.

50. Bienstock, Ueber d. Bacterien d. Faeces, in Zeitschr. f. klin. Medicin,
VIII.

51. Cohn, Beitr. I, Heft 2, p. 169.— G. Hauser, Ueber Faulnissbacterien
u. deren Beziehung z. Septicaemie, Leipzig, 1885. I have made little use
of this work in the text, because I am unable sufficiently to understand its
morphology without personal investigation. The whole of the phenomena
of ' pleomorphism,' on the strength of which the writer designates his forms
by the special generic name Proteus, an unacceptable one in any case,
appear to me, on comparing the figures, scarcely to deserve the appellation.
But the figures do not help us in determining the morphological relations,
at least if we go beyond the habit of the groups ; I have taken fruitless
pains to arrive by their means at a clear idea of the conformation of the
Spirilla-forms which he describes. Photography is no doubt a useful
assistant in microscopical studies, and I have used it myself for twenty-five
years ; but there are limits to its capabilities, and the details required in this
case are not given in Hauser's figures. With all due acknowledgment of
the advance made in Hauser's work, I say what I have now said in order to
justify my casual treatment of it.

52. H. Nothnagel, Die normal in d. menschl. Darmentleerungen vorkom-
menden niedersten pflanzl. Organismen, in Zeitschr. f. klin. Medicin, III
(1881).— Kurth, Bacterium Zopfii, in Bot. Ztg. 1883, 369.— Miller, Ueber
Gahrungsvorgange im Verdauungstractus, &c., in Deutsche med. Wochen-
schrift, 1885, No. 49. — W. de Bary, Beitr. z. Kenntn. d. niederen Organismen
im Mageninhalt, in Archiv f. experim. Pathologic u. Pharmacologie, XX.

53. The literature of Sarcina has been carefully collected by Falkenheim
in his paper Ueber Sarcina, published in Archiv f. experim. Pathologic,
XIX, p. 339.

Literature and Notes. 185

The species of Sarcina which I am able to distinguish are characterised
as follows :

a. Sarcina ventriculi, Goodsir (see Fig. 14 of this book). Large cube-
shaped packets, with very many members, that is, consisting usually of
64-4096 cells, the single packet brownish-gray in transmitted light under
the microscope, of a dirty greyish-white colour when seen in mass by the
naked eye in reflected light. Single cells, 3-4 /* in size, stained a dirty
violet by Schulze's solution.

In large quantities of material from the human stomach I generally find
two distinct forms side by side, a large-celled one which is represented in
Fig. 14, and another in which the cells are smaller (2 /*) and less clearly
translucent. I can give no information respecting the genetic relations of
the two forms.

b. Sarcina Welckeri, Rossmann (Welcker in Henle's u. Pfeffer's Zeitschr.
f. rat. Med. V, 199). Small cube-shaped packets, containing at most 64
cells, quite colourless. Single cells about I p in size, membranes not
coloured by Schulze's solution, protoplasm coloured yellow by the same
solution. It occurs in the urinary bladder of the living human subject ;
repeatedly found in patients. I know the species as coming from a
young man, who, according to his own observation, voided them with the
urine for more than twelve months, in varying, often in very large, quanti-
ties. The urine is usually abnormally rich in phosphates ; the patient is in
other respects in good health. The Sarcina did not grow with me on
gelatine and agar ; once doubtfully and not in any abundance in sterilised
urine at a temperature of 35°C. Most of the attempts to cultivate it in urine
gave negative results.

c. Sarcina flava. Small packets, containing from 16 to 32 cells, con-
nected together in the majority of cases either into large regular cubes or
into irregular heaps ; the single packet colourless in transmitted light under
the microscope, of a beautifully bright yellow colour when seen in mass in re-
flected light. Single cells 1-2 p in size. Reaction with iodine as in Sarcina
Welckeri. Grows well on gelatine, which it quickly liquefies, on agar and
on other substances. Appears to be comparatively abundant ; is cultivated
in laboratories, and described without statement as to the source from which
it is obtained. See Crookshank, Introd. to practical Bacteriology, London,
1886. My material comes from the Pathological Institute at Greifswald,
where the yellow Sarcina made its appearance spontaneously as an isolated
colony in a gelatine culture of vomited matter, in which Sarcina ventriculi
had not been found. It is at all events distinguished from S. lutea of
Schroter by its power of liquefying gelatine.

d. Sarcina minuta, provisionally a new species (see Fig. 15 of this
book). Small cube-shaped packets, formed of 8-16 cells, connected
together in the majority of cases in irregular heaps, less frequently in
larger cubes ; quite colourless. Single cells about i /* in size. Reactions
with iodine as in Sarcina Welckeri. Made its appearance once spon-

1 86 Lectures on Bacteria.

taneously in a culture of sour milk on a microscopic slide. Grows well
but slowly on gelatine and in a saccharine solution with extract of meat,
forming in the solution the regular cube-shaped packets, on the gelatine the
irregular heaps. Closely resembling Sarcina Welckeri under the microscope.

e. Sarcina fuscescens. Small cube-shaped packets of 8-64 cells, readily
separating into smaller groups (tetrads) or into single cells. Single cells
about 1-5 p in size. Reactions with iodine as in Sarcina Welckeri. Forms
small brownish scales or mould-like films on the substrata mentioned
below. This form was obtained by Falkenheim in gelatine cultures of the
contents of a human stomach containing Sarcina ventriculi, with which,
however, there was no apparent genetic connection. It grew in connected
packet-form on infusion of hay ; culture on other ordinary nutrient substrata
(gelatine, potatoes, &c.) was accompanied by the separation mentioned above
into single cells and smaller cell-groups. The above description is taken
from Falkenheim's paper on Sarcina in Archiv f. experim. Pathologic, XIX,
p. 339 ; the form or species is not known to me by personal observation.

To the above must be added the distinct and described species, Sarcina
intestinalis, Zopf (Spaltpilze, p. 55 of the third edition), from the intestinal
canal of the domestic fowl ; S. lutea, Schroter (Krypt. Fl. v. Schlesien), a
saprophyte which makes its appearance in Fungus-cultures ; and Schroter's
S. rosea and S. paludosa, which live in bog-water.

Other forms, belonging apparently to the genus Sarcina, are mentioned
by J. Eisenberg (Patholog. Diagnostik), but they are without any special
description, and cannot therefore be compared with the preceding species.
A ' Sarcina in the mouth and lungs' has been considered by H. Fischer, in
the Deutsches Archiv f. klin. Medicin, XXXVI, p. 344 ; but it is not even
clear from his description whether the cells or divisions of cells are arranged
according to two or three dimensions ; we are therefore unable to compare
this supposed form with the rest of the species.

The names Sarcina littoralis, Oersted, S. hyalina, Kiitzing, and S. Reiten-
bachii, Caspary (also misprinted Reichenbachii), have been copied into the
literature of the Bacteria. The proximate source of these names is Winter's
Pilzflora v. Deutschland, &c. Merismopoedia littoralis, Rabenhorst, M.
hyalina, Kiitzing, M. Reitenbachii, Casp., have thus been placed in the
genus Sarcina ; this appears to me to be incorrect, because, as the name
Merismopoedia implies, the cells in accordance with the directions of their
divisions, form not many-layered packets, but tables of a single layer, and
because it is uncertain, at least in the case of the two last forms, whether,
like other species of Merismopoedia, M. punctata for example, they do not
contain chlorophyll or phycochrome. These forms, therefore, do not belong
to this place ; like other species of Merismopoedia they live in bogs and in
sea-water.

54. Rasmussen, Ueber d. Cultur v. Mikroorganismen aus d. Speichel
(Spyt) gesunder Menschen ; Dissert. Kopenhagen, 1883. Known to me
only from an abstract in the Bot. Centralblatt, 1884, XVII, p. 398.

Literature and Notes. 187

55. W. Miller, Der Einfluss d. Mikroorganismen auf d. Caries d. menschl.
Zahne, in Archiv f. exp. Pathol. XVI, 1882; — Id., Gahrungsvorgange im
menschlichen Munde in Beziehung zur Caries d. Zahne, &c., in Deutsch.
med. Wochenschrift, 1884, No. 36. — T. Lewis, Memorandum on the comma-
shaped Bacillus, &c., in the Lancet, Sept. 2, 1884.

56. For the earlier literature of Anthrax (up to 1874) see O. Bollinger,
in Ziemssen's Handb. d. speciellen Pathologic u. Therapie, 3, and the rich
material in Oemler, Experimentelle Beitr. z. Milzbrandfrage in Archiv f.
Thierheilk, II-VI. For the first discovery of the Bacillus, see Rayer in
Memoires de la Soc. de Biol. II, 1850, p. 141 (Paris, 1851).— Pollender
in Casper's Vierteljahrsschr. VIII, 1855. Of the very numerous works of
a more recent date may be mentioned : Pasteur in Compt. rend. LXXXIV
(1877), p. 900; LXXXV (1877), P- 99; LXXXVII (1878), p. 47; XCII
(1881), pp. 209, 266, 429. — R. Koch, Die Aetiologie d. Milzbrandes, in
Cohn, Beitr. z. Biol. d. Pfl. II, 277 ;— Id. in Mittheil. a. d. Reichsgesund-
heitsamt I, and II in conjunction with Gaffky and Loffler. — H. Buchner in
Unters. aus d. Pflanzenphysiol. Inst. z. Miinchen, 1882. — Chauveau in Compt.
rend. XCI (1880), p. 680; XCVI (1883), pp. 553,612, 678, 1471 ; XCVII
(1883), pp. 1242, 1397; XCVIII (1884), pp. 73, 126, 1232. — Gibier in
Compt. rend. XCIV (1882), p. 1605.— E. Metschnikoff, Die Beziehung d.
Phagocyten z. d. Milzbrand-Bacillen, in Virchow's Archiv, XCVII, 1884. —
A. Prazmowski in Biolog. Centralblatt, 1884.

57. Pasteur in Compt. rend. XC (1880), pp. 239, 952, 1030 ; XCII (1881),
p. 426. — Semmer, Ueber d. Hiihnerpest, in Deutsche Zeitschr. f. Thier-
medicin, IV (1878), p. 244. The disease described by Perroncito, in Archiv
f. wiss. u. pract. Thierheilk. V (1879), p. 22, must be of another kind. —
Kitt, Exper. Beitr. z. Kenntn. d. epizootischen Geflligeltyphoids, in Jahresber.
d. k. Thierarzneischule in Miinchen, 1882-1884, p. 62, Leipzig, 1885. This
excellent work contains an exact account firstly of the form of the Micro-
coccus and its behaviour in cultures, and secondly of experimental investiga-
tions into infection and the phenomena of the disease which follows upon the
infection. Though it confirms Pasteur's statements in some points, it tends
at the same time to throw doubt on others, by making it highly probable
that Pasteur did not work with pure material, free from other Bacteria. It
makes no mention of the state of stupor. When the animals, especially
fowls, succumbed to the disease, death usually occurred in twenty-four
hours and suddenly. It is possible that Pasteur examined one infectious
disease and Kitt another; after the latter's thoroughly trustworthy repre-
sentations, Pasteur's statements certainly require critical examination. If
on the whole I have left them for the present in the text, I have done it
with this reservation, and especially on account of their importance for the
development of the doctrine of contagia viva, which importance they retain
even if they prove not to be entirely correct.

58. The following works may be consulted in special connection with
this section, but the reader is at the same time referred to the medical

1 88 Lectures on Bacteria.

literature generally, and especially to Liebermeister's Introduction to In-
fectious Diseases in Ziemssen's Handbuch, II. J. Henle, Patholog. Unters.
I, Berlin, 1840.— The works cited in note 56. — de Bary, Die Brandpilze,
Berlin, 1853 ; — Id., Recherches sur le developpement de quelques cham-
pignons parasites in Ann. d. sc. nat. (Botanique), ser. 4, XX. — Frank, Die
Krankh. d. Pflanzen, Breslau, 1880. — de Bary, Morphol. and Biol. of the
Fungi, &c., Clarendon Press, 1887; — Id., in Jahresber. ii. d. Leistungen u.
Fortschr. d. Medicin, herausg. von Virchow u. Hirsch, II (1867), Abth. I,
p. 240; — Id., Ueber einige Sclerotienkrankheiten, &c., in Bot. Ztg., 1886. —
v. Recklinghausen, in Berichte d. Wiirz burger phys.-med. Ges., 1871. —

E. Klebs in numerous papers, especially in Archiv f. experiment. Pathol. u.
Pharmacol. I (1873). — v. Nageli, Die niederen Pilze, Miinchen, 1877.

59. O. Obermeier, in Berliner klin. Wochenschr. 1873. — Cohn, Beitr.
z. Biol. d. Pfl. I, Heft 3, p. 196. — v. Heydenreich, Unters. ii. d. Paras, d.
Ruckfalltyphus, Berlin, 1877. — R. Koch in Mittheil. d. Reichsgesundheit-
samts, I.

60. R.Koch, Die Aetiologie d. Tuberculose, in Mittheil. d. Reichsgesund-
heitsamts, II. — Malassez et Vignal, Tuberculose zoologique in Compt. rend.
XCVII (1883), P- 1006; XCIX (i884\ p. 203.

61. Neisser in Centralblatt f. d. med. Wissensch., 1879, and in Deutsche
Med. Wochenschr., 1882, No. 20. — Bockhardt, Beitr. z. Aetiologie u.
Pathologic d. Harnrohrentrippers, in Sitzungsber. d. phys.-med. Ges. z.
Wiirzburg, 1883, p. 13. — E. Bumm, Der Mikroorganismus d. Gonorrhoischen
Schleimhaut-Erkrankungen, Wiesbaden, 1885. — See also Nagel in Jahres-
bericht, &c. d. Ophthalmologie.

62. From the very copious literature of wound-infection, I cite here only

F. J. Rosenbach, Mikroorganismen bei d. Wundinfectionskrankheiten d.
Menschen, Wiesbaden, 1884. — J. Passet, Unters. ii. d. eitrige Phlegmone d.
Menschen, Berlin, 1885. In these books and in Baumgarten's Jahres-
bericht will be found further information concerning the literature of the
subject.

63. v. Recklinghausen u. Lukomski in Virchow's Archiv, LX. — Fehl-
eisen in Deutsche Zeitschr. f. Chirurgie, XVI, p. 391. — Koch in Mittheil. d.
Reichsgesundheitsamts, I.

64. Sattler, Die Natur d. Trachoms, &c., in Ber. u. d. Versammlung
d. ophthalmol. Ges. z. Heidelberg, 1881, p. 18; 1882, p. 45. — Michel, in
Sitzgsber. d. Wiirzb. phys.-med. Ges., 1886.

65. Kuschbert u. Neisser in Deutsche med. Wochenschr., 1884, No. 21.
— Schleich, Zur Xerosis conjunctivae, in Nagel's Mitth. aus d. ophth. Klinik
z. Tubingen, II, p. 145.

66. C. Friedlander, Ueber d. Schizomyceten b. d. acuten fibrinosen Pneu-
monic, in Virchow's Archiv, LXXXVII (1882), p. 319 ; — Id. in Fortschritte
d. Medic. I, 1883. For more recent confirmatory statements, see in Baum-
garten's Jahresbericht.

67. On leprosy, see Neisser in Ziemssen's Handb. d. spec. Pathol. u.

Literature and Notes. 189

Therapie, XIV. For more recent works on leprosy, by Unna and others,
see in Baumgarten's Jahresbericht, and also for discussions on the Bacillus
of Syphilis.

68. Mittheil. d. Reichsgesundheitsamts, I.

69. Bellinger in Ziemssen's Handb. III. — Loffler u. Schiitz in Deutsche
med. Wochenschrift, 1882, p. 707. — O. Israel in Berliner klin. Wochenschr.,
1883, p. 155. — Kitt in Jahresber. d. k. Thierarzneischule Miinchen, Leipzig,
1885.

70. Bellinger u. Feser in Deutsche Zeitschr. f. Thiermedicin, 1878-1879.
— T. Ehlers, Unters. ii. d. Rauschbrandpilz ; Dissert. Rostock, 1884.— Kitt
in Jahresber. d. k. Thierarzneischule Miinchen, Leipzig, 1885.

71. E. Klein in Virchow's Archiv, XCV (1884), p. 468.— For Loffler,
Lydtin, Schottelius, and Schiitz, see Baumgarten's Jahresbericht, 1884, p. 101.

72. Klebs und Tommasi Crudeli, Studien U. d. Ursache d. Wechselfiebers
u. ii. d. Natur d. Malaria, in Archiv f. experim. Pathol. XL — Cuboni u.
Marchiafava in Archiv f. experim. Pathol. XIII. — Ceci in Archiv f.
experim. Pathologic, XV and XVI. — Ziehl in Deutsche med. Wochen-
schrift, 1882, p. 647. — Marchiafava u. Celli, N. Unters. ii. d. Malaria-
Infection, &c., 1885. — See Baumgarten's Jahresbericht, 1885, p. 153. I know
these authors only from this report. Laverans' book, cited in it, I do not
know. A criticism of the statements of the Italian observers, as they lie
before me, would be out of place here ; I would only counsel them to study
attentively the zoologico-botanical literature of that portion of natural
history with which their writings are occupied, before they deal with it so
independently, and employ terms like ' plasmodium,' for the word is
applied with the utmost precision to a portion of developmental history
which the authors have never observed in the cases which they are dis-
cussing.

73. Gaffky, Zur Aetiologie d. Abdominaltyphus, in Mitth. aus d. k.
Reichsgesundheitsamt, II, 372, where the literature is given at length.

74. Fr. Loffler, Unters. ii. d. Bedeutung d. Mikroorganismen fur d. Ent-
stehung d. Diphtherie beim Menschen, bei d. Taube u. beim Kalbe in Mitth.
aus d. k. Reichsgesundheitsamt, II, p. 421.

75. J. M. Klob, Pathol. anatom. Studien ii. d. Wesen d. Choleraprocesses,
Leipzig, 1867.— R. Koch in Berliner klin. Wochenschrift, 1884, Nos. 31-
32 a; — Id. in Verhandl. d. zweiten Conferenz z. Erorterung d. Cholerafragen in
Berlin, klin. Wochenschrift, 1885, No. 37 a. — E. van Ermengem, Recherches
sur le Microbe du Cholera Asiatique, Paris et Bruxelles, 1885. — F. Hueppe,
Ueber d. Dauerformen d. sogen. Kommabacillen, in Fortschritt d. Medicin,
III, 1885, No. 19, and in Deutsche med. Wochenschrift, 1885, No. 44. —
For Nicati u. Rietsch, Doyen, Watson Cheyne, Babes, and others, see the
citations in Baumgarten's Jahresbericht, 1885.— Finkler u. Prior in Tagebl.
d. sieben u. funfzigsten Ver. Deutsch. Naturf. u. Aerzte z. Magdebourg,
p. 216 ; — Id., Forschungen U. Cholerabacterien im Erganzungsheft z. Central-
blatt f. allg. Gesundheitspflege, I. — Emmerich, Vortr. im Aerztl. Ver. z.

190 Lectures on Bacteria.

Miinchen reported in Berl. klin. Wochenschrift, 1885, No. 2 ; — Id. in Arch,
fur Hygieine, III. — H. Buchner in Arch, fur Hygieine, III. — Emmerich u.
Buchner, Die Cholera in Palermo, in Miinchener med. Wochenschrift,
1885, No. 44. — v. Sehlen, Bemerkungen u. d. Verhalten d. Neapler Bacillen
in d. Organen, &c., in Miinchener med. Wochenschrift, 1885, No. 52. —
J. Ferran, Die Morphologic d. Cholera-Bacillus u. d. Schutz-Cholera-
Impfung, by Dr. Max Breiting, after Dr. Ferran, in Deutsch. median.
Zeitung, IV (1885), p. 160, and Ueber d. Morphol. d. Komma-Bacillus in
Zeischr. f. klin. Medicin, edited by Leyden, Bamberger, and Nothnagel,
IX (1885), p. 375, t. 1 1. — Cholera, Inquiry by Doctors Klein and Gibbes, and
Transactions of a Committee convened by the Secretary of State for India
in Council, 1885. — See also E. Klein in Proceedings of the Royal Soc. of
London, XXXVIII, No. 236, p. 154. — T. Lewis in the Lancet, Sept. 2, 1884.
The account given in the text is founded on the literature quoted
above, and has been modelled chiefly on van Ermengem's excellent book.
The botanical description of the Spirillum of cholera is also founded partly
on the numerous descriptions and figures which we possess, partly on my
own examination of Finkler's and Prior's form. I was limited to this,
because my request for a specimen of living material of the Spirillum of
cholera, addressed to those most able to grant it, was refused, and my other
occupations precluded the possibility of my travelling in search of the
disease. I still call Koch's form and others like it by the name of Spirillum,
simply for the sake of shortness and simplicity. Hueppe proposes that it
should be called Spirochaete ; Schroter would use the word Microspira as
the generic name for the arthrosporous spiral Bacteria. My only objection
to this is that changes and shifting of names in this group of organisms
appear to me at present to be of little use and not desirable. The different
species are still so unequally known that fresh changes may at any moment
be required, and the best plan, therefore, is to be content with a simple
intelligible expression for each case, and await the time when our knowledge
will allow of our introducing a correct nomenclature, and one that may last
for some time.

76. See the compilation by Judeich and Nitsche, Lehrb. d. mitteleurop.
Forstinsectenkunde. — Pasteur, Etudes sur la maladie des vers-a-soie, Paris,
1870, with notices of the literature. — Frank R. Cheshire and W. Watson
Cheyne, The Pathogenic History and History under Cultivation of a new
Bacillus (B. alvei), the cause of a disease of the hive-bee, hitherto known
as foul brood, in Journ. of Roy. Microsc. Society, ser. a, V. — S. A. Forbes,
Studies on the contagious diseases of insects, in Bull, of the Illinois State
Laboratory of Nat. Hist., II (1886).— Also Metschnikoff in Virchow's
Archiv, XCVI, p. 178.

77. J. H. Wakker, Onderzoek d. Ziekten van Hyacinthen, Harlem, 1883,
1884.— See also Bot. Centralblatt, XIV, p. 315.— T. J. Burrill, Anthrax of
fruit trees, or the so-called fire-blight of pear trees, and twig-blight of apple
trees, in Proceedings of American Association for the advancement of

Literature and Notes. 191

Science, XXIX, 1880 ; — Id., Bacteria as a cause of disease in plants, in the
American Naturalist, July, 1881. — J. C. Arthur, Pear Blight, in Annual
Report of the New York Agricult. Experiment Station for 1884 and 1885 ; —
Id. in Botanical Gazette, 1885 > — Id. in American Naturalist, 1885. —
E. Prillieux, Corrosion de grains de ble, &c. , par les Bacteries, in Bull. Soc.
Bot. de France, XXVI (1879), PP- 3T> 167.— Reinke u. Berthold, Die Zer-
setzung d. Kartoffel durch Pilze, Berlin, 1879. — van Tieghem, Developpe-
ment de 1'Amylobacter dans les plantes a 1'etat de vie normal, in Bull.
Soc. Bot. de France, XXXI (1884), p. 283.

INDEX.

Achorion, 146.
Arthrobacterium aceti, 86.

Bacillus, 73.

— alvei, 174.

— Amylobacter, 5, 12, 17, 19, 21,
34, 39, 5°, 53, 54, 5§, 69, 70,
71, 99, &c., 104, 116, 179.

— Anthracis, 12, 17, 21, 34, 50, 51,
52» 54, 59, 64, n6, 122, &c.

— butylicus, 53, 100.

— butyricus, 100.

— crassus, 3.

— erythrosporus, 19.

— lacticus, 94.

— Malariae, 170.

— Megaterium, 16, 17, 21, 29, 39,
51, 59, 104 154.

— Melittopntnorus, 174.

— of butyl-alcohol, 57, 70.

— of butyric acid, 100.

— of lactic acid, 94, 97.

— of leprosy, 170.

— of syphilis, 170.

— of tubercle, 51, 152, 158.

— of typhoid fever, 171.

— of typhus, 151.

— subtilis, 12, 17, 20, 29, 34, 39,

5°, 51, 52, 54, 57, 59, I02> I04,
124, 134.

— Ulna, 17.

— Ureae, 84.

— virens, 4.
Bacterium aceti, 86.

— chlorinum, 55.

— merismopoedioides, u.

— of lactic acid, 97.

— photometricum, 58.

- Termo, 50, 53, 105, &c., 119.

— Zopfii, 18, 22, 53, 116.
Beech, 112.

Beggiatoa, 3, 5, 23, 30,66, 73, 79,81.

— alba, 81.

— arachnoidea, 80.

Beggiatoa mirabilis, 80.

— roseo-persicina, 5, 58, 80.
Botrydium granulatum, 26, 30.
Butyl -alcohol, Bacillus of, 57, 70.
Butyric acid, Bacillus of, 100.

Calothrix, 77.
Capitate Bacteria, 100.
Cholera, Spirillum of, 160.
Cladothrix, 7, 10, 23, 73, 76, 77,

78, 79-

— dichotoma, 76.
Clathrocystis roseo-persicina, 80.
Clostridium butyricum, 100.
Coccobacteria septica, 28.
Comma-bacillus, 163.

— of mucous membrane of mouth,
120.

Cordyceps, 109, in.
Cornalian bodies, 175, 176.
Crenothrix, 3, 7, 23, 30, 75, 76,

79-

— Kiihniana, 75.
Cystopus, 113, 114.

— candidus, 113.

Diplococci, 9.
Dispora, 99.

— caucasica, 96.
Drum-stick-bacillus, 105, 116.

Erysipelas, Micrococcus of, 64.
Erythema migrans, 169.
Eurotium, 39.

Favus, 146.
Filamentous yeast, 67.
Finger-erysipelas, 169.
Fission-algae, 37.
fungi, 2, 37.

— -plants, 37.

— -yeast, 67.
Frog-spawn, 12.

bacterium, 12, 90.

Index.

Galeobdolon luteum, 48.
Garden-cress, 63, 113.
Gonococcus, 156, &c.

Hay-bacillus, 12, 134.
Hydrocharis, 48.
Hydrodictyon, 26, 30.

Itch, 115, 146.

Kefir, 13, 95, &c.

Kefir, Bacterium of, 55, 95, 99,

!54-
Kefir-grains, 13, 95.

Labiatae, 48.

Laboulbenia Muscae, 39, in.

Lacerta viridis, 123.

Lactic acid, Bacillus of, 94, 97.

— Bacterium of, 97.
Lepidium sativum, 63, 113.
Leprosy, Bacillus of, 170.
Leptothrix, n.

— buccalis, 5, 119.

— ochracea, 78.

Leuconostoc, 6, 13, 22, 23, 73, 90,
91.

— mesentenoides, 23, 90, 91.

Merismopoedia hyalina, 185.

— littoralis, 185.

— punctata, 185.

— Reitenbachii, 185.
Micrococcus aceti, 54, 86, 87, 88.

— amylovorus, 178.

— Bombycis, 175.

— Gonococcus, 156.
— lacticus, 33, 94.

— nitrificans, 86.

— of diphtheria, 172.

— of erysipelas, 64.

— of fowl-cholera, 141.

— of tooth-caries, 121.

— of ulcer, 64.

— Pasteurianus, 5, 88.

— prodigiosus, 14, 39, 53, 94.

— Ureae, 24, 39, 84, 168, 175.
Microspira, 189.
Microzymes, 47.

Monads, 9.

Monas prodigiosa, 14.
Mother of vinegar, 6, 84, 86.
Mucor, 26.

Mucorini, 58, 70, 71.
Mycoderma aceti, 86.
Mycothrix, n.
Myxomycetas, 112.

Naples Bacillus, 165.
Nosema Bombycis, 175.
Nostoc, 36.
Nostocaceae, 6, 36, 77.

Oenothereae, 112.
Ophiodomonas, 79.
Oscillatorieae, 8, 36, 80, 82.

Palmella, 12.

Panhistophyton ovatum, 175.
Penicillium glaucum, 39, 56.
Phytophthora infestans, 112, 179.

— omnivora, 112.
Proteus, 183.
Pythium, 112.

Relapsing fever, 151.
Rusts, 1 08.

Saccharomyces, 70, 71, 90, 98.

— Cerevisiae, 68, 69, 98.

— Mycoderma, 89.

— of beer-yeast, 70, 90, 98.
Salvia glutinosa, 48.
Saprolegnieae, 38.
Sarcina, 73, 117.

— flava, 1 1 8, 184.

— fuscescens, 185.

— hyalina, 185.

— intestinalis, 185.

— littoralis, 185.

— lutea, 1 1 8, 184, 185.

— minuta, 117, 184.

— of the lungs, 185.

— paludosa, 185.

— Reichenbachii, 185.

— Reitenbachii, 1,854

— rosea, 185.

— ventriculi, 5, n, 116, 117, 118,
184.

- Welcheri, 118, 184.
Schizomycetes, 2.
Schizophytes, 37.
Sclerotinia, 112.
Scytonema, 77.
Sempervivum, 112.

Index.

193

Spirillum, 10, 27, 50, 60, 73, 120,

151, 160.
— -'amyliferum, 5, 17.

— of cholera, 160.

— tenue, 82.
- Undula, 82.

Spirochaete, 6, 27, 189.

— buccalis, 120.

— Cohnii, 119, 120, 151.

— dentium, 1 20.

— Obermeieri, 151, 158.
Sprouting yeast, 67.
Staphylococcus, 168.

— albus, 168, 169.

— aureus, 168, 169.
Streptococcus, 24, 168, 169.
Syphilis, Bacillus of, 170.

Tapeworms, 108, 115.
Trianea bogotensis, 48.

Trichina spiralis, in.
Trichinae, 108, 115, 146.
Tubercle, Bacillus of, 51, 152, 159.
Typhoid fever, Bacillus of, 171.
Typhus, Bacillus of, 151.
Tyrothrix, 52, 104. »

— filiformis, 52.

— tenuis, 52, 104.

Ulcer, Micrococcus of, 64.

Ulothricheae, 82.

Urea, Micrococcus of, 24, 39, 84,

168, 175.
Uredineae, 108.

Vibriones, 10, 159.

Vinegar, Bacterium of, 70, 94.

— Micrococcus of, 57, 86, &c.

Zoogloea, 12.

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