TIMOTHY UEARY

d Corner Book

PLATE I.

Entamoeba histolytica.

Chilomastix mesniii

omonas hominis.

Entamoeba coli

Some of the Intestinal Protozoa of Man, as they appear when alive and active.

THE INTESTINAL

PROTOZOA OF MAN

EY

CLIFFORD DOBELL, and F. W. O'CONNOR,

M.A., F.R.S., Protistologist to

the Medical Research Council,

National Institute for Medical

Research, London.

R.C.S., L.R.C.P., D.T.M. & H.
Wandsworth Scholar, London
School of Tropical Medicine.

TIMk,. uEARY

' ' O, wonder !
' ' How many goodly creatures are there here
" How beauteous mankind is ! 0 brave new world,
" That has such people in't ! "

— Shakespeare, Tempest, V. i.

NEW YORK.

WILLIAM WOOD & CO

/oAT/

PRINTED IN GREAT BRITAIN.

To OUR MUTUAL FRIEND

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Digitized by the Internet Archive

in 2012 with funding from

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PREFACE.

The following treatise is addressed to all Zoologists and Medical Men
who are interested in the Intestinal Protozoa of Man, but more especially
to those whose professional duties demand an intimate practical know-
ledge of these organisms. During the recent Great War the need for
such a work became urgent : and although the War is now ended, and
interest in the subject has waned, there must still be many workers,
especially in the tropics, to whom a work of this character would be —
if properly executed — of very great service.

It appeared to the present authors that such a book — touching
upon the two fields of Zoology and Medicine — ought to be written
jointly by a zoologist and a medical man : for by such collaboration
many mistakes, due to the limited knowledge of either, might obviously
be avoided. This consideration, and a mutual interest in the subject,
prompted the authors of the following work — Captain O'Connor and
myself — to enter into partnership. It was originally agreed between us
that we should write the book together, though one of us should be
specially responsible for the medical parts, the other for those parts
which were purely protozoological.

Unfortunately, it proved impossible to carry out our original inten-
tions. The work was first planned at the end of 191 8 : but in the
autumn of the following year, when the book had only been sketched
out and begun, Captain O'Connor left England on a scientific expedi-
tion to the Gilbert and Ellice Islands. Further collaboration thus
became impossible, and the completion of the work consequently
devolved entirely upon me. As many papers on this subject have been
published recently, and as I have continued my own researches during
the last few years, it will be understood that the book, as it now appears,
is in many ways very different from that originally planned.

For several sections of the book I am solely responsible. The most
important of these are : the Introduction (Chap. I) ; the section dealing

PREFACE

with the coprozoic organisms— based largely upon hitherto unpublished
researches ; the lists of synonyms, and keys for the determination of
genera and species, together with all discussions of systematics and
classification ; the references at the end of the volume, and the general
bibliographic work throughout. I have also drawn all the illustrations,
with the exception of figs. 97-102 (PI. VI), which I have merely redrawn
from Captain O'Connor's originals— these having proved unsuitable for
reproduction. Footnotes which contain my personal opinions are dis-
tinguished by bearing my initials, whenever it has seemed desirable or
necessary to indicate their authorship.

I have thought it right to narrate these particulars here. But my
object in so doing is not that I may claim the greater share of credit—
if any there be— for our joint performance, but to exonerate my partner
from blame for the mistakes which have doubtless been made. During
the last eighteen months, whilst I have been engaged in writing and
revising the book, and in passing it through the press, I have been
entirely deprived of his counsel. I have been unable to discuss with
him any of the new work which has appeared. I have changed my
views on various subjects as I have learned new facts, and I have had
no means of ascertaining whether his views have undergone corres-
ponding changes. Consequently, although Captain O'Connor permitted
me — in fact besought me — to make any alterations which appeared to
me necessary during the progress of the work, I feel that I have been
compelled to take far greater liberties with his contributions than any
ordinary collaborator would have a right to take. And while it is my
hope that I have not, in the following pages, expressed any views from
which Captain O'Connor would dissent, yet I feel it incumbent upon
me to point out here that, for any mistakes which have been made, a
far greater share of responsibility lies upon my shoulders than upon his.
During the preparation of this work I have fortunately been able to
consult Captain S. R. Douglas, I. M.S. (ret.), on medical matters outside
my competence. He has also had the kindness to read through Chapters
III, VII, and VIII, which have profited by his help and criticism. For
these services we offer him here our sincere thanks. I wish also to
thank Professor W. Bulloch, F.R.S., for supplying me with a number of
references to works which I should else have overlooked. We are
further indebted to the Editor of Parasitology, Professor G. H. F.
Nuttall, F.R.S., for permission to republish fig. 28 (PI. Ill); and to
Lieutenant-Colonel W. Byam, R.A.M.C., and the Oxford University
Press, for allowing us to use figs. 27 (PI. Ill) and 109-111 (PI. VII),

PREFACE VII.

which were drawn originally for Byam and Archibald's forthcoming
treatise on The Practice of Medicine in the Tropics.

I would point out here that the figures have all been drawn — unless
the contrary is expressly noted — from actual specimens, with the aid of
the camera lucida. They are not diagrammatic. But the figures on the
Frontispiece (PI. I), though not intended to appear schematic, were
drawn from memory and imagination. They are composite pictures —
made accurately to scale, and as correct as possible in their details, but
not copied from any particular specimens. It is impossible to draw an
actively moving protozoon with the camera lucida ; and the artist who
professes to depict such an organism " from life " must always, in reality,
first observe it accurately, and then make his drawing from memory —
combining the thousands of changing images which have fallen upon
his retina into a single fixed and lifeless picture. The figures on Plate
VIII are frankly " diagrams " of the same sort, so drawn for a special
purpose. They are attempts to show to others, as accurately as is
possible by means of single images, the appearances which I have seen
upon innumerable occasions. Not one of these figures has been copied
from any particular specimen, but each is a general description — with
the brush instead of the pen — of the thousands of similar individual
objects which have passed before my eyes. It is really impossible to
convey an exact impression of such objects by means of drawings ; and
when such drawings have been more or less effectively executed, it is
almost impossible to overcome the difficulties involved in the process
of reproduction. The methods by which I have, in the present case,
" faked " the figures into a semblance of reality, are too obvious to
require comment.

It has been our aim, throughout this work, to be as brief and
accurate as possible. We have made no attempt to treat the subject
in an encyclopaedic manner, but have aimed rather at producing a
practical handbook — a book which will help the beginner, and at the
same time assist more serious students in the prosecution of their
studies. A work of this character would be of little use if it did not
contain full and accurate references, and I have therefore devoted
special attention to the bibliographic aspects of the subject. Every
work cited has been consulted in the original, and every effort has
been made to insure accuracy in quotations and references. Those
who have any knowledge of the subject, and who are acquainted with
the almost endless bibliographic errors in most works dealing with
it, will realize the toil which this has entailed. The references represent,

Vlll. PREFACE

indeed, the intermittent labour of many years : but I think the time
taken over them has not been mis-spent, for it has enabled us to avoid
the repetition of many text-book traditions of the unfounded but
long-lived type familiar to all students of scientific literature.

It has not been possible to take notice of many works which have
appeared in the last few months, but an attempt has been made to
incorporate at least a reference to every work of importance which
has come to my notice up to the time of going to press. No effort
has been made, however, to cite every work that has been written on
the subject, since this would have made our references run into many
thousands. Hundreds of references have, indeed, been weeded out
in the final revision. Judicious selection, rather than compendious
collection, has been aimed at in this respect.

It seems to me that it is the duty of every scientific worker to study
and weigh what his predecessors and contemporaries have written, and
that he should be as careful in quoting them as he is in making and
recording his own observations. To neglect to notice the work of
others, or to misquote it, is often something more than incivility : it
easily leads an author to claim — or to appear to claim — as his own
a discovery or observation to which he has no title. But in dealing
with the works of others one must constantly note their errors — no
less than their good parts. To summarize without criticizing is not
possible in a work which aims at being scientific. Error and truth
cannot be added together. Consequently, criticism also is a duty to
every collector of facts. I have often been taken to task, by reviewers
of my previous publications, for the "severity" of my criticisms of the
work of others. I wish, therefore, to make this explanation. All my
criticisms are directed against opinions or interpretations — not against
persons. If a statement is true, it will withstand the severest criticism.
If, on the other hand, it is false, it cannot be too severely condemned.
I thus see no reason to reproach myself for the severity of any criticisms
which I may have made, unless they have unwittingly been unjust to
persons or unjustified in matters of fact.

But it is easy to destroy and hard to build, and I would therefore
end with the words of the ingenious Dr. Edward Tyson,* who long
ago excused himself to perfection upon a like occasion : " My design
here," said he (and it is ours also), " is not the raising of any Hypothesis,

* See his once celebrated memoir on the Tape-worm, Phil. Trans. Roy. Soc, 1683.
No. 146.

PREFACE IX.

but the enquiring into the truth of those of others. It being much
easier to spy others faults, then to avoid them our selvs. In
what I have said I have done the former ; but can no ways secure
my self as to the latter. But in the whole, if I have not hit the
mark ; I have fairly aimed for it, and it may be some help, and
direction to others in the prosecution of this subject."

Clifford Dobell.
London,
April, 1 92 1.

" E ben piu facile insegnare una veritk,
che stabilirla sopra le rovine di un errore ;
e ben piu facile l'aggiungere che il sostituire."

— Leopardi.

CONTENTS.

Chapter I. Introduction. The Intestinal Protozoa of Man

II. The Intestinal Amoebae of Man

III. Amoebiasis

IV. The Intestinal Flagellates of Man. " Flagellosis :
V. The Intestinal Coccidia of Man. Coccidiosis

VI. The Intestinal Ciliates of Man. Balantidiosis

VII. The Diagnosis of Intestinal Protozoal Infections

VIII. The Treatment of Intestinal Protozoal Infections

IX. The Coprozoic Protozoa of Human Faeces ...

References

Index ...

Plate I, Frontispiece.
Plates II — VIII, at end of Volume.

*9

40

5S
94
ic6

125
148
164
187
205

; Reade not to Contradict, and Confute ;
Nor to Beleeve and Take for granted ;
Nor to Finde Talke and Discourse ;
But to weigh and Consider."

— Bacon, Of Studies (ed. 1625).

THE INTESTINAL PROTOZOA

OF MAN.

CHAPTER I.
INTRODUCTION. THE INTESTINAL PROTOZOA OF MAN.

TO speak of Man as a Microcosm — " an abstract or model of the
world," as Bacon has it — is an ancient and familiar figure of
speech. But the modern scientific writer can hardly stop short at this
metaphor : he knows that, within this microcosm, there is a less poetic
and still smaller world which has been revealed to the inquiring eye of
the microscopist. Man's body is, indeed, itself a macrocosm for in-
numerable micro-organisms ; and it is to one of the microscopic com-
munities inhabiting one small province of this very little world — the
Protozoa living in the intestine of Man — that the following treatise is
devoted.

The object of this first chapter is to introduce the Intestinal
Protozoa of Man to the reader. In the following chapters he will have
an opportunity of cultivating their acquaintance more closely ; but
this acquaintance cannot ripen into intimacy unless he combines the
perusal of this book with a study of the organisms themselves.

Historic Note. — In the year 1681, Antony van Leeuwenhoek,
the illustrious Hollander who discovered the Protozoa and is rightly
regarded as the Father of Protozoology, described a " little creature "
which he had observed, with the aid of magnifying glasses, in his own
stools.* This little creature was the flagellate protozoon now known
as Giardia intestinalis, and its discovery marks the beginning of our
knowledge of the Intestinal Protozoa of Man.

The discovery excited but a passing interest, and lay almost
forgotten for over a century and a half. Then, in the year 1854, two

* See Dobell (1920), where these observations are considered in detail.

2 THE INTESTINAL PROTOZOA OF MAN

similar little animals were found in human stools by the French parasit-
ologist Davaine, who subsequently named them " Cercomonas hominis A "
and " C. hominis B." These have since been rediscovered, redescribed,
and renamed Chilomastix and Trichomonas. Other forms belonging
to the same group of organisms have also been found and studied
by Davaine's followers down to the present day.

A much larger animal was found in human stools by the Swedish
physician Malmsten in 1856. His organism differed so strikingly from
those already mentioned that it clearly belonged to a different group.
It is now called Balantidium and has been studied and redescribed by
many later workers. About the year i860 another Swede, Kjellberg,*
discovered yet another different kind of organism, this time living
actually in the tissue of the human bowel. This was the first of the
animals now called Coccidia to be described in the human gut ; and
its discovery has been followed by the finding of several similar
forms which have received the attention of many subsequent
investigators.

Finally, a fourth kind of "little creature" was discovered t in human
stools by two Anglo-Indian medical officers, Lewis and Cunningham,
in the years 1870 and 1871. Soon afterwards — in 1875 — a similar
discovery was made by Losch in Russia. The organisms which these
observers studied are known as amoebae, and belong to a different
group of animals from any of those previously noticed. They have
now been very thoroughly studied by later workers, and their numbers
have been augmented accordingly.

The discoveries briefly related above are all landmarks in the subject
with which the present work deals. They mark the beginning of our
knowledge of four different groups of microscopic animals which inhabit
the human bowel : and the following up of these several discoveries has
resulted in the accumulation of an immense mass of facts which now
almost form a special science by themselves. It is now known that all
these animals belong to one great group of the animal kingdom — the
Protozoa — of which they form, however, an almost infinitely minute
part. That they have attracted so much attention is due to the circum-

* The discovery was reported by Virchow in i860. See Dobell (1919) for further
details.

f This discovery is usually incorrectly attributed to Lambl (i860). Cf. Dobell
(1919 a, pp. 8-9, and 71 et seq.) where additional details will be found.

INTRODUCTION 3

stance that sonic of them — like the organisms found by Malmsten and
Losch — are associated with human diseases : and although only a few-
can claim this unenviable distinction, it has inevitably invested the
others also with a particular human interest. Some conception of the
present magnitude of this branch of Protozoology can be formed from
the scope and size of the present volume.

Having made the foregoing brief allusion to the history of our
subject, by way of introduction, we shall attempt in the rest of this
chapter to define, very briefly, the Protozoa : to survey, very rapidly,
the forms which live in the human intestine : and to point out how
these various forms live in this environment. Detailed descriptions will
be given in later chapters.

The Protozoa. — The Animal Kingdom is usually divided into two
main groups, or sub-kingdoms — Protozoa and Metazoa. The latter
group comprises all the animals whose bodies are built up of the
morphological units called " cells," and may accordingly be defined as
consisting of all the multicellular animals. The former group is usually
defined, in contrast, as comprising the "unicellular" animals. For
reasons discussed elsewhere (Dobell, 191 1) the term "unicellular"
appears objectionable and misleading ; for it implies that the body of
an individual protozoon is homologous with a single cell in the body of
a metazoon, and not with a whole metazoal individual. If we regard
the whole organism as an individual unit, then a whole protozoon is
strictly comparable with a whole metazoon, and not with a part of it.
But the body of a protozoon, though it often shows great complexity of
structure, is not differentiated internally into cells — like the body of a
metazoon. Consequently, it differs from the latter not in the number of
its cellular constituents, but in lacking these altogether. We therefore
define the Sub-kingdom of the Protozoa as the group which contains

ALL NON-CELLULAR ANIMALS.

This is not the place to define " cell" and "animal " : and we shall
therefore entrust the comprehension of the foregoing definition to the
common sense of the reader.

Classification of the Protozoa. — The Protozoa are classically
subdivided into four main groups, which are generally called Classes,
but which probably correspond more closely, in systematic status, to the
groups called Phyla among the Metazoa. Various names have been
proposed for these main groups, but we shall follow the usual conven-

4 THE INTESTINAL PROTOZOA OF MAN

tion and call them (i) Rhizopoda, (2) Mastigophora, (3) Sporozoa, (4)
Ciliophora.

These four groups, or Phyla, of the Protozoa, can be roughly dis-
tinguished by means ot the characters supplied by the external organs
of locomotion of the animals placed in them. These characters have
been used for classifying the Protozoa ever since 1773, when they were
first used for this purpose by the Danish zoologist O. F. Miiller.
Modern protozoologists have found such simple characters inadequate,
when used alone. Nevertheless, they will suffice for our present
purpose, and will enable us to distinguish the four main groups as
follows : —

(1) The Phylum Rhizopoda comprises those Protozoa whose
external organs of locomotion are typically pseudopodia — temporary
prolongations or extensions of the protoplasm of the body, familiar
to everyone as the means of movement in Amoeba.

(2) The Phylum Mastigophora consists of all those Protozoa
which move, in their fully developed and typical condition, by means
of whip-like filaments or flagella — familiar to all who have studied
Euglena, or any other common flagellate.

(3) The Phylum SPOROZOA contains a number of exclusively para-
sitic forms, which in their motile stages — when present — move without
the aid of any special external locomotory organs. The several
common species of Monocystis, parasitic in earthworms, supply familiar
examples — with their slow, worm-like motions, performed by the body
as a whole.

(4) The Phylum Ciliophora contains all the Protozoa which move,
in their typical active stages, by the agency of many little hair-like
threads or cilia — exemplified in the familiar Paramecium and other
common ciliates.

Each of these Phyla contains a vast array of species, variously
collected into genera, families, orders, and higher groups. It will be
unnecessary, however, to discuss their classification in detail here, and
we shall limit ourselves to a consideration of the systematic position of
those species alone with which the present work is concerned. It will
suffice to note the general grouping of our forms, and their more obvious
relations to one another.

The human intestine harbours protozoa belonging to all the four
Phyla just enumerated. As these groups contain organisms as different

INTRODUCTION 5

from one another and as distantly related as the members of different
Phyla among the Metazoa, it will be clear that many of the intestinal
protozoa of man have little but their habitat in common. Among
themselves they show great diversities, which are expressed by placing
them in different systematic groups. The Rhizopods in the human gut,
for example, are closely related to the Rhizopods in the guts of other
vertebrates and to those leading an independent existence in water :
they are but remotely related to the Ciliates found in man, though they
chance to share the same habitation. In other words, the organisms
with which we have to deal form, as a whole, an "unnatural" group-
in the systematist's sense — and are treated together merely because
Nature has assembled them in a common domicile.

The Rhizopoda are represented in the human intestine by five species
of amoebae belonging to four different genera — (1) Entamoeba, with two
species E. coli and E. histolytica ; (2) Endolimax, with one species E.
nana ; (3) Iodamoeba, and (4) Dientamoeba, each also with but a single
species — /. biltschlii and D. fragilis respectively. All these belong to
the Class called Amoebaea, which comprises all the naked rhizopods
resembling the well known Amoeba and its allies.

Among the Mastigophora, we find five distinct species — each be-
longing to a different genus — and several other doubtful forms which
require further investigation. All of these belong to the Class Flagellata
— a very large group containing many families and genera. The genera
and species found in the human gut are : (1) Trichomonas hominis, with
several varieties, (2) Chilomastix mesnili, (3) Giardia intestinalis, (4)
Embadomonas intestinalis, (5) Enteromonas hominis. To these some still
uncertain forms may ultimately have to be added.

The Sporozoa of the human bowel all belong to the group known as
theCocciDiA, and are represented by four species placed in two different
genera: (i) Eimeria, with the species E. wenyoni, E. oxyspora, and E.
snijdersi, and (2) Isospora, with the single species /. hominis.

The Ciliophora found in man all belong to the Ciliata, a very large
Class containing numerous species. Those of man belong to the genus
Balantidinm, represented by the species B. coli and B. miniitum (some-
what doubtful), and possibly by others also. A species of another genus
— Nyctotherus — has also been described, but its existence appears still
rather uncertain.

All the organisms just mentioned will have to be considered in detail

6 THE INTESTINAL PROTOZOA OF MAN

in the ensuing chapters : but it will be convenient here to notice certain
general characters which all the members of our " unnatural " group
have in common. These concern chiefly their lives and habits, their
distribution, and their relations to man.

Life-histories. — So many wonderful life-histories have been de-
scribed— and even proved to occur — in the Protozoa, that the mere
mention of the name often leads the less instructed to expect some
marvellous revelation. It will be well to state at the outset, therefore,
that the intestinal protozoa of man all lead — so far as we know at
present — comparatively simple lives which can be understood, in their
main outlines, by anybody. Most of them develop in a straightforward
manner, and their development can be described without the use of
numerous technical terms. Many of the exciting doings which have
been attributed to these animals are now known to rest upon mal-
observation, misinterpretation, and unscientific use of the imagination ;
and no excuse will be needed, therefore, for ignoring these mistakes at
this point, and omitting to use some of the superfluous terms which
they have introduced into biological language.

From the most general standpoint, the life of an intestinal protozoon
consists typically of two main periods — a period of freedom or activity
(often curiously called a "vegetative" stage) and a period of rest. It
may be noted, in passing, that the first period can hardly be called one
of "freedom" and "activity " in the case of the Coccidia ; for during the
corresponding stages in these organisms, the individuals are intracellular
and sedentary — only the young forms being free and motile. But it is
characteristic of all the intestinal protozoa that during this first period
of relative freedom and activity they feed, grow, and multiply actively
— multiplication being effected always by a process of simple or multiple
fission. This period is, moreover, invariably passed — in the case of
the organisms under consideration — within the human bowel. On the
other hand, the resting period is always passed outside the human body,
within a special protective capsule or cyst.

The " free " forms, living and multiplying in the body of man, give
rise to the condition called infection : while the resting or encysted
forms, capable of external existence, serve to convey infection from
one man to another. Infection with any intestinal protozoon is, in
nature, always acquired through the mouth, by swallowing a living cyst
containing the resting form of the particular organism. In ordinary

INTRODUCTION 7

circumstances the free forms cannot live outside the body for more
than a very short time, and they die if swallowed — in other words,
they are non-infective.

The two periods or cycles of development alternate, more or less
regularly, with one another. When a cyst is ingested, it passes intact
through the stomach into the intestine. Here it hatches and liberates
its contained organism (or organisms), which seeks its appropriate
place in the bowel and there begins its development as an active or free
form. After living and multiplying for some time in this form, its
offspring secrete cysts round themselves, and then pass out of the
intestine with the stools. The cycle of events is repeated if these cysts
are fortunate enough to get swallowed again by a human being.

The above is a brief outline of the life of each of the intestinal
protozoa of man. Each has its own peculiar structure and mode of
life, and each its own characteristic encysted form, which can be
recognized in the faeces by the trained microscopist. Individual details
of structure, and complications in the mode of development, will
receive attention later. It is only necessary here to take a very general
view, and to emphasize the two main stages in the life-cycle — the
" active " form and the cyst. When these are understood, the details
are easily learned : but failure to understand these simple generalities
has led, unfortunately, to many errors in the past, and for this reason
it seems necessary to stress these elementary points. When they are
clearly and generally comprehended it will become impossible for
certain current but inaccurate expressions to survive. It will no longer
be possible for a writer to describe a patient as " infected with cysts,"
or to speak of "cyst-carriers," or to ask for methods of medication
which will " kill the cysts " in preference to the active forms — all
which expressions, and others akin to them, are obvious absurdities.

It will be noted that the life-cycle as a whole requires but two
environments — the human bowel, and some suitable resting place
outside it. No secondary or intermediate host is necessary for the
completion of the developmental cycle of any of the intestinal protozoa
of man. In this connexion, however, it must be noted that other
animals may assist in the dispersal of the cysts, and thus aid in spreading
infections : and this leads us to consider the usual modes of
dissemination of the intestinal protozoa of man in nature.

Dissemination. — The cysts of all the intestinal protozoa of man

8 THE INTESTINAL PROTOZOA OF MAN

are comparatively delicate structures, and their contents are incapable
of withstanding desiccation. In damp faeces, however, or in water, the
cysts can usually survive and remain infective for several weeks. It
thus seems probable that, in nature, water plays an important part in
their dissemination : and it may be assumed that the swallowing of
water, or damp uncooked foodstuffs, accidentally contaminated with
faecal matter containing cysts, is the usual means whereby infections
spread from man to man. All unhygienic conditions which favour con-
veyance in this manner must, accordingly, be regarded as contributing
to the dissemination of infections.

Food and drink may, of course, become contaminated with faeces
in innumerable ways. It is impossible to discuss them all here, but we
must mention one of them which is of special interest — namely, con-
tamination by flies. It has been demonstrated by Wenyon and
O'Connor (1916, 1917), Flu (1916), Buxton (1920), and others, that
house-flies are able to spread the cysts of the common species of in-
testinal protozoa. Wenyon and O'Connor have shown that a fly, when
it feeds upon human faeces containing cysts, does not digest them, but
passes them alive and unchanged through its alimentary canal, and
voids them again — still living — with its own faeces. The time taken in
passing through the fly is, sometimes, astonishingly short — cysts taken
in at the fly's mouth being redeposited within as little as 5 to 30
minutes. A large number of flies, after feeding upon a stool containing
numerous cysts, might therefore disseminate them over a comparatively
wide area in a short space of time. Each speck of such fly faeces, if
swallowed with food or drink before it has time to undergo complete
desiccation, is capable of infecting a human being. It is thus clear
that the part played by flies in the spread of infections is not negli-
gible, and may be of prime importance : and it is also evident that the
destruction of flies, as a prophylactic measure against the spread of
infections, merits serious attention.

It has recently been urged by Roubaud (1918) that the fly may, in
reality, do more good than harm in this respect. He argues that, since
the minute quantity of faecal matter deposited by a fly readily dries up,
and any protozoal cysts which it may contain are thus killed, the fly
may, in reality, contribute to the destruction rather than to the dispersal
of cysts in nature. Infective faeces, when devoured by flies, is reduced
to a fine state of division ; and the prompt desiccation which results
renders the contained cysts non-infective in a very short time.

INTRODUCTION 9

This consideration is, no doubt, of importance when we are con-
sidering what happens under hot and dry atmospheric condition-,.
When the air is humid, however, or when there are opportunities for
the flies' faeces to be deposited in or on damp comestibles intended
for human consumption, it is clear that we cannot— without further
evidence — regard the activities of the fly as beneficial, or even as harm-
less. Recently Woodcock (1918) has attempted to show that the part
played by flies — in the dissemination of amoebic cysts — is compara-
tively unimportant. He considers the humidity of the atmosphere to
be the factor of primary importance determining the survival and
dispersal of cysts. It is evident, however, that dampness of the air is
the very factor which would prevent the faeces of flies from drying too
rapidly ; and consequently, even if it were proved that humidity is of
great importance, it would in no way invalidate the conclusion that
flies play a most important part in the dissemination of the intestinal
protozoa of man. Both factors are, doubtless, intimately connected,
and deserve careful consideration.

It may be noted here that Stiles (1913) had earlier suggested that the
prevalence of intestinal protozoa in a community might be used as a
criterion of the extent to which their food and drink are exposed to
contamination with human faeces — as a measure of the effectiveness of
the sanitary arrangements within the community : and Stiles and Keister
(1913) have already attempted to utilize this criterion in the special
case of the carriage of Giardia cysts by house-flies.

Geographical Distribution. — It is now certain that most of the
intestinal protozoa of man are cosmopolitan in their distribution. They
are not restricted, as is often assumed, to the tropics, but are known to
occur in human beings in all parts of the world where search has been
made for them. In all probability the gaps in our present knowledge,
in this respect, make the distribution of some forms wrongly appear
discontinuous ; though it is possible, or perhaps even probable, that
future work will show that some species — for example, the Coccidia —
are limited to certain geographical areas. On the other hand, although
all races of man have not yet been examined with this object in view, it
is reasonably certain that most races of man harbour Entamoeba coll and
E. histolytica — and probably the other intestinal amoebae — and all the
common species of flagellates. These are known to occur in such
widely separated places that it can hardly be doubted that their real

10 THE INTESTINAL PROTOZOA OF MAN

distribution is world-wide. It is also reasonable to conclude that all
the common intestinal protozoa of man have lived in man for ages.
They are not recent intruders but age-long companions of the human
species.

There is nothing very novel in this wide geographical distribution,
though it has but recently become evident : for the cosmopolitan
occurrence of the Protozoa generally has long been a commonplace
observation to zoologists.

One of the most interesting of the facts which have emerged from
the recent activity in the study of the intestinal protozoa of man, is the
demonstration that all the commoner forms occur, apparently indi-
genously, in the British Isles. Even Entamoeba histolytica — previously
assumed to be more or less restricted to the tropics — has been shown to
occur in no inconsiderable proportion of the inhabitants of these
Islands. We owe the establishment of this fact chiefly to the work of
Matthews and Malins Smith,* but their observations have been confirmed
and extended by others. One of us has recently reviewed and sum-
marized all the investigations undertaken to elucidate this problem, so
that it will be unnecessary to deal with it in detail here.f It will suffice
to note that most of the commoner species of known human intestinal
protozoa occur at the present day in Britain — the most noteworthy
forms which have not yet been recorded being Balantidium and the
Coccidia.

It is clear that Britain cannot occupy an isolated position in this
respect, and that further investigations will show that all the intestinal
protozoa of man are much more widely distributed than was generally
supposed until quite recently. Hitherto the greatest attention has been
paid to the distribution of E. histolytica, but there are already sufficient
records available to show that most of the other intestinal protozoa are
at least as widely dispersed.^ But we cannot discuss this subject in

* See especially Yorke, Carter, Mackinnon, Matthews, and Smith (1917), Matthews
and Smith (1919, 1919a), Dobell (1921).

tSee Dobell (1921).

% Among more recent contributions to this subject the reader may be referred to
the following : Galliard and Brumpt (1912), Paviot and Garin (1913), Landouzy and
Debrd (1914), Bloch (1916) — French cases; Kuenen (1918) — Dutch cases; Fischer
(1920) — German cases; Yakimoff (1917)— Russian cases; Kofoid, Kornhauser, and
Plate (1919), Cort and McDonald (1919) — United States cases. There are also
numerous other works dealing with the occurrence of intestinal protozoa in the
inhabitants of temperate climates, but it would lead us too far to discuss — or even to
attempt to cite — all of them. See also the papers on French cases of Balantidiosis
cited on p. 119 infra.

INTRODUCTION I I

detail here. We must pass on to the consideration of another impor-
tant and equally large subject.

Incidence of Infection. — The recent Great War has fostered an
immense amount of research upon the intestinal protozoa of man, and
has led to the publication of a very large volume of records from all
the chief theatres of military operations. It is impossible to attempt to
summarize this work here, where we shall merely note what seem to be
the most important general conclusions to be drawn from it.

The recorded findings as a whole — after due allowance has been
made for the very considerable but inevitable proportion of errors con-
tained in them — tend to show that intestinal protozoa are far commoner
in man, in all parts of the world, than had previously been supposed.
But at the same time they have revealed that these organisms are of less
importance, from a medical standpoint, than was formerly believed. It
has now become clear that the majority of the intestinal protozoa occur
comparatively frequently in human beings everywhere ; but that very
few species are responsible for the causing of human diseases, and that
none give rise to epidemics of such diseases. In the War, the amount
of disease due to intestinal protozoa was, in all probability, when the
number of individuals involved is taken into account, almost negligible.

Nevertheless, the hundreds of thousands of cases of intestinal disease
which occurred in the course of the War afforded great opportunities
for studying intestinal organisms of all sorts ; and it is partly because so
much importance was at first attached to the intestinal protozoa that the
fact of their comparative unimportance has emerged. By far the most
important intestinal protozoon, from the medical standpoint, is
Entamoeba histolytica — the organism which " causes " the disease known
as amoebic dysentery, and other pathological conditions. Special
attention has therefore been directed to this parasite, and as a result we
now have fuller information about it than about most of the other
intestinal protozoa. It is certain that this amoeba occurs in a very
considerable percentage of persons all the world over, and it is probable
that at least 10 per cent, of the entire population of the globe is infected.
The number may, indeed, be much higher. The majority of the other
intestinal amoebae, and most of the flagellates, occur with at least equal
frequency : and in the case of some of them — such as Entamoeba coli
and Giardia — there is evidence to show that they are even more com-
monly present in mankind generally. These conclusions, by themselves,

12 THE INTESTINAL PROTOZOA OF MAN

indicate that intestinal protozoa must have relatively little pathological
significance.

There is, however, some indication that all the intestinal protozoa
of man occur with greater frequency in tropical aud subtropical countries
than in temperate and cold ones. But it is still questionable whether
this inequality of distribution has any direct relation to climate or tem-
perature : it is probable that it depends primarily upon the more
insanitary conditions and greater opportunities for the spread of infec-
tion which are present in hotter countries generally.

We can say no more on this subject here, and will make no attempt
to summarize the published records dealing with the incidence of intes-
tinal protozoa in the various races of man, and in the various armies
engaged in the War.- Our space is circumscribed, and we have yet
to consider some other topics of importance from a more general
standpoint.

The Relation of the Intestinal Protozoa to Man.— It is
most important that all who begin the study of the intestinal protozoa of
man should rid themselves of any prejudices that they may have against
so-called " parasites." This term is loosely used, in common speech,
for any organisms that live inside other organisms ; and preconceived
notions derived from this reproachful name have been responsible for
much misunderstanding and confusion in discussing the protozoa of
man. A few general remarks on this subject will therefore be made here.

Animals which live inside other animals are called collectively
Entozoa, and those which harbour them are called their Hosts ; and
a moment's reflexion will show that such an association of two
organisms may be of divers kinds. It is clear that such an association
may be beneficial to both host and entozoon, or harmful to both : or
it may be beneficial or harmful to one member of the pair, and
indifferent to the other. Let us consider each of these possibilities
in turn.

* Numerous references will be found in the Tropical Diseases Bulletin. The reader
interested in this subject may be referred to the following recent works, which will
also supply him with numerous further references to the immense literature dealing
with the incidence of intestinal protozoal infections : Aubert (1917), Bahr and Young
(1919), JBaylis (1920), Bentham (1920), Boney, Crossman, and Boulenger (1918), Brumpt
(1918), Chatton (1918a), Derrieu (1920), Dobell (1917), Dobell, Gettings, Jepps, and
Stephens (1918), Dobell (1921), Flu (1918a), Lebceuf and Braun (1916), MacAdam and
Keelan (1917), Mackinnon (1918), Matthews and Smith (1919^), O'Connor (1919),
Ravaut (1917), Smith and Matthews (1917, 1917a), Wenyon (1916), Wenyon and
O'Connor (1917). Hundreds of additional papers could easily be cited.

INTRODUCTION

1 3

(1) When the association benefits both parties, the condition is
one of Symbiosis — a not very frequent state in nature. An example
is afforded by some of the flagellates living in termites ("white ants").
In return for the food and lodging which the termite gives to the
flagellate, the latter helps the former to digest its own food. No such
symbiotic arrangement appears to exist between man and any of the
protozoa which he harbours in his gut.

(2) When the entozoon lives at the expense of its host, the
phenomenon is known as Parasitism. The entozoon is a Parasite — in
the biological sense — and is always more or less harmful. When the
harm done becomes manifest, the host is said to suffer from a Disease,
of which the parasite is colloquially— and therefore inaccurately —
termed " the cause."

The intestinal protozoa of man furnish several instances of
parasitism, and illustrate several different degrees of this condition.
Entamoeba histolytica, for example, is a truly parasitic rhizopod, which
lives upon its host's tissues. The man who harbours it never derives
any benefit from its presence, but the amoeba itself is always vitally
benefited. Sometimes the parasite, by its inroads into the tissues of the
body, makes its host ill. He then suffers from a disease — dysentery —
which is said to be "caused" by the parasite, and is called, in
consequence, Amoebic Dysentery. A comparable condition is seen
in the case of Balantidium coll. This ciliate also attacks the tissues,
and "causes " the disease distinguished as Balantidial Dysentery.

In addition to the two organisms just mentioned there are all the
Coccidia which live in the human bowel. All of these also are
parasites — living at the expense of human tissue. But as a rule they
do not " cause " any clearly recognizable disease, and their harmfulness
is therefore less obvious. It should be remembered, moreover, that
E. histolytica and Balantidium coli often appear to cause no obvious
symptoms of disease, because their pathogenic capabilities are masked
and therefore overlooked.

There is at present no clear evidence that any of the other intestinal
protozoa are truly parasitic in man.

(3) There is a third condition which may be called Commensalism,
in which the entozoic organism benefits from the association while
its host is neither distinctly benefited nor harmed. This state is well
illustrated by Entamoeba coli and other intestinal amoebae of man,

14 THE INTESTINAL PROTOZOA OF MAN

and by the common flagellates Trichomonas and Chilomastix. These
animals feed chiefly upon the waste food-products and bacteria in
the human colon. Lazarus-like they live upon the crumbs from the
rich man's table. The food eaten by the host ultimately provides
nourishment for the entozoic organism also, and in this sense the
two feed in common. But although the association here is a vital
necessity for the entozoon, it is of no moment to its host. It probably
makes no difference to a man whether his faeces serve to support a
Trichomonas inside his body or a brood of putrefactive bacteria
outside of it.

It will be obvious that to stigmatize such inoffensive dependents
as " parasites," and to regard them as dangerous producers of disease,
is not warranted. By far the greater number of the so-called " para-
sitic protozoa " of the human bowel probably belong to this class of
harmless commensals. It is, indeed, even possible that some of them
are not merely inoffensive, but actually beneficial to their hosts : for
in consuming waste products and bacteria in the large bowel they
may play a useful part as scavengers. In this connexion we need not
discuss the view, which is sometimes advanced, that they probably
injure their host by the "toxins" which they excrete. It will suffice
to note that the " toxins " of intestinal protozoa exist, at present, only
in the imagination of those who regard with horror any organism
which can be loosely termed a " parasite."

The organisms which we here call commensals are sometimes
described as Saprozoic, because — like certain free-living (i.e., not
entozoic) forms — they feed upon decomposing organic matter. More
often they are quaintly called " saprophytic " — a botanical term
obviously inappropriate to animals. These terms have a significance
too wide and inexact to denote the precise relation which we wish
to imply here by the word "commensalism."

Between the true tissue-parasites and the commensals or scavengers
like E. coli, there is a group of entozoa which may be called food-
robbers.* These do not wait for the crumbs to fall from the rich
man's table, but seize and claim a share of what is still — so to speak —
on his plate. Among the intestinal protozoa of man, Giardia is a
good example of this kind of hanger-on. This animal lives in the
small intestine, and obtains its nourishment by absorbing a small

We borrow this term — a very apt one — from Minchin (19 12).

INTRODUCTION

*5

share of the food which has been partly digested, in this situation,
by its host, for his own sustenance. It is questionable how far Giardia
disturbs, in this manner, the bodily oeconomy of its host : but the
amount of harm which it does is probably negligible, in ordinary
circumstances, and it is clearly not easy to justify the contention that
such an organism is a " dangerous parasite."

(4) The remaining possible types of entozoic habit may be dismissed
in a few words. If both entozoon and host suffer ill consequences
from their association, the combination cannot long survive as a normal
and natural state. An individual instance of such a condition would be
called a " disease " ; and it would be pathological for the entozoon as
well as for its host. As a normal relation between two species, it clearly
could not become established. On the other hand, if the association
positively benefited neither entozoon nor host, the relation would be
casual, and not such a one as Nature would be likely to perpetuate.

Since the state of being infected with an entozoic protozoon is some-
times strikingly manifested by its results — for example, when the condi-
tion can be regarded as constituting a human disease — it has been found
convenient to invent words to denote these states. Infection with
amoebae is thus called Amoebiasis ;'* infection with Coccidia, Cocci-
DIOSIS ; infection with Balantidinm, BALANTIDIASIS. We shall use
these terms in discussing these conditions : but we would here make
it clear that we do not use them necessarily to denote diseases — as is
often done. Infection is not necessarily accompanied by clinical signs
of disease ; and to restrict the use of such terms to certain consequences
of infection, rather than to the condition of infection generally, is not
only inconvenient but also leads frequently to a misunderstanding of
the true relations existing between an entozoon and its host, and their
joint relations to the diseases which may result.

Infection with flagellates is sometimes called " Flagellosis," and some
writers have gone so far as to distinguish infections with different
genera of flagellates by distinctive terms. For example, infection with
Trichomonas is sometimes called (horribile dictu) " Trichomonosis " or
" Trichomoniasis " ; whilst infection with Giardia — otherwise known as
Lamblia— is called " Giardiasis " or " Lambliasis." Such terms are not

* This term — introduced by Musgrave and Clegg (1904) — is now in general use.
and we therefore employ it. " Amoebosis " would be a more orthodox word, and
philologically less objectionable.

l6 THE INTESTINAL PROTOZOA OF MAN

only clumsy contraventions of the laws of language but also super-
fluities. At the present time it appears unnecessary to employ more
than a single term for each type of infection — the types being deter-
mined by the zoological groups to which the particular infecting
organisms belong. We shall therefore use a term such as Amoebiasis to
denote infection with any kind of amoeba, and Coccidiosis for infection
with any kind of coccidium. It would be absurd to subdivide Cocci-
diosis into the two conditions "Eimeriosis" and " Isosporosis " because
man happens to be parasitized by coccidia belonging to the two genera
Eimeria and Isospora.

Coprozoa. — The protozoa which live in the human intestine are
usually seen, of course, in human faeces discharged from the body.
Such material, however, forms a suitable medium for the growth and
development of some of the free-living protozoa which usually live
in decomposing organic infusions. These protozoa, which show a
preference for faecal matter, but which do not live entozoically in
the faeces while it is still in the intestine, are termed Coprozoic or
Coprophilic. They cannot be regarded as parasitic or commensal,
and their occurrence in human faeces is largely a matter of chance :
for they occur at least equally often in the faeces of other animals,
and in decomposing organic substances of many kinds. These copro-
zoic protozoa are of importance, however, because their occasional
presence in stale human faeces has led to their confusion with the true
intestinal forms.

Human faeces, after leaving the body, may contain coprozoic
amoebae, flagellates, and possibly even ciliates : and every worker en-
gaged in the study of the intestinal protozoa should make himself
familiar with the commoner species. A brief account of some of
these will be given in Chapter IX, and no further mention of them
will therefore be needed at this point.

We shall now conclude this introductory chapter with a Table
(p. 17), which gives a synopsis of the chief intestinal protozoa of
man, and indicates at a glance their relations to one another in the
zoological system as briefly noted in the preceding pages. The Table
will also serve as a rough table of contents to the ensuing chapters.

INTRODUCTION

17

Sub-
Kingdom

Phylum

Class

Genus

Species

<
O
SI
O

h
0

OS

Oh

<

Q

O

Oh
O

N

5

Oh

<:
w
<:

CQ

w
0

<

Entamoeba

coli

histolytica

Endolimax

nana

Iodamoeba

biltschlii

Dient amoeba

Jvagilis

Oh
O
E
Oh
O
O

H
CO
<
2

H

<d

W
O
<!
J
En

Trichomonas

hominis

Chilomastix

mesnili

Giardia

intestinalis

Embadomonas

intestinalis

Entevomonas

hominis

<
O

O
X
O

Oh
CO

3
0

u

0
u

Eimeria

wenyoni

oxyspora

snijdersi

Isospova

hominis

<

Oh
O

Oh
O

O

<

H

0

Balantidinm

coli

minutum

Nyctothevus

/aba

1 8 THE INTESTINAL PROTOZOA OF MAN

Bibliographic Note.

The following note is inserted merely for the benefit of beginners, who are
unfamiliar with the enormous mass of literature on the Protozoa.

The Intestinal Protozoa of Man are dealt with in most of the larger works on
Tropical Medicine and on Protozoology or general Parasitology. In most of these,
however, the descriptions are now out of date, and consequently incorrect or incom-
plete. Beginners are therefore likely to find the majority of such works puzzling
and misleading rather than helpful. Much attention is also paid to the intestinal
protozoa — both of man and of other animals — in the zoological text-books of Brumpt
(1913), Minchin (1912), and Doflein (1916) ; and these works will be found useful
for reference — especially Brumpt's admirable compendium. Even these are, however,
already more or less out of date. Among the older works on the Protozoa, as a
whole, by far the most authoritative and trustworthy is the monograph by Biitschli
(1880- 1 889): but beginners, with no knowledge of more recent developments, are
hardly likely* to find this work very useful — though it is indispensable to every
serious student of the group.

The intestinal protozoa of man have been considered collectively, as a separate
group, by several previous workers, among whom maybe mentioned Bensen (1908a),
Wenyon (1915), and Brug (1918). Individual groups of these organisms have also
been, from time to time, more or less completely monographed : the amoebae by
Schuberg (1893), Craig (191 1), Hartmann (1913), James (1914), Dobell (1919a), and
others; the flagellates by Rodenwaldt (1912), Jollos (1913), etc.; the coccidia by
Dobell (1919) ', and the ciliates by Jollos (1913a) and Prowazek (1914). Most of the
recent works on intestinal protozoa have been reviewed in the Tropical Diseases
Bulletin (London) and the Bulletin de Vlnstitut Pasteur (Paris) — the former published
since 1912, the latter since 1902. For references to current literature these two
periodicals will be found invaluable. Copious references to the literature of this
subject will also be found in the Zoological Record, the Zoologischer Jahresbericht,
and Stiles and Hassall's Index-Catalogue of Medical and Veterinary Zoology.

It may not be superfluous to point out, or to emphasize, in this place, that a sound
knowledge of the Intestinal Protozoa of Man cannot be gained — even by a proto-
zoologist expert in other branches of the science — by reading alone. To understand
these organisms properly it is necessary to study them in the laboratory. Moreover,
it is hardly possible to understand the forms living in man without some knowledge
at least of those in other animals — and, in fact, without some grounding in the
elements of the Science of Protozoology. The subject is a special one, and — like all
special subjects — it cannot be properly grasped without some knowledge of general
principles.

19

CHAPTER II.

THE INTESTINAL AMOEBAE OF MAN.

It has already been noted, in the preceding chapter, that the Rhizopod
Protozoa are represented in the human bowel by five species of
amoebae. These will be described in some detail in the present
chapter.

Every elementary student of biology is familiar with an organism
called "the Amoeba," or more boldly — if with less justification —
" Amoeba proteus." Most of what he is taught about this animal is
of more than questionable authenticity : but he probably learns, more
or less correctly, that it — or something to which the name is applied —
is a creature of apparently great simplicity of parts, having very few
organs and leading a pleasingly simple life in ponds. The amoebae
living in man are — at least superficially — similar organisms, but they
are unfortunately not quite so simple as "the Amoeba" of the
elementary text-book.

All the amoebae of man are of very small size. Their bodies are
naked masses of protoplasm, of ever-changing shape during life. The
organisms move and capture food by means of temporary extensions
of their bodies (pseudopodia), and have few other noticeable organs —
merely nuclei and cavities (vacuoles) containing ingested food. The
organs known as contractile (or pulsating) vacuoles (or vesicles) —
typically present in free-living forms — are invariably lacking. The
protoplasm is differentiated, as in other animals, into nuclear and
cytoplasmic parts ; the nuclear apparatus differing in different genera
and sometimes attaining some structural complexity, the cytoplasm
being as a rule but little differentiated. The latter can always, however,
be seen to consist of two parts — an inner and granular endoplasm
forming the bulk of the animal, and a thin outer layer of clear

20 THE INTESTINAL PROTOZOA OF MAN

ectoplasm. These are the free forms of the organisms, which live
inside the body of man, where they multiply by simple fission into
two.

The encysted forms are derived from the free forms by the simple
process of rounding off, eliminating all food, and secreting a delicate
and transparent surrounding capsule or cyst wall. Inside the cyst
other changes take place — especially nuclear multiplication, and the
laying up of reserve food material — so that the fully-formed cysts
often differ strikingly from the active amoebae. When fully formed,
the cysts pass out of the body with the stools, and then remain in
a resting condition for some time. If they are neither dried nor
heated they can live outside the body for days or even weeks, but
they undergo no further development unless they happen to be
swallowed by a human being. They then pass intact through the
stomach and into the small intestine, where they hatch and liberate
their contained amoebae. These then pass on with the gut con-
tents until they reach their proper place in the bowel — usually the
large intestine — where they settle down and begin their entozoic life
anew.

No conjugation or sexual process has yet been proved to occur
in the life-cycle of any of the amoebae of man.

Owing to the apparent paucity of structures present in amoebae,
the distinction of the various genera and species is often by no means
easy. The most important structural characters are those supplied
by the nuclear apparatus and the cysts. By means of these it is
possible to distinguish the four genera and five species found in the
human bowel with certainty. It will be most convenient, however,
to describe each species first, and give a key to the genera and species
— based on the nuclear and other characters — later, when the terms
employed and the structures to which they are applied, are familiar
to the reader. We shall therefore begin by describing each species
separately, and will summarize the descriptions in tabular form
afterwards (see p. 39).*

* It should be noted here that throughout this chapter we follow the nomen-
clature and descriptions given elsewhere by one of us (Dobell, 1919a) : and in many
cases we give, without discussion, the conclusions there reached. The reader desirous
of further details is referred to that work. A synopsis of the genera and their chief
synonyms will be found on p. 38 infra.

THE INTESTINAL AMOEBAE OF MAN 21

(i) Entamoeba histolytica Schaudinn, 1903.

Chief synonyms :

"Amoeba coli " Losch, 1875.

"Amoeba dysenteriae " Councilman & Lafleur, 189 1.

"Amoeba coli felis" Quincke & Roos, 1893.

Entamoeba dysenteriae (Counc. & Lafl.) Craig, 1905.

Entamoeba tetragena (Viereck) Hartmann, 1908.

Entamoeba mimita Elmassian, 1909.

Loschia (Viereckia) tetragena Chatton & Lalung-Bonnaire, 191 2.

Entamoeba hartmanni Prowazek, 1912.

Entamoeba brasiliensis Aragao, 1912 (pro parte).

Loschia histolytica (Schaudinn) Mathis, 1913.

Entamoeba mimitissima Brug, 1917.

Entamoeba tennis Kuenen & Swellengrebel, 19 17.

Entamoeba histolytica, the " Dysentery Amoeba," was discovered
in Russia by Losch (1875), in the stools of a patient suffering from
dysentery. In the period of nearly half a century which has since
elapsed, it has been studied and described by a large number of
workers : and, as a result, it is now the most fully investigated and
best known of the species living in man.

The active amoeboid FORMS of this parasite (see Frontispiece, and
PI. II, fig. 1) usually measure 20 fj, to 30 fi in diameter when rounded
and at rest. Their endoplasm is colourless, finely granular, and uniform
in appearance : their ectoplasm clear and well developed.

The single nucleus is a delicate vesicle, inconspicuous or invisible
during life. When carefully fixed and stained, it is seen (PI. II, fig. 1)
to have the following structure. The nuclear membrane, which is very
thin, and achromatic, is lined internally with a layer of fine chromatin
granules — usually in contact with one another. They are usually of
nearly equal size, so that the nucleus appears in optical section as a
finely beaded ring. At the centre of the nucleus there is a small
structure, the karyosome, which consists of two parts — an inner granule
or tiny sphere of chromatin, surrounded by a clear achromatic zone.
In the stained nucleus an achromatic network, free from chromatin
granules, fills up the space between the karyosome and the peripheral
layer of beads. The nucleus as a whole usually measures from 4^ to
7 fx in diameter — according to the size of the organism. The chromatic

22 THE INTESTINAL PROTOZOA OF MAN

part of the karyosome has a diameter of about 0*5 fi or slightly more,
but seldom attains 1 yx.

The mode of nutrition is peculiar in this species, being mainly by
absorption and not by ingestion of solid food as in the more familiar
free-living amoebae. Solid food is, however, at times ingested : but
such food is also of a peculiar character. It consists entirely of red
blood corpuscles and, more rarely, fragments of tissue-cells of the host.
Red corpuscles are sometimes seen in large numbers, in various stages
of digestion, in the endoplasm — more than a score being sometimes
distinguishable : and these inclusions give the organism a very charac-
teristic appearance (see Frontispiece). Bacteria and other particles in
the host's faeces are probably never ingested by normal individuals.

The movements of this parasite are also very characteristic. A
normal individual, just removed from its host, and examined in a
suitable medium and under favourable conditions of temperature, dis-
plays astonishing activity. It flows, almost in a straight line, across
the field of the microscope — in an extended form which suggests a slug
moving at express speed. In this condition the anterior end consists
of a single large pseudopodium, advancing so rapidly that no sharp line
can be seen separating the ectoplasm from the endoplasm. The red
corpuscles contained within such an organism flow about and roll
round one another with every movement, as though the protoplasm
were a mobile liquid. This rapid locomotion seldom persists for more
than a very short time outside the body. The animal soon ceases to
progress, and becomes more or less sessile. In this condition it usually
continues to undergo pronounced changes of shape, accompanied by
the emission of a few large, blunt, and blade-like pseudopodia. These
pseudopodia are perfectly hyaline and highly refringent, and are com-
posed entirely of ectoplasm — a fairly sharp line of demarcation being
visible between their clear protoplasm and the granular endoplasm.
(Cf. PI. I.) Movements of this type may continue for hours, before
the animal finally rounds up, ceases to move, and dies. No similar
movement is performed under the microscope by any of the other
intestinal amoebae of man.

Reproduction is effected by simple fission, which probably takes
place as a rule in the tissues of the host. The process is illustrated in
PI. II, figs. 2 — 7. The nucleus first divides, by a peculiar method,
forming first a spindle (figs. 2, 3), then a dumb-bell figure (figs. 4, 5),

THE INTESTINAL AMOEBAE OF MAN 23

and finally constricting into two (fig. 6). Fission of the cytoplasm
then follows, resulting in the formation — after the daughter nuclei have
undergone their reconstruction — of two daughter amoebae (fig. 7)
exactly like their parent and equal to one another in size.*

Encystation, which takes place in the gut of the host, is accom-
plished in the following manner. The active forms pass from the
tissues into the lumen of the gut, and there undergo one or more
divisions, leading to a decrease in size — the size eventually attained by
the daughter amoebae being proportional to the size of the cysts which
they are about to form. At the same time they get rid of the red
corpuscles or other food fragments which they may contain. As a
result, peculiar small amoebae, with very clear protoplasm, are formed
(PI. II, figs. 8, 9). These are known as the PRECYSTIC FORMS of
the parasite, and were described originally by Elmassian (1909) as a
distinct species — E. minuta. They are, in consequence, still sometimes
known as " minuta " forms — to distinguish them from the large active
"histolytica" forms. The precystic amoeba is directly converted into
a cyst by the simple process of rounding up into a small ball of
protoplasm, and secreting a delicate and transparent capsule or cyst
wall round itself.

The CYSTS of E. histolytica (PI. II, figs. 10 — 16) are usually round or
slightly ovoid structures measuring as a rule anything from about 7 /a
to about 15 //. in diameter, though larger and smaller specimens may
be found (vide infra). They were discovered by Quincke and Roos
(1893) ; and rediscovered later by Huber (1903), Viereck (1907), Hart-
mann (1908), and Elmassian (1909), who mistook them for those of
other species.f Schaudinn (1903), on the other hand, entirely over-
looked them. Their development has now been studied by many
workers — the first correct account having been given by Walker (191 1).

When first formed, the cyst (PI. II, fig. 10, and PI. VIII, fig. A)
contains a single nucleus, like that of the precystic amoeba. Its diameter
measures about one third of that of the whole cyst. The wall of the
cyst is thin, colourless, and uniform, and in a cyst of medium size
has a thickness of about 0*5 /x. In addition to the nucleus, the cyst

* For a fuller account of the division of this species see Dobell (1919 a), p. 40 et seq.
Division was probably first observed inii. histolytica by Harris (1894).

t Viereck (1907) regarded them as belonging to a variety of E. coli, and named
this supposed variety tetragena. Hartmann (1908) called them E. africatta, and
Elmassian (1909) E. minuta.

24 THE INTESTINAL PROTOZOA OF MAN

typically contains two other structures — chromatoid bodies and
glycogen vacuoles. The former — sometimes called " chromidial "
(Schaudinn) or "crystalloid" bodies (Chatton) — are highly refringent
rods or masses (PL VIII, fig. A1) of a substance which stains deeply
with chromatin stains (PI. II, figs. 10 — 12, etc.). They are variable in
shape and size (cf. figs.), and are sometimes absent. Occasionally they
are present in the precystic amoebae, before they form their cyst walls ;
but as a rule they first make their appearance within the cyst.*

The glycogen vacuole appears in the living cyst (PI. VIII, fig. A1)
as a faint clear area : but when the cyst is placed in iodine solution,
it stains as a reddish brown patch, with an indistinct outline (PI. VIII,
fig. A2). As judged by these appearances, the glycogen is not abundant
in the cysts of this species. Sometimes more than one glycogen vacuole
is present (cf. fig. B2, PI. VIII).

The development of the cyst is very simple, and consists merely in
an increase in the number of nuclei. The originally single nucleus
(PL II, fig. 10) divides into two (fig. 11), and each daughter nucleus
again divides so that ultimately four nuclei are present (fig. 12). With
increase in their number, the nuclei undergo a steady reduction in
size — the four nuclei finally present having each a diameter of approxi-
mately one sixth of that of the whole cyst. The resting nuclei at all
stages are like those in the full-grown amoebae; but they frequently
show a slight concentration of the chromatin granules at one point on
the periphery, so that the nuclear " ring " — in optical section — has a
crescentic thickening on one side (cf. fig. C3, PL VIII).

Mature cysts of this species are therefore 4-nucleate, and typically
contain chromatoid bodies and a small amount of glycogen (figs. C, C2,
C3, E1, E2, E3, PL VIII). In this condition they leave the body. Out-
side they undergo no further development, but if kept in suitably damp
faeces or water for some time, it can be seen that the chromatoid
bodies and glycogen gradually disappear — both being used up, appa-
rently, as reserve food material.

E. histolytica is a species which has a number of distinct RACES,

* Dehorne (1919) has recently described "crystalloids" in the adult amoebae
present in liver-abscess pus. We have also observed these, but regard them as an
abnormality— since the amoebae do not encyst in this situation. It may be noted that
the figures of Dehorne depict degenerate amoebae (as shown by their nuclei), and
that the "crystalloids" in them resemble crystals rather than chromatoids in many-
cases ( ? Charcot-Leyden or haematoidin crystals).

THE INTESTINAL AMOEBAE OF MAN 25

distinguishable by the size of their cysts. The diameter of the cysts
formed by a given race is variable, but the average diameter constant :
and races have now been shown to exist whose cysts measure from
6,8//- to 15*0 fx in mean diameter. The commonest races are those
with cysts averaging 7-9/4 or about 11*5 fi to 13*5 ft. Examples of such
races are shown in PI. II, figs. 10-16 (3 races), and are strikingly com-
pared in PI. Ill, fig. 28. (See description on Plate.) So far as is known
at present, the races differing in the sizes of their cysts differ from one
another in no other character — either morphological or physiological.
Such races were first described by Wenyon and O'Connor (1917), and
have been investigated in detail by Dobell and Jepps (1918).* The
races with the smallest-sized cysts have been erroneously described
and named as distinct species by several workers — e.g., by Prowazek
(1912*7) who called them " E. hartmanni," Kuenen and Swellengrebel
(1917) who called them " E. tenuis," and Brug (1917*1) who called them
" E. mimitissima."

If the ripe cysts — belonging to any race — are swallowed by a human
being, they probably pass intact through the stomach : but on reaching
the small intestine they hatch, and liberate their contents. The details
of this process require further study : but there is some evidence that
each cyst liberates a single 4-nucleate amoeba in the small intestine,
and that its division into four small uninucleate amoebae — which
establish the new infection — takes place subsequently (Chatton, 19 176).
The cyst walls are insoluble in gastric juice, but soluble in trypsin
(Ujihara, 1914) ; and it is certain that the cysts never hatch in the
colon, where they are formed, or outside the body. Whatever the
early stages of development may be, it is clear that the young amoebae
from the cysts must pass on rapidly into the large bowel, where they
soon establish themselves in or on the mucous membrane. They
then grow — probably directly — into the large active forms previously
described.

This completes the life-history, as far as it is known, of E. histolytica.
Conjugation and "autogamy," described by some workers — most
recently by Yoshida (1920) — have not yet been proved to occur, and

* The existence of such races is denied by Mathis and Mercier (1917), and also
apparently, by Noller (1921)— but owing, as it would appear, to inadequate knowledge
of the facts. On the other hand, Smith (1918, 1919) admits that such races exist,
but considers that there is clear evidence of the existence of only two.

26 THE INTESTINAL PROTOZOA OF MAN

the published descriptions of such phenomena are clearly based upon
misunderstandings of various sorts. If any sexual process occurs, it is
probably in the earliest stages of the life-cycle, which are still imper-
fectly known : but the occurrence of such processes is still purely
hypothetical. " Spore formation," of a peculiar kind, was described
by Schaudinn (1903), but it is now certain that his description was
incorrect.

Degeneration is very frequently seen in both the amoebae and the
cysts passed in human stools, and has been frequently misinterpreted —
degenerate specimens being regarded as new species or normal stages in
development. It is impossible to describe all the degenerative stages
which may be encountered, but the following points may be noted here.
Degeneration in the active amoebae is at first chiefly noticeable in the
nuclear structure. The peripheral chromatin beads become clumped
into a few irregular masses on the internal surface of the nuclear
membrane : the karyosome disintegrates : chromatin granules become
scattered through the clear zone between it and the periphery : and
finally the whole nucleus may break up and disappear. Degeneration of
the cytoplasm is usually marked by vacuolation and bacterial invasion.
In the cysts, similar degeneration of the nuclei occurs, while the
chromatoid bodies disintegrate, the glycogen becomes diffusely distri-
buted through the protoplasm, and the latter becomes progressively
vacuolated and bubbly in appearance. Finally the cyst presents the
appearance of a very thin capsule containing only a few granules.

Abnormal development occurs sometimes, and results in the forma-
tion of more or less monstrous amoebae or cysts. The latter may
contain abnormal numbers of nuclei (3 or 8), and show a variety of
freakish shapes. Cysts containing more than four nuclei are, however,
excessively rare : and for purposes of diagnosis their occurrence may be
ignored.*

Further noteworthy points in the life-history and habits of this
species will be considered in the next chapter. The other species
occurring in man must now be briefly described ; and in these des-
criptions reference will be made chiefly to those characters in which
they differ from E. histolytica.

* Rodenhuis (1919a), among recent workers, has described the finding of a number of
8-nucleate cysts of this species. The proof that they really belong to E. histolytica is,
however, by no means conclusive : and this applies to most of the similar records
previously published.

THE INTESTINAL AMOEBAE OF MAN 27

(2) Entamoeba coli (Grassi) Casagrandi & Barbagallo, 1895.

Chief synonyms :

"Amoebae" Lewis, 1870 ; Cunningham, 1871.

Amoeba coli Grassi, 1879 (nee Losch, 1875).

Amoeba coli mitis } _ . , _ „ Q

V Quincke & Roos, 1093.
Amoeba intestini vulgaris J

Entamoeba hominis Casagrandi & Barbagallo, 1897.

Entamoeba williamsi Prowazek, 191 1.

Entamoeba brasiliensis Aragao, 1912 (pro parte).

Losch ia coli Chatton & Lalung-Bonnaire, 1912.

Entamoeba coli, the large harmless amoeba of the human colon, was
probably first seen by Lewis (1870) and Cunningham (1871) in India.
Since then it has been studied by very many workers. With the
exception of its habits, and certain minor structural differences which
serve to characterize it as a distinct species, this organism closely
resembles E. histolytica — both morphologically and as regards its
life-cycle.

The active adult AMOEBA (PI. I, and PI. II, fig. 17) is usually of
about the same size as the corresponding forms of E. histolytica — i.e.,
about 20 /x to 30 fi in diameter, when rounded. Its nucleus is also
similar, but is distinguishable— in normal, well-stained specimens— by
the following structural characters (cf. fig. 17, PI. II). It is somewhat
richer in chromatin, the peripheral layer being composed of slightly
larger beads : the chromatic part of the karyosome is slightly larger,
attaining a diameter of 1 fi in large individuals : the karyosome as a
whole is correspondingly larger, and its position in the nucleus is
almost always eccentric — not central, as in E. histolytica : furthermore,
granules of chromatin are usually present in the comparatively clear
zone between the karyosome and the peripheral layer of chromatin.
(Compare the nuclei in figs. 1 and 17, PI. II.)

In its mode of nutrition E. coli is radically different from E. histo-
lytica, for it is a commensal organism feeding upon the micro-organisms
and faecal fragments present in its host's colon. This difference is
reflected in the constitution of its cytoplasm, which is bulky and
granular and usually contains numerous food vacuoles charged with
bacteria, yeasts, starch grains, vegetable debris, and other particles

28 THE INTESTINAL PROTOZOA OF MAN

derived from its host's faeces. (Cf. PI. II, fig. 17, and PL I.) The
vacuoles never contain red blood-corpuscles, however, or fragments of
the host's tissues. In addition to the food vacuoles, others containing
liquid are often seen. They have pointed ends, and are irregularly
spindle-shaped, resembling gashes in the protoplasm. (Two are shown
in the specimen figured on PI. I.)

E. coli appears to be a voracious feeder, and it ingests not only food
particles but even crystals, sand-grains, and other insoluble structures.
It even ingests the cysts — and more rarely the active forms — of other
protozoa present in its host's intestine. Individuals have been seen
which have thus engulfed cysts of E. histolytica (Wenyon and O'Connor,
1917 ; O'Connor, 1919), Giardia (Grassi, 1888; O'Connor, 1919),
Isospora (O'Connor, 1919), and free forms of Giardia and Trichomonas
(Grassi, Casagrandi and Barbagallo, O'Connor, etc.). Ingested cysts or
amoebae have also been noted recently by Cragg (1919), who appears to
regard them — for reasons which are not clear — as playing a part in some
kind of " conjugation."

The method of multiplication in this species is probably, like that
of E. histolytica, by simple fission into two. All the stages have not yet,
however, been studied. A process of multiple fission, or " schizogony,"
has also been described (Schaudinn, 1903 ; Mathis and Mercier 1917a ;
and others) ; but the evidence is far from conclusive, and it appears
probable that no such process really occurs in this species.

When freshly removed from its host, and examined under the most
favourable conditions, E. coli sometimes displays considerable activity.
As a rule, however, it appears extremely sluggish, and shows little
locomotory movement — its motions consisting chiefly in changes of
shape, without evident progression. At such times it has a character-
istic appearance (see figure on PI. I). No sharp line of demarcation
separates the ectoplasm from the endoplasm; and the formation of large,
clear, blade-like pseudopodia — so characteristic of E. histolytica — is never
seen. (Compare figs, on PI. I — Frontispiece.)

It should be noted here that degenerate, motionless, or dead
specimens of E. coli are frequently indistinguishable from similarly
abnormal forms of E. histolytica. The degenerate nuclei are often closely
similar, and determination of the species from this character is therefore
possible only when one is dealing with perfect specimens. Again,
bacteria are so frequently present in dead and degenerate individuals of

THE INTESTINAL AMOEBAE OF MAN 29

E. histolytica that their presence in the cytoplasm is a character which
must be cautiously considered when attempting to identify the species
of a given specimen.

Cyst formation is preceded, as in E. histolytica, by the formation of
PRECYSTIC AMOEBAE of smaller size than the adult forms (PI. II, fig. 18).
They are sluggish, free from all food inclusions, and contain relatively
large nuclei. Their size is proportional to the size of the cysts which
they are about to form. Precystic amoebae of this species are often
almost or quite indistinguishable from those of E. histolytica ; and
degenerate specimens of either species can never, in practice, be identi-
fied with certainty, and are thus a constant source of difficulty in
determination and of error in diagnosis.

The CYSTS of E. coli, which were first studied by Cunningham (1871),
are similar to those of E. histolytica ; but they usually are larger, have
slightly thicker walls, and always contain, when mature, 8 nuclei.
Development occurs in exactly the same way as in E. histolytica —
namely, by a simple process of successive nuclear divisions, accom-
panied by decrease in the size of the nuclei as they increase in number.
The cyst is thus at first uninucleate (PI. II, fig. 19) and then succes-
sively 2-nucleate, 4-nucleate, and 8-nucleate (PI. II, figs. 20-22). The
resting nuclei, at all stages, are structurally similar to those in the full-
grown amoebae. The 4-nucleate stage is probably of short duration, as
it is the one least often seen in the stools ; and when encountered, some
of the nuclei are usually seen undergoing division (cf. figs. M1, M2, M3,
PI. VIII).

Glycogen is almost always present in the cyst at certain stages, and
is relatively abundant. It is formed in the uninucleate stage, and is very
conspicuous in binucleate cysts. When these are placed in iodine
solution, the glycogen appears as a solid mahogany-brown mass, with
a sharply defined outline (see PI. VIII, figs. K2, L2). At the 4-nucleate
stage the glycogen is absent or scanty, and in typical 8-nucleate cysts
it is rarely demonstrable (PI. VIII, figs. M2, N2).

Chromatoid bodies are not conspicuous in E. coli cysts as a rule, but
most cysts contain a few deeply-staining granules or irregular small
bodies (PI. II, fig. 22). At times, however, well- developed chromatoids
are present. They are usually in the form of spicules, splinters, or
filaments — often appearing as sheaves of spicules (PI. II, fig. 25) or more
rarely as coiled threads (PI. II, fig. 24). The cysts with such inclusions

30 THE INTESTINAL PROTOZOA OF MAN

were described by Prowazek (1911) as those of a distinct species — "E.
williamsi." Chromatoids were probably first seen in the cysts of this
species by Grassi (1879a).

Occasionally cysts containing more than 8 nuclei are found in this
species (PI. II, fig. 26). Such supernucleate cysts are probably abnormal
— some or all of the nuclei having undergone an extra division. Cysts
with 16 nuclei {i.e., double the typical number) are commonest : those
with less (10, 12, etc.) or more (up to 20) being rarely seen. Some
authors, but on very inadequate grounds, have regarded these super-
nucleate cysts as normal stages in the life-cycle.

E. coli, like E. histolytica, is a species divisible into numerous RACES
distinguishable by the dimensions of their cysts. Cysts may be found
of any diameter from 10 fi to 30 /u,, or even more; but as a rule they
measure from 15 yu to 20 /m. Matthews (1919) has shown that there are
probably at least four distinct races, the average sizes of whose cysts are
15^, i6'5/t, 187/X, and 217^. In all these races there is, of course,
considerable individual range of size around the mean. Fig. 23 (PI. II)
is a cyst belonging to a strain forming very small cysts, and may be
compared with fig. 22 on the same Plate — from a race with cysts of larger
and more usual size.

The remainder of the life-cycle of E. coli is probably like that of
E. histolytica, but it has been insufficiently studied. It is certain, at all
events, that the ripe cysts undergo no further development, after leaving
the body, unless they happen to be swallowed by a human being : and
it has been experimentally proved that infection is brought about by
swallowing the cysts (Grassi, 1888 ; Calandruccio, 1890 ; Walker and
Sellards, 1913). The cysts probably hatch in the small intestine, and
liberate amoebae which establish themselves later in the colon.

Sexual phenomena have been described in this species, but have not
been proved to occur. Schaudinn (1903) described a process of
" autogamy" in the cyst — based upon a series of errors of observation.
More recently Mathis and Mercier (1916a) have attempted to show that
the cysts of this species are sexually dimorphic : but at present no
good evidence has been adduced for " gamogony " or sexual differentia-
tion of any sort.

THE INTESTINAL AMOEBAE OF MAX 3 1

(3) Endolimax nana (Wenyon & O'Connor) Brug, 1918.
Chief synonyms :

" Small amoeba " Wenyon, 1912.
" Free-living amoebae " James, 19 14 (pro parte).
Amoeba Umax Wenyon, 1916 (nee Dujardin, 1841).
Entamoeba nana Wenyon & O'Connor, 1917.
Endolimax intestinal Is Kuenen & Swellengrebel, 191 7.
Vahlkampfia nana (Wenyon & O'Connor) Brug, 1917.

Endolimax nana, the common small amoeba of the human bowel,
was probably seen by many of the earlier workers ; but it is only
in recent years that its individuality has been correctly recognized.
Owing to its small size, it has often been mistaken for a young form
of one of the larger species ; and because of its nuclear structure, it
was frequently confused with the small species of coprozoic or free-
living amoebae. It was first recognized as a distinct intestinal species
by Wenyon and James, and was first named by Wenyon and O'Connor
in 1917.

Like the preceding species, this organism appears to be quite
harmless to its host. It feeds chiefly upon the small micro-organisms
in the gut-contents, and does not attack the tissues.

E. nana usually measures, when rounded, about 8/z, in diameter —
ranging from about 6^ to 12 jjl. The living organism (see PI. I) is
not as a rule very actively motile, when seen outside the body. It
usually progresses slowly when first observed, and soon shows no
movement save change of shape. Before long it rounds up and dies,
and such rounded and more or less degenerate amoebae are the forms
most commonly seen in the stools.

The most characteristic feature of this species is its nucleus, which
has a structure very different from that seen in the genus Entamoeba.
The nucleus is vesicular, with a delicate membrane, free from chromatin,
and measures from about 1 fju to 3 fi in diameter in fixed and stained
specimens. (See PI. IV, figs. 29 — 32.) All the chromatin is contained in
a relatively large and typically irregular karyosome, which shows great
variation of form in different individuals (cf. figs.). The karyosome
usually consists of one fairly large and eccentrically placed mass,
connected by strands or processes with other smaller masses or granules.
The arrangement of these parts appears to be very variable, and it is

32 THE INTESTINAL PROTOZOA OF MAN

therefore impossible to regard any particular picture as "normal" or
" typical." The types shown in the figures are all common, but by no
means exhibit all the peculiar forms of karyosome seen in this species.
Apart from the karyosome and its connected parts, no other chromatin
structures or granules are visible in the nucleus. It should be specially
noted here that in degenerate nuclei the chromatin is usually clumped
in a single large mass, placed eccentrically at one pole.

The cytoplasm displays few noteworthy features. There is the usual
clear ectoplasm, bordering the finely granular endoplasm, in which
numerous minute food vacuoles containing ingested bacteria are usually
present. Between ectoplasm and endoplasm no sharp line of division
is, as a rule, distinguishable. The pseudopodia are few, blunt, and
thick. (See fig. on PI. I.)

It is probable that E. nana reproduces, like other amoebae, by fission
into two. No complete description of the process, however, has yet
been given ; and dividing individuals are extremely rare in the stools.

This species forms very characteristic cysts. The precystic
amoebae — unlike those of species of Entamoeba — are not noticeably
smaller than the ordinary active forms, from which they differ only in
containing no food inclusions. They form colourless, thin-walled cysts
which are usually oval — not round (PI. IV, figs. 35-37). At first the
cyst is uninucleate (fig. 35) ; and it then becomes, by successive
nuclear divisions, binucleate (fig. 36) and finally quadrinucleate (fig. 37).
Multiplication of the nuclei is accompanied by reduction in their size,
so that the nuclei in the fully-formed cyst are very minute. Apart from
this, the nuclei appear to be structurally identical at all stages of
development. The cysts usually measure 7-9 //, in length.

Glycogen is occasionally, but by no means always, present in the
cysts of this species. When present, it usually appears as a single mass,
staining deeply with iodine. (See PI. VIII, fig. H2.)

Chromatoid bodies are absent from E. nana cysts ; but a few tiny
bright granules are always visible in living cysts (PI. VIII, figs. G', H1, I'),
and these sometimes appear deeply coloured in stained preparations.
From their microchemical reactions they appear to consist of volutin.
In addition to these minute granular inclusions, the cysts rarely contain
granular or filamentar structures, which stain deeply with iron-haema-
toxylin. Their nature is still uncertain (PI. IV, fig. 38).

Supernucleate cysts, containing as many as 8 nuclei, are sometimes

THE INTESTINAL AMOEBAE OF MAN 33

found in this species (PI. IV, fig. 39). They are, however, rare. Their
nuclei are small and display the structure characteristic of the species,
but the cysts themselves are generally of abnormally large size.

It is probable that there are several races of E. nana, distinguish-
able— as in E. coli and E. histolytica — by the dimensions of their cysts :
but up to the present this has not been conclusively demonstrated.

Nothing is yet known of the early stages of development of this
species. Presumably the cysts, when swallowed, hatch in the small
intestine, and liberate small amoebae which establish a new infection.
It is possible that the amoebae live in the small bowel, but the exact
distribution of the organism in the intestine is still uncertain.

E. nana is sometimes parasitized by a minute micro-organism
belonging to the genus Sphaerita Dangeard. The infected amoebae are
very conspicuous, owing to the presence of the spore-morulae of the
parasites in their cytoplasm (PI. IV, figs. 33, 34). The spores appear as
minute bright spheres, in the fresh state, but are usually coloured deeply
in stained preparations.

(4) Iodamoeba butschlii (Prowazek) Dobell, 1 9 19.
Chief synonyms :

Entamoeba butschlii Prowazek, 1912.

" Spherical bodies " Wenyon, 1915. [Cysts.]

" Iodine cysts" or " I. cysts " Wenyon, 1916. [Cysts.]

" Pseudolimax " Kuenen & Swellengrebel, 1917.

Endolimax williamsi Brug, 1919 (nee Prowazek, 191 1).

Endamoeba nana Kofoid, Kornhauser, & Swezy, 1919 {pro parte).

" Endolimax pileonucleatus Brug" Rodenhuis, 1919.

This species,* which has only recently become known, differs con-
siderably in its nuclear structure and in the form of its cysts from those
previously described. Its cysts were described under the name of
" Iodine cysts" or "I. cysts" by Wenyon (1916), and became somewhat
widely known by this name before their true nature was ascertained.

The active AMOEBAE of /. butschlii (see fig. on PI. I) resemble, when

* The species has recently been discussed — especially as regards its nomenclature
— at great length by Noller (1921) and Brug (1921 a). Their views do not lead me to
suppose that what I have elsewhere written on the subject (1919 a) is in any way
incorrect. Some of their opinions, on the other hand, are obviously untenable — e.g.,
Brug's opinion that the organism may be called Endolimax by anyone who so
desires. (C. D.)

34 THE INTESTINAL PROTOZOA OF MAN

alive, small specimens of E. cold. They are usually about 9-13 //, in
diameter when rounded, but may measure anything from about 5 ft to
20 jx. They are generally but slightly motile outside the body, their
movements being similar to those of E. coli. As a rule they degenerate
and die very quickly after leaving the intestine.

The nuclear structure serves to distinguish this species with certainty,
but it can be seen in perfectly fresh and very carefully fixed and stained
specimens only. The nucleus (PI. IV, figs. 43, 44) is a small vesicle with
a diameter of about 2-3*5 f1 • ^s membrane is distinct and easily stained,
and is usually achromatic though occasionally showing a very few
minute darkly staining granules imbedded in it. The chromatin of the
nucleus is, however, almost entirely contained in a single large central
karyosome (cf. fig. 43), which is usually spherical, and intensely and
homogeneously stained, but occasionally shows a paler centre (fig. 43).
Between the karyosome and the nuclear membrane there is a " clear
zone," which is almost filled with a single layer of small granules
(cf. fig. 43). These granules do not stain as intensely as the karyosome
with chromatin stains. On the other hand, they are readily coloured by
plasma stains — such as eosin. Very careful fixation and staining, and
a high magnification with well-adjusted light, are necessary to demon-
strate their presence.

The cytoplasm displays few peculiarities. It is finely granular and
homogeneous in appearance, and usually contains numerous food
vacuoles charged with the minute bacteria upon which this amoeba
feeds.

/. butschlii probably multiplies in the bowel by simple fission, but the
process has not yet been properly described. Dividing specimens are
extremely rare in the stools. A few stages have recently been figured
by Rodenhuis (1919).

The cysts of this species are very characteristic, and formed in the
following way. precystic amoebae are first formed, differing in
appearance from the ordinary active forms (PI. IV, fig. 45). They are
entirely devoid of food inclusions, and very sluggish. They possess,
when alive, clear glassy-white protoplasm and a relatively large nucleus.
When stained, it can be seen that the increase in the size of the nucleus
is due chiefly to the increase in the number of granules lying in the
clear zone between the karyosome and the nuclear membrane. (Cf. figs.
43 and 45.)

THE INTESTINAL AMOEBAE OF MAN

35

The precystic amoebae become more or less rounded, and then
secrete their cyst walls. When fully formed, these are relatively thick, but
colourless, as in the other species already described. Cyst formation is
accompanied by important changes in the protoplasm. In the early
stages, a patch of glycogen makes its appearance in the cytoplasm —
staining at first palely and diffusely with iodine, but later becoming
large, dense, and sharply contoured, and staining a deep mahogany
brown with this reagent. (See PI. VIII, fig. F2.) In addition to this
glycogen mass, other inclusions also make their appearance in the cyst.
These are a number of small and brightly refractile granules (PI. VIII,
fig. F1), which give some of the staining reactions of volutin. The
glycogen mass and the volutin granules are the two typical cystic
inclusions in this species — no chromatoid bodies being formed. The
glycogen is sometimes absent, while occasionally two or even three
separate masses may be seen.

In the mature cyst there is only one nucleus, but it differs in struc-
ture from that seen in the active form and the precystic amoeba. The
granules in the " clear zone" become massed at one pole, whilst the
karyosome is no longer central but closely pressed against the nuclear
membrane at the opposite pole. (See PI. IV, figs. 46 — 48.) It is usually
large, and stains deeply ; and the nucleus thus has the appearance of a
signet ring — especially when the cyst is examined in iodine solution
PI. VIII, fig. F2).

The precystic amoebae and cysts of this species are not smaller than
the active forms. The cysts, when fully formed, usually measure about
9-12 fi in diameter; but they are often difficult to measure, as they are
subject to great variation in shape. Instead of being spherical, they
are frequently more or less lobed or irregular (PL IV, fig. 48).

Living cysts appear white and hyaline, except for the dull area
occupied by the glycogen mass, and the bright beads of volutin (PI. VIII,
fig. F1). In iodine, the glycogen mass is their most striking feature
(PI. VIII, fig. F2), but the nucleus also becomes visible. When fixed
and stained, by ordinary methods, the nucleus shows its finer structure,
the volutin grains are more or less distinctly visible, and the
glycogen — being soluble in water — has disappeared, and its place is
represented by a large vacuole (PI. VIII, fig. F3, and PI. IV, figs. 47, 48).

Binucleate cysts are rarely encountered in this species ; and they
are probably to be regarded — like the supernucleate cysts of the other

36 THE INTESTINAL PROTOZOA OF MAN

species — as abnormalities. It is possible that this species is also
divisible into a number of races distinguishable by the sizes of their
cysts, but this has not yet been demonstrated. The cysts are so com-
monly irregular in outline that it is by no means easy to determine their
diameters with accuracy.

Outside the body the cysts undergo no further changes, save that
the glycogen — as in the other species — gradually disappears. When
the cysts are swallowed, they probably hatch in the small intestine and
liberate their contents as a single uninucleate amoeba which establishes
the new infection. But the process has never been studied.

The cysts of this species have frequently been mistaken for those
of other organisms. Flu (19 18), for example, regarded them as
degenerate cysts of E. histolytica, whilst Brug (1919) has referred them
to "£. williamsi" — a name proposed by Prowazek (1911) for an
organism which was chiefly, in reality, E. cold. ,More recently, Kofoid,
Kornhauser, and Swezy (1919) have regarded /. biitschlii as a large
race of E. nana — a view which is undoubtedly untenable. /. biitschlii
is certainly a well characterized species, belonging to a genus which
must be regarded — owing to its nuclear structure and cysts — as quite
distinct from that of any of the other intestinal amoebae of man.*

(5) DlENTAMOEBA FRAGILIS JeppS & Dobell, 1918.

This is the smallest, and apparently the least common, of the
amoebae of the human intestine. It was probably discovered by
Wenyon in 1909, but rediscovered and first described by Jepps and
Dobell (1918).

The active FORMS (PI. IV, figs. 40, 41) measure, when rounded,
from 3"5/a to 12 //, in diameter; their usual size being about 8-9 fi.
They are actively motile, and show a distinct demarcation between
their ectoplasm and endoplasm. The latter is finely granular, and
usually contains numerous food vacuoles filled with tiny bacteria,
upon which the organism feeds. When moving actively the amoeba
has a snail-like appearance, its clear leaf-like pseudopods being in

* In a recent note it is stated by Noiler (1921) that /. biitschlii occurs in the pig.
No evidence is adduced, however, to prove that the similar amoebae found in pigs are
identical with those in man. The proposal recently made by Rodenhuis (1919) to
change the name of the organism to " Endolimax fiileonncleatus Brug " — an impossible
combination, in any case — is contrary to the Rules of Nomenclature, and needs no
discussion.

THE INTESTINAL AMOEBAE OF MAN 37

advance and its endoplasm massed in a somewhat concentrated " bod}7 "
posteriorly (see fig. on PI. I).

The most characteristic feature of this amoeba is its nuclear
system. Unlike the other amoebae, already described, it is typically
a binucleate organism (PL IV, figs. 40, 41). Its two nuclei are identical
in structure, and may be placed either close together or more or less
widely separated in the endoplasm. Their size is proportional to that
of the whole animal, and ranges from o*8 p in diameter in very small
up to 2"3 /j, in very large individuals. As a general rule, each nucleus
measures about 2 p in stained specimens. The nuclei are spherical
and vesicular, with extremely delicate limiting membranes. The
chromatin is in the form of granules, of variable size, massed together
in the centre of the nucleus so as to form a fairly large karyosome
(PL IV, figs. 40-42). Between the karyosome and the membrane there
is a clear zone, free from granules but crossed at intervals by extremely
fine radiating strands of linin. Tiny granules can sometimes be
seen in the nuclear membrane at the points where the linin threads
join it.

About 80 per cent, of the amoebae of this species are binucleate —
as just described. The remainder — mostly small forms — are uni-
nucleate (fig. 42). Their nuclei are exactly like those of the binucleate
forms in structure.

The amoebae of this species sometimes display peculiar fissure-like
vacuoles in their cytoplasm (cf. PL IV, fig. 40). Outside the body
they degenerate very rapidly, and in doing so become filled with much
larger vacuoles, which give them a peculiar bubbly appearance.
The vacuoles ultimately coalesce, and the whole organism then
becomes a mere ring of protoplasm — in optical section — surrounding
a clear central space. Such degenerate specimens can easily be mis-
taken for Blastocystis.

It is probable that this species reproduces by fission into two, but
the details of the process require further investigation. It seems
probable — from the occurrence of uninucleate individuals — that each
binucleate specimen, when fully grown, divides, by simple fission of
the cytoplasm, into two uninucleate individuals : and these young
uninucleate forms then, during their growth, undergo a nuclear
division so as to become binucleate once more. This interpretation
is supported by the fact that organisms containing a single dividing

38 THE INTESTINAL PROTOZOA OF MAN

nucleus have been seen, but no specimens in which both nuclei are
dividing. If this supposition is correct, then Dientamoeba differs in
this respect from the other known binucleate rhizopods.

In spite of very careful search, no cysts of this species have ever
been discovered. The rest of its life-cycle is therefore still in doubt,
and its manner of conveyance from host to host is unknown. The
organism is so delicate, and perishes so rapidly outside the body,
that direct infection with active forms appears to be excluded.

It is not certain whether this amoeba inhabits the large intestine
or the small, or possibly both. At present, from the evidence avail-
able, it seems probable that it lives in the colon. It appears to be
a quite harmless commensal, and is thus more interesting to the
zoologist than to the medical practitioner.

Determination of the Genera and Species.

Now that the amoebae of the human bowel have been briefly
described, and their characters duly noted, we may give a key for the
determination of the five species and their respective genera. This
key will also serve to summarize, to some extent, what has been said
in the preceding part of the present chapter. The species have been
referred to four different genera, and we therefore give first a short
summary of the synonymy of these genera for the guidance of the
student.

Genera and Synonyms.
Genus i. Entamoeba Casagrandi & Barbagallo, 1895.
Syn :

Poneramoeba Ltihe, 1908.

Loschia )

\ Chatton & Lalung-Bonnaire, 1912.
Viereckia j

Proctamoeba Alexeieff, 1912.

Amoeba (pro parte), Endamoeba, Entameba, Endameba, etc.

auctorum variorum [non Endamoeba Leidy, 1879].

Genus 2. Endolimax Kuenen & Swellengrebel, 1917.
Syn :

Entamoeba (pro parte) Wenyon & O'Connor, 1917, et aliorum.
Vahlkampfia Craig, 1913, et aliorum.

THE INTESTINAL AMOEBAE OF MAN

39

Genus 3. Iodamoeba Dobell, 1919.
Syn :

Entamoeba (pro parte) Prowazek, 1912, et aliorum.

Endolimax (pro parte) Brug, 1919.
Genus 4. Dientamoeba Jepps & Dobell, 1918.

Key to Genera and Species.

1. (a) One nucleus present in active amoeba ...
(b) Two nuclei present ...

2. (a) Nucleus with small spherical karyosome

and peripheral layer of fine chromatin
beads

(b) Nucleus with large irregular eccentric

karyosome, and no peripheral chroma-
tin granules

(c) Nucleus with large central spherical karyo-

some, surrounded by a layer of achro-
matic granules

3. (a) Ripe cyst 4-nucleate ; glycogen diffuse;

large chromatoids generally present ...

(b) Ripe cyst 8-nucleate ; glycogen dense, in

early stages only ; large chromatoids

occasionally present, but often absent

4. Ripe cyst 4-nucleate ; glycogen rarely present ;

chromatoids absent

5. Ripe cyst i-nucleate ; glycogen in a dense

mass ; no chromatoids

6. Nuclei with central granular karyosomes, and

no peripheral chromatin. [Cysts un-
known] ...

Genus Dientamoeba 6.

Genus Entamoeba 3.

Genus Endolimax 4.

Genus Iodamoeba 5.
. . E. histolytica.

E. coli.

E. nana.

I. bittschlii.

D. fragilis.

* This key is not intended, of course, as a complete diagnosis or description of the
species and genera. It is founded merely upon the most striking and easily recogniz-
able differential characters of the amoebae concerned.

4o

CHAPTER III.
AMOEBIASIS.

The term "Amoebiasis" was invented by Musgrave and Clegg (1904)*
to denote a condition of "infection with amebas." We use it here in
its widest sense, and define it as the state of being infected with amoebae.
In the present context, of course, we use the term with special applica-
tion to man : and as man harbours at least five species of intestinal
amoebae, it will be seen that it may cover a variety of conditions. In
practice, however, it is convenient to restrict the meaning of the word,
and to use it more especially to denote infection with Entamoeba
histolytica.

The reason for this is obvious. E. histolytica is a facultatively
pathogenic tissue-parasite, and the state of being infected with it may
be a diseased condition : at all events, it may be, and often is, a condi-
tion which is clinically recognizable. Infection with the other amoebae,
which are probably all quite harmless, is not recognizable by any
symptoms : and consequently a special word to denote infection with
these species is rarely required.

Accordingly, the present chapter will treat especially of Amoebiasis
in the restricted sense — the infection of Man with Entamoeba histolytica,
and the consequences which this state may entail. It is impossible to
deal with this large subject in detail in a work of the present scope,
and we shall therefore confine our attention to the salient points.

Pathogenesis and Aetiology. — The relation of E. histolytica to
its host, and to the diseases which it plays a part in producing, may
now be regarded as, in the main, accurately determined. We owe this
chiefly to the work of E. L. Walker (191 r, 1913), carried out in the
Philippine Islands.

As we have often noted already, E. histolytica is a tissue-parasite. It

* By these authors the word is spelled "Amebiasis" — a spelling which is not
agreeable with English usage.

AMOEBIASIS 41

lives upon living tissue only, and apparently cannot nourish itself in
any other way. In the large intestine of man,* which is its usual home,
it lives at the expense of the tissues forming the wall of the gut. The
amoebae apply themselves to the mucous membrane, and secrete a
powerfully cytolytic ferment which destroys the cells. The cytolvsed
tissue is then absorbed by the amoebae, and forms their chief food
supply. More rarely they ingest solid fragments of tissue and blood
corpuscles. By this process the lining of the gut is more or less eroded
or ulcerated — the ulceration frequently extending into the submucous
tissue, or even more deeply. It is thus clear that infection with this
parasite must always produce a more or less pathological condition of
the colon of its host.

As a rule, the damage done to the gut wall of the host is compen-
sated by regeneration on the part of the tissues. These are able to
keep pace with the inroads of the amoebae, and a condition of equili-
brium is thus established between host and parasite. Such a state of
equilibrium must be regarded as the "typical" or "normal" con-
dition in E. histolytica infections. Neither host nor parasite suffers
any appreciable harm from the arrangement : neither the one nor
the other can be regarded as being in a definitely "diseased " state.

When the parasites and their host do not live in harmony with one
another — as happens in a certain proportion of cases — pathological
conditions result. These affect both the host and the parasite. In
the case of the host, they are manifested as diseases, which may be
classified into two main groups : (1) Primary or intestinal disorders,
resulting from irritation of the intestine — most frequently manifested
as diarrhoea and intestinal irregularities of various kinds, but leading
in severe cases to a typical form of dysentery (Amoebic Diarrhoea,
Amoebic Dysentery) ; (2) Secondary disorders consequent upon the
wandering of the parasites from their primary site of infection, in the
gut wall, into other organs— especially the liverf — where they give rise
to inflammatory and suppurative conditions (Amoebic Hepatitis ;
Hepatic, Pulmonary, or Cerebral; Abscesses, etc.). All these diseased
conditions of man are harmful to the parasite also ; for they disturb

* E. histolytica was first found in the tissues by Koch in 1883 (see Koch and
Gaffky, 1887) and shortly afterwards by Kartulis.

t E. histolytica was first found in the pus of hepatic abscesses by Kartulis (1887).

X The presence of the parasite in abscesses of the brain was first demonstrated by
Kartulis (1904)-

42 THE INTESTINAL PROTOZOA OF MAN

its food supply, interrupt its normal life-history, and lead to a great
wastage and mortality among the amoebae concerned. In amoebic
dysentery, for example, the amoebae are cast out of the body in large
numbers before they can encyst ; and they consequently perish and
are unable to propagate their species. Similarly, in the case of
secondary infections of the organs, the parasites, though they may
enjoy a brief spell of reproductive activity in their new breeding
ground, are doomed to extinction. They are unable to encyst in any
situation save the gut, and from this site alone can they escape to the
exterior ; but in the internal organs they are cut off from the outside
world with no means of continuing their race. The various amoebic
diseases are thus " diseases " for the parasites as much as for their
hosts.*

It will be clear that E. histolytica is a parasite which is by no means
always recognizably " pathogenic." It always destroys its host's tissue,
but by no means always gives rise to any outward manifestations of
disease.

It should be expressly noted here that a patient suffering from
amoebic dysentery, and passing large numbers of active amoebae in
his bloody stools, is not infective to others. Ingestion of such active
forms cannot, in nature, give rise to a new infection. Outside the
body of man the amoebae are unable to encyst : they always perish
ultimately, and usually very rapidly. But the healthy, or apparently
healthy person, displaying no symptoms of his infection, is capable
of infecting his fellows. In his gut the amoebae complete their normal
development ; and in his stools their ripe cysts pass out — ready to
infect any other individual unfortunate enough to swallow them.

It will be understood that all factors which are conducive to the
formation, preservation, dispersal, ingestion, and development of the
cysts must be regarded as aetiologically important : but our space will
not permit us to do more than mention the subject of general aetiology
of amoebiasis at this point. It will also be evident that, from their
very nature, amoebic diseases can never occur in epidemic form.f

Pathology and Morbid Anatomy. — As already noted, the ripe

* The foregoing paragraph is taken, with slight modification, from Dobell (1919a)
P- 37-

t The " epidemics of amoebic dysentery " which have frequently been recorded
are now known to rest upon mistakes of various sorts.

AMOEBIASIS 43

cysts of E. histolytica pass, when swallowed, unopened and intact
through the stomach and into the duodenum. Here they probably
hatch, and liberate their contained amoebae. The amoebae then pass
on with the contents of the bowel into the great gut, where they
proceed to establish themselves.

i. Primary or Intestinal Amoebiasis. — The large bowel is almost
invariably the site selected for infection. Very rarely is the small
intestine affected, though cases have been recorded by Harris (1898)
and Kuenen (1909). Any part of the large intestine may be attacked,
but the commonest parts are the caecum, flexures, and rectum. The
vermiform appendix is sometimes invaded : and in long-standing cases
the whole of the large bowel may be involved, with the exception
of a small area immediately above the anal sphincter.

Our knowledge of the earliest changes which take place on infection
is based chiefly on the results of experiments upon artificially infected
cats and dogs. In sections of the gut of such animals it can be
seen that the amoebae congregate on the surface of the healthy
mucous membrane, and gradually erode it. They apparently secrete
a ferment which dissolves the epithelial cells, and then come to lie
in the pools of cytolysed tissue so formed. They do not dislodge
the cells mechanically, or burrow actively into the healthy tissues.
Frequently they pass down the crypts of Lieberkuhn and attack the
cells in this situation. At these early stages, when the condition is
one of superficial erosion rather than ulceration, the affected areas of
the mucous membrane appear to the naked eye as minute hyperaemic
patches, owing to the dilatation of the surrounding capillaries.

Later, the initial lesion may give place to a very characteristic form
of ulceration. The amoebae continue to multiply, and, as they do so,
pass more deeply into the tissues. They may be arrested for some
time by the muscularis mucosae, but ultimately they break through
into the submucous layer. Here they continue the destruction of the
tissue, invading it in all directions and so undermining the mucous
membrane. The typical amoebic ulcer is formed in this way. It is
a crater-like cavity in the lining of the bowel, its edges being well
defined and overhanging, and the cavity itself filled with necrotic
tissue which often projects in blackish shreds or tufts into the lumen
of the gut. The amoebae are always found most plentifully at the
periphery and base of the ulcer, in contact with the healthy tissue

44 THE INTESTINAL PROTOZOA OF MAN

in which it is formed. Such ulcers have been aptly compared with
button-holes in the mucous membrane.

The ulcers, when solitary, may measure anything from a fraction
of a millimetre up to several centimetres in diameter. Very frequently
adjacent ulcers coalesce, and so give rise to a confluent type of
ulceration which may involve a very large area. The ulcer may
increase not only laterally in the submucous tissue, but also in depth
— the amoebae finally reaching the muscular layers of the gut wall and
penetrating these as far as the peritoneum. Perforation of the latter
may ultimately occur, giving rise to peritonitis. The ulcers are usually
surrounded by a halo of hyperaemia, but the mucous membrane
between them usually appears healthy. Their edges are frequently
swollen and embossed.

Histologically the following changes are seen. First, histolysis of
all the tissues in contact with the amoebae : then dilatation of the
surrounding capillaries, quickly followed by stasis and thrombosis :
then some round-celled infiltration of the adjacent tissues : finally,
a more or less extensive necrosis. Owing to the destruction of the
capillary vessels, blood corpuscles are usually plentiful in the necrosed
tissue, and free endothelial cells may also often be seen. Polymor-
phonuclear leucocytes are not typically present in or around amoebic
ulcers ; and when present in large numbers they probably indicate a
secondary bacterial infection. The necrosed tissue in the ulcer cavity
is a gelatinous coagulum containing cells in all stages of disintegra-
tion, and usually irregular lumps and globules of a chromatin-staining
substance which is probably derived from the nuclei of the destroyed
cells.

The microscopic appearances of typical amoebic ulcers are depicted
on Plate III, fig. 27, A, B, C. The drawings show a section through an
early ulcer (A) in which the mucous membrane alone is involved ; and
a later ulcer (B) in which the amoebae have penetrated deeply into the
submucous tissue. Fig. 27, C is a more highly magnified portion of the
wall of the ulcer shown at B. It shows the amoebae in contact with
the healthy tissue (below and to the left), and with the cytolysed tissues
surrounding and behind them in the cavity of the ulcer (above and to
the right). Red blood-corpuscles are present in some of the amoebae ;
and in this section (C) also, the deeply stained masses formed by
chromatolysis of the nuclei of the necrosed tissue-cells, are conspicuous.

AM0EBIAS1S 45

In such a typical and uncomplicated amoebic ulcer, the destruction of

the tissue appears to be purely local and mechanical — by erosion and
dissolution — and no obvious reaction on the part of the surrounding
cells is visible.

In experimentally infected animals, amoebae are usually present in
the ulcers and on the surface of the mucous membrane in vast numbers.
In human material, however, they usually appear to be far less numerous.
But there can be little doubt that this is a post mortem phenomenon-
many of the amoebae having died and disintegrated before the tissue
was fixed. Christoffersen (1917) found that when he took special pre-
cautions to preserve the amoebae in situ, they were as abundant in man
as in animal infections — being so tightly packed, indeed, that they
resembled "stones in a pavement."

Job and Hirtzmann (1916) have described an intracellular stage in
the development of E. histolytica in early lesions ; but no other workers
have confirmed their observation, and we believe it to be erroneous.

As the amoebae pass through and destroy the tissues, these re-
generate : and when a particular area has been forsaken by the amoebae,
or when the latter have been removed by specific treatment, more or
less complete healing takes place. Fibrous tissue is formed, and the
mucous membrane and other layers are more or less replaced by this or
by regenerated tissue. The scars of old ulcers have a characteristic
parchment-like appearance, and are often of a greyish colour. Con-
siderable thickening of the wall of the bowel, and, if the ulceration has
been deep, the formation of peritoneal adhesions, are not uncommon
sequelae.

The lymphatic glands which drain the infected areas are generally
enlarged, and show inflammatory changes. In chronic cases they may
become hard and fibrous.

2. Secondary Amoebiasis. — The destruction of the blood-vessels in
the wall of the gut gives the amoebae an opportunity of entering the blood
stream. When they gain access to the radicles of the portal vein they
are sometimes carried by this vessel to the liver ; and after colonizing
this viscus they may pass from it into the general circulation, and so be
borne to other organs — such as the lung or brain — in which they are
capable of establishing themselves. It is in this way that secondary
infections are generally brought about.

Amoebic Hepatitis and Hepatic Abscess. By far the commonest site

46 THE INTESTINAL PROTOZOA OF MAN

of secondary infection is the liver. When the amoebae reach this organ
they attack its substance as they did the intestine : that is to say, they
cytolyse and absorb the cells, and cause a more or less extensive
necrosis. In early stages, this gives rise to hepatitis : but as the amoebae
continue to destroy the tissue they finally cause the formation of an
abscess in the liver. The necrosed tissue accumulates in the abscess
cavity — having no outlet, like that formed in the gut wall — and forms
the peculiar "pus" so characteristic of these lesions. This is not
ordinary pus, but a viscous matter formed of necrosed tissue, containing
cellular debris of all sorts, blood, some bile, and occasional crystals of
haematoidin and cholesterin, with fat droplets. It is generally said to
resemble anchovy sauce, but is far more stringy and viscid. It should
be noted that, in typical uncomplicated cases, the " pus " from amoebic
abscesses is bacteriologically sterile.

An amoebic abscess may be formed in any part of the liver, but its
commonest site is the right lobe. It may be single, but often more than
one is formed ; and several small abscesses may fuse to form a single
large one. At times these abscesses attain a very great size, becoming
larger than a child's head and containing over a gallon of pus. They
tend to enlarge upwards towards the diaphragm or forwards towards the
abdominal wall. Unless evacuated by operation they may ultimately
burst into the lung, or through the abdominal wall. Occasionally they
rupture into the peritoneal cavity, or into the stomach, duodenum, colon,
kidney, or inferior vena cava.

The amoebae are not distributed uniformly through the pus, but lie
chiefly in contact with the healthy tissue at the periphery of the abscess,
which enlarges in a centrifugal direction as a result of their inroads.
Histological changes similar to those seen in the gut may be seen in the
tissues adjacent to the amoebae. No pyogenic membrane is formed
round the abscess ; but old abscesses, after removal or destruction of
the amoebae, may become encapsuled and fibrous, and finally calcified.

A small portion of the wall of an amoebic abscess of the liver is
shown in fig. 27, D (PI. III). Above, the amoebae are seen lying in and
near the healthy liver tissue, with the necrosed tissue ("pus") in the
abscess cavity occupying the lower part of the figure.

Pulmonary Amoebic Abscess. Amoebae may gain access to the lung
either directly, from a liver abscess rupturing into it through the
diaphragm, or indirectly by way of the circulation. An amoebic abscess

AMOEBIASIS 47

of the lung may then be formed, in a similar manner to one in the liver.
The commonest site of such an abscess is the lower lobe of the right
lung.

Lung abscesses often rupture into the air passages, and the pus is
then coughed up. It is reddish and viscid, resembling that of a liver
abscess ; but as a rule it is less copious, since pulmonary abscesses are
rarely of large dimensions.

Cerebral Amoebic Abscess. Very rarely E. histolytica reaches the brain,
and there gives rise to abscesses similar — mutatis mutandis — to those in
the liver or lung. Such abscesses rarely attain a large size, and have
hitherto always proved fatal. The cavity is filled with " pus " — necrosed
brain tissue, etc. — and the amoebae are found, as in a liver abscess,
imbedded in the wall. Only about 50 cases of amoebic abscess of the
brain have been recorded.

Other lesions. Invasion of other organs or tissues by E. histolytica
has been described. Cases of amoebic abscess of the spleen have been
reported by Maxwell (1909) and Rogers (1913). Nasse (1892) reported
the finding of amoebae in phagedaenic ulcers in the skin, and similar
observations have been made more recently by Carini (1912, 1912a),
Dagorn and Heymann (191 2), Heymann and Ricou (1916), and others.
If these observations are correct, it appears probable that E. histolytica
usually infects the skin by way of the wound made for the purpose of
draining a liver abscess. No cases of "natural" infection of the skin
appear to be on record.

E. histolytica has been found occasionally in, the urine. The first
such case was described by Baelz (1883), who named the organisms
"Amoeba urogenitalis." More recently, apparently authentic cases of
"urinary amoebiasis " have been recorded by Fischer (1914a) and
Walton (1915). It is still uncertain how the amoebae enter the urino-
genital system, and what parts of it they are able to infect. Craig (191 1,
p. 233) states that, in a case which he studied, there was a minute fistula
between the bladder and an amoebic ulcer in the colon. A number of
other cases in which " amoebae " have been reported in the urine may
be ignored here, as they appear to rest, for the most part, upon errors of
observation and interpretation.*

Various complications which may follow amoebic infection — such as

* See Dobell (1919a), pp. 125-129.

48 THE INTESTINAL PROTOZOA OF MAN

strictures of the gut, peritonitis and appendicitis, bacterial infections of
divers sorts, pleural and peritoneal adhesions, haemorrhages, etc.— can
be merely mentioned here. Discussion of these conditions would take
us too far afield.

Parasitology of the Lesions. It is most important to remember the
relation of E. histolytica to the lesions which it forms, and the relation of
the secondary infections to the life-cycle of the parasite. We therefore
emphasize these points in terminating the present sketch of the Path-
ology of Amoebiasis.

The normal development of E. histolytica begins with the growth and
multiplication of the active forms of the parasite : it ends with encysta-
tion and exit from the human body. To nourish themselves, grow, and
divide, the active forms must destroy tissue ; and so long as the tissue is
suitable, the amoebae will continue to feed upon it. Having fed for
some time at the expense of the tissue of the gut, the active amoebae
emerge from the ulcers which they have formed, and transform them-
selves into precystic amoebae and finally into cysts. This transformation
usually takes place only in the lumen of the gut. When the active forms
pass more deeply into the body, from their normal site in the gut wall,
they may reach an organ — such as the liver — which will serve them as
food. But in such a situation they are entirely cut off from the outside
world. If they were to encyst in such places it would be of no avail, for
the cysts would have no chance of emerging to infect a fresh host.
They would merely perish in situ. What actually occurs is that the
amoebae in the secondary sites of infection apparently make no attempt
to encyst.* They continue to breed, in the active state, as though they
had been transplanted into a rich culture medium. Their multiplication
goes on until the whole brood is destroyed by the natural defensive
mechanism of the host, by surgical interference, or otherwise.

If this is borne in mind, it is easy to understand how it is that
different clinical conditions may present us with different forms of the
parasite. The ordinary person infected with E. histolytica passes the
cysts of the parasite in his stools. But he has the active forms of
the amoeba in the tissues of his gut wall, and precystic amoebae in the

* Mayer (1919) states that he has found cysts of E. histolytica in amoebic liver
abscesses produced experimentally in two cats. Confirmation of this observation is
required. If it is correct, it must be an unusual form of development in an abnormal
host, and probably has no further significance.

AMOEBIASIS 49

contents of his intestine. If the amoebae irritate his gut sufficiently, he
suffers from diarrhoea (Amoebic Diarrhoea). In his stools we then Find,
therefore, large numbers of precystic amoebae — often mixed with cysts
in all stages of development. If the injury to the intestine is sufficiently
severe, the patient suffers from Amoebic Dysentery. Blood and mucus
escape from the ulcerated areas, carrying with them numerous amoebae
from the damaged tissues. The amoebae now found in the stools are
therefore the large active forms, often containing ingested red corpuscles.
In typical cases of acute dysentery, precystic amoebae and cysts arc-
absent from the stools. All infections of the organs resemble deep ulcers
in the bowel. They contain large tissue-inhabiting amoebae only —
never cysts or precystic forms : and the amoebae must be sought, in all
such cases, in the living tissues forming the walls of the abscesses, and
not in the necrotic tissue (" pus ") contained in them.

The foregoing points are well worthy of remembrance by all to
whom it falls to examine stools or abscess matter for diagnostic
purposes. To diagnose an amoebic disease with certainty it is not
sufficient to prove that the patient is infected with E. histolytica. It
must be proved also that the parasites are present, in the lesions
concerned, in their appropriate stage of development.

Symptomatology. — Clinical signs of infection with E. histolytica
may be present or absent. When present, the infected individual may
be extremely ill : when absent, he may be indistinguishable from normal
healthy persons. All intermediate conditions may be encountered. We
shall briefly note here the most important manifestations of amoebiasis,
beginning with the subject of '■ carriers."

Carriers. The " normal " individual, when he becomes infected with
E. histolytica, displays no definite symptoms of his infection. He lives
in a state of equilibrium with his amoebae : for although they are
continually consuming the lining of his colon, he is able to make good
their depredations by continual regeneration of tissue. This condition
is favourable to the amoebae ; for as long as their host can supply them
with food, and as long as his bowels work in a normal manner, they are
able to pass their lives in comfort. After multiplying in the wall of the
bowel, they pass into its lumen ; and there, if their host does not empty
his bowel too frequently, they have ample time to encyst, and so pass
out — at the proper stage of development — with his stools.

A "healthy" person, infected in this way, is called a carrier of
4

50 THE INTESTINAL PROTOZOA OF MAN

the parasite. As he shows no outward and visible signs of his infection,
he can only be distinguished, when alive, by the cysts of the amoebae
which appear from time to time in his stools. We may define the
carrier, accordingly, as the person who passes cysts of E. histolytica in
his stools, but otherwise exhibits no outward signs of infection.

E. L. Walker (191 1, 191 3), whose work first gave us a precise con-
ception of carriers, has subdivided them into two groups, which he
calls contact and convalescent carriers. The former are persons who
have never suffered any ill effects from their infections : the latter those
who have displayed symptoms of disease, due to their infections, in the
past, but who have since recovered and regained their health without
losing their amoebae. Probably the vast majority of persons who
become infected belong to the class of more or less healthy contact
carriers.

It is important to remember that the term "carrier" is used in a
somewhat peculiar sense in reference to amoebiasis. The term has a
definite and special meaning, which differs from that with which it is
often used by bacteriologists. It should also be remembered that if the
host " carries" anything, it is obviously the amoebae in his gut wall.
He is therefore correctly called a " carrier of E. histolytica," or an
" amoebic carrier" ; but to call him a " cyst-carrier " — as is all too often
done — is obviously absurd.

There can be no doubt that the carrier of E, histolytica, though he
display no symptoms, always has a more or less eroded or ulcerated
gut. He frequently, indeed, has definite ulcers visible to the naked eye
post mortem, as the observations of Musgrave (1910), Bartlett (1917), and
others, have shown.

Carriers have a great practical importance, for they are the people
who are responsible for spreading E. histolytica. They suffer no
inconvenience themselves from their infections, and are therefore not
suspected of harbouring the parasite : but they discharge the cysts —
the only infective forms of the amoeba — with their faeces, and thus
constitute a constant source of infection to others.

At times carriers may show slight symptoms referable to their
infections, such as intestinal irregularities (diarrhoea, constipation,
" indigestion," " debility," etc.) : at other times they may become more
definitely ill, and develop symptoms of dysentery or other amoebic
diseases. This leads us to consider the symptoms of such conditions.

AMOEBIASIS rj

Amoebic Dysentery and Diarrhoea. The commonest intestinal symp-
tom of amoebiasis is diarrhoea — Amoebic Diarrhoea, as we may term
it. This ailment may develop at any time in a carrier of the parasite,
or may manifest itself ab initio — as soon as the amoebae establish them-
selves in the body. It may be more or less severe and of variable
duration. The stools are loose, and contain mucus but no blood — or
very little, only recognizable by the microscope. Large numbers of
precystic forms of E. histolytica are usually present in the stools, and
frequently cysts also ; and an occasional active form from the gut wall
— containing ingested red corpuscles — may also be seen.

If the diarrhoea becomes more severe, it may develop into true
dysentery — Amoebic Dysentery.* This disease may also arise suddenly,
upon first acquiring infection, or may develop from a preceding carrier
condition. It is characterized by bloody mucous stools, containing
numerous active amoebae— many of them containing red corpuscles —
but few or no precystic forms and no cysts. The dysentery^ is generally
accompanied by tenesmus, and as many as thirty or forty stools per
diem may be passed — or the patient may attempt to pass them, for in
severe cases, though there is almost continuous straining, very little is
evacuated. The patient has a tired, anxious, and drawn expression.
His tongue is dry and furred, and his appetite impaired.

Physical examination shows a rigidity of the abdominal wall, and
elicits a tenderness over the colon — often especially over the caecum.
A cord-like thickening at the site of the lesion — due to spasm of the
muscles of the gut wall — is often palpable. The temperature is
generally normal, sometimes subnormal. At times, however, and
especially at the beginning of a first attack, a slight rise of tempera-
ture may be noted. The pulse is at first normal, but if the disease
continues, it becomes increased in frequency and diminished in tension.
The blood count is also usually normal, though the contrary is often
stated. (Cf. Low (1916), Fischer (1919), etc.)

The disease may be acute or chronic — an initial acute attack, if
untreated, frequently subsiding into a most persistent and intractable
form of dysentery. Fatal cases are not unknown, but are less frequent
nowadays owing to better treatment. The patient becomes weaker and
weaker, blackish sloughs appear in his stools — which often have a most

* This term was introduced by Councilman and Lafleur (1891).

52 THE INTESTINAL PROTOZOA OF MAN

offensive smell — and death results from exhaustion. It is often extra-
ordinary how patients will, in spite of the pain and inconvenience,
remain at their work and refuse to go to bed. In fatal cases they
generally become exhausted gradually : but sometimes the patient
collapses suddenly, and his condition may be choleraic in type.
Haemorrhage may also occur, or death may result from peritonitis, due
to perforation of the intestinal wall.

Amoebic dysentery is clinically classifiable into varieties called
fulminating, gangrenous, subacute, etc. — designations which will be self-
explanatory after what has already been said.

Secondary Infections. When the amoebae leave the gut wall and
gain entrance to the liver or other organs, more or less severe symptoms
of disease are always present.

Amoebic Hepatitis and Amoebic Abscess of the Liver may be regarded
as early and late stages respectively of the same process. The symptoms
of both are alike, but differ in intensity. They are chiefly enlargement
and tenderness of the liver, with increased dulness on percussion ;
irregular fever — the temperature often showing a rise at nights ; noc-
turnal sweats, and occasional rigors; and sometimes persistent cough,
nausea or vomiting, and a trace of jaundice. A leucocytosis is generally
present (up to about 20,000 total leucocytes per c.mm., of which 70 to 80
per cent, are polymorphs).

Dysentery may precede or accompany the formation of a hepatic
abscess, but may also be absent. Not uncommonly, the formation of
an abscess appears to arrest an attack of dysentery, or diminish its
intensity.

It is a curious fact that amoebic abscess of the liver is much com-
moner in men than in women. It is also commoner in white people
in the tropics than in resident natives, although the latter are probably
more heavily infected, as a whole, with E. histolytica. The disease is
uncommon in temperate climates, notwithstanding the fact that the
parasite is of common occurrence.

Amoebic abscesses may attain a very large size, and unless treated
surgically are frequently fatal. Sometimes, when left to themselves,
they rupture spontaneously, and thus cause the death, or more rarely
the recovery, of the patient. Even with proper surgical and therapeutic
treatment, hepatic abscess is a dangerous disease.

Amoebic Abscesses in the Lung or Brain usually — but not invariably —

AMOEBiASIb 53

follow dysentery and hepatic abscess. The symptoms — mutatis
mutandis — are similar to those of liver abscess and abscesses of the
same organs resulting from other causes. Pain is usual at the site of
the abscess — pain in the chest, in the case of a pulmonary abscess ;
headache, often severe, in cerebral abscess. Pyrexia, rigors, and night
sweats are common symptoms ; but with abscess of the brain the tem-
perature may be normal. In the latter disease mental and nervous
symptoms will, of course, also be present — according to the site of the
abscess. The duration of the disease is usually short, and its termina-
tion death. A pulmonary abscess may, however, burst into the lung,
and drain itself by this route — the pus being expectorated, and spon-
taneous recovery occurring.

It will be readily understood, from what has already been written,
that a healthy carrier of E. histolytica is liable to develop symptoms of
primary or secondary disease at any time. The amoebae are in his
tissues, and in close proximity to numerous possible points of entry into
the circulation. But we do not know at present what factors determine
whether the amoebae stay in the gut or migrate into the internal organs
by way of the blood-stream. An infected person may suffer from acute
or chronic dysentery, but never show any signs of secondary infection.
He may, on the other hand, get an abscess in his liver or brain without
ever having suffered from dysentery or diarrhoea. A man may have a
liver abscess almost as soon as the amoebae establish themselves in his
intestine : but on the other hand, he may suffer from chronic amoebic
dysentery for years, and suddenly develop a liver abscess at the end of
the period. Convalescent carriers (see p. 50) are sometimes compara-
tively free from symptoms for long periods, and then suddenly relapse
with dysentery, or develop secondary infections. At present there
appears to be no law governing these conditions, and their irregularity
and apparent inconsequence are extremely puzzling.

The available evidence shows that infections with E. histolytica are
very persistent. When an infection is once acquired, it probably persists
as a rule — unless eradicated by specific treatment — for the rest of life.
(Cf. Wenyon and O'Connor (1917), Dobell and Stevenson (1918), etc.)
There is no fully authenticated case of spontaneous cure on record.
Consequently, all who once become infected with this parasite are liable
to suffer from amoebic disease at some subsequent time. For the
average case, however, the risk is probably small.

54 THE INTESTINAL PROTOZOA OF MAN

But few accurate data are available for the determination of the
relation between the " carrying " period and the onset of symptoms,
but the observations of Walker (see Walker and Sellards, 191 3) have
thrown some light on the matter. Walker experimentally infected iS
out of 20 men with E. histolytica. Infection — determined by the appear-
ance of cysts in the stools — was established in from 1 to 44 days, the
average period being 9 days. Four of the 18 infected men developed
dysenteric symptoms subsequently, the times intervening between the
infective feeding and the onset of symptoms being 20, 57, 87, and 95
days. The remaining men showed no symptoms during the period of
observation — that is, 14 of the 18 remained contact carriers. It will be
evident from these figures that it is impossible to define any " incuba-
tion period " in amoebic diseases.

In the foregoing experiments, it will be observed that 2 of the
20 men never became infected at all ; and it should be added that
some of the other 18 required more than one feeding with the infective
material before they became infected. At present we know nothing
about immunity to amoebic infection, but these observations suggest
that there may be some kind of natural resistance to infection — a
resistance which differs in different individuals.

All the evidence goes to show that whether an infected person
suffers, or does not suffer, from his infection, depends rather upon his
own susceptibility than upon the virulence of the parasite. The same
strain of amoebae will produce dysentery in one host, and not in
another : and the same strain in the same host may sometimes cause
symptoms and sometimes none. Examples of this are furnished by
Walker (1913), who experimentally infected a man by causing him to
swallow cysts from the stools of a convalescent carrier. The second
man became a contact carrier. From his cysts a third man was
infected, who also became a contact carrier. But a fourth, infected
from him, developed an attack of acute amoebic dysentery 20 days after
ingesting the cysts. It seems evident, therefore, that the factors
determining dysentery must be sought in the susceptibility of the host
rather than in the pathogenicity of the parasite. At present there is no
evidence to prove that different strains of parasites differ in
"pathogenicity" or "virulence."

Reference has already been made several times to the wide
geographical distribution of E. histolytica. It would seem to follow

AMOEBIASIS 55

that the amoebic diseases must be equally widespread : but it is a
curious fact that the frequency of infection with the parasite, and the
prevalence of amoebic dysentery and liver abscess, do not appear to
coincide exactly or to run strictly parallel.

Amoebic dysentery and hepatic abscess are commoner in the tropics
than elsewhere — as the frequent application of the epithet " tropical " to
these diseases indicates. But they also occur in temperate countries —
for example, in Britain. Yet with us they appear to be very rare, for
scarcely a dozen authentic cases of indigenous amoebic dysentery have
been recorded in the British Isles. On the other hand, there is now
good evidence to show that a large proportion — probably between
7 and 10 per cent.— of the population of Britain is infected with
E. histolytica : * and it is certain, therefore, that thousands of carriers
of this parasite exist in our midst.

It is probable that the percentage of carriers in all tropical
countries is higher than 10 per cent. How high it actually is, it is not
yet possible to state for any particular country, since really accurate
and extensive records are not available. It is clear, however, that the
percentage of carriers in the tropics cannot be more than ten times as
great as it is in Britain. On the other hand, amoebic diseases appear to
be more than ten times as prevalent in some parts of the tropics. It is
not easy, therefore, to reconcile these apparently conflicting facts.

Some would have us believe that residence in the tropics
u conduces" — in some undefined way — to the development of amoebic
disease in carriers of the parasite. Others speak of a particular state of
the bowel, or the co-existence of certain intestinal bacteria, as the
factors which determine the appearance of symptoms. Such
" explanations," however, belong to the ignotum per ignotius category,
and are not worth discussion until they can be formulated in more
precise and scientific terms. At the moment it seems preferable,
therefore, to suspend judgement upon this problem.f

Amoebiasis in Animals other than Man. — Many animals besides
man harbour intestinal amoebae. It is not possible to discuss these
organisms here ; but it is necessary to say something about the
experimental infection of animals with E. histolytica, since this subject
is of present interest and of some practical importance.

* For a summary of the observations bearing upon this subject see Dobell (1921).
f See also on this subject Dobell (1921", p. 67, where a tentative explanation along-
biological lines is suggested.

56 THE INTESTINAL PROTOZOA OF MAN

E. histolytica has been successfully transmitted to dogs by Losch
(1875), Hlava (1887), Harris (1901), Dale and Dobell (1917), and
others ; and an amoeba which appears to be identical has been found
occurring spontaneously in these animals, in which it causes dysentery
(Kartulis, 1891 ; Darling, 1915 ; Ware, 1916 ; Bauche and Motais, 1920).
The cat appears to be more easily infected, but spontaneous infections
of this host are not recorded. Among those who have studied
E. histolytica in cats may be mentioned Kartulis (1891), Quincke and
Roos (1893), Marchoux (1899), Wenyon (1912), Dale and Dobell (1917).
Both cats and dogs appear to be most susceptible to infection when
young. They may be infected by feeding them upon the cysts of the
parasite, or by injecting active amoebae into the large intestine. When
infection is established, it produces an acute and usually fatal dysenteric
condition, similar to that seen in man. The amoebae appear to be
incapable of encysting in these strange hosts : at all events, no authentic
case of a dog or cat becoming a true carrier of the parasite is yet on
record.

Amoebic abscess of the liver has also been produced experimentally
in cats by Marchoux (1899),* Craig (1905), Huber (1909), Wenyon
(1912), Dale and Dobell (1917), Mayer (1919), etc., and also in dogs
(Harris, 190 1). Kartulis has observed a spontaneous case of amoebic
liver abscess in a dog.

Baetjer and Sellards (1914), and Chatton (1917^, 1918), have suc-
ceeded in infecting guinea-pigs with E. histolytica; and Huber (1909)
has succeeded in infecting rabbits. The lesions produced in these
animals seem to be peculiar.

Lynch (1915ft) claims to have infected the rat, though most other
workers have been unsuccessful with this animal. Recently, however,
Brug (19196) states that he has found E. histolytica in wild rats (Mus
rattus) in Java, and has also succeeded in infecting a rat experimentally
by feeding it upon cysts from human faeces. If these observations are
correct, as they seem to be, then it appears that the rat can become a
true carrier of E. histolytica, for Brug found cysts of the amoeba in the
faeces of his infected rats. Nobody has yet succeeded in infecting mice,
or any other rodents.

* In my book on the Amoebae of Man (1919a) I— like most other workers—
unfortunately overlooked this important work of Marchoux. I am indebted to
Prof. Mesnil for calling my attention to the omission. (C. D.)

AMOEBfASIS 57

Several species of monkeys, including anthropoid apes, harbour
amoebae, which are not at present distinguishable with certainty from
E. histolytica and E. coli. It is possible that they are the same species,
but there is much uncertainty regarding their identity. They have
been studied by Chatton (1912^), Mathis (1913^), Prowazek dgiia),
Swellengrebel (1914), and others.* It should be noted that monkeys
appear to suffer from spontaneous amoebic dysentery (Eichhorn and
Gallagher (1916), and others), and also from liver abscess (Castellani,
1908).

None of the other amoebae of man can be experimentally trans-
mitted to animals — so far as is known at present.! And for this reason,
the rectal inoculation of kittens with the amoebae from human stools
has sometimes been advocated as a means of confirming a diagnosis of
E. histolytica. When successful, the result is conclusive : but when no
infection follows, no conclusion can be drawn, since failure to infect
cats with E. histolytica is a by no means uncommon consequence of
such experiments.

The reader desirous of pursuing the subject of amoebiasis further
may be referred to the following works, which deal with it from various
aspects :

Councilman and Lafleur (1891) — especially for the early history and
literature, and the classical account of the morbid anatomy. For later
work, containing important corrections and additions, see especially
Dopter (1905, 1907), Kuenen (1909), Christoffersen (1917), Dobell
and Low (192 1). A good recent account of amoebic abscess of the
liver is given by Abriol (1917), and the works of Legrand (1912) and
Armitage (19 19) embody most of what is known about amoebic abscess
of the brain. On carriers, and other general matters, see Walker and
Sellards (1913) and Dobell (1919^). Clinical and other general infor-
mation will be found in the books by Rogers (1913) and Phillips (1915),
and in the larger treatises on tropical diseases — such as Hanson's or
Mense's well-known works.

* The reader interested in them will find a fuller discussion of these interesting
forms — with further references — in Dobell (1919a), p. 131.

f What appears to be a species of Iodamoeba — similar to /. biitschlii — has recently
been described, under the name " Endolimax kueneni" from the intestine of a monkey
{Macacus cynomolgus) by Brug (1921). Noller (1921) avers that /. biitschlii itself
occurs in pigs.

5§

CHAPTER IV.
THE INTESTINAL FLAGELLATES OF MAN. "FLAGELLOSIS."

The Mastigophora, or Flagellate Protozoa, are represented in the
human bowel by at least five species — possibly by more. Three of these
are common and well known. The rest are very small, and appear to
be rare. Each species belongs to a different genus : but although these
genera are now readily distinguishable, for the most part, and easily
defined, there is still much confusion in their nomenclature. This is
very largely due to the inadequacy of the earlier observations and
descriptions, and the unfortunate bestowal of the name " Cercomonas"
on all forms indiscriminately. It will help the beginner if he bears in
mind that there is really no species belonging to this genus in the
human bowel.*

We shall begin by describing the various species of flagellates found
in the human gut, and will say a few words about their genera after-
wards, as it will be easier to sort these out after the reader has become
conversant with the organisms to which the generic designations are
assigned.

(i) Giardia intestinalis (Lambl) Alexeieff, 1914.

Chief synonyms :

" Dierkens " Leeuwenhoek, 1681.

Cercomonas intestinalis Lambl, 1859.

Dicercomonas (Dimorphus) muris Grassi, 1879 (1881).

Megastoma enter icnm Grassi, 1881.

Megastoma intestinale -(Lambl) Blanchard, 1885.

Lamblia intestinalis (Lambl) Blanchard, 1888.

Giardia lamblia Stiles, 1915 [in Kofoid & Christiansen, 1915].

Giardia enterica (Grassi) Kofoid, 1920.

* Species may, however, occur coprozoically in human faeces. Thev are considered
on p. 178 infra.

THE INTESTINAL FLAGELLATES OF MAX 59

Giardia intestinal is was discovered, in his own stools, by Leeuwenhoek,
and described by him in a letter written to the Royal Society in 1681.*
Later, it was rediscovered by Lambl (1859), who named it Cercomonas
intestinalis. Grassi (1879-1888) devoted much attention to this organism,
and gave it several different names. His final account of it, written in
collaboration with Schewiakoff (1888), contains the first approximately
correct and complete description.

As will be seen from the foregoing list of synonyms, the organism
has received various names. Its nomenclature appears, however, to
present no particular problem a present — the name which we here use
being obviously the correct one,f though we may note that Kofoid
(1920) has recently tried to justify the view that the correct name is
Giavdia enterica, and not G. intestinalis. This appears to rest upon an
error. Kofoid states that the specific name intestinalis, proposed by
Lambl (1859), is preoccupied, because Diesing (1850) had previously
transferred Ehrenberg's Bodo intestinalis to the genus Cercomonas. But
Ehrenberg's "Bodo " was really, in all probability, a Hexamita (Dujardin,
1841) : % consequently, Diesing's mistake does not render Lambl's name
unavailable.

Giavdia intestinalis (see PL V, figs. 58, 59) is a small flagellate with
a very complicated structure. It is bilaterally symmetrical, all its organs
being paired — right and left. Its shape may be roughly compared with
that of a pear, from which a large slice has been cut off obliquely at the
thicker end. The thicker end is the anterior, and the surface from
which the slice has — according to our simile — been cut, is not in reality
flat, but concave : moreover, it is not circular in outline but rather
reniform — having an inpitting posteriorly. The whole of this area,
which marks the ventral surface, thus forms a large cup-like depression
at the anterior end of the body. It is supported round its edge by
deeply stainable skeletal fibres, and acts as a sucker for the temporary
attachment of the animal to the intestinal wall. This peculiar sucker-

* See Dobell (1920), and compare Chap. I, p. 1 supra.

t The synonyms of the genus Giardia will be found on p. 86 infra. It may be
noted here that in a recent paper Reuling and Rodenwaldt (1921) express a desire to
retain the name Lamblia as a subgenus of Giardia.

% As pointed out some years ago by one of us (Dobell, 1909).

60 THE INTESTINAL PROTOZOA OF MAN

like organ is generally called the " sucking disc." * Its structure will
be most readily comprehended from inspection of the figure on PL I
and figs. 58 and 59 (PI. V).

The hind end of the body tapers to a very fine tail, which, when the
animal is alive and active, is usually recurved dorsally (PI. I).

The length of the organism, from the rounded anterior extremity to
the tip of the caudal process, is usually from 10 fi to 18 /a. The body as
a whole is covered with a thin but tough pellicle, and is comparatively
rigid. It shows no changes of shape save a slight bending of the tail,
and some contraction and expansion of the sucker.

The internal structure is complex, and is in intimate relation with
the flagellar apparatus. There are two nuclei, and four pairs of flagella,
as well as certain fibres serving as a skeleton. The disposition and
connexions of these parts are as follows (see PL V, fig. 58). The two
nuclei are small oval vesicles, lying imbedded in the protoplasm at the
anterior end of the body, dorsally to the sucker. In ventral view — as in
fig. 58— they thus appear to lie within the sucker itself. Each nucleus
has a deeply staining central karyosome (sometimes more than one), and
a thin but well-defined nuclear membrane. Running lengthwise down
the middle of the body there are two slender threads or rods — the
axostyles — which are closely apposed for the greater part of their length.
Anteriorly they terminate, before reaching the extremity of the body, in
a pair of minute basal granules, or blepharoplasts : posteriorly they pass
to the extreme tip of the tail, and there end in a similar pair of tiny
blepharoplasts, in close contact. At the anterior pole of each nucleus
there is also a minute granule, and from this a delicate thread passes to
the blepharoplast at the anterior end of the axostyle on the same side.
The nuclei are thus anchored, as it were, to the anterior ends of the
axostyles.

A peculiar bar or block of a deeply stainable substance is often
visible in the middle or posterior part of the organism. Sometimes it
is comma-shaped or filamentar, sometimes double, and sometimes
absent altogether. This is the "parabasal body" of some workersf —

* It is clearly improper to call the sucker a " cytostome," as has been done by
Kofoid and Christiansen (1915) and some other recent writers.

tThis structure was called the "darkly staining body" by Wenyon (1907) and
" ratselhafter Korper" by Bensen (1908). Alexeieff, and Kofoid and his collaborators,
suggested its homology with the parabasal bodies of other flagellates. It is somewhat
difficult, however, to discover any grounds for regarding it as homologous with the

THE INTESTINAL FLAGELLATES OF MAX 6l

a structure oi unknown function. It lies dorsally to the axostyles —

which themselves lie near the ventral surface — and usually transversely
to them. (Cf. PL V, fig. 59.)

The flagella are eight in number, arranged in four pairs. (See !.
(1) An anterior pair, arising from the blepharoplasts at the anterior end-,
of the axostyles, crossing over one another, and then passing round the
antero-lateral margins of the sucker until they emerge at the side
free flagella. (2) A middle pair, arising from — or very near to — the
anterior blepharoplasts, then following the axostyles as far as the
posterior margin of the sucker, where they diverge and pass backwards
and outwards through the protoplasm until they emerge as free lateral
flagella — springing from the sides of the body about midway between
the posterior edge of the sucker and the tip of the tail. (3) A ventral
pair, larger and more powerful than the others, arising out of the
depression at the posterior edge of the sucker, and apparently rooted
in thickenings of the axostyles themselves. These flagella often lie
side by side for a part of their length, and lash in unison. (4) A
caudal pair, long and very slender, arising from the minute bleph-
aroplasts at the posterior tips of the axostyles.

The exact connexions and dispositions of these parts are extremely
difficult to determine with precision, owing to their minute size and
great complexity. Different individuals — differently stained, and lying
in different positions — do not always present the same apparent struc-
ture ; and although we have examined a very large number of specimens
(belonging to several species of the genus), we are still in some doubt
regarding several details of the anatomy of this organism. The " axo-
styles," for example, sometimes appear rather as the walls of a tube,
seen in optical section. They are usually connected at the anterior
end by a somewhat indistinct structure interposed between the bleph-
aroplasts (PI. V, fig. 58.) Sometimes, also, there appears to be but a
single axostyle, slightly split at the anterior end. The internal portions
of the middle pair of flagella often appear to be quite continuous with
their external or free portions : at other times there appear to be minute
blepharoplasts — as in fig. 58 — at the points where they emerge. The
origins of the middle and the ventral pairs of flagella are also exces-

bodies to which Janicki (191 1) originally gave this name. At present I regard the
application of the name "parabasal body" to the structure present in Giardia as
hardly justifiable — or at least premature. (C. D.)

62 THE INTESTINAL PROTOZOA OF MAN

sively difficult to determine. At times they appear to arise directly
from the axostyles, at other times they seem to be given off from
blepharoplasts lying upon the axostyles : and very often the caudal
flagella appear to be simple prolongations of the axostyles themselves
— no basal granules or other structures being visible to indicate a break
in their continuity. We believe that many of the published pictures
of Giardia are extremely schematic. They certainly do not all agree
with one another in the points just noted," and we find it difficult to
reconcile the very plain diagrams which some authors have given, with
the very puzzling appearances often presented by the organisms them-
selves. We therefore describe only the main structures with any
confidence, and regard some of the details as still open to question.

Giardia intestinalis is an inhabitant of the small intestine — as Lambl
first noted. The active flagellates live chiefly in the duodenum, but —
judging by analogy with other species — they may be found scattered
through the ileum also, as far as the ileo-caecal valve. In their natural
surroundings they are probably actively motile, but they probably pass
a considerable part of their existence attached by their suckers to the
surface of the mucous membrane. In freshly passed stools, the or-
ganisms lash their flagella vigorously ; but they do not, as a rule, show
rapid progressive movements — merely "skipping" up and down. They
also show a tendency to attach themselves by their suckers to foreign
bodies in the faeces, or to the microscopic slide or coverglass.

The cytoplasm of Giardia is remarkably free from inclusions of all
sorts ; and as the4animal possesses no mouth, it must be assumed that
it obtains its nourishment by absorbing the partly digested food in
which it swims in its host's intestine.

Multiplication is effected, as in other flagellates, by longitudinal
binary fission. f It is very difficult to obtain individuals which are
undergoing division, as they rarely appear in the stools. Moreover,
the dividing forms are very difficult to interpret, owing to their great
structural complexity.

Figures of various stages in the process have been published else-
where by one of us in a joint work (Wenyon and O'Connor, 1917), and

*Cf., for example, the flagellar insertions figured (partly in other species) by Wenyon
(1907), Bensen (1908), Kofoid and Christiansen (1915, 1915^), and Wenyon (1915).

fNoc (1909) describes multiple fission also, but his account and figures are far
from convincing.

THE INTESTINAL FLAGELLATES OF MAX

63

we reproduce them here (Text-fig. A). The finer details have not yet
been completely elucidated, but the figures will give the reader some
idea of the appearance of dividing organisms and of the complexity of
the process. The nuclei appear to divide by mitosis, and the axostyles
and other fibrillar structures apparently split to form those of the two
daughter individuals.*

Text-fig. A.

Encystation occurs in the lower parts of the gut. A single in-
dividual secretes a cyst wall around itself, and thus becomes completely
encapsuled (PI. V, fig. 60). The fully formed cysts have uniform and
rather thick walls. They are oval, and measure 10-14/* in length. At
first the remains of the flagella and their fibrillar connexions are clearly
visible inside the cysts, but later they disappear or break up. The two
nuclei become detached from the axostyles, and soon undergo a mitotic
division. As a result, there are then four minute nuclei at the anterior
pole of the cyst (PI. V, fig. 61). At the same time, the marginal fibres
of the sucker become detached, and come to lie as very obvious cres-
centic bodies freely in the cytoplasm. They soon begin to split or fray

* Similar dividing forms of G. muris have been described and figured by Kofoid
and Christiansen (191 $a).

64 THE INTESTINAL PROTOZOA OF MAN

out, and the products of this multiplication or disintegration are then
scattered through the cyst. The axostyles also split, and likewise the
" parabasal " bodies, which grow in length and sometimes appear to
break up. The final appearance of the contents of the cyst is thus very
confused, and difficult to interpret. Some idea of the complex con-
stituents of typical cysts can be obtained from figs. 60 and 61 (PI. V),
in which all the visible structures have been delineated as exactly as
possible with the aid of the camera lucida.

The development observed within the cyst seems to be essentially a
process of duplication of the organs preparatory to division. As a rule,
however, complete division into two organisms does not occur within
the cyst. The cysts present in the stools are usually binucleate (fig. 60),
or quadrinucleate (fig. 61). Some authors have regarded the develop-
ment within the cyst as involving a process of conjugation, but we
believe such an interpretation to be unwarranted. There is no evidence
at present of the existence of conjugation, or any other sexual process,
in the life-cycle of this species.

The cysts of G. intestinalis were first noted by Grassi (1879^), who
regarded them as being possibly those of coccidia. Later (i88i«, 1888),
he established their connexion with the flagellate forms. They are very
characteristic structures, and cannot be easily confused with any other
objects present in human faeces.

Several other points relating to the cysts may be briefly noted in
conclusion. As will be seen from the figures, the protoplasm does not,
as a rule, completely fill the cyst — a slight space being left at one or
both ends. When placed in iodine solution, the protoplasm usually
stains more or less brown (PI. VIII, fig. P2), probably indicating the
presence of a small amount of diffuse glycogen. In every infection,
however, if careful search be made, it will be found that certain cysts of
this flagellate are stained a slatey blue with iodine. These cysts are
usually very small (7-10 /i), and appear to contain degenerating organ-
isms. It can be seen, moreover, that the blue colour is confined to the
cyst wall — the contents being stained yellowish. This may, perhaps,
indicate the presence of starch in the cyst wall. These small blue-
staining cysts are very common, but we have been unable to ascertain
their precise significance. We regard them as the results of some kind
of degenerative process.

The encystation of Giardia probably takes place in the lower end of

THE INTESTINAL FLAGELLATES OF .MAN 65

the ileum, and possibly also in the large bowel. Like those of the
intestinal amoebae, the cysts are unable to withstand desiccation, but
will remain apparently unchanged in moist faeces for a week or two at
least. They presumably hatch, when swallowed, in the small intestine
and liberate two small flagellates from each — formed by completion of
the division which begins in the cyst before it is discharged from the
body. The earliest stages of development are, however, still unknown
in this or any other species of the genus.*

(2) Trichomonas hominis Davaine, i860, emend.
Chief synonyms :

Cercomouas [sp. 2] Davaine, 1854.
Cercomonas hominis (B) Davaine, i860.
Cercomouas obliqua Moquin-Tandon, i860.
" Cercomonad A" Cunningham, 1871.
Monocercomonas hominis Grassi, 1879.
Trichomonas iiitestinalis Leuckart, 1879 (pro parte).
Trichomonas hominis Grassi, 1888.
Cercomonas coli hominis May, 1891.
Tricomonas confusa Stiles, 1902.
Entamoeba nndidans Castellani, 1905.
Hexamastix Ardin Delleili Derrieu & Raynaud, 1914.
Pentatrichoinouas bengalensis Chatterjee, 1915.

The first recognizable notice of this organism is to be found in the
work of Davaine (1854), who found it in the stools of a patient with
typhoid fever. He referred it to the genus "cercomonas" (sic), and
noted that it differed from a similar flagellate which he had found in the
stools of cholera patients (—Chilomastix, in all probability!) in having
its caudal filament inserted somewhat laterally, and in showing "an
undulating movement " in its contours. Only a single anterior flagellum
was made out. Later, Davaine (i860) published a figure of this species,
but included it with the other (=Chilomastix) under the common name
Cercomonas hominis ; though he distinguished them from one another as
" varieties or species," called B and A respectively. The organism was

* The species most fully studied are those of rodents. Fairly full descriptions of
some of these, with references to other works, will be found in the recent papers of
Kofoid and Christiansen (1915, ioiStf), and Boeck (1917, 1919)- A species of this
genus also occurs in the domestic cat, and another in tadpoles.

t See p. 71 infra.

66 THE INTESTINAL PROTOZOA OF MAN

subsequently referred to the genus Trichomonas Donne — by Leuckart
and others — and its name therefore became Trichomonas hominis
Davaine.* It has, however, been renamed by several later workers, as
will be evident from the list of synonyms given above.

As a point of historic interest, it may be noted that this is the
organism which Lambl (i860) found in human faeces and interpreted
as an "amoeba" — a mistake which has won him the unmerited dis-
tinction of having discovered the intestinal amoebae of man.f The
degenerating amoeboid forms of Trichomonas have been since described
as "amoebae" by numerous other authors. It is also worthy of note
that a very large proportion of the records of "Trichomonas" from man
are based, in all probability, not upon this species but upon Chilomastix
mesnili — a form which appears to be much commoner in human stools,
and which has been regularly mistaken for Trichomonas.

Trichomonas hominis (PL I, and PI. V, figs. 69-71) is a small and
active flagellate. In shape it is usually oval ; but its body is metabolic,
and frequently becomes spherical, fusiform, or irregular. The length
ranges from about 7 yu, to 20 //, (living specimens), but most frequently
lies between 10 fx and 15 /jl — or less, when rounded. Posteriorly the
body ends in a pointed caudal process.

Like the other species of the genus, this organism has a complicated
structure. It is difficult to study accurately, on account of its small
size : and it is an unfortunate peculiarity of this species that it is
especially difficult to fix and stain. T. hominis usually shrinks con-
siderably when fixed, and becomes more or less rounded ; and its
internal structures are difficult to demonstrate even by the best cyto-
logical methods. Well stained specimens show the following structures,
which can mostly be made out — with perseverance — in the living
organism also.

At the anterior end there is a single oval vesicular nucleus (PI. V,
tigs. 70, 71), containing a small karyosome and a variable number of
minute chromatin granules arranged on an indefinite linin network.
It is bounded by a thin but definite nuclear membrane. At the anterior
pole of the nucleus, and thus at the anterior tip of the body, there is a
group of small blepharoplasts. It is extremely difficult to determine

* But see p. 71 infra, where Davaine's " Cercomonas" is further discussed. For
the generic synonyms of Trichomo?ias see p. 86.

tCf. Dobell (1919^) pp. 8-9, and 71 et seq., and see also p. 2 supra.

THE INTESTINAL FLAGELLATES OF MAX 67

their precise number, but there are at least three, and possibly more
(lig. 71). They lie in contact with the nuclear membrane, and serve
as points of insertion for a number of important organs — the flagella,
the undulating membrane, and the axostyle.

The flagella are usually three or four in number (figs. 70, 71). They
are very slender threads, of approximately equal size — their length
being slightly greater than that of the body when rounded, or about
equal to it when extended. They are all directed forwards, and are
free for the whole of their length ; but they arise so close together that
they often appear to be fused together towards their roots. In life they
are lashed with great vigour. They appear to take their origin from at
least two of the blepharoplasts.

The undulating membrane — one of the most characteristic features
of the genus — is a longitudinally disposed frill or fin, which is supported
by fibrous structures at its margin and its base. The margin is sup-
ported by a flagellum, which arises (see figs. 70, 71) from one of the
blepharoplasts, and then passes backwards in an undulating line to the
posterior end of the body, where it becomes free. The base of the
membrane, at the point of attachment to the body, is supported by a
stout and deeply stainable fibre, which may be called the basal fibre.
This structure also arises from a blepharoplast anteriorly. It gradually
tapers at the hind end, and terminates there in the protoplasm (figs. 70,
71). During life, the undulating membrane displays a continuous
rippling motion, the waves passing rapidly along it from before back-
wards. It does not pass straight backwards from the anterior end, but
is slightly wound round the body, and with the continuous rotation of
the organism — when actively swimming — appears to lie first on one
side, then on the other : and this, no doubt, explains why Davaine
observed an undulating movement of the body " dans tout le contour."

i The membrane is widest in the middle, and narrows gradually towards
its two ends.

The axostyle is a feebly stainable rod, which arises from one of the
blepharoplasts, passes round the nucleus, and then lies centrally in the

! longitudinal axis of the body. It passes to the extreme hind end
where it projects as a spike — forming, with the protoplasm investing its
root, the caudal process. The axostyle is probably skeletal in function.*

* Kofoid and Swezy (1915), for other species, consider that the axostyle is itself
actively motile. From very careful observations on a number of species I am satisfied
that this view is. incorrect. I believe that the view expressed above — which I put for-
ward more than twelve years ago — is the correct one. (C. D.)

68 THE INTESTINAL PROTOZOA OF MAN

It is flexible, and appears to be passively bent with the movements of
the body. It is difficult to demonstrate the exact relations of the
axostyle to the nucleus and blepharoplasts in T. hominis. In other
species, however, their connexions can be more easily made out.*

At the anterior end of the body there is a small slit, lying close
against the nucleus. This is the mouth — seen as a crescentic mark in
the figure on PI. I, and in figs. 70 and 71, PL V. It lies towards one
side of the body, which may be called ventral. The undulating mem-
brane is on the opposite side, and may therefore be described as dorsal.
It is difficult, however, to apply such terms as "dorsal," "ventral," or
"lateral," to Trichomonas, as its body is slightly twisted, and not
bilaterally symmetrical. Both mouth and membrane are somewhat
obliquely or spirally disposed in relation to the long axis of the body.

The food of the organism, ingested through the mouth, lies in small
food-vacuoles in the cytoplasm (fig. 71, etc.), where it undergoes diges-
tion. It consists chiefly of small bacteria. Apart from food bodies,
there are no inclusions in the cytoplasm. A permanent anus is lacking.

T. hominis is usually described as having three anterior flagella.
Specimens with four or five are, however, also encountered. By some
authors they are regarded as constituting distinct subgenera,! called
respectively Tetrairidiomonas (Parisi, 1910) and Pentatrichomonas
(Mesnil, 1914 ; Chatterjee, 1915). The forms with five flagella have
even been regarded as generically distinct from Trichomonas, and have
also been named " Hexamastix Ardin Delteili," by Derrieu and Raynaud
(i9i4).:

* In some of the larger species the axostyle appears to pass round the nucleus, in
close contact with its dorsal surface. In others, I believe the axostyle completely
encapsules the nucleus — as in Lophomonas — so that the nucleus really lies inside the
expanded anterior end of the axostyle. It is possible that this is the case also in
T. hominis, but I have not been able to determine the point with certainty. (C. D.)

t I regard these so-called subgenera rather as varieties. There seems, moreover,
to be some misunderstanding regarding the use of these names. The type species of
Trichomonas is T. vaginalis Donne, 1837. This, according to Kunstler (1883, 1884),
Reuling (1921), and others who have studied it carefully, possesses 4 anterior flagella.
Consequently, the 4-flagellate form being the type, no special name is required for it.
" Tetratrichomonas" appears, therefore, to be superfluous. It is the 3-flagellate form
which requires a distinctive name, and for this Kofoid (1920) has just proposed
" Tritrichomo?ias" In my experience the 4-flagellate form (typical Trichomonas) is
the commonest in human stools, but the 3-flagellate variety is also common. (C. D.)

J This generic name — as Mesnil (191 5) has pointed out — is not available, as Hexa-
mastixhad previously been proposed for other flagellates by Alexeieff (1912^, 1914a).
The same organism was named Pentatticho?nonas bengalensis by Chatterjee (1915).
The subgenus Pentatrichomonas was suggested almost simultaneously by Mesnil and
Chatterjee. Their publications both appeared during the first few days of January,
1915, though Mesnil's is dated December, 1914. I do not know which of them has
priority. (C. D.)

THE INTESTINAL FLAGELLATES OF MAN' 69

Degenerating "amoeboid" forms of Trichomona, are commonly
seen in the stools. The organism loses its flagella and other organs, and
then — without undergoing any appreciable locomotion — shows a series
of curious changes of shape. A rapid undulation of a part of the
surface is all that may be seen : but frequently a finger-like " pseudopo-
dium " is thrust out at the anterior end, passes along the body towards
the hinder extremity, and is finally drawn into the protoplasm in this
region. The whole process may be repeated again and again for hour^
— or even days. Such degenerating individuals are very characteristic
of Trichomonas, and do not really show much resemblance to amoebae.
They have, however, been mistaken for such organisms by several
workers. Lambl (i860) first described them as "amoebae," and
Castellani (1905) named them " Entamoeba undulans." They were also
noted — and correctly interpreted — by Cunningham (1871),* Roos (1893),
and others. t

T. hominis multiplies in the bowel by longitudinal division ; but
stages in the process are excessively rare in the stools, and consequently
no account of it can yet be given. The division of trichomonads is a
complicated process, and conflicting accounts of the details, as observed
in other species, have been published. It is impossible to discuss them
here, and the reader is therefore referred to the original descriptions. \

In spite of prolonged search by many workers, the cysts of T. hominis
— if it form any — have not yet been discovered. The " cysts " attributed
to this species by Prowazek (1904), and other workers in Germany, are,
in reality, Blastocystis (see p. 141). Lynch's (1916) " cysts of Tricho-
monas'" are really those of Chilomastix, and those observed by Boyd
(1919) and others in "cultures" appear to be merely rounded and
degenerating individuals. It is still uncertain how infection is con-
veyed from one human being to another. It should be added, how-
ever, that the cysts of some other species are known. §

* Cunningham called them " Cercomonad A," however, and was not aware that
they belonged to the genus Trichomo7ias.

t Cf. pp. 2, 66, supra.

% See Prowazek (1904), Wenyon (1907), Dobell (1909), Mackinnon (1910, 1912),
Kuczynski (1914, 1918), Kofoid and Swezy (1915), etc. In spite of the criticisms to
which my work on T. batracho7-um has been subjected by some of these authors, I
believe that my observations were, in the main, correct. I hope to return to the subject
on a future occasion. The work of Kofoid and Swezy, on related species, appears to
me to be in some respects—£\£"., the behaviour of the axostyle — very unconvincing, and
their figures and descriptions are by no means easy to reconcile. (C. D.)

§The cysts of T. batrachorum were described by Dobell (1909), and those of
T. caviae have recently been ^observed by Brug (1917) and others. The former are
small and oval, the latter large and spherical.

70 THE INTESTINAL PROTOZOA OF MAN

Several authors claim to have succeeded in cultivating T. hominis,
but some of the claims — such as that of Escomel (1913) — appear to be
unjustified. It is probable that free-living flagellates, with which the
cultures were contaminated, were mistaken for Trichomonas. Lynch
(1915, 1915a) claims to have cultivated T. hominis, T. vaginalis, and the
species found in the human mouth,* in acid broth. Boyd (1918, 1919),
however, finds that T. hominis will not grow in an acid medium, though
he was able to obtain cultures in an unsterilized neutral suspension of
faeces in saline solution. Ohira and Noguchi 1917) succeeded in
cultivating the oral species in diluted ascitic fluid, and Pringault (1920)
states that he has obtained " some growth " of T. hominis in this
medium. At the present time, however, it is not possible to cultivate
this organism with certainty in any medium. All the attempts which
we ourselves have made have been failures : but we may note that in
certain liquid stools we have been able to keep T. hominis alive and
active for periods up to a month.

It may be added that Chatton, who has successfully cultivated a
Trichomastix from an African gecko, has recently announced that he
has been able to cultivate also the Trichomonas of the guinea-pig. His
medium consists of meat bouillon mixed with rabbit's blood. (For
details see Chatton, 1920.)

(3) Chilomastix MESNILI (Wenyon) Alexeieff, 191 2.

Chief synonyms :

Cercomonas [sp. 1] Davaine, 1854.
Cercomonas hominis (A) Davaine, i860.
Cercomonas davainei Moquin-Tandon, i860.
" Cercomonad B" Cunningham, 1871.
Cercomonas intestinalis Marchand, 1875.
Trichomonas intestinalis Leuckart, 1879 {pro parte).
Monocercomonas hominis Grassi, 1881 (pro parte).
M onocercomonas hominis Epstein, 1893.
" Trichomonas intestinalis (Marchand) " Roos, 1893.
Macrostoma mesnili Wenyon, 19 10.

*The species in the human mouth has been described by many workers — Kunstler
(1888), Prowazek (1902), Goodey and Wellings (191 7), etc. It is almost certainly dis-
tinct from T. hominis and T. vaginalis, and according to Goodey, differs from these
in having no free flagellum at the posterior end of the undulating membrane.

THE INTESTINAL FLAGELLATES OF MAN 7 1

Tetramiins mesnili (Wenyon) Alexeieff, 1910.
Fanapepea intestinalis Prowazek, 191 1.
Difdmus tunensis Gabel, 19 14.
Cyathomastix hominis Prowazek & Werner, 1914.
Chilomastix davainci (Moq.-Tand.) Kofoid, 1920.

As will be evident from the foregoing list of synonyms, this
organism has long been known and has frequently been named. It
appears to have been first recognizably described by Davaine, who
found it in the stools of persons suffering from cholera. He first called
it merely "cercomonas" (Davaine, 1854) — it being the first of the two
different species to which he gave this name. Later (Davaine, i860) he
redescribed it, and named it "Cercomonas hominis, variete ou espece A "
(his variety B, as already noted on p. 65, being Trichomonas). From
his figures and description of the organism — with its " trait longitudinal
vers l'extremite anteYieure, donnant l'apparence d'un orifice buccal ? " —
it is impossible to doubt that Davaine was dealing with Chilomastix.

The organism was seen again by Cunningham (1871), in India, but
called by him " Cercomonad B" ; and by Marchand (1875), who wrongly
identified it with Lambl's " Cercomonas intestinalis " (=Giardia). Leuckart
(1879) and other early workers confused it with Trichomonas, and
Leuckart's " Trichomonas intestinalis" included both species.* Grassi's
(1881a) species " Monocercomonas hominis" — to judge from some of his
figures — included Chilomastix as well as Trichomonas : but the organism
called "Monocercomonas hominis " by Epstein (1893) was undoubtedly
Chilomastix — not Trichomonas. This is true also of the flagellate incor-
rectly named " Trichomonas intestinalis (Marchand) " by Roos (1893).

Wenyon (1910) recognized the present species as a form distinct from
Trichomonas, and named it Macrostoma mesnili. This generic name —
which had been introduced by Alexeieff — not being available, it was
later proposed, by Alexeieff (1910) and others, to transfer the organism to
the genus Tetramitus. To this genus, founded by Perty (1852), it certainly
does not belong — as Alexeieff afterwards realized ; and he therefore
introduced the new generic name Chilomastix (Alexeieff, 19126)+ for
this species and an allied one found in Amphibia.

* Although this is not generally recognized, it is undoubtedly the case : for Leuckart's
" T. intestinalis'1'' included the flagellates described by Marchand (1875), which were
certainly Chilomastix and not Trichomonas.

t The name had already been tentatively suggested by this author at an earlier date
(Alexeieff, 1910J. A list of the synonyms of Chilomastix will be found on p. 87 infra.

72 THE INTESTINAL PROTOZOA OF MAN

In i860 Davaine's two species of " Cercomonas" were renamed by
Moquin-Tandon, in a work which was unfortunately overlooked until
attention was recently drawn to it by Kofoid (1920). Moquin-Tandon
called the species A of Davaine (= Chilomastix) by the new name Cerco-
monas davainei, and species B (= Trichomonas) C. obliqua. Arguing on
grounds of page priority in Moquin-Tandon, and "awarding" (his own
expression) hominis to Trichomonas, Kofoid therefore regards Chilomastix
davainei as the correct name of the organism here discussed. A good
case can, it is true, be made out for this combination. Nevertheless,
Moquin-Tandon was not entitled to rename both Davaine's species ; and
as the application of the names which he introduced is still debatable,*
we must, for the present, regard them both as doubtful. Moreover, they
have never been in common use, and are unknown to the majority of
workers. Consequently, we prefer, at present, to follow tradition, and
refer to Trichomonas the species hominis of Davaine, while adopting
Wenyon's specific name (mesnili) for Chilomastix — this being the first
available if Moquin-Tandon's names are eliminated.

It remains to add that the nomenclature of this flagellate has
been further complicated by the introduction of three other generic
synonyms — Fanapepea by Prowazek (1911a), Cyathomastix by Prowazek
and Werner (1914), and " Difdmus" by Gabel (1914). But these require
no further discussion here.

Chilomastix mesnili (PI. V, fig. 74) is one of the larger flagellates of
the human intestine. It is somewhat oval or pear-shaped, but with a
distinct asymmetry, and measures usually from about 10 /i to 15 /x in
length ; though larger and smaller individuals (ranging from some
6/t to over 20 p) may also be encountered. At the hind end of the
body there is usually a very definite "tail," or caudal prolongation,
which varies in length. The form of the body is relatively constant,
and it appears rigid in comparison with a Trichomonas. The cytoplasm

* An even better case than Kofoid's can be made for the view that the organisms
here called Trichomonas hominis and Chilomastix mesnili should really be named
respectively Trichomonas obliqua, Moquin-Tandon and Chilomastix hominis Davaine.
It is only necessary to use the argument of page sequence consistently throughout to
attain this result. Why Kofoid applies it to Moquin-Tandon and not to Davaine is
not clear. From the evidence submitted by Kofoid, moreover, it seems not improbable
that both Moquin-Tandon's names have priority over Davaine's. If this is really so,
then the two species should be called Chilomastix davainei and Trichomonas obliqua.
At present it is hardly possible to say which are the really " correct " names. (C. D.)

THE INTESTINAL FLAGELLATES OF MAN 73

appears somewhat denser, and the body as a whole is invested with a
thin but definite pellicle.

The finer details of structure are not easily made out. and various
conflicting accounts of them have been published. We shall base our
description upon our own observations,* and mention some of the
discrepancies in other descriptions later.

The most striking peculiarity of the organism, when seen alive, is its
large and complicated buccal apparatus. This is seen as a large and
slightly spiral longitudinal cleft or groove, which extends from the
anterior end for a distance of one third to one half of the length of
the body (see fig. on PL I). Its lips are raised, and unequal. We shall
call the surface on which the mouth lies, ventral; and consequently we
can distinguish the two lips as right and left. The right appears the
more elevated owing to the presence of a spiral groove which runs
round the body outside and to the right of the lip itself. (See fig. 74,
PI. V. The right lip appears on the left of the mouth in this figure,
as the organism is seen from its ventral surface.) This groove is
variable in depth, being sometimes very conspicuous, and encircling
the whole body, but at other times almost invisible. Its spiral course,
and that of the mouth itself, is always laeotropic.

The nucleus is oval and vesicular, and lies at the anterior extremity
of the body. Its membrane stains readily, and it contains a fine linin
network (in fixed specimens) studded with chromatin granules of
variable size. A small eccentric karyosome — sometimes more than
one — is usually visible. (Cf. PI. V, figs. 74, 75.)

At the anterior pole of the nucleus, and in close contact with its
membrane, is a group of blepharoplasts. These are extremely difficult
to study accurately, and to count correctly ; for they are usually in
contact with one another and can only be resolved in well fixed and
stained specimens viewed somewhat obliquely, and with the microscope
and illumination adjusted most accurately. In such individuals it can
be seen that they are six in number, and arranged in a circle (fig. 76).!

* The description is based chiefly upon my observations and preparations —
repeatedly checked during the last five years — and, as regards the finer details,
controlled by an examination of the larger species C. caulleryt, which I have studied
frequently since 1907. (C. D.)

t In the specimen here depicted the blepharoplasts are unusually widely separated.
The specimen was selected for delineation for this reason.

74 THE INTESTINAL PROTOZOA OF MAN

They give origin to the flagella, and certain fibrils which support the
lips of the mouth.

Three free and anteriorly directed flagella arise from the three
dorsally situated blepharoplasts (uppermost in fig. 76). These flagella
are approximately equal in length, and uniform in thickness. At the
anterior end of the buccal cleft there are three ventrally situated
blepharoplasts, which give origin to the following structures : (1) a long
fibril supporting the right lip, and arising from the blepharoplast on
the right side ; (2) a shorter fibril supporting the left lip, and rooted in
the left ventral blepharoplast ; (3) a very slender flagellum, which lies
within the mouth and arises from a blepharoplast lying between those
just described. This flagellum displays a continual flickering motion in
the living organism. The relations of these parts will be evident on
inspection of fig. 76 (PI. V).

The fibril supporting the right lip is longer and has a more complex
course than the one in the left lip : for while the left one is short and
almost straight, the right passes backwards to the posterior end of the
buccal aperture, which it almost encircles, and then sinks, in a spiral
course, deeply into the protoplasm (figs. 74, 76). This right fibril thus
forms an incomplete loop round the hind end of the buccal groove :
and it can be seen that the actual opening of the mouth, whereby food
enters the body, is in this loop. The anterior part of the groove, along
which the buccal flagellum lies, is merely a channel which conducts the
food to the aperture at its hind end.* (The mouth opening of the
organism shown in fig. 74 is in the clear area in the centre of the incom-
plete circle formed by the right fibre (left in figure) at the posterior
border of the buccal fissure.)

Food which enters the mouth is inclosed in vacuoles in the cytoplasm,
and such vacuoles are present in variable numbers in most individuals.
They usually contain small bacilli and cocci, which form the chief food
of this animal.

No other organs, such as an axostyle or undulating membrane, are
present in this form. The tail appears to have no central skeletal
support, and its protoplasm is homogeneous and free from vacuoles.

In previous descriptions of Ch. mesuili various discrepancies are

* These features are more clearly seen in C. caulleryi, but they can also be made
out in C. mesnili. The position of the mouth opening is particularly well seen in an
individual which — as sometimes happens— gets a large bacillus stuck in its mouth at
the moment of ingestion.

THE INTESTINAL FLAGELLATES OF MAN 75

noticeable. Most of these descriptions are, moreover, incomplete.*
The most detailed accounts are those recently published by Chalmers
and Pekkola (1918) and Kofoid and Swezy (1920). We may note, in the
latter work, the following points. Kofoid and Swezy describe three
blepharoplasts and a " centrosome," united to one another and to the
nucleus by an intricate arrangement of threads. -As we have already
remarked, we believe there are six blepharoplasts (and no recognizable
centrosome) directly attached to the nuclear membrane. The fibril
supporting the right lip they call the " parabasal body," and that of the
left lip the " parastyle." It is difficult to understand their grounds for
thus homologizing one of these fibrils with the parabasal bodies of other
flagellates ; nor is it clear why the other fibril should be distinguished
by a particular name. These authors also describe a " peristomal fiber"
in the floor of the buccal groove, and apparently believe that it
surrounds the opening of the mouth. We believe there is no such fibre,
and that the mouth opening is not situated in this position. Their
description of the morphology of the mouth appears to us to be
undoubtedly incorrect in this and some other details. It should be
noted that these authors apply the term "neuromotor system" to "the
integrated fibrillar system uniting the karyosome, centrosome, blepharo-
plasts, flagella, and other motor organs, and the fibers of the oral region."
We doubt the existence of some of these connecting fibres, and we see
no advantage in thus lumping together organs possessing such different
functions, and designating them by an inclusive name. There appears
to us, moreover, to be little justification for applying such a term as
"neuromotor" to the skeletal fibres supporting the lips of the buccal
groove.

It may be noted that some observers — most recently Boeck (1921) —
are of the opinion that there is an undulating membrane within the
buccal groove — the buccal flagelkim forming its margin. We believe
this to be probably an incorrect observation, but the mistake— if it be
one — is very easy to make, as the movements of this flagellum appear
very like those of an undulating membrane. Prowazek (191 1, 19126)
describes " Fanapeftea " as often possessing only two anterior flagella. +

* Some of them — such as that of Chatterjee (1915a)— are so obviously imperfect that
it is useless to try to discuss them.

t A subgenus Tetrachilomastix has been founded by da Fonseca (1916) for a similar
form — not found in man — possessing 4 anterior flagella instead of 3.

70 THE INTESTINAL PROTOZOA OF MAN

We regard this also as an incorrect observation — believing this genus
to be merely a synonym of Chilomastix. Rodenwaldt (191 2) has figured
what appears to be a Chilomastix with an axostyle, and Prowazek and
Werner (19 14) have named it — from his figure — Cyathomastix. This
also, we think, is probably merely a malobservation.

Chilomastix mesnili lives in the large intestine, and possibly also in
the small.* That it inhabits the large bowel is clear from the mode of
its occurrence in the stools in association with other protozoa of known
habitat (e.g., Giardia and Entamoeba coli) in persons infected with these
organisms also. It has also been demonstrated in sections of the large
bowel by Wenyon (1920).

Cultivation. Boeck (192 1) has recently succeeded in cultivating
this flagellate — in association with bacteria — in a medium consisting of
a modified Locke's solution and serum :f but no other worker seems to
have had a similar success. By frequent subculture Boeck was able to
keep a strain in vitro for about four and a half months, at the end of
which it was accidentally lost.

Multiplication is effected by longitudinal binary fission, but stages
in the process are extremely rare in the stools. A few have been noted
by various workers, but no complete description of the division of this
flagellate has yet been published. Boeck (192 1) has recently seen
various stages in his cultures, and has also observed multiple fission —
into four daughter-individuals; but he has not yet given a sufficiently
detailed description of these phenomena. Division has not yet been
adequately studied in any other species of the genus.

The CYSTS of Ch. mesnili (PI. V, fig. 77) are minute oval structures
with a projection at the narrower end, which corresponds to the anterior
end of the free form. Their shape may be compared with that of a
lemon. (Cf. also PI. VIII, figs. J1, J2, J3.) Usually they measure 7-5 /*
to 8*5 fi in length, but larger and smaller specimens may be found.
When first formed they sometimes contain a lump of glycogen, of
variable size (cf. Dobell and Jepps, 1917). The cyst wall is thin,
colourless, and uniform in thickness, except at the pointed end, where
it is slightly thickened.

* Boeck (1921) states definitely that "the habitat of the parasite is the small intes-
tine,'-' but he gives no evidence in support of this statement.

t The most successful medium was found to be four parts of Locke's solution
(containing 0*25 per cent, dextrose — instead of the usual o"i per cent.) mixed with one
part of human serum. The medium was alkaline (o"2 per cent, to phenolphthalein)
at the beginning, and increased in alkalinity with the growth of the implanted
organisms.

THE INTESTINAL FLAGELLATES OF MAN 77

The cyst contains a single nucleus of relatively large size (fig. 77),
which at first lies anteriorly {i.e., at the pointed end) but later takes up
a more central position. It is spherical, and usually shows a
condensation of its chromatin at one pole, so that it has the form of a
signet-ring in optical section (cf. PI. VIII, figs. J2, J3). This form of
the nucleus is also seen in flagellates which are about to encyst.* The
other conspicuous structures within 1he cyst are the fibrils which
support the buccal apparatus. These persist in the mature cyst and
give it a very characteristic appearance. Their blepharoplasts become
detached from the nuclear membrane, so that they lie freely in the
cytoplasm — the entire skeletal support of the mouth lying longitudinally,
in the form of an incomplete sling, in the cyst (fig. 77). The buccal
flagellum can usually be made out also, lying in its normal position
inside the remains of the mouth. The three blepharoplasts of the
anterior flagella also persist, and can often be made out in well stained
specimens (fig. 77). They become detached from the nuclear membrane
at an early stage.

Neither the buccal fibrils nor the nucleus can usually be seen in the
living cyst, which appears to have a homogeneous internal structure
save for the presence of a few bright and very small granules (PI. VIII,
fi&- J1)- These granules give some of the microchemical reactions of
volutin, and probably consist of this or some allied substance. They
are sometimes — but not always — visible in cysts stained with iron-
haematoxylin.

Cysts of Chilomastix remain in this uninucleate condition for two or
three weeks outside the body, if kept moist. They then begin to
degenerate — the buccal structures undergoing fragmentation, and the
nucleus and cytoplasm disintegrating. Like the cysts of the other
intestinal protozoa, they are unable to withstand drying.

Kofoid and Swezy (1920) have described a very complicated
arrangement of threads and granules within the cysts of this species.
Even if their account is correct — which we do not believe — it appears to
be physically impossible to prove the existence of so many structures in
so small a cyst : for they figure systems of points and lines whose
actual existence could hardly be demonstrated by the finest optical
apparatus. They appear, however, to have no doubts themselves

* The nuclei of such individuals resemble that of the specimen shown in fig. 75
(PI. V).

78 THE INTESTINAL PROTOZOA OF MAN

regarding their own interpretation of the optical images which they
depict.* But another equally remarkable feature in their description
is their account of nuclear division within the cyst. They describe and
figure a mitosis of the nucleus, and the formation of two daughter
nuclei : and they even say that " it is probable that one or two other
nuclear divisions follow in the cysts, though we have not been able as
yet to find them." We can find no justification whatsoever for such
a statement, and we are completely at a loss to account even for the
single nuclear division which they describe. Although we have kept
cysts for many weeks, in varying conditions, until they finally
degenerated and died, and although we have examined thousands
upon thousands of cysts in human faeces, we have never yet seen a
single cyst containing more than one nucleus. If nuclear division
does occur within the cyst, it must be excessively rare.

Finally, it should be noted that the 4-nucleate cysts doubtfully
attributed to this species by Wenyon (19 15) were in reality those
of Endolimax nana, as he showed subsequently (Wenyon and
O'Connor, 1917) ; whilst those of Swellengrebel (1917) really belong
to E. histolytica. On the other hand, Lynch (1916) really observed the
cysts of Chilomastix, but wrongly referred them to Trichomonas. The
cysts were overlooked by most of the earlier workers who observed
Chilomastix, and were first carefully described by Wenyon and
O'Connor (19 17) and Dobell and Jepps (1917), though well known to
these and many other English workers for some time previously.

(4) Embadomonas intestinalis Wenyon & O'Connor, 19 17, emend.

Synonym :

Waskia intestinalis Wenyon & O'Connor, 1917.

This little flagellate was found by Wenyon and O'Connor (1917) in
Egypt, and was placed originally in a new genus — Waskia. It should be

* Some of the details of structure which they depict in the cysts of this organism
are undoubtedly incorrect. I may say that I first found these cysts in the winter of
191 5- 16, before they had been described, and I then identified them and studied them
in detail. My pupils and fellow- workers who studied them at the same time readily
confirmed my observations, and in the course of several years not one of them
succeeded in finding a single cyst containing more than one nucleus though search was
constantly made for such specimens. (C. D.)

THE INTESTINAL FLAGELLATES OF MAN 79

referred, however, to the genus Embadomonas Mackinnon, 191 1 (emend.
1915),* as Chalmers and Pekkola (1918) and others have pointed out.

E. intestinalis (PI. V, fig. 72) is a minute and more or less ovoid
flagellate, measuring some 5-6/* in length by 3-4 y, in breadth. Jt
possesses a single anteriorly placed nucleus, with a small central
karyosome or a few rather indefinite chromatin granules. Immediately
behind the nucleus, the body has a large and elongated depression — the
mouth. This is supported round its edges by fibres, as in Chilomastix.
On the surface of the nuclear membrane lying towards the mouth there
are two blepharoplasts, which give origin to two flagella. One of these
is long and thin, and projects anteriorly. The other is shorter and
thicker, and arises just behind it, lying, during life, partly within the
mouth. By means of its two flagella the animal performs characteristic
movements. The long anterior flagellum serves for progression : the
short one moves more slowly, and independently, and causes a jerky
movement of the organism as a whole.

Food, consisting of minute bacilli and cocci, is taken in through the
mouth, and is then seen to lie in tiny vacuoles in the cytoplasm. There
is no permanent anus, and no axostyle or undulating membrane can be
made out.

The structural details of this flagellate are excessively difficult to
determine, owing to its extremely small size. It is probable, however,
that its structure is almost identical with that of the larger species of
the genus (from insects), excellently described by Mackinnon (19 15).

A few stages of multiplication, by longitudinal fission, have been
observed by Wenyon and O'Connor (19 17) ; but the process has not
been made out in every detail.

The cysts are very minute somewhat pear-shaped structures (PI. V,
fig- 73)- They measure 4*5 fi to 6 /a in length,f and resemble those of
Chilomastix — though of course they are considerably smaller. They are
uninucleate, and contain a long deeply-staining looped thread, which

* From a careful examination of specimens of the type species, kindly given to me by
Dr. Mackinnon, and from a study of some of Captain O'Connor's original preparations
of "Wasfo'a," I consider that there is no room for doubt on this question. It may be
noted, however, that da Fonseca (1920) maintains that Embadomonas and Waskia are
distinct genera, though he does not give any cogent reasons for this view. (C. D.)

t These figures are given by Wenyon and 0'Connor(i9t7) for living cysts. According
to my measurements (stained specimens) the length of the cysts is 4-4*5 m, their breadth
approximately 3 \l. Their shape is most aptly compared, I think, with that of a grape-
seed. (C. D.)

8o THE INTESTINAL PROTOZOA OF MAN

is evidently— as in Chilomastix— the remains of the fibril supporting the
margin of the mouth in the free flagellate.*

It is still uncertain what part of the bowel this flagellate inhabits. It
is very small and difficult to study, and appears to be very rare. A
similar species has recently been described from the caecum of a
Brazilian monkey (Cebus caraya) by da Fonseca (1917). For this species
he proposes the name " Waskia" wenyoni. It measures 14 jx by 12 fi,
and is therefore considerably larger than E. intestinalis. It should be
added that the " dividing" forms seen by Wenyon and O'Connor (1917)
appear to be regarded by this author not as stages in division, but as the
normal forms of the animal. " Waskia " wenyoni is thus said to have
"two cytostomes" and a double set of flagella.f It is not easy to
comprehend Fonseca's reasons for adopting such an interpretation.

(5) Entekomonas HOMlNiS da Fonseca, 1915, emend.

Synonyms :

? Octomitns hominis Chalmers & Pekkola, 1916.
Tricercomonas intestinalis Wenyon & O'Connor, 191 7.
" Monocercomonas" Chatterjee, 1917.
Trichomastix hominis Chatterjee, 191 7.
Dicercomonas sondanensis Chalmers & Pekkola, 1919.
Diplocercomonas sondanensis Chalmers & Pekkola, 1919.
Enteromonas Bengalensis Chatterjee, 1919.

The organism, or organisms, to be noticed in this section must be
regarded as still somewhat problematic : and the views here put forward*
are tentative — further investigations being necessary to establish their
correctness (or error).

In 1 9 15 da Fonseca described a new flagellate found by him in

* Wenyon and O'Connor (1917) describe the nucleus as becoming drawn out in the
cysts. The above is the interpretation of the appearances which I believe to be correct
— after studying these cysts with great care. Details are, however, extremely difficult
to determine accurately. (C. D.)

t See especially the recent " redescription" of " Waskia " by da Fonseca (1920).

% For this section, and the opinions expressed in it, I alone am responsible. Up to
the time when Captain O'Connor left England, we had been unable to come to any
definite conclusions concerning the identity or diversity of the various flagellates here
discussed. I have now been compelled to write this section entirely by myself, and
with insufficient material at my disposal to settle some of the disputed points. If my
judgement is at fault, it is only fair to point out that my collaborator is in no way to
blame. (C. D.)

THE INTESTINAL FLAGELLATES OF MAN 8 1

human faeces, in Brazil, and named it Enteromonas hominis. He has
since published several redescriptions of it (da Fonseca, 1916, 1918,
1920). According to his latest observations (1920) the flagellate— which
is very small — possesses three anterior flagella. Two of these are short,
and directed forwards; the third is longer, and recurrent, but not attached
to the surface of the bod)'. Fonseca has not yet described the cysts of
this organism.

Wenyon and O'Connor (1917) and O'Connor (1919) found a similar
flagellate in Egypt, and named it Tricercomonas intestinalis. It appears,
however, to differ from Fonseca's form in having four flagella — three
(not two) directed forwards, and the posteriorly-directed one adherent
to the surface of the body. The cysts of this flagellate were, moreover,
described and figured (Wenyon and O'Connor (191 7), PI. III).

Chalmers and Pekkola (1917, 1917a, 1918), later found — also in
Egypt— an organism believed by them to be identical with that
described by Fonseca. They added practically nothing worthy of note
to his observations except the statement that the three anterior
flagella are all equally long and all directed forwards.

An apparently similar flagellate was found in India by Chatterjee
(1917), who first named it " Monocercomonas," and shortly afterwards
Trichomastix hominis (1917a). From his confused account of this
organism* — obviously based, in part at least, upon inexact observations
— it appears to differ from Tricercomonas chiefly in that the trailing
flagellum is not attached to the body, whilst " in some specimens only
two anteriorly directed flagella are seen and one posteriorly directed."
No cysts were described, and it seems clear that the organism is not, in
any case, a Monocercomonas or Trichomastix (= Eutrichomastix). The
same author has more recently (Chatterjee, 1919) described a " new "
species of" Enteromonas," from another case, and named it E. bengalensis.
It is impossible, however, from the figures and description, to identify
this organism with certainty.

Leger (1918) believes he has seen Fonseca's Enteromonas in French
Guiana. He saw only two anteriorly directed flagella on his organisms,
but notes that in one individual they seemed to be doubled in number.
The posterior flagellum, according to his account, " se porte en arriere

* The two accounts appear to me to relate to the same organism, but I am not
certain whether this is the author's own view. His papers are hard to understand, and
bristle with misspelled names, misquotations, and other unfortunate errors. (C. D.)

6

82 THE INTESTINAL PROTOZOA OF MAN

le long du corps, sans etre cependant reuni a celui-ci par une membrane
ondulante." (It is not clear from this whether or no it is adherent to
the body.) Cysts are not described.

Chalmers and Pekkola (1919) have more recently described, again
from Egypt, another "new" flagellate, apparently identical with Tri-
cercomonas save in that it possesses two anteriorly directed flagella
instead of three. Its cysts were not described. At first this organism
was called Dicercomonas soudanensis, but its generic name was subse-
quently changed to Diplocercomonas (Chalmers and Pekkola, 1919a) —
the first name not being available.

It appears not improbable that all these different descriptions really
refer to one and the same species. Allowance must be made for the
fact that all the workers — Wenyon and O'Connor excepted — have
studied a very small amount of material, and it must be remembered
that the organisms in question are all extremely minute, and admittedly
difficult to study. No adequate cytological descriptions have yet been
given of any of them, and the published figures are obviously, in many
cases, inaccurate (e.g., as regards the insertion of the flagella). It seems
far more probable that some of the descriptions are incorrect, than that
six species, belonging to five distinct genera, really exist — all so much
alike, and differing only in such comparatively trivial points as have
been described."* Tentatively, therefore, we include all these flagellates
in one species, which, by the rule of priority, must be called Enteromonas
hominis da Fonseca.

The apparent discrepancies in the published descriptions seem to be
capable of simple explanations. It may be taken that Wenyon and
O'Connor's account of " Tricercomonas " is essentially correct, and that
this organism has usually three free anterior flagella — only two of which
can sometimes be made out in stained preparations (" Diplocercomonas"
of Chalmers and Pekkola). Sometimes the attachment of the posteriorly
directed flagellum to the body is incomplete, or has not been made out
(da Fonseca's "Enteromonas"), or the posterior flagellum has been

* I have been led to this view partly from reading the published descriptions, and
partly as a result of studying some of Capt. O'Connor's original preparations of
" Tricercomonas. ^ I have also been able to study preparations of (apparently) the
same organism given to me by Miss M. W. Jepps, who encountered it in a military
patient at Southampton. In these preparations all the flagellar arrangements described
by different workers may be seen in different specimens, but their interpretation is often
a matter of great difficulty. I attach particular importance, therefore, to the observa-
tions made by Wenyon and O'Connor on the living animals. (C. U.)

I

THE INTESTINAL FLAGELLATES OF MAN 83

entirely overlooked (Chalmers and Pekkola's " fiulcronwnas"). The
organisms described by Chatterjee and Leger might be — from the in-
complete accounts — either " Tricercomonas " or " Enteromonas." There
are no sufficient characters given to distinguish them from either.

It appears somewhat significant that the describers of " Enteromona "
have varied their descriptions from time to time. At all events, the
circumstance appears to favour the conclusion here reached. In his
earlier accounts, Fonseca (1915, 1916) stated that " Enteromonas"
possesses 3 anterior flagella — 2 short ones directed forwards, and a
longer one trailed behind. After the appearance of Chalmers and
Pekkola's papers — in which these authors stated that there were 3
flagella of equal length, all directed forwards— Fonseca (1918, 1918a)
came to the conclusion that they were right : " none of the three
flagella," he writes, " is constantly recurrent, all three are habituallv
directed forwards." But now (Fonseca, 1920) he reverts to his original
account, and describes and figures the organism with 2 flagella directed
forwards and a longer one trailing behind. Meantime Chalmers and
Pekkola have found similar forms, with the posterior flagellum adherent
to the body, but have referred them to the new genus " : Diplocercomonas."
It thus seems highly probable that the real arrangement is that described
in " Tricercomonas," and the other accounts rest upon inexact or in-
complete observations.

We draw these conclusions with some hesitancy, and believe it
possible — but not probable — that two distinct organisms are included
in the genus Enteromonas as here constituted : (1) Enteromonas as
defined by Fonseca (1920), with 2 anteriorly directed flagella, and one
posteriorly directed and free ; and (2) Tricercomonas, as defined by
Wenyon and O'Connor (1917), with 3 free anterior flagella and a longei
posteriorly directed one adherent to the surface of the body. Further
investigations alone can determine these points — the discovery of the
cysts of the flagellates described by da Fonseca, Chatterjee, and
Chalmers and Pekkola, being especially desirable.

Enteromonas hominis is a very small oval or rounded flagellate, of
somewhat changeable shape, measuring usually 4/4 to 8/x, in length
when alive. Stained specimens measure somewhat less. The flagellate
(PI. V, figs. 62, 65) possesses a single vesicular nucleus, situated at the
anterior end and containing a large central karyosome. The nucleus

84 THE INTESTINAL PROTOZOA OF MAN

is more or less drawn out at its anterior pole, and at this point there are
at least two (probably more) minute blepharoplasts (fig. 65), which give
origin to the four flagella. These are approximately equal in length.
Three of them are free, and directed forwards : the fourth, which may
be slightly longer, is directed backwards. It passes over the surface of
the body, to which it is adherent ( ? always), and terminates freely at
the hind end, or sometimes laterally (figs. 62, 65). The cytoplasm con-
tains food vacuoles, inclosing ingested bacteria. There is no permanent
mouth, however, and no axostyle, no undulating membrane, or other
conspicuous organ.

The details of structure are extremely difficult to make out with
precision, owing to their minute dimensions. The figures (PI. V,
figs. 62-65) here given were all drawn from specimens in the same pre-
paration,* and the apparent variations which they exhibit, from the
typical structure just described, are adduced in support of the interpre-
tation of the genus here advanced. In figs. 62 and 65 we see the typical
form, with its full complement and typical arrangement of flagella,
Fig. 63 shows an individual in which the posteriorly directed adherent
flagellum is not visible — either because it is unstained or because it
has become detached. This is a form corresponding with Fonseca's
Enteromonas. The individual shown in fig. 64 possesses apparently only
two anterior flagella instead of three. This is the type of organism
named Diplocercomonas by Chalmers and Pekkola. It appears highly
probable that all these organisms, obtained simultaneously from the
same patient, belong to the same species, and that the differences in
structure are more apparent than real.

Multiplication by longitudinal fission has been observed by
Wenyon and O'Connor (1917), who have figured a few stages. We
have at present insufficient material at our disposal to describe the
process in detail.

The cysts of this species have also been described by Wenyon and
O'Connor (1917). They are elongate oval structures, measuring 6-8 /u,
in length by 3-4 fx in breadth.f When first formed (fig. 66) they con-

* The preparation is one of Capt. O'Connor's original slides containing the type
species of Wenyon and O'Connor's genus " Tricercomonas." I have restained it,
and now preserve it as a type specimen of the genus Enteromonas as here defined.
(C. D.)

t According to my measurements (of stained cysts — in which the walls are usually
clearly discernible), the correct dimensions of the cysts are 6-6*5 Z4 by 4-4-5 /*. The

THE INTESTINAL FLAGELLATES OF MAX 85

tain a single nucleus. This subsequently divides into two (fig. 67) ;
and each of these daughter nuclei again divides, so that the mature
cyst is 4-nucleate (fig. 68). The nuclei at all stages occupy a charac-
teristic position at the poles of the cyst. Small deeply stainable blocks
or rodlets of " chromatoid " substance are sometimes present in the
cysts of this species — usually at the ends, near or around the nuclei.

It is still uncertain what part of the intestine this flagellate inhabits.
Its geographical distribution appears to be wide : and it may be noted
that Fonseca (1918a) has recently described another species of Entero-
monas from the rabbit, in Brazil. Some of the describers of E. hominis
regard it as pathogenic, but their evidence seems very questionable.

In conclusion, we may refer to the curious flagellate described
under the name " Octomitus hominis " by Chalmers and Pekkola (1916).
This organism appears to resemble a " Tricercomonas " with two sets of
flagellar organs. From the description and figures it is probably not
an Octomitus, as it possesses only one nucleus (?) and blepharoplast (?).
We suggest that it may be a dividing form of " Tricercomonas " (i.e.,
Enteromonas, as here defined) : and we may note — as it may throw
some light on this form — that Fonseca (1920) states that he has observed
" multiflagellate " individuals of Enteromonas hominis. Further in-
formation about this remarkable " Octomitus " is much needed.

Synonymy and Homonymy of the Genera of Flagellates
occurring in the human intestine.

In the foregoing descriptions of the intestinal flagellates of man it has
frequently been necessary to refer to their genera. Some of these are
still in a condition of great confusion, owing to wrong identifications,
misapplication of names, the introduction of new names for forms
already named, and the re-introduction of designations already pre-
occupied or abolished. We propose, therefore, to recapitulate and
amplify what has already been said in this chapter, concerning the
generic names of the forms in question, in the following tables, which
we offer for the use of students of the group. These tables, in con-
junction with the references to original works given at the end of the

measurements given above are those of Wenyon and O'Connor. In stained prepara-
tions the cysts are smaller than those of Endolimax nana, which they otherwise
resemble somewhat. (C. D.)

86 THE INTESTINAL PROTOZOA OF MAN

book, will, it is hoped, enable the reader to obtain a clear and correct
conception of the nomenclature and systematics of this confused and
somewhat difficult group of organisms.*

Genus i. Giardia Kunstler, 1882, emend. Alexeieff, 1914.
Synonyms :

Cercomonas Lambl, 1859.

[nee Cercomonas Dujardin, 1841.]
Hexamita Davaine, 1875 (pro parte).

[nee Hexamita Dujardin, 1841.]
Dicercomonas subgen. Dimorphus Grassi, 1879.

[nee Dicercomonas Diesing, 1865.]

[nee Dimorphus Haller, 1878.]
Megastoma Grassi, 1881.

[nee Megastoma Swainson, 1837, e* a^]
Lamblia Blanchard, 1888.

Genus 2. Trichomonas Donne, 1837, emend. Ehrenberg, ii
Synonyms :

Trico-monas Donne, 1837.

Cercomonas (pro parte) Davaine, 1854, i860.

[nee Cercomonas Dujardin, 1841.]
Saenohphus Leuckart, 1863.
Monocercomonas Grassi, 1879.
Cimaenomonas Grassi, 1881.

Including the "subgenera" Tetratrichomonas Parisi, 1910 ; Penta-
trichomonas Mesnil, 1914 (? Chatterjee, 1915) = Hexamastix Derrieu &
Raynaud, 1914 [nee Alexeieff, 191 2] ; and Tritrichomonas Kofoid (1920).

* For these tables I alone am responsible. I have made every effort to make them
as correct as possible, and I hope that, brief though they be, they contain everything of
importance to the systematise (C. D.)

f I am not certain whether this name should not really be accredited to Dujardin.
He suggested it to Donne, who misspelled it; but Dujardin (1841) himself gave it
correctly in his own work. (C. D.)

THE INTESTINAL FLAGELLATES OF MAN 87

Genus 3. CH1L0MASTIX Alexeieff, 1910.
Synonyms :
Cercomonas (pro parte) Davaine, 1854, i860.

[nee Cercomonas Dujardin, 1841.]
Trichomonas (pro parte) Leuckart, 1879, et al.

[nee Trichomonas Donne 1837, emend.]
Monocercomonas Epstein, 1893.

[nee Monocercomonas Grassi, 1879.]
M acrostoma Alexeieff, 1909.

[nee M acrostoma Latreille, 1825, et al.]
Tetramitus Alexeieff, 1910.

[nee Tetramitus Perty, 1852.]
Fanapepea Prowazek, 191 1.
Difdmus Gabel, 19 14.
Cyathomastix Prowazek & Werner, 1914.

Genus 4. Embadomonas Mackinnon, 1911, emend. 1915.
Synonyms :

? Fanapepea (pro parte) Prowazek, 191 1.*
Waskia Wenyon & O'Connor, 1917.

Genus 5. Enteromonas da Fonseca, 1915, emend.
Synonyms :

Tricercomonas Wenyon & O'Connor, 1917.
Monocercomonas Chatterjee, 1917.

[nee Monocercomonas Grassi, 1879.]
[nee Monocercomonas Epstein, 1893.]
Trichomastix Chatterjee, 1917.

[nee Trichomastix Vollenhoven, 1878.]

[nee Trichomastix Blochmann, 1884, = Eutrichomastix Kofoid
& Swezy, 1915.]
Dicercomonas Chalmers & Pekkola, 1919.
[nee Dicercomonas Diesing, 1865.]
[nee Dicercomonas Grassi, 1879.]
Dipiocercomonas Chalmers & Pekkola, 1919.

* It seems to me possible that some of the smallest forms placed in this genus by
Prowazek (1911a) should be referred to Embadomonas rather than to ChUomasHx.
(C. D.)

88

THE INTESTINAL PROTOZOA OF MAN

Key for Determination of Genera and Species.
We give below a key for the identification of the flagellates found
in the human intestine. The characters used are those of the free
flagellates and also of their cysts — since the latter are of importance
for distinguishing some species from similar ones which occur in other
hosts.

i. (a) Free flagellate with 2 flagella

(b) „ „ „ 3-6 flagella

(c) „ „ „ 8 flagella

2. Very small (5-6 /*) ; flagella anterior, un-

equal ; mouth large ; cysts piriform,
4-5-6 /a long

3. (a) With an axostyle and undulating mem-

brane
(6) With neither axostyle nor undulating
membrane

4. With 3-5 free anterior flagella, and a pos-

teriorly directed one forming the
margin of the undulating membrane ;
cysts unknown ...

5. (a) With 3 free anterior flagella, and a

fourth smaller one lying within the
large mouth
(6) With 3 (or 2 ?) anterior free flagella, and
one posteriorly directed and more or
less adherent to surface of body

6. Length ca. 7-20 p ; cysts 7-9 fi long, lemon-

shaped ..

7. Very small (4-8 jm) j cysts elongate oval, 4-

nucleate, 6-8 /m long

8. Bilaterally symmetrical, with large anterior

ventral sucker ; 2 nuclei, 2 axostyles,
and flagella in 4 pairs ; cysts oval, ca.
12 fi long

Genus Embadomonas 2.

3-

Genus Giardia 8.

E. intestinalis.
Genus Trichomonas 4.

T. hominis.

Genus Chilomastix 6.

Genus Enteromonas 7.

C. mesnili.

E. hominis.

itestinalis.

* The " subgenera " (see p. 68) found in man are :

(1) Trichomonas (= Tetratrichomonas), with 4 free anterior flagella.

(2) Tritrichomonas, with 3 free anterior flagella.

(3) Pentatrichonionas, „ 5 „ „ „

the intestinal flagellates of man 89

Intestinal "Flagellosis."

The condition of being infected with intestinal flagellates is some-
times termed " Flagellosis," though various other designations have also
been used.* By some workers the condition is regarded as more or less
pathological, and "flagellosis" is thus considered to be a disease. We
do not share this view, and regard it as almost certain that intestinal
flagellates are usually harmless to their hosts. It is impossible to
discuss here all the facts, and all the inferences drawn from them, which
have been adduced by those who regard the intestinal flagellates of man
as pathogenic : but we shall note the chief points, and attempt to give
some justification for our opinions.

Much confusion has, undoubtedly, arisen in the past owing to the
indiscriminate use of the word " parasite." There is a natural tendency
to regard all "parasites" as harmful; and intestinal flagellates, being
regarded as " parasites," are consequently suspect. But it should be
remembered that the intestinal flagellates of man, and of most other
animals, are not parasitic in the strict sense of the term: they are more
properly called commensal.f It is, indeed, still very doubtful whether
any truly parasitic intestinal flagellates exist — in any host. In the vast
majority of cases, at any rate, no harmful effects due to their presence
can be demonstrated.

Again, it is to be remembered that the frequent finding of flagellates
in the stools of persons suffering from diarrhoea or dysentery does not
in any way incriminate these organisms as "causes" of the disorders
observed. Flagellates are, it is true, found more often in persons with
diarrhoea than in healthy persons — but for the simple reason that the
stools of healthy persons are seldom examined : and careful examination
of the stools of healthy people has shown that they are probably infected
with flagellates quite as frequently as patients suffering from diarrhoeic
disorders.

If a person naturally infected with intestinal flagellates happens to
suffer from diarrhoea, examination of his stools will then usually reveal
their presence : but if his stools are normal, only the cysts of these
flagellates will, from time to time, be discoverable in them — not the
active forms. Consequently, the circumstance that active flagellates are
not usually found in the stools of healthy people does not imply that
such people are not commonly infected. An attack of diarrhoea often

* Cf. Introduction, p. 15. f Cf. Introduction, p. 13.

9° THE INTESTINAL PROTOZOA OF MAN

leads to the discovery of flagellates in a person not previously suspected
of harbouring them : and it is probably true that the so-called "flagellate
diarrhoeas " are not diarrhoeas " caused " by flagellates, but diarrhoeas
which have " caused " the flagellates to make their appearance in the
stools.

We sometimes read of cases of " flagellate diarrhoea " in which a
"cure" has been effected by some form of treatment. This or that
drug was administered, and the diarrhoea ceased : the flagellates then
disappeared from the stools. Evidence of this sort is then considered to
corroborate the belief in the pathogenicity of the flagellates concerned.
All such cases, however, have a very different complexion when care-
fully examined. All the so-called "specifics" for flagellate infection
hitherto advocated are probably without action upon these organisms :
at all events, nobody has yet produced any good evidence to show that
any drug whatever can eradicate an infection with intestinal flagellates.*
It appears highly probable that all the "cures" which have been claimed
are based upon insufficient examination of the stools after treatment.
More prolonged examination would have shown that the flagellates were
still present in these "cured" cases.f Consequently, if a cure of the
clinical condition was effected, without removing the flagellates, the
evidence really indicates that the flagellates were not causally concerned
in the production of the disorder.

Often, too, we read that some intestinal flagellate was the "cause" of
a patient's intestinal disorder because "no other cause could be found."
The absurdity of such statements is obvious. If such reasoning were
permissible, one would have to suppose that many cases of diarrhoea, in
which neither flagellates nor other organisms can be found, are due to
no cause at all.

Evidence has been adduced to show that some of the intestinal
flagellates are capable of invading the tissues, and causing definite
lesions in the bowel. This evidence has recently been reviewed by
Haughwout (1918), and most of it is highly unconvincing. Perhaps
the strongest evidence is that just brought forward by Wenyon (1920),
who has found Trichomonas present in the wall of the bowel : but here,
as in all such cases, it remains doubtful whether the invasion of the
tissues — which, in Wenyon's case, appeared otherwise normal — occurred

*Cf.p. 159.

1 1 have examined many such cases, and always with the same result. (C. D.)

INTESTINAL FLAGELLOSIS 91

before or after the death of the patient. The evidence in other c;
also requires further explanation. Biland (1905), for example, has found
peculiar lesions in the intestine of a patient infected with Trichomonas.
But the lesions were in the small intestine and no flagellates were found
in them, whilst the normal habitat of this flagellate is the large intestine.
Again, in the often-quoted case of Fairise and Jannin (191 3), the ulcera-
tion, believed by them to have been caused by Giardia, was found in
the large bowel ; whereas this flagellate lives in the small intestine.
Cysts of Giardia were found in the ulcers, moreover, — a very remarkable
phenomenon. It is clear that such findings themselves require to be
explained. They are not, as they stand, easily intelligible ; and they are
far too ambiguous to be used, at present, as evidence of the pathogeni-
city of the intestinal flagellates.

Trichomonas hominis has occasionally been observed to ingest red
blood-corpuscles, and this has been regarded by some observers as
evidence of its pathogenicity (cf. Woodcock, 1917 ; Haughwout and de
Leon, 1919). It is clear, however, that the mere fact that a flagellate is
able to eat a blood-corpuscle, when presented to it, supplies no evidence
whatever that the flagellate itself attacks the tissues or has been in any
way responsible for the appearance of the corpuscles in the stools.*
Haughwout and de Leon (1919) could find no other likely cause for
their patient's dysentery than the numerous " Pentatrichomonas" in her
stools : and they observed many of the flagellates, in the bloody mucous
stools, containing ingested red corpuscles. But in similar cases which
one of us has studied (O'Connor, 1919), careful investigation showed
that the patients were suffering in reality from bacillary or bilharzial
dysentery — which was sufficient to account for the corpuscles present
in the stools. The presence of trichomonads concomitantly, and the
fact that they were ingesting red corpuscles, can hardly, in such cases,
be regarded as evidence of the pathogenicity of these flagellates. The
obvious conclusion to draw is that Trichomonas will sometimes eat
blood-corpuscles when they happen to be available : any further infer-
ence appears unwarranted.

Among the older observers opinion was divided as to the patho-
genicity of the intestinal flagellates. Grassi (1888) and others regarded
them as harmless. Most physicians, however, considered them — and

* It may be noted here that the amoeba of the frog {Entamoeba ranarum), as I have
shown elsewhere (Dobell, 1909), will ingest red blood-corpuscles when these happen to
be present in the gut contents. It is certain, in this case, that the amoeba is not
pathogenic, and does not attack the tissues. (C. D.)

92 THE INTESTINAL PROTOZOA OF MAN

still consider them — harmful to a greater or less extent. Among recent
workers who have endeavoured to incriminate one or other of the
intestinal flagellates* as " causes " of human disease, may be mentioned
Brumpt (19 1 2), Nattan-Larrier (1912), Mello-Leitao (1913), Escomel
(1913, 1919), Mathis O914), Gabel (1914), Lynch (1915a), Rhamy and
Metts (1916), Kennedy and Rosewarne (1916), Chatterjee (1917),
Sangiorgi (1918a), Labbe (1919), Boeck (1921). We believe that few
who read these and similar recent papers in a critical spirit will find
any conclusive evidence of the pathogenicity of the flagellates concerned.
It is impossible, however, to discuss all these works in detail here, and
we must therefore be content, after briefly expressing our own view of
the facts, with referring the reader interested in the subject to the fore-
going papers and others to which these will lead him.

There is one other point which must be mentioned before con-
cluding. This is the debated question as to whether the intestinal
flagellates found in man occur also in other animals. It is often stated
that man acquires his infection from some other host : for example,
Giardia and Trichomonas are known to occur in rodents, and it has
been assumed that these animals act as "reservoirs" of human infection.

Stated briefly, the facts appear to be as follows. Species of Giardia
occur in rats, mice, guinea-pigs, rabbits, and other rodents, and also in
the cat.f At present it is not certain whether these are of the same or
of different species, nor whether any or all of them belong to the
species found in man (G. intestinalis Lambl). They are all very much
alike, though some authors {e.g., Bensen, 1908) believe that they are
distinguishable. Attempts have been made by many workers (e.g.,
Perroncito (1888), Russell (1916), Fantham and Porter (1916), etc.)
to infect rodents with G. intestinalis by feeding them upon cysts from
human stools, and in most of such experiments success has been
claimed. The evidence is, however, still far from conclusive, since
the animals used for such experiments all belong to species which are
themselves very commonly infected in nature with forms of Giardia

* It is, perhaps, a mistake to discuss flagellates in general as possible " causes" o
diarrhoea : for it is possible that some of them are harmless, others harmful. At
present, however, there appear to be no sound reasons for discriminating between the
species in this way. It seems to us, on the other hand, to be clearly unjustifiable to
discuss simultaneously whether the flagellates and ciliaies are pathogenic — as has been
done recently by Haughwout (1918) : for the case against Balantidium has been
clearly made out, but the pathogenicity of such an organism in no way incriminates
protozoa belonging to quite a different group.

f This was first shown by Grassi (1881). The form in the rabbit had been
previously seen, and named Hexamita duodenalis, by Davaine (1875).

INTESTINAL FLAGELLOSIS 93

not certainly distinguishable from G. intestinalis. Jt is extremely diffi-
cult to obtain " clean " animals for such experiments, and the evidence
so far produced cannot, therefore, be regarded as supplying a definite
proof that G. intestinalis can be transmitted to any laboratory animal.
The same objections apply, mutatis mutandis, to the experiments which
have been carried out with Trichomonas and Chilomastix. The confi-
dence of the experimenters in the success of their experiments can
hardly counterbalance the obvious deficiencies in their controls.

Moreover, it seems hardly necessary to regard rats and mice, or
any other animals, as "reservoirs" of human flagellate infections. Such
a conception was, no doubt, plausible in the days when these flagellates
were believed to be uncommon in man, and, in this host, productive
of disease : but now that we know that healthy people everywhere are
very frequently infected with Giardia and other flagellates, it seems
unnecessary to look for "reservoirs" outside the human species itself.
Indeed, experiments such as those of Fantham and Porter (1916) appear
to prove too much. They claim to have shown that laboratory animals
can be experimentally infected with Giardia intestinalis, and that it is
definitely pathogenic to these animals. But the experiments appear to
show that the Giardia of man is not merely pathogenic but frequently
fatal to mice and other animals. If this is so, it is hardly possible to
reconcile the fact with the contention that mice act as a" reservoir "
of human Giardia infection. We know, too, that mice are almost
always infected with Giardia in nature, without any harmful results
being demonstrable. It thus appears impossible to accept all these
conclusions.

At the present time it seems to us best to regard the flagellates of
rodents as belonging to species which are distinct from those occurring
in man, but the question can be answered only by further observations
and experiments.

We may, in conclusion, sum up this section by saying that, in our
opinion, there is as yet no good evidence to prove that any intestinal
flagellate found in man is pathogenic, but that there is very considerable
evidence to show that most and probably all of them are harmless.
Moreover, the evidence that the species found in man are identical
with those of other hosts is inconclusive, and there is at present no
good reason to suppose that any host but man can or does act as a
natural " reservoir" of human infection.

94

CHAPTER V.
THE INTESTINAL COCCIDIA OF MAN. COCCIDIOSIS.

It has been noted already in the Introduction (p. 5), that the Phylum of
the Protozoa called Sporozoa is represented in the human bowel by
several species belonging to the Class Coccidia. These will be briefly
described in the present chapter.

The Sporozoa form a very large group of exclusively parasitic
protozoa. If we leave out of account the so-called " Neosporidia " — a
group whose inclusion is, nowadays, more than questionable — then the
Sporozoa may be said to consist of three closely related classes, forming
a well-defined and "natural" group. These are (1) the Haemosporidia
— containing the malarial parasites and their allies ; (2) the Coccidia ;
(3) the Gregarinida — a group of parasites occurring in invertebrates only.
The first two are so intimately related to one another that they are
commonly included in one group — the Coccidiomorpha (Doflein).

The Coccidia themselves form a very homogeneous group, with a
characteristic life-cycle of some complexity. In its general outline this
life-cycle is closely similar to that of the malarial parasites ; though a
coccidium usually, but not always, passes the whole of its life in a single
host — not, like a malarial parasite, in two hosts. Unfortunately, the com-
plete life-cycle has not yet been worked out for a single one of the intes-
tinal coccidia of man. Only fragments of their life-histories are at
present known. In order that the known stages may be correctly under-
stood, therefore, we must preface our description of them with a short
account of the development of a typical member of the Coccidia.
This will be readily followed with the aid of the accompanying
diagram (Text-fig. B).

The young coccidium (a) is a minute and usually oval organism,
living within a cell — usually epithelial — of its host. (In the figure, the
cells are supposed to be those of the epithelium lining the gut — as seen
in a diagrammatic partial cross-section.) The little parasite contains a
single nucleus, probably of a complicated structure. The young

THE INTESTINAL COCCIDIA OF MAN

or

organism soon grows, at the expense of the host-cell, into a large,
plump, asexual individual or schizont (b). It then reproduces by a
process of multiple fission, or SCHIZOGONY — its nucleus first dividing
repeatedly (c), and its cytoplasm then splitting (d) to form as many
vermiform young as there were nuclei. These young forms are called

Text-fig. B.
Diagram illustrating the Life-history of a Coccidium.

merozoites (or schizozoites), and in their formation a small portion of
the parent schizont is usually left over as a residual body, which
ultimately dies and disintegrates. The merozoites are actively motile.
They wriggle out of their host-cell (e), and soon find a new one, which
they promptly invade (/). Having bored into it, they round themselves
off and cease to move (a), and then begin the process of schizogonic

q6 THE INTESTINAL PROTOZOA OF MAN

development anew (a-f). The events just described constitute the
asexual part of the life-cycle.

Sooner or later, schizogony ceases, and a sexual cycle is initiated.
The merozoites (e), instead of becoming schizonts once more, develop
into male and female individuals (so-called " microgametocytes "
and " macrogametocytes "). In the males (g, h), the nucleus multiplies
(i) and finally gives rise to a brood of microgametes, which are usually
flagellate, and which break away from the body of the male and swim
off (k) in search of macrogametes. The females (/, m) do not form
broods of gametes, but each becomes converted, as a whole, into a single
macrogamete (//). When a microgamete encounters a macrogamete,
it penetrates it at one pole— ultimately entering its nucleus (o). This
process of fertilization — which is accompanied by very complex
nuclear changes— results in the formation of a uninucleate zygote,
which, in the case of intestinal coccidia, usually falls into the lumen of
the gut (p). It may be noted that there is probably no reduction of the
chromosomes during the formation of the gametes — the so-called
" nuclear reduction " occurring at these stages being merely a fragmen-
tation of the karyosome of the sexual individual. The chromosome
cycle in the Sporozoa is peculiar, and reduction occurs immediately
after — not before — fertilization (Dobell and Jameson, 1915).

The zygote (p) secretes a cyst wall round itself — the oocyst.
Within this, the protoplasm contracts ; and the nucleus then under-
goes division into a variable number (4 in the diagram) of daughter
nuclei (q). Around these nuclei the cytoplasm now segments, so as
to form an equal number of rounded masses (r) — the sporoblasts,
or precursors of the spores. In this process a portion of the parent
protoplasm is usually left over, forming an OOCYSTIC RESIDUE (shown
as a granular mass in r). Each sporoblast now secretes, in its turn,
a cyst wall around itself — the SPOROCYST — and becomes a spore.
Inside each spore, the nucleus divides (r), as a rule, forming a variable
number (2 in the diagram) of daughter nuclei. The cytoplasm seg-
ments around these to form an equal number of uninucleate vermiform
germs, or sporozoites (s), — a small quantity of protoplasm being
usually left over in the process to form a SPOROCYSTIC residue.
The spores are now ripe. (Fig. s represents a ripe oocyst, containing
4 spores (each inclosing 2 sporozoites) and an oocystic residue.) Fer-
tilization always takes place inside the host, but the formation of the

THE INTESTINAL COCCIDIA OF MAN

97

spores within the fertilized oocyst (sporogony) may take place outside.
The oocyst is usually very resistant, and serves to protect the spores
during their development. The sporozoites, contained within the ripe
spores, are the forms which are capable of infecting a fresh host. When
living spores are ingested, and thus enter the gut, their walls burst
and liberate the sporozoites (1). These then seek their suitable host-
cells, which they invade (/) ; and thereupon they grow into the young
parasites (a) with which our description began.

The development just described is seen, with various modifications,
in all coccidia. It was first correctly made out by Schaudinn and
Siedlecki in 1897, whose observations have since been abundantly
confirmed. In the case of the intestinal coccidia of man, however,
only certain stages of the sporogonic cycle are at present known : and
though we must assume that the other stages are conformable with
those already worked out in allied species, the schizogonic and sexual
cycles are still unknown.

The classification of the Coccidia is largely based upon the
characters furnished by their oocysts and spores. Of especial importance,
from the systematic standpoint, are the size and shape of the spores,
the number of them present within the oocyst, and the number of
sporozoites contained within each spore. The presence or absence of
oocystic and sporocystic residues is also of systematic importance.

The intestinal coccidia of man belong to two different genera —
Isospora and Eimeria — which are readily distinguishable as follows :

Genus 1. Isospora Aime Schneider, 1881 (= Diplospora Labbe, 1893).

Oocyst containing two tetrazoic spores (i.e., each inclosing four

sporozoites).
Genus 2. Eimeria Aime Schneider, 1875 (= Coccidium Leuckart,

1879). Oocyst containing four dizoic spores (i.e., each inclosing

two sporozoites).

In the human intestine there is but one species belonging to the first
genus, but three distinct species in the second. Brief descriptions of all
these will now be given.*

* The descriptions are, in the main, condensed from an earlier memoir by one of us
(Dobell, 1919), in which a more detailed account of the Coccidia of man will be found.

98 THE INTESTINAL PROTOZOA OF MAN

(i) Isospora hominis (Rivolta) Dobell, 1919.
Chief synonyms :

" Psorospermien " Virchow, i860; Leuckart, 1863; Eimer, 1870.

Cytospermium hominis Rivolta, 1878.

Coccidium perforans (pro parte) Leuckart, 1879, et aliorum.

"Coccidies intestinales " Railliet & Lucet, 1890.

Coccidium bigeminum (Stiles) var. hominis Railliet & Lucet, 1891.

Coccidium hominis (Rivolta) Labbe, 1896.

Coccidium bigeminum (Stiles) Blanchard, 1396, et aliorum.

Eimeria stiedae (Lindemann) Llihe, 1906, et aliorum.

Isospora bigemina (Stiles) Doflein, 191 1, et aliorum.

Isospora Wenyon, 1915, et aliorum.

This species was probably discovered in Berlin by a Swedish
physician named Kjellberg, about the year i860. His observations
were briefly recorded by Virchow (i860). The parasites were seen in the
villi of the small intestine. They appear to have been seen in a similar
situation by Eimer (1870), and were first named, though not studied,
by Rivolta (1878). The oocysts were possibly first seen in the faeces,
during life, by Railliet and Lucet (1890) ; but the first accurate account
of them was given by Wenyon (1915, 1915^). Since then the}7 have
been studied by many workers.

The schizogonic and sexual cycles are completely unknown at
present ; but presumably these stages occur in the small intestine,
and resemble the corresponding stages in Isospora rivoltae Grassi
{=Coccidium bigeminum Stiles) — a common parasite of the cat.

The oocysts, which are passed in human faeces in an incompletely
developed condition, have the following characters. They have an elon-
gate ovoid form (PI. VI, figs. 97-102), the narrower end usually being
drawn out into a sort of neck. They measure, as a rule, some 25-33 H-
in length, by 12-5-16 /x in breadth at the widest part. More slender
specimens are not uncommonly seen. The wall of the cyst (oocyst
proper) is thin, smooth, and colourless, and very resistant to most
fixatives and other reagents. It consists of at least two layers — the
innermost being thin and membranous, the outer hard and porcel-
laneous in appearance. At the narrower end an inconspicuous micro-

THE INTESTINAL COCCIDIA OF MAN 99

pyle — through which the microgamete entered — may sometimes be
made out.

When discharged from the body in the stools, the oocysts are usually
unsegmented, their protoplasmic contents being contracted into a ball
(PI. VI, fig. 97), and rilled with highly retractile granules of variable size.
Among these the single nucleus is usually visible as a rather large
clear area (fig. 97). Development takes place outside the body, and
generally requires one or two days for its completion. The spherical
mass of protoplasm first divides into two daughter masses (fig. 99) —
the sporoblasts — its division being preceded by that of the nucleus
(fig. 98). The two sporoblasts then rapidly become ovoid, and secrete
cyst walls (sporocysts) around themselves, thus becoming converted
into spores (fig. 100). The spores, as in other coccidia, have double
walls — an inner and permanent wall (endospore), and an outer
deciduous layer (epispore). They measure about 12-14 yu by 7-9 /*.

Further development takes place inside each sporocyst. The
originally single nucleus divides, by two successive divisions, into four
nuclei. Around each of these the cytoplasm collects to form the four
worm-like or sausage-shaped sporozoites, each with a single nucleus
at one of its ends. In this process of differentiation a large granular
mass of protoplasm (sporocystic residue) is left over (fig. 100). This
residue is at first very conspicuous in the spore, but later it disintegrates.
There is no definite residue in the oocyst itself in this species, though
a few granules are sometimes visible — especially at the narrow end of
the cyst (cf. fig. 99).

Degenerate oocysts, which will not develop outside the body, are
sometimes found in human faeces (figs. 101, 102) : and an abnormal
development, resulting in the formation of a single sporocyst containing
eight sporozoites, has been observed (Wenyon and O'Connor, 1917).

When the spores are fully formed, no further development occurs
outside the body. If the ripe cysts are swallowed by a' human being
they probably hatch in the small intestine, and liberate their contained
sporozoites. These then become actively motile and invade the epithe-
lium of the gut wall, where they grow and multiply. Such stages are,
however, as noted already, still unknown in the present species : and
they are postulated on the ground that a similar development occurs in
related species found in other animals.

IOO THE INTESTINAL PROTOZOA OF MAN

(2) ElMERIA WENYONI Dobell, 1919.
Synonym :

Eimeria (Coccidium) Wenyon, 1915.

This species was discovered and described by Wenyon in 191 5.* It
is a rare coccidium, and resembles E.falciformis, a common parasite of
mice. The only stages hitherto seen are the fully developed oocysts,
discharged in human faeces. Their earlier stages of development, and
the schizogonic and sexual stages of the parasite in the tissues of man,
are still undiscovered ; but it is probable that these earlier stages must
be sought in the epithelium lining the small bowel.

The mature OOCYST of E. wenyoni (PI. VI, fig. 104) is approximately
spherical, having a diameter of about 20 p. Its outer surface is rough
and rugose, its inner smooth and lined with a thin membrane. Con-
tained within the oocyst are four oval spores, measuring about ioyu, by
7 fi. The sporocysts are superficially rough and somewhat irregular,
owing, apparently, to the presence of persistent remnants of the episporal
coats upon them. No oocystic residue is present. Each spore contains
two typical vermiform sporozoites, lying with their blunter nucleate
extremities directed towards opposite poles of the spore. In addition to
the sporozoites, each spore contains a sporocystic residue, in the form of
one or two highly refractile rounded masses.

(3) Eimeria oxyspora Dobell, 1919.

Synonym :

Eimeria oxyphila Mesnil, 1919.!

This species of Eimeria was described by Dobell (1919), and is, like
the preceding, apparently a rare organism. Up to the present the fully
developed oocysts are the only stages which have been seen. They
differ greatly from those of E. wenyoni.

The fully formed OOCYSTS (PI. VI, fig. 103), as passed in the stools,
are large spherical structures measuring about 36/i, in diameter. Each
contains four long, whetstone-shaped spores and a small oocystic residue
in the form of a few bright granules. The wall of the cyst (oocyst

* See Wenyon (1915^).

t The employment of this name by Mesnil appears to be inadvertent, and merely
the result of a misprint.

THE INTESTINAL COCCIDIA OF MAN 101

proper) is slightly yellowish, and composed of at least two layers— the
inner thick and uniform, and the outer, which appears composite
incrusted with foreign particles from the faeces.

The four spores are provided with tough walls (sporocysts), and
appear slightly rough externally— especially at their ends— owing to
the presence of persistent remains of the epispores. The spores are
equally sharply pointed at both ends, and measure 30-32 fj, in length
by 7*5 yu, in breadth at the middle. Each contains two very long
sporozoites and a sporocystic residue in the form of a number of small
highly refractile granules. The sporozoites are blunt at one end, pointed
at the other, and lie with their blunt ends directed towards opposite
poles. Each has a large oval nucleus at the blunt end, situated sub-
terminally. Between the nucleus and the blunt extremity (probably the
posterior end of the sporozoite), there are always two or three minute
fusiform bodies, of unknown nature. They are very brightly refractile,
and resemble crystals. At the other side of the nucleus — that is, in the
cytoplasm between it and the pointed end— a few rather feebly refractile
granules can be made out.

The other stages of this parasite are unknown, but probably occur in
the epithelial lining of the small intestine.

(4) ElMERIA SNIJDERSI Dobell, 1021.

This species was recently discovered by Snijders (1921) in Sumatra.
It somewhat resembles the preceding form, and, like it, is known only
from the fully developed oocysts found in the stools.

The OOCYSTS (PI. VI, fig. 105) are very large — even larger than those
of E. oxyspora. They are spherical, and measure 40/i to 48/4 in
diameter — the average being about 45 yu,. Their walls consist of at least
two layers, and inclose the four dizoic spores typical of the genus, and a
small oocystic residue in the form of a few scattered granules.

The spores are like those of E. oxyspora, but are relatively shorter,
and spindle-shaped (fig. 105). They have the usual double sporocysts
(permanent endosporal and deciduous episporal coats), and contain two
long vermiform sporozoites and a small sporocystic residue in the form
of one or two refractile globules. The length of the spores is about 22/j,
to 24/i, their breadth 7"5/t. No "crystalline" bodies, like those of
E. oxyspora, have been observed at the blunter ends of the sporozoites.

102 THE INTESTINAL PROTOZOA OF MAN

E. snijdersi thus differs from E. oxyspora in having larger oocysts and
shorter and relatively plumper spores. Its habitat in the body is still
unknown : but, like the other species of Eimeria in man, it probably
lives in the epithelium of the small intestine. Snijders (1921) observed
a few unsegmented — probably degenerate — oocysts in the faeces of the
only infected individual whom he studied ; but apart from these, no
other stages in the life history have yet been seen.

Key to the Genera and Species.

We give below a simple key for the determination of the genera
and species of coccidia hitherto found in human faeces — a key based
entirely upon the characters supplied by the oocysts and spores, since
the other stages are still insufficiently known.

1. (a) Ripe oocyst elongate, with 2 tetrazoic spores Genus Isospora 2.
(b) Ripe oocyst spherical, with 4 dizoic spores ... Genus Eimeria 3.

2. Spores oval, 12-14/A X 7-9/* ... • •• ••• l.hominis.

3. (a) Oocyst ca. 20/i; spores oval, ca. ioyu, x 7//, ...E. wenyoni.

(b) Oocyst ca. 36/i; spores whetstone-shaped,

ca. 31/i X 7'5/i ... ... ... ...E. oxyspora.

(c) Oocyst ca. 45 fi ; spores spindle-shaped, ca.

23 P X 7'5 yu. ... ... ... ... ...E. snijdersi,

Intestinal Coccidiosis.

Coccidiosis is the general name given to the condition of being
infected with coccidia, but we are here concerned only with intestinal
coccidiosis in man — a subject about which very little is known.

The commonest intestinal site of infection with coccidia — speaking
generally — is the small intestine : but species of coccidia which inhabit
the stomach {e.g., Cryptosporidium in the mouse) and the large gut
(e.g., Eimeria zurni in cattle) are known. From the fact that Kjellberg*
and Eimer (1870) appear to have observed coccidia in the epithelium
of the small intestine of man, and since oocysts have since been found
in human faeces, it thus seems probable that the small bowel is the
site of infection selected by at least one of the coccidial parasites of man.

Since the Coccidia are always tissue-parasites, they must always

* See Virchow (i860).

COCCIDIOSIS 103

produce a more or less pathological condition in their host. Never-
theless, no clinically recognizable disease due to their presence has yet
been observed in man. Even in those cases in which, from the number
of oocysts passed in the stools, a heavy infection appears to have been
present, no definite symptoms referable to the infection have been
elicited. This is in agreement with the observations made upon
coccidiosis in other animals. The Coccidia parasitize both vertebrates
and invertebrates, and frequently occur in their hosts' tissues in
immense numbers : but in spite of this, their hosts often appear to be
unaffected, in genera health, by their presence.

In agreement with this apparent lack of pathogenicity, the lesions
due to coccidial invasion show, in most animals, surprisingly little tissue
reaction. At the site of infection there is often little to be seen but
cellular destruction, the surrounding tissues appearing perfectly healthy.
Sometimes, however, the parasites apparently cause considerable hyper-
trophy of the neighbouring tissues — a condition usually seen in the
well-known hepatic coccidiosis of the rabbit. Eimeria stiedae, the
parasite here implicated, invades the epithelium of the bile ducts, which
frequently undergo, in consequence, a prodigious proliferation. Heavy
infection, moreover, may lead to serious consequences, as is well seen
in the case of E. stiedae and E. zurni. The former may cause a fatal
disease in the rabbit, and the latter causes sometimes a severe and even
fatal form of dysentery in cattle. Apart from such inferences as can be
drawn from similar examples of coccidiosis in animals, nothing definite
can yet be said about the pathology, morbid anatomy, pathogenesis, or
symptomatology, of intestinal coccidiosis in man.

It should be noted that a condition of hepatic coccidiosis has been
described in man. It appears to be due to a species of Eimeria which
has not yet been properly investigated. The parasite was discovered in
France by Gubler (1858), and has since been observed, apparently, by
several other workers.* The oocysts of this species are oval structures,
measuring some 20 fi in length : and it must be presumed that they are
passed out in the faeces of infected individuals. Further information
about this coccidium is much needed. It has usually been supposed
that it is identical with E. stiedae of the rabbit, but this is almost certainly
incorrect.

* For a full account of this organism — so far as it is known— see Dobell (1919'
p. 190.

104 THE INTESTINAL PROTOZOA OF MAN

All the intestinal cocci dia of man are still very imperfectly known.
It was thought until recently that they were of the same species as those
occurring in rabbits, cats, and dogs : but this is not correct. The para-
sites of man appear to be peculiar to man,* and careful attempts which
have been made to transmit them to other animals (by Wenyon and
O'Connor) have all been completely negative. It should also be noted
here that many of the earlier cases of " coccidiosis " described in man
are now known to have been based upon mistakes of observation and
interpretation.

Intestinal coccidiosis is a rare condition in man. By far the com-
monest species hitherto found is Isospora honiinis, with which over
70 cases of infection have now been recorded (Wenyon, 1915, 1916 ;
Woodcock and Penfold, 1916; Roche, 1917 ; Cragg, 1917 ; Brumpt,
191 8 ; and others). All the infections were, apparently, observed in
persons who had been in Egypt, Gallipoli, Greece, Mesopotamia, and
neighbouring countries. It is possible, therefore, that the infection is
endemic in these areas. f E. wenyoni was found by Wenyon (19156)
in a single patient who had been in Gallipoli. Three further cases
were observed by Roche (1917) in Salonika, and Chatton (1918a) and
Brumpt (1918) appear to have seen a few more in Tunis and France
respectively. Nothing else is known about the distribution or incidence
of this parasite.

E. oxyspora and E. snijdersi have been seen but once each — both of
them in patients suffering from chronic amoebic dysentery acquired in
the tropics. The patient with E. oxyspora came from Ceylon, the one
with E. snijdersi was studied in Sumatra. It is still too early to draw
conclusions regarding the distribution of these parasites, therefore,
though there is some evidence to show that all the species of Eimeria
found in man have a tropical or a subtropical habitat.

In conclusion, it must be noted that coccidiosis in man appears to

* Reichenovv (1920), in a work just published, appears to dissent from this view, on
the grounds that the coccidia hitherto found in man may ultimately be found to para-
sitize other hosts. But this is an objection which may be urged against any parasite
whatsoever which has ever been described from any host, and one which can never be
disposed of until all the parasites of all animals are fully known. At present the
coccidia found in man have been shown to occur in man only : they have been found
in no other host. Until they have been shown to occur elsewhere, we see no impro-
priety in saying that they are " peculiar to man." This is a true statement of fact as
at present ascertained. (C. D.)

t Noc (1920) has recently described a case of Isospora infection found in Senegal in
a French soldier who had never been in Macedonia or the Dardanelles.

COCCIDIOSIS 105

be a transient condition. In most of the cases hitherto observed the
oocysts have been found in the stools on very few occasions, and have
disappeared completely when the infected individuals were kept under
observation. All the species of Eimeria were seen to behave in this
way. More persistent infections have been observed, however, in the
case of Isospora (Roche, 191 7 ; O'Connor, 1919). There is some reason
to suppose that many coccidial infections are transitory, and tend to
die out of their hosts with time. There is nothing to show that the
schizogonic cycle can be repeated indefinitely ; and the occurrence of
oocysts in the stools may mark the completion of development and
the final exit of the parasite. Heavy and persistent infections, often
seen in animals, are probably a result of frequent re-infection ; and
the transitory character of human infections may be due to the circum-
stance that such re-infection has generally been prevented.

o6

CHAPTER VI.
THE INTESTINAL CILIATES OF MAN. BALANTIDIOSIS.

The protozoal Phylum known as the Ciliophora contains an immense
number of organisms. It is represented in the human bowel, however,
by very few species — at least one, and possibly as many as three or four.
All these belong to the Class Ciliata (or Infusoria, sensu stricto) and its
Order Heterotricha.

A typical ciliate — such as the familiar Paramecium of ponds — is a
moderately large protozoon, more or less bilaterally symmetrical, and
covered more or less completely with a coat of hair-like cilia, which
serve for locomotion. It has a permanent mouth and other organs —
such as nuclei, contractile vacuoles, etc. — and shows a considerable
degree of structural complexity. It multiplies by transverse fission into
two. The typical ciliate is hermaphrodite, and has a remarkable and
peculiarly complicated sexual process called conjugation. Encystation
occurs at some time in the life-cycle of most species.

One of the most characteristic features of the Ciliata, besides their
cilia, is their nuclear apparatus. This consists of two nuclei, or two sets
of nuclei, known as meganucleus (or macronucleus) and micronucleus.
The former are to be regarded as somatic nuclei, the latter as germinal
nuclei — respectively comparable with the nuclei of the body-cells and
germ-cells of a metazoon .

The ciliates found in the human bowel belong to the less specialized
forms, and have a comparatively simple structure and life-history. They
belong to the genera Balantidium Claparede & Lachmann, 1858, and
Nyctotherus Leidy, 1849. The species will now be described in detail.*
There are three which appear to be valid, and several doubtful forms
which require further investigation.

* A key to the genera and species will be found on p. 118 infra. From the systematic
standpoint, the genera — which have been long established, and are well known — require
no special discussion here.

THE INTESTINAL CILIATES OF MAN 107

(1) Balantidium coli (Malmsten) Stein, 1862.
Chief synonyms :

Paramaecium f coli Malmsten, 1857.

Plagiotoma coli (Malmsten) Claparede & Lachmann, 1858.

Leucophrys coli (Malmsten) Stein, i860.

Holophrya coli (Malmsten) Leuckart, 1863.

This, the commonest of the intestinal ciliates found in man, was
discovered* in 1856 by Malmsten, a Swedish physician, in Stockholm.
He described and namedf it in the following year— his account of the
parasite being accompanied by admirable figures executed by the
zoologist Loven. Malmsten found the organism in the stools of two
patients suffering from dysentery : but his discovery was extended soon
afterwards by Leuckart and Stein, who found that the organism occurs
very frequently in pigs. Many analogous observations have been since
recorded by later workers, and the parasite has been many times
redescribed. In recent years it has also been found in monkeys.

Balantidium coli is the largest protozoon encountered in the human
intestine. It is roughly oval in shape, and in length usually measures —
in our experience — from about 50/i to 70^, with a breadth, at the widest
part, of some 40/i to 6o/x. Different authors have given various dimensions
for the forms which they have studied ; and these range from as little as
25//,, as a minimal length, up to over 200/1, as a maximum. Many
observers describe specimens attaining a length of ioo/x or even more.
In the free-living ciliates — such as Paramecium — it is now well known,
as a result of the work of Jennings and others, that many species are
composed of a number of distinct races distinguishable by their average
sizes. £ The species Paramecium caudatum, for example, is divisible
into at least half-a-dozen such races, whose mean lengths range from
about 230 ix to about 175/A. It seems highly probable that further
investigation will show that similar races, differing in their dimensions,
exist in Balantidium.

* It is frequently stated — owing to a series of mistakes — that this organism was
discovered by Leeuwenhoek. See Dobell (1920) for the history of this matter.

f Malmsten (1857) referred the parasite to the genus Paramecium with some doubt.
He says: "Da diese Darminfusorien sich aim meisten den Paramaecien zu nahern
scheinen, so konnte man die Art einstweilen Paramaecium? coli nennen." Op. cif.,
P- 3°5-

t Full references to the literature of this subject will be found in an earlier work by
one of us, Dobell (1914).

108 THE INTESTINAL PROTOZOA OF MAN

The general form and structure of B. coli is shown in fig. 109 (PI.
VII), and somewhat diagrammatically in fig. 106 on the same Plate.
The latter figure depicts an individual viewed from the left side. The
animal is slightly asymmetrical, and more pointed at the anterior
than at the posterior end. Situated subterminally at the anterior end is
a small triangular area leading into a funnel-like pit — the mouth {mo.).
The surface of the body on which this is placed is called ventral, the one
opposite to it dorsal. The dorsal surface is rather more convex than the
ventral, and frequently appears to bulge somewhat in consequence.
The asymmetry is especially conspicuous when the animal rotates in the
process of swimming. As a rule it retains its shape unaltered ; but it is
not rigid, and is often seen to be bent or distorted by the pressure of the
surrounding bodies among which it moves in the faeces. Balaniidium
is generally described as being "slightly metabolic," but its changes in
shape appear to be produced passively.

The whole body is invested with a coat of very fine cilia, arising in
parallel longitudinal rows from minute basal granules. The rows of
cilia give the animal the appearance of being striated. The main part of
the body consists of granular endoplasm, in which the internal organs
are situated. This is surrounded by a thin layer of ectoplasm, of
a clear, alveolar structure, and the whole body is invested externally by a
very thin and delicate cuticle, through which the cilia emerge. The
cilia within the mouth are longer than those on the general body surface.
The mouth itself is not quite symmetrical ; and it contains, according to
some observers, a delicate undulating membrane. The triangular ciliary
field in front of the mouth has a somewhat specialized structure, as in
other Heterotricha, and is termed the peristome. It appears to be a
region specialized for " tasting " and capturing food. The mouth itself
leads into a gullet, which is very short, its narrow internal opening ending
abruptly in the endoplasm.

The single large meganucleus (N) lies near the middle of the body,
deeply imbedded in the endoplasm. It is kidney-shaped or bean-
shaped ; but as it lies transversely, it often appears oval in sideview. It
contains densely packed chromatin granules, and a few larger nucleoli,
and is bounded by a membrane. The micronucleus (n) is very small,
and spherical. It usually lies closely applied to the meganucleus, in
the depression or bay on its ventral surface.

Two rhythmically contractile vacuoles are present in this species.

THE INTESTINAL CILIATES OF MAX 109

One lies more anteriorly in the mid-dorsal region (c. v. 1), the other
dorsally at the hind end (c. v. 2). In the living animal they frequently
appear to be connected by a system of lacunae, or ducts with accessory
vacuolar dilatations. They pulsate slowly, and are often difficult to
make out — especially the anterior one. At the extreme hind end of
the body there is a minute obliquely placed duct-like structure, per-
manently opening to the exterior. It is usually termed the "anus";
but to judge from its relation to the posterior contractile vacuole — into
which it sometimes appears to open — it is probably the duct of the
vacuolar system.*

In addition to the foregoing structures, the endoplasm contains more
or less numerous food vacuoles (/. v.), containing ingested matter.
Food particles are taken in at the mouth, pass through it into the endo-
plasm, and there become surrounded with a drop of liquid to form a
food vacuole, in which digestion takes place. These vacuoles, which
thus function as stomachs, circulate in the endoplasm during the pro-
cess of digestion. When the contained food has been digested, the
insoluble faecal residue is cast out of the body, t

B. coli ingests all manner of faecal debris in its host's intestine.
It also eats red blood-corpuscles, when these are available, leucocytes,
and tissue fragments. Starch grains are often seen in the vacuoles,
and Glaessner (1908) has found that the organism contains a diastatic
ferment. He also extracted a haemolysin, but no proteolytic ferment.

This ciliate lives in the more fluid part of the contents of the large
intestine — especially in the caecum. It has also been found in the
appendix. At times it is found deeply imbedded in the tissues, which
it is apparently able to attack and destroy (vide infra).

Like most other ciliates, B. coli multiplies by transverse fission
into two. All the stages of division have not been carefully studied,
but the chief stages have been seen by various observers, and there can
be little doubt that its division is like that of other species of the genus.
The micronucleus first divides by mitosis: then the meganucleus is
constricted into two (amitosis) : finally the cytoplasm constricts trans-
versely, and two daughter individuals are thus formed. The posterior
individual forms a new mouth at its anterior end, and more or less

* These remarks are based upon observations on B. coli from pigs. (C. D.)
f Through the " anus," according to some workers. We have not been able to
confirm this observation.

110 THE INTESTINAL PROTOZOA OF MAN

extensive reorganization and reconstruction of the ciliary coat and
other parts occurs in both individuals.

A remarkable process of "budding" was described by the earlier
Russian workers, and a process of "sporulation" has been more recently
described by Walker (1909), but these accounts seem open to question.
No such processes are known to occur in related ciliates.

Conjugation has been described by some of the early observers
and more recently by Brumpt (1909, 1913) in this species; but the
phenomenon has not been observed by most other workers, and
requires further investigation.

B. colt encysts in the intestine, and its cysts pass out, like those of
other protozoa, with the faeces of its host. The animal rounds itself
off, secretes a cyst wall, and after revolving actively inside it for some
time, comes to rest. Its ciliary covering then degenerates more or less
completely. Food bodies are digested or eliminated before encystation,
and the most conspicuous structure in the cyst is the meganucleus
(PI. VII, fig. no). Irregular refractile bodies (sometimes said to be
fat) are often present in newly formed cysts, and the posterior con-
tractile vacuole persists for a considerable time, pulsating rhythmically.
The cyst wall is colourless or slightly yellowish, fairly thick, and very
tough. It consists of two distinct layers — outer and inner, the former
being the thicker. The cysts are round, or slightly ovoid, and com-
monly measure 50^ to 60 /x in diameter. They are thus the largest
protozoal cysts encountered in human faeces.

As a rule the cysts contain a single individual, but specimens con- .
taining two individuals have been described. It is not clear whether
these are formed as a result of the division of the originally single
organism within the cyst — as seems most probable— or from the
encystation of two individuals together. According to Brumpt (1909)
two individuals may associate and form a common cyst, in which,
later, they fuse.

Infection is acquired by swallowing the cysts, which probably hatch
in the small intestine : but the details of the process have still to be
investigated. The cysts are able to live for a considerable time — at least
several weeks — in faeces, in which they remain apparently unchanged
if prevented from drying.

THE INTESTINAL CILIATES OF MAN III

(2) Balantwium MlNUTUM Schaudinn, 1899.

This small and apparently rare ciliate was described some years ago
by Schaudinn (see Jakoby and Schaudinn, 1899). It has the following
structure.

The body (PI. VII, fig. 107) is oval or somewhat piriform— its
breadth being about two-thirds of its length. The dimensions vary
from 20-30 /u, by 14-20 /*.* The anterior end is somewhat pointed, but
appears slightly truncated and bent to one side : the posterior end is
plump and rounded. The cilia on the body are very long and fine.
The buccal apparatus is more strongly developed than in B. coli. It
consists of a relatively long peristomial groove, extending from the
anterior extremity to the equator — or even further backwards — and
there ending in a short gullet which sinks into the endoplasm. The
mouth-parts are furnished with long vibratile cilia.

There is only one contractile vacuole, which lies dorsally, on the
left side, at the hind end of the body.

The meganucleus is spherical, measuring 6-7/1, in diameter, and
centrally placed. It is surrounded by a delicate membrane, and con-
tains irregular chromatin granules arranged on a linin network. The
micronucleus is a minute sphere, about 1 p in diameter, and usually
lies in front of the meganucleus.

Multiplication is effected in the typical manner by transverse
division. Conjugation was not observed : but encystation is said to
occur in the usual way — the cysts being usually oval, however, and
not spherical (dimensions not stated).

Schaudinn studied these ciliates in only two infections— one found
by Jakoby, the other by Schulz.f in Berlin. Both patients suffered
from diarrhoea, and their stools contained the organisms in immense
numbers. No evidence of the pathogenicity of this species was ob-
tained, however; and Schaudinn was of the opinion that it is
probably harmless.

Brooks (1903) states that " Dr. Russell " found B. minutum in the
stools of soldiers in Porto Rico, but we have been unable to find any
further account of these cases.

* These are the dimensions recorded by Schaudinn: but it should be noted that
the measurements stated in the text do not agree with those of his figures. I assume
that his description is correct, and that the magnification of his figures is wrongly
stated. The same remarks also apply to his account of Nyctotherus faba. (C. D.)

1'This case is very doubtful ; see p. 115, footnote, infra*

112 THE INTESTINAL PROTOZOA OF MAN

Recently Sangiorgi and Ugdulena (1917) have found a ciliate which
they appear to regard as a variety of B. mimitum, but which they
propose to call " Balantidium minutum, sp. Italicum" (meaning "var.
italicum" f). They found the organism in the stools of a soldier, and
were able to cultivate it easily in peptone-water.* Its size varied from
28-8/1, to 36*8 fjb, by iV2 fjb to 25-6 fju, and it is stated that in cultures it
formed cysts measuring 12-8/1 by 11 "2 fi. The meganucleus is said to
have an antero-lateral position. From this description it thus appears
doubtful whether the organism was really a Balantidium at all ; and
it seems more probable that it was a free-living ciliate which had
accidentally gained access to the stools. A rough figure of the or-
ganism, which appears to confirm this interpretation, has more recently
been published by Sangiorgi (19 19).

Pinto (1919a) has lately recorded the finding of B. minutum in
Brazil (State of Parana) ; but he gives no description of his organism
so named— merely recording that it was present in 5 out of 3,917
samples of faeces examined at various places.

It will be seen that our knowledge of B. minutum is still very
defective. The only certain case in which it has yet been found
appears to be that studied by Jakoby and Schaudinn.

(3) NYCTOTHERUS FABA Schaudinn, 1899.

A single case of infection with this organism has been described by
Schaudinn (see Jakoby and Schaudinn, 1899). The patient in whose
stools the ciliates were found suffered from diarrhoea, and was also
infected with Balantidium minutum.

The organism (PI. VII, fig. 108) is bean-shaped, and somewhat
flattened dorso-ventrally. The peristomial region extends from the
anterior end backwards to the middle of the body, where it terminates
in a short, oblique gullet, which enters the protoplasm as a narrow
tube. The body is clothed with short and fine cilia, whilst the
peristome is furnished with longer and stronger ones. The length of
the body is 26-28 /x, its breadth 16-18/A.f It is thus the smallest
species of the genus yet described.

* See also, in this connexion, Sangiorgi (1918^).

f See the remarks on Schaudinn's measurements of the preceding species — p. ill
footnote, supra.

THE INTESTINAL CILIATES OF MAN 113

There is a single large contractile vacuole, situated at the posterior
end, and discharging its contents through a tubular duct or " anus "
like that of Balantidium coll.

The meganucleus is a centrally placed sphere, measuring 6-7 /x in
diameter. Its structure is peculiar, in that the chromatin granules are
massed into four or five large blocks. The* micronucleus is spherical
or comma-shaped, measures some 1-1*5/1. in diameter, and is closely
appressed to the meganucleus.

Neither division nor conjugation was seen in this species. It is
stated to form oval cysts (dimensions not recorded), distinguishable
from those of B. minutum by the characteristic structure of the
meganucleus.

No evidence was elicited to indicate that this organism is patho-
genic, and Schaudinn believed it to be harmless.*

A ciliate believed to belong to this species has been recently described,
from the stools of a soldier in Italy, by Sangiorgi and Ugdulena (1917).
They were able to cultivate it, and give its length as 20*8//, to 57"6/x. It
was considerably larger, therefore, than Schaudinn's specimens. From
the rest of their description, also, it appears doubtful whether this
ciliate was really N. faba. It is said, however, to have possessed a
similar meganucleus, and to have had a single posterior contractile
vacuole: and it is described as forming cysts measuring ii'2/a in
diameter. The identity of this ciliate appears to be still questionable.

Pinto (1919^) states that he has found one case of N. faba infection
in Brazil, but he gives no details.

It is thus clear that further information about Nyctotherus faba is
much to be desired. Schaudinn's case appears to be the only certain
one on record. f

Doubtful Ciliates.

Under this heading we must now briefly notice several ciliates which
have been found, at various times, in human faeces, but which are
of doubtful systematic status and questionable relation to man.

Most of these doubtful forms have been seen but once, and not one
of them has yet been studied or described by a recognized authority

* It may be remarked that no pathogenic species of this genus is known. Other
species occur in frogs, cockroaches, etc.

t Cf. p. 115, footnote, infra.

1 14 THE INTESTINAL PROTOZOA OF MAN

upon the Ciliata. Consequently — since the identification of genera and
species among ciliates is by no means easy for the inexperienced — the
opinions recorded by the describers are not always such as a protozo-
ological systematist can unreservedly accept.

Moreover, it seems highly probable that most, if not all, of these
doubtful forms were, in reality, free-living species which had accidentally
contaminated the material examined. In most cases there is insufficient
evidence to prove that the "parasites" discovered were true entozoic
organisms : and the circumstance that they have sometimes been
identified — more or less accurately — as well known free-living species,
also points to the same conclusion. It must be remembered that free-
living ciliates may occasionally be found in the water or saline solution
used in diluting faeces for examination,* and the contamination of stools
may also occur in other ways. It should also be remembered that no
free-living species belonging to entozoic genera — such as Balanildium —
are known, though many have been described in error.

The first case which we must note is that of Guiart (1903), who
described a ciliate from the diarrhoeic faeces of a Frenchwoman. He
believed it to have been present in the intestine, but was able to cultivate
it by adding water to the faeces. The organism measured 35-55 /x by
25-35 fi, and was identified as " Chilodon dentaius Dujardin." Later,
Manson and Sambon (1909) reported the finding of a similar organism
in the stools of "a person apparently healthy who had just returned
from Northern Rhodesia." It was identified as " Chilodon uncinatus
Blochmann," and its dimensions were given as 36-44/4 by 20-30 /x.
From the descriptions it seems clear that all these authors were really
dealing with Chilodon : but it is difficult to believe that in these cases the
" infections " were not really due to contamination, in some way, of the
stools examined. Chilodon (several species) is one of the commonest of
free-living ciliates, occurring in water and infusions everywhere ; but
no entozoic species are known. Further evidence is needed, therefore,
to prove that any speciesf can occur in man. It should be noted that
Manson and Sambon regarded their case as one of "pseudo-parasitism."

* See p. 139, infra.

f There are, properly speaking, no such species as " C. dentaius Dujardin" and
" C. uncinatus Blochmann." The genus Chilodon was founded by Ehrenberg in 1833,
and C. uncinatus was one of his species. C.dentatus was a combination of names
introduced by de Fromentel in 1874 — probably for the same species, and is there-
fore merely a synonym. It appears probable that both Guiart, and Manson and
Sambon, observed this species — i.e., C. uncinatus Ehrbg., one of the commonest species
of the genus, occurring in water almost everywhere. Chilodon is also known, it may be
added, as an external parasite of freshwater fish (cf. Andre, 1912). (C. D.)

THE INTESTINAL CILIATES OF MAN I I 5

The finding of Colpoda cucullus in human faeces has been reported
by Schulz (1899). This observation— if correct— must assuredly have
been due to contamination of the material examined : for this organism,
which is extremely common in infusions of many sorts, never occurs,
so far as is known, inside other animals— being an exclusively free-
living form.*

Difficulties of a different sort are presented by a remarkable organism
described under the name of " Nyctotherus africanus" by Castellani
(1905). He found it in "a Baganda native affected with sleeping
sickness." According to the description it is roughly hour-glass shaped,
with a meganucleus and micronucleus, a contractile vacuole, and
a "peristome " which is said to be "on the posterior zone." The animal
is stated to measure 40-50 fi by 35-40 p, and to be covered with
extremely fine cilia. From the description and figures of this organism
we can only say with certainty that it is not a Nyctotherus. f We cannot
determine its true systematic position, since we know of no other ciliate
displaying similar morphological peculiarities.

In the following year, Krause (1906) described a ciliate which he
found, in Germany, in the faeces of a young woman with typhoid fever.
He was able to preserve it alive outside the body for 5 weeks, in an

* The statements of Schaudinn and Schulz regarding this case are not easy to
reconcile, and raise a number of doubts in my mind. Schaudinn (Jakoby and

Schaudinn, 1899) says that a second case of infection with Balantidium 7ninutu7ii

in addition to Jakoby's — was shown him by Schulz, who was then about to describe it.
Schaudinn appeared to be in no doubt regarding the identity of the organism. In his
own paper, however, Schulz (1899) states that he found a ciliate which at first he
thought to be "Balantidium Protozoon " (sic), but which was identified by Schaudinn
himself "as Colpoda cucullus. He adds that Schaudinn told him that this organism had
been found living parasitically only once previously— by Kiichenmeister, in a horse :
but he makes no mention of B. minutum. (It is true that these authors misspell one
another's names — Schaudinn referring to "Dr. Schultz,1' and Schulz returning the
compliment by alluding to " Dr. Schandinn " : but their identity can hardly be in doubt.)
Prowazek (1914) gets over the difficulty by simply stating that Schulz described a case
of B. minutum infection, but called the organism Colpoda cucullus. It is very difficult,
however, to reconcile the statements ot Schaudinn and Prowazek with those of"
Schulz ; and it is almost inconceivable that any protozoologist could confuse two such
very different organisms as B. minutum and C. cucullus. It seems to me remarkable,
further, that although Schaudinn described B. minutum and N. faba as long ago as'
1899 — since when hundreds of thousands of human stools have been examined — no real
confirmation of his findings has been forthcoming. If Schulz's case is eliminated as
too doubtful to be accepted, then these two organisms have each been found once only,
and then both in the same patient. In view of this singular state of affairs, I add
Schaudinn's two ciliates to the intestinal protozoa of man with much misgiving. (C. D.)

t The only real reason which Castellani appears to have had for placing this animal
in the genus Nyctotherus, seems to be the peculiar structure of its meganucleus, which
is described as similar to that of N. faba. But this organism itself — whatever it may
have been — has a meganucleus quite unlike that of any other Nyctotherus which (so
far as I know) has ever been described. (C. D.)

Il6 THE INTESTINAL PROTOZOA OF MAN

alkaline medium. It is described as an oval organism, 90-400 fi long by
60-250 ft in breadth.* There are said to be two contractile vacuoles,
but the cilia are not arranged in rows. Owing to the methods of
fixation and staining employed, it is impossible to attach much import-
ance to the other cytological characters noted. The figures depict,
apparently, distorted specimens with broken-down nuclei. Cysts were
observed, and are figured as roughly spherical. Krause proposed! to
call the ciliate " Balantidium colt giganteum." According to Doflein
(1916) and others, this organism should be placed in the genus
Nyctotherus, and therefore called N. giganteus. We cannot concur in
this view, for we are unable to determine the systematic position of the
ciliate from the imperfect description and obviously faulty figures
hitherto published. It is possible — if the measurements are correct —
that it was a strain of Balantidium coli of unusually large size, but we
cannot advance this hypothesis with any confidence. We believe, in
any case, that there is no evidence that it was a Nyctotherus.

Martini (1910) observed a little oval ciliate, with a large peristome
and a long caudal filament, in the stools of three patients suffering from
ctysentery in Tsingtau. The organism measured 30-43 /x by 11-15 /-i, anc^
it was found that it would live for some weeks, and even multiply,
in saline solution containing faeces and kept at room temperature.
Martini proposed — on grounds which seem inadequate, to say the
least — to call the organism " Uronema caudatum," and to add it to
the list of human "parasites" capable of "causing" dysentery.
Fischer (1914) believes that he has been able to confirm these obser-
vations at Shanghai. From the published description and figures,
however, we believe this to have been another free-living ciliate, and
not one which occurs in the human intestine.^

Castellani (1914, 1914^) has described an organism, found in human
stools, under the name of " Entoplasma." From the description we
cannot identify it : but from a preparation of the organism which the

* Krause (1906), p. 446. On p. 451 the breadth is given as 60-150 /x.

f This name is proposed on p. 452, op. cit. In the title the animal is called
" Balantidium giganteum."

% It seems clear from Martini's account that his organism was not a Uronema. The
genus Uronema was founded by Dujardin (1841), the type species being U. marinum
Duj. Martini's form appears to be a Cyclidium — as now defined. Species of this
genus are very common in water, and infusions of all sorts, all the world over. These
genera, and those allied to them, have been accurately studied and defined by Biitschli,
Schewiakoff, Roux, and others — in works well known to all protozoologists. (C. D.

THE INTESTINAL CILIATES OF MAN 117

author kindly showed to one of us (CD.), we have formed the opinion
that it was probably a Balantidium, or some other ciliate, which had been
deformed by drying and the method of preparation adopted.- Brug
(19180), however, has suggested that " Entoplasma" is a dried and
deformed Chilomastix, but its large size disproves this interpretation.

The ■' Balantidium" obtained in cultures from the spleen by
Marshall (191 1), and that found in the blood and in blood-cultures
by Hinkelmann (1919) must also be mentioned here, as they must at
present be included among the doubtful ciliates. They will be noticed
in more detail later (vide p. 121 infra).

Barlow (1915) believes that a "Balantidium " which he has found in
human stools in Spanish Honduras is a distinct variety of B. coli, and
proposes for it the name " Balantidium coli, variety Houdurense." The
organism is said to be uncommon, and to measure 100-175 n by 70-
100 /a. It has a smaller mouth than the type, and shows no ciliary
striation. But its most remarkable peculiarities are that its "nucleus"
is inconspicuous and spherical (only 10-14^ in diameter), whilst " what
appeared to be a kineto-nucleus could occasionally be made out."
"Only rarely" is a "vacuole" present, and then it is not contractile :
but to make up for this, the organism possesses an " anal orifice" which
is "very contractile." It seems clear that this animal can hardly be
placed in the genus Balantidium, and it certainly cannot be regarded as
a variety of B. coli. It may be suggested that the author's observations
were inexact, and that he was possibly dealing with a free-living ciliate
belonging to a different genus.

This interpretation undoubtedly applies to the ciliate recently
described under the name of ''Balantidium coli sp. Albauense" by
Sangiorgi (1919). From the rude figure illustrating his description, and
from the circumstance that the organism was found in wells in Valona
(Albania), there can be no doubt that it was a free-living species
(unidentifiable from the incomplete account given), and not a variety or
species of Balantidium.

Key to the Genera and Species.

We give below a simple key to the genera and species of ciliates
which occur in the human intestine. We include only those species

* We understand that this is also the opinion of Dr. C. M. Wenyon, who first
suggested this possibility to us.

Il8 THE INTESTINAL PROTOZOA OF MAN

which have been sufficiently studied for it to be possible to identify them
with certainty — all the doubtful forms just mentioned being left out of
account. The characters utilized for the purpose of determination are
those of the full-grown active organisms.

(a) Body oval ...

(b) Body bean-shaped ...

(a) Peristome very short, subterminal ; mega-

nucleus kidney-shaped ; 2 dorsal con-
tractile vacuoles. Length 50 /* or more

(b) Peristome long, extending to middle of

body ; meganncleus spherical ; 1 pos-
terior contractile vacuole. Length 32/i
or less
Peristome extending to middle of body;
meganucleus spherical ; 1 posterior
contractile vacuole. Length 28/4 or
less

Genus Balantidium 2.
Genus Nyctotherus 3.

B. coli.

B. minutum.

N.faba.

Balantidiosis.

Infection with Balantidium coli is termed Balantidiosis (or Balanti-
diasis). The term is applicable, of course, to infection with any species
of the genus. The other ciliates of man are both rare and — so far as is
known — harmless, so that no special term has been applied to the con-
ditions with which they are associated. On the other hand, B. coli is, at
times, a pathogenic parasite, and produces a definite disease with
characteristic symptoms and lesions.

Pathogenesis, Aetiology, etc. — It appears probable that Balan-
tidium coli is a natural parasite of the pig, to which it appears to be
usually harmless. It may also be a natural inhabitant of monkeys, for
it has been found in these animals in several parts of the world. Man
appears to be an accidental host, and to acquire his infection, as a rule,
from the pig.

When a man becomes infected with the parasite he often displays no
symptoms, and becomes a carrier — like a carrier of E. histolytica. The
relation of parasite and host in such circumstances is not yet fully
understood : and it is not certain whether the ciliate attacks the tissues

IiALANTIDIOSIS HO

of the gut, or lives as a harmless commensal upon its contents — as other
species of the genus commonly do in other hosts. In man, however,
B. coli is at times a definite tissue-parasite. It attacks and invades the
mucous and submucous layers — sometimes even the muscular layers —
of the large intestine, and produces an ulceration closely resembling
that seen in E. histolytica infection. The result is a condition of colitis,
with symptoms of diarrhoea or, in severe cases, dysentery (Balantidial
Dysentery, or Ciliate Dysentery). Secondary infection of other organs,
such as is sometimes seen in amoebiasis, probably does not occur.

This disease is most prevalent among people who tend pigs or handle
their carcases — swineherds, farm labourers, slaughterers, sausage-makers,
etc. Strong (1904), in a review of all the cases of human balantidiosis
then known, found definite evidence of association with pigs in 25 per
cent, of the patients. Since then, several striking cases — such as that
of Young and Walker (1918) — showing the aetiological relation of the
pig to human infection, have been reported.

Incidence and Distribution. — Balantidial infection has been
described in persons of both sexes, and of all ages from 1 year to about
70. It has a world-wide distribution, apparently, but appears to be
particularly prevalent in certain countries. Among these may be
specially mentioned Sweden, Finland, Russia, and the Baltic provinces
generally. Indigenous cases are also reported from Germany, Italy,
France,* and the Balkans. The wide distribution of the parasite is
shown, however, by recent records of its occurrence in the Ladrone
Islands (Prowazek, 1913), the Philippines (Strong, 1904 ; Walker, 19 \yi ;
etc.) Java (Brug, 1919c), Honduras (Barlow, 191 5), Brazil (Axter-
Haberfeld, 1915; Pinto, 1919, 1919a), and Venezuela (Tagliaferro, 1918;
Paez, 1919). No indigenous cases of human infection have yet been
reported in Britain, though the parasite is common in British pigs.

Pathology and Morbid Anatomy. — The lesions of balantidiosis,
when present, are confined to the large intestine. The parasites cause
irritation of the mucous membrane, giving rise to a catarrhal condition,
and in more severe cases cause erosion and ulceration. Balantidial
ulcers appear, both macroscopically and microscopically, closely similar
to those caused by E. histolytica. They have now been studied by many
workers, and there appears to be no longer any doubt as to the part

* Indigenous French cases have been recently reported by Lanzenberg (1918), Weil
and Bergouignan (1919), and Tixier (1919).

120 THE INTESTINAL PROTOZOA OF MAN

played by B. coll in their formation. (See especially Walker (19 13a),
who gives an excellent summary of the evidence.)

The earliest change appears to be hyperaemia of the mucosa, often
with punctiform haemorrhages. Vascular dilatation, round-celled infiltra-
tion, and a local eosinophilia, are also commonly seen. A greater or
less degree of erosion and superficial necrosis is usually visible.

Definite ulceration occurs when the parasites penetrate into the
tissues. According to Walker (1913a) they do this in a purely mechanical
manner — displacing the cells of the healthy mucous membrane, and
pushing their way into the tissue between the crypts. " The parasites,
which are capable of amoeboid* movements, pass between the cells like
migrating leucocytes." Later, they multiply in the mucous and sub-
mucous tissues, forming nests or colonies. When deep in the wall of
the gut, they appear to nourish themselves, like E. histolytica, by secreting
a ferment which dissolves the cells. Necrosis, with the formation of
submucous abscesses and open ulcers, then occurs. In the necrotic
areas the balantidia are found peripherally, in contact with the healthy
tissues. (PI. VII, fig. in.) Sections of balantidial ulcers show, in ad-
dition to numerous parasites, coagulation necrosis of the tissues,
dilatation of the vessels, round-celled infiltration, and sometimes a
localized eosinophilia. Polymorphonuclear leucocytes, when present,
probably indicate a secondary bacterial infection. The necrotic tissue
closely resembles that seen in amoebic ulcers.

To the naked eye the ulcers appear rounded or irregular, often with
undermined edges. The mucosa between adjacent ulcers is frequently
hyperaemia Od ulcers are filled with blackish necrotic tissue,
resembling that in the corresponding amoebic lesions. f The presence
of the characteristic parasite supplies, in fact, the only means of distin-
guishing balantidial from amoebic ulcers with certainty.

Balantidia may be found not only in the tissue of the gut wall but
also in the blood and lymph vessels in this situation, and even in the
lymphatic glands draining the infected areas of the bowel (Bowman,
1909; Walker, 1913a). The parasites do not appear to go further into
the body : but according to an old and very questionable observation,

* It is unlikely that the movements are truly amoeboid. The " amoeboid " shapes of
the parasites in the tissues are probably caused by pressure of the surrounding struc-
tures. No ciliates — so far as I am aware— are capable of forming true pseudopodia
like anamoeba. (C. D.)

f Excellent figures will be found in the work of Bowman (1909).

BALANTIDIOSIS 121

they have been coughed up in the sputum — supposedly from a hepatic
abscess which had ruptured into the lung (Stokvis, 1884).*

Maliwa and von Haus (1920) have recently published some remark-
able observations made upon a young woman at Innsbruck. The
patient is said to have passed Balantidiam coli in immense numbers in
her urhie.f She suffered from urethritis, cystitis, ureteritis, pyelonephr-
itis of the left kidney, and anuria. On operation the parasites were not
found in the kidney, though they were present in the left ureter and the
bladder.^ No suggestion is offered to account for their presence in
this singular situation, and unfortunately no examination of the stools
appears to have been made. A fuller account of the parasites found —
with figures— is to be desired, since this appears to be a unique case.

Marshall (191 1) cultivated a ciliate, which he believed to be a
Balantidium, from the spleen of a patient who died of kala-azar. It
measured 42'5/a by 34/A, and from his description it seems clear that
the organism was really a free-living ciliate — not Balantidium — with
which his culture had become accidentally contaminated. It appears
probable, also, that contamination with free-living ciliates is the true
explanation of the remarkable findings of Hinkelmann (1919), who
claims to have found Balantidium coli in the peripheral blood of human
beings. The same author claims to have found the parasite in the
urine also, and to have cultivated it, from the blood, in a medium of
blood and water ; but his figures and description of the organisms —
and others obtained by similar methods — render it highly probable
that he was dealing, in reality, not with Balantidium but with free-
living ciliates from the distilled water employed in the experiments.

Good accounts of the pathology of balantidiosis have been given
by Strong (1904), Bowman (1909, 1911), Walker (1913a), Brumpt (1913),
and Manlove (1917), to whose works the reader may be referred for
further details.

* This case is of interest from another standpoint. The patient, a member of a good
family in Holland, has been degraded by the carelessness of bibliographers into " a
native of" or "a soldier from" the Sunda Isles: and this extraordinary error is,
apparently, the only foundation for the statement almost invariably made — when the
geographical distribution of balantidiosis is under discussion— that B.coli occurs in
that part of the world ! Cf. Brug (1919c), who has recently directed attention to this
mistake, which appears to have originated with Mitter (1891).

t "Es zeigten sich zwischen den Eiterzellen massenhaft Balantidien, die bei wieder-
holten Untersuchungen zu finden waren " (spaced in original).

% The case is complicated by a number of other infections which were found in the
lesions (Streptococci, Staphylococci, Go;wcoccus, and Bacillus coli).

122 THE INTESTINAL PROTOZOA OF MAN

Symptomatology, etc. — Carriers of Balantidium usually display no
symptoms. They are not distinguishable from normal healthy persons
save by the parasites which they pass from time to time in their stools.

When symptoms of infection are present, they are those of a colitis,
with diarrhoea — most commonly — or, in severe cases, an intractable
and chronic dysentery. The stools are usually liquid, often contain
much mucus, and sometimes blood and pus. Tenesmus and colic
are common symptoms, and the colon is usually painful on pressure.
Loss of appetite, nausea, thirst, and general debility, are often seen.
From ten to fifteen stools per diem (or more) may be passed, with
much straining and pain. The diarrhoea or dysentery may be con-
tinuous or intermittent, and periods of apparent recovery, followed
later by relapses, are to be expected : but very often the dysentery,
when once established, becomes chronic. The symptoms are said in
some cases to resemble those of cholera or typhoid (cf. Krause, 1916).
In long-standing cases there is usually emaciation and a secondary
anaemia. Eosinophilia has been described,* but it appears probable
that the blood-count is usually normal in uncomplicated cases (cf.
Bel and Couret (1910), Payan and Richet (1917), etc.). In typical
cases, moreover, there is no pyrexia.

Numerous cases of balantidiosis without symptoms have been
observed. Walker (1913^), for example, states that only 11 out of 57
cases seen in the Philippines displayed symptoms : but he notes that
" every person parasitized with Balantidium colt is liable sooner or
later to develop balantidial dysentery." Pinto (19 19) has recently
studied 11 cases in Brazil, all without symptoms. In cases which
do develop symptoms, the prognosis is not favourable. The disease
is usually intractable, and the mortality probably high — 29 per cent,
according to Strong's (1904) statistics.

It is to be noted that Manlove (1917) has found that, "as in
amoebiasis, extensive intestinal lesions in balantidiasis may be present
without giving rise to symptoms."

Balantidiosis of Animals other than Man. — Species of
Balantidium occur in many animals — particularly in Amphibia. The
common English frog, for example, harbours three different species
in its gut. Balantidium coli appears to be able to live in three different

* E.g., Weil and Bergouignan (1919) observed an eosinophilia of 5 per cent, in
their patient.

BALANTIDIOSIS 1 23

hosts — man, monkey, and pig ; and in this it di iters from all the other
known species. The identity of the forms in these three different hosts
was for long in doubt, but recent experiments appear to have settled
the matter definitely.

The Balantidium of the pig was discovered by Leuckart (1863) in
Germany, and identified by him as B. coli — the human species, then
recently discovered by Malmsten. The Balantidlum of monkeys was
discovered in orang-utans in the Zoological Park in New York by
Brooks (1903).* It was later studied in Macacus cynomolgus, of Tonkin,
by Noc (1908) and Brumpt (1909). The identification of these forms
with one another, and with the species found in man, rests chiefly upon
the experimental evidence adduced by Brumpt (1909) and Walker
(1913a). It is now generally admitted that the Balantidia occurring
naturally in all these hosts are morphologically indistinguishable.

Brumpt (1919) succeeded in transmitting Balantidium from monkey
to monkey by rectal injection of the active ciliates from the stools.
He also passed the monkey's Balantidium into young pigs. Finally,
he succeeded in parasitizing a monkey with the Balantidium naturally
occurring in the pig. Brumpt considers that he was dealing throughout
with Balantidium coli.

Walker (1913a) experimentally infected 12 out of 13 monkeys by
feeding them with cysts of the Balantidium of the pig. Further, he
succeeded in infecting 2 out of 4 monkeys by rectal injections of
active ciliates from human stools.

It thus appears probable that the same species of Balantidium can
live in man, monkey, and pig ; and the identity of the Balantidium
of the monkey with that of the pig appears to be proved. Experimental
infection of man with the Balantidium of either the pig or the monkey
has not yet been achieved, however ; and it may be recalled that
Grassi and Calandruccio (see Grassi, 1888a) failed in their attempts
to infect human beings by causing them to swallow Balantidium cysts
from pigs' faeces. They came to the conclusion that the ciliates in
the pig belong to a different species from those in man. Nevertheless,
direct infection of man by means of the cysts in pigs' faeces has
probably been accomplished unintentionally. The evidence is par-

* Brooks also found " B. coli" in some "giant turtles from the Galapagos Islands,"
and he believed that " it was from these animals that our orangs received their infection."
But this inference is doubtless incorrect. It is improbable that the Balantidium of
these reptiles is B. coli. (C. D.)

124 THE INTESTINAL PROTOZOA OF MAN

ticularly striking in the case recorded by Young and Walker (1918) —
a gut-stripper in a packing factory, who often got pigs' faeces* into
his mouth, and became intensely infected with Balantidium apparently
as a direct consequence. There is also much indirect evidence pointing
to the conclusion that man acquires balantidiosis through association
with pigs.

Attempts to infect dogs, cats,f rabbits, and other animals with
B. coli (from human stools) were made by the earlier workers. The
results were practically always negative ; but the experiments, it must
be noted, were not always carried out in a manner conducive to
success, and it is possible that more careful work might lead to
different results. Experiments which consist in feeding animals upon
active ciliates — not on cysts — are doomed to almost certain failure :
and from such experiments no satisfactory conclusions can be drawn.

B. coli is usually stated to cause no ulceration in the pig's gut.
In Brumpt's experiments, however, one of his experimentally infected
pigs showed lesions " identical in every way with those described
in man." The observations of Noc, Brumpt, and Walker appear to
prove that the monkey behaves towards Balantidium in the same way
as man — sometimes showing no lesions, but sometimes acquiring a
typical ulceration of the colon, accompanied by diarrhoea or dysentery.

* " The patient stated that he was accustomed to stand ankle deep in hog dung,
and that every day he was sprinkled with it and frequently got the fecal material in his
mouth." Op. tit., p. 508.

t Behrenroth (1913) states that he succeeded in obtaining a temporary infection
in a cat. It is also stated that Casagrandi and Barbagallo were able, by special
methods, to infect this animal (cf. Strong (1904), Walker (1913^, and others). We
have not been able to consult their work on this subject.

125

CHAPTER VII.

THE DIAGNOSIS OF INTESTINAL PROTOZOAL
INFECTIONS.

In previous chapters we have described the Protozoa which live in
the human intestine. In the present chapter we shall try to give,
with equal brevity, some account of the best methods used for dis-
covering and identifying such organisms, together with practical sug-
gestions regarding methods of collecting and preserving material for
examination. We shall also add, parenthetically, a few cautionary
hints for the use of the novice who is unfamiliar with protozoologv
and protozoological methods.

The Collection of Material.— The protozoa living in the bowel
are usually studied, of course, in the stools discharged from the body.
Since only the cysts of such organisms are able — as a general rule — to
live outside the body for more than a few hours, it is of the utmost
importance to pay attention to the following points when collecting
material for examination.

(i) Stools should always be obtained as fresh as possible, and examined
Immediately. As a general rule, stools which are more than a few
hours old are unsuitable for examination — except for cysts, which may
be found and identified in faeces kept for at least several days, and
sometimes for a week or more.

(2) Stools should always be collected in clean and dry receptacles.
It is most important that neither water nor antiseptics should be left
in bed-pans or other utensils into which the stools are passed ; and
care must be taken to insure that urine is not mixed with the faeces.
Antiseptics and urine rapidly kill the entozoic protozoa, and water
may contain free-living forms which may lead to mistakes in diagnosis.

It is also necessary to prevent foreign particles, such as sand and
dust, from becoming mixed with the faeces. This may be difficult
under field conditions ; but the use of stool-pans with closely fitting
lids — only removed for the act of defaecation, and immediatelv re-

126 THE INTESTINAL PROTOZOA OF MAN

placed — and precautions to prevent toilet-paper, tow, or other cleansing
material from coming into contact with the ground, will help to obviate
these difficulties.

(3) A natural stool — passed spontaneously — should, whenever
possible, be obtained for examination. Stools obtained by the ad-
ministration of purgatives are less suitable for protozoological examin-
ation than those passed naturally. If purgatives must be employed,
however, salines (e.g., magnesium or sodium sulphate) are the best.
Castor oil, and similar substances, should be avoided, as the presence
of oil drops in the faeces makes them troublesome to examine under
the microscope. Enemas may be useful, but are not usually to be
recommended. Noc (1916) advocates rectal injections of thymol for
this purpose, and he states that lumps of mucus from the surface of
amoebic ulcers (containing E. histolytica) can be obtained by this
method. Others (e.g., Lyons, 1920) have recommended scraping
material directly from the ulcers with the aid of the sigmoidoscope.
But such methods are not adapted to everyday use.

(4) Whenever possible the whole stool should be obtained for in-
spection. It should be sent to the laboratory as soon as possible —
the receptacle being clearly labelled with the name of the person who
passed it, and the date and hour of defaecation. If the stool is to be
examined at once, it may be placed in a hot air cupboard — which
will preserve the activity of the protozoa for a short time. If the
stool must be kept for some time — an hour or two, or possibly days —
it should be put in a cold place. Active protozoa and cysts degenerate
and perish much more rapidly when warm than when cold.

(5) When the stool has to be sent to a laboratory at a distance,
it is usually sufficient to send a sample in a glass or tin tube, such as
is now obtainable for the purpose. Glass specimen tubes, measuring
about 3ins. by 1 in., and provided with well-fitting corks — into which
a glass or metal spoon or spatula has been thrust — answer admirably.*
In sending such specimens, it is important to select a suitable sample.

* These tubes are fully described in the Report on " The Laboratory Diagnosis
of Acute Intestinal Infections," published by the Medical Research Council (Special
Report Series, No. 51, 1920). It should be remembered that, if such samples
are sent by post, in the United Kingdom, they must be carefully packed in metal
or wooden cases (hollow wooden blocks are now obtainable for the purpose),
securely sealed, and marked " Fragile, with care. Pathological specimen." They
must be sent by Letter Post — not Parcel Post. (Post Office Regulations.) Failure to
comply with these conditions may lead to the official destruction of the specimen
and prosecution of the sender.

THE DIAGNOSIS OF" INTESTINAL PROTOZOAL INFECTIONS 1 27

(And don't forget to label it — a surprisingly common oversight.) When
the stool is formed and solid, any part may be sent — a piece about
the size of a hazel-nut or walnut being ample. When the stool is
uniformly soft or liquid, any portion will do. When partly soft or
liquid and partly formed, select a portion of each part. When blood
and mucus are present, mixed with faeces, select specimens of each
part — if necessary, inclosing the bloody mucous part and the faecal
part in separate receptacles.

It is, of course, most important to make sure that the tube is
previously clean and dry; and, especially in the case of liquid stools,
that antiseptic fluids have not been left or allowed to dry in it. (With
a little practice one can soon learn to select the most appropriate parts
for examination from a whole stool. The chief thing to remember is
the obvious thing — any part of a homogeneous stool will do, but
samples of all the various parts of a heterogeneous stool should be
selected for examination.)

Similar precautions should be taken in selecting samples of liver
abscess pus for examination. It is important to remember that E.
histolytica is usually present in the wall of the abscess, and not in
the first gush of pus obtained on opening it.

Examination of the Stool.— The stool must be examined, of
course, under the microscope ; but before doing so, it is advisable
to make a careful macroscopic inspection, and to record the results.

(a) Macroscopic Examination. The following points should be
noted. (1) The consistency of the stool or sample — whether hard or
soft, formed or unformed, liquid or semi-solid, etc. (2) The colour
of the stool. (3) Whether blood, mucus, or pus can be seen by the
naked eye. According to the results of this inspection, the stool may
be classified as normal (brown and formed), loose (brown, semi-solid,
etc.), diarrhoeic (soft to liquid; brown, yellowish, greenish, etc.), and
dysenteric (loose or liquid, and containing blood and mucus). The
presence of any obviously undigested food, sloughs, etc., should also be
noted.

(b) Microscopic Examination. To make a proper microscopic
examination of a stool for the presence of protozoa, a good micro-
scope and accessories are indispensable. The microscope must be
fitted with a mechanical stage, a snbstage condenser, with rackwork for
raising and lowering and an iris diaphragm, and good lenses. Three

128 THE INTESTINAL PROTOZOA OF MAN

objectives are almost indispensable — a low power (fin.), medium
power (-Jin.), and high power (^in. oil immersion), and at least two
oculars {e.g., No. o or i, and No. 4, 5, or 6). An ocular micrometer,
which may be permanently fixed in the high-power ocular, and which
must be accurately calibrated for each objective and tube-length
employed, is also necessary for anything but the most random work.

A good source of illumination is also requisite. Artificial light is
preferable to daylight for routine work, since it can be kept constant
and uniform, and because daylight is usually inadequate for the high-
power work that is often necessary. A good electric lamp provided
with a screen of ground glass, or an incandescent gas lamp, or even
an oil lamp, will suffice : but a better type of microscope lamp is,
of course, to be preferred.

Other apparatus, if obtainable, may be necessary or desirable.
When it is remembered that it is often necessary to make out with
precision the smallest details in complicated organisms or cysts which
are smaller than a human red blood-corpuscle, it will be realized that
the apparatus just mentioned is the irreducible minimum ; and that
for the best work, the best apparatus obtainable, and all the skill and
resources of the best microscopist, are not superfluous. (But more
mistakes in diagnosis are made as a result of misuse of a good micro-
scope than from the employment of bad apparatus : and nobody who
is not accustomed to use a high-power instrument should attempt to
diagnose protozoal infections for any purpose but his own diversion
or instruction. Experience has proved conclusively that observations
made by the inexperienced are practically worthless. The beginner
should bear these points constantly in mind, and, as a general rule,
should at the outset seek the help and guidance of an experienced
and reliable worker. To those with no previous knowledge of proto-
zoology, the task of self-instruction presents almost insuperable
difficulties.)

Preliminary Microscopic Examination. The fresh stool should first
be examined in such a way that any protozoa which it contains are
kept alive and active. To do this, a small portion of the stool is
mounted as a thin film under a coverglass. Clean and thin slides
should be used, and No. 1 coverglasses. (Large squares (fin.) are
best. Remember that good oil-immersion lenses will not usually work
through a coverglass more than 0-140 mm. in thickness.) If the stool

THE DIAGNOSIS OF INTESTINAL PROTOZOAL INFECTIONS 1 29

is liquid, a drop may be placed in the middle of the slide with a
platinum loop,* and the coverglass carefully lowered on to it and
pressed down. If the stool is solid or thick, it must diluted to a
suitable consistency before applying the coverglass. This should be
done by placing a drop of sterile physiological saline solution (075 —
0*9 per cent. NaCl in distilled water, or Ringer's fluid) on the slide.
A particle of the stool is then taken on the platinum loop and emulsi-
fied by stirring in the drop. A thin and uniform mixture should be
made before the coverglass is applied. (Be careful to prevent the
faeces from drying on the loop before stirring into the saline ; and
do not put the faeces on the slide first and add the saline afterwards.
And don't forget to burn off the loop in the flame after making the
preparation !) A good preparation made in this way should appear
uniform ; and the film itself should be free from air-bubbles and
so thin that the smallest print is clearly legible through it. (Practice
only will teach you how to make the best kind of film.)

As a rule it is unnecessary to seal the preparation (with paraffin or
wax, round the edges of the coverglass) or to use a warm stage : though
for special purposes these precautions may be necessary. A dark-ground
illuminator is sometimes useful, but its use cannot be recommended to
beginners.

The preparation should be examined under the microscope in a
systematic manner. (Don't push the slide about at random, but
begin at one corner of the coverglass and work steadily through from
side to side or up and down). It is best to begin with the ^in. objective
and the lowest ocular. All protozoa and their cysts can be seen with
this combination, though their finer details cannot be made out. When
an organism, or other object, requires more detailed study, the oil
immersion lens can be substituted for the ^in. (A revolving nose-
piece on the microscope is almost indispensable, and greatly facilitates
the changing of objectives. Beginners should not try to work quickly.
Rapid and accurate work is possible for experts only — after long
practice.)

Different parts of the stool — collected as described above — should,
of course, be examined successively, and the constituents of each part
duly noted.

* Under field conditions it is preferable to use long thin sticks for this purpose. A
new one is used for each case, and then burnt or thrown into lysol. Wooden matches
will also serve in an emergency.

9

130 THE INTESTINAL PROTOZOA OF MAN

If living and active protozoa, or cysts, are found, they should be
examined with the greatest care. Their chief features should be
accurately noticed, and an attempt then made to identify them. For
this purpose the figures on Plates I and VIII will be of service, as a
preliminary step. Afterwards, any special points should be looked up
in the descriptive chapters. The determination should then be verified
by making preparations in iodine, and, if necessary, permanent fixed
and stained preparations.

Iodine Preparations are made in the same way as those in saline
solution, but using a watery solution of iodine (i per cent, iodine in
2 per cent, potassium iodide) in place of the salt solution. (The iodine
solution should be fairly fresh. Old solutions lose their efficacy.
Emulsify very thoroughly, as the iodine coagulates faecal matter, and
cysts and other small objects are therefore difficult to find in badly-mixed
preparations.) Iodine kills all the protozoa and their cysts. It fixes them,
stains them more or less yellow, and makes their nuclei more clearly
visible. The nuclei in cysts can thus be more readily counted, and their
structure approximately determined. Iodine has the additional advantage
of staining glycogen a deep brown colour — the presence or absence of
this material in cysts being a great aid to diagnosis. The flagella of
flagellates can also be more easily seen in this medium than when
they are alive and moving, and their number, position, and insertion
can thus be more accurately determined.

In studying cysts mounted in iodine solution the beginner will find
the figures on PL VIII helpful. The appearances should be carefully
compared with those of the living cysts on the same Plate, and the
descriptive chapters consulted for more detailed information.

All wet preparations, after they have been examined, should be
thrown into a pot containing lysol or cresol (5 per cent.) in order to
sterilize them. The tubes of faeces, when finished with, should be put
into a larger vessel containing the same disinfectant — their corks being
first removed or loosened — and left there until they can be cleaned again
for future use. (The beginner must always remember that cysts are
infective, if swallowed : and that even though protozoa are not found in
the specimen, pathogenic bacteria may be present. The usual bacterio-
logical precautions should therefore always be observed in handling
stools.)

THE DIAGNOSIS OF INTESTINAL PROTOZOAL INFECTIONS 131

If a fresh film, or an iodine preparation, is examined under a low-
power with the condenser in focus and its iris diaphragm fully open, too
much light will be concentrated on the object. To reduce the light and
increase the visibility, the diaphragm should be partly closed, or the
condenser racked down. (The latter method — unjustly condemned by
some microscopists— is usually the better, and is equally defensible
theoretically. The correct adjustment of the illumination can be learned
by practice only.)

The foregoing methods of examining fresh stools are essentially those
which we, and most of our fellow-workers, always employ.* They are,
we believe, the simplest, most direct, and best. Other methods have
been advocated, and some of these may now be mentioned. Direct
observation of the living organisms or cysts, however, should never be
omitted — no matter what other methods may also be employed. (It is
worth while to spend a long time in examining fresh material, and
becoming thoroughly familiar with the appearance of the living
organisms at all stages of development. Those who are really expert,
through long practice, can usually make an exact and rapid diagnosis bv
this method alone.)

Some workers {e.g., Stitt (191 1), Cutler and Williamson (1917), Boeck
(i9i7<2),t and others) advocate the use of saline solution containing
neutral red (1 part in 10,000). This does not kill the active protozoa,
and may stain them, and the various objects among which they move,
more or less ; while cysts remain white, and appear slightly more con-
spicuous by contrast. Kuenen (1914), Brug (1918), and some of the
other Dutch workers, emulsify the faeces with eosin (2 per cent.) for a
similar purpose. This rapidly kills most active forms, however, and is
not to be recommended for general use. Donaldson (1917) recommends
the use of iodine solution combined with a red stain (rubin S or eosin)4
Cysts appear bright yellow and brown, on a red background, when
examined in this medium. This method, however, is merely a substi-
tute for the ordinary iodine method — described above — and will not

* They were originally described by Wenyon (191 5) and have been copied with
various modifications by other workers {e.g., Inman ( 1917), Matthews (1918), etc.).

f This author actually recommends " N/10,000" neutral red solution, but presumably
means the concentration given above.

if The formula is: 5 per cent, aqueous solution of potassium iodide, saturated with
iodine, and mixed with an equal volume of a saturated aqueous solution of rubin S.
eosin, or red ink (Stephens's).

132 THE INTESTINAL PROTOZOA OF MAN

enable one to dispense with the examination of the living organisms or
cysts also. Methylene violet and methyl violet (Sangiorgi, 1918) and
methylene blue solution also have their advocates. Riegel (1918)
extracts the azure from Manson's methylene-blue with chloroform, stains
coverglass films of faeces in the azure-chloroform solution so obtained,
and then mounts and examines them in liquid paraffin.* Amoebae,
cysts, etc., are variously stained by this method — and, of course, killed.
This, and other methods of rapid staining and fixation (e.g., Mathis's
method (1914a) — rapid fixation is osmic vapour, followed by staining in
haematoxylin solution) are not, in our opinion, to be recommended.
If fixation and staining are required, they should be practised with the
best cytological reagents.

It should be remembered that there are no true specific stains which
will enable one to discriminate any particular protozoon, or its cysts,
with absolute certainty. The claims made for some reagents in this
respect are not justified. With some stains also (e.g., neutral red), the
reaction of the stool may make a considerable difference to the result.
(Methods involving drying at any stage — recommended in some of the
older medical works — are absolutely useless for the accurate study of
any protozoa, and must always be avoided.)

Methods for concentrating protozoal cysts in stools have been
devised and advocated by some workers. Cropper and Row (19 17)
mix the faeces with ether, after emulsification with saline solution ;
remove the layer of ether, containing the larger faecal particles ; spin
the saline residue in the centrifuge ; and then examine the deposit at
the bottom of the tube — in which most of the cysts are collected. This
method may be useful for detecting cysts when present in very scanty
numbers (cf. also Boeck, 1917a, and Carter and Matthews, 1917). In our
experience, however, it does not enable one to detect small infections
with greater certainty or speed than the direct method here advocated.
It has the additional disadvantage of requiring more time, apparatus,
and reagents for the various manipulations ; and of distorting, killing,
or injuring free protozoa and cysts, and so making their identification
more difficult.

Carles and Barthelemy (1917) have elaborated a method of con-
centrating cysts by emulsification, sieving, flotation, and centrifuging —

* For details — discussed with great prolixity — the reader should consult the original.

THE DIAGNOSIS OF INTESTINAL PROTOZOAL INFECTIONS 1 33

a method too complicated to be described in detail here. Barthelemy
(1917) speaks highly of the results obtained by this method, but we
have not tried it.

Methods of counting the cysts present in faeces have been devised
by Cropper (1918, 1919) and Porter (1916). Those interested in such
methods should consult the original papers — especially that of Cropper
(1918), in which his apparatus is fully described.

Permanent Preparations of protozoa in stools can be made in many
different ways. We shall describe only the simplest and generally most
useful methods. It requires much practice to make really good pre-
parations, and success depends here — as in all other fields of cytology
— upon obtaining perfectly fresh material, containing healthy organisms,
upon proper fixation, and upon suitable and accurate staining. (One
of the most important things for the beginner to remember is that
the preparations must never be allowed to dry at any stage in the
proceedings.)

A moist film preparation is made by smearing a little of the material
to be mounted — suitably diluted, if necessary, with normal saline solu-
tion— upon a clean coverglass ; and then, without allowing it to dry,
dropping the coverglass film-side downwards upon the surface of the
fixing fluid, contained in a small Petri dish, hollow-ground glass block,
or watch-glass. (Hold the coverglass by its edges between the thumb
and forefinger of the left hand, and make the smear by carefully
spreading the material — as uniformly as possible — with the platinum
loop. Thin films are best, but are more apt to dry before they fall on
the fixative. If the loop touches the finger or thumb accidentally, wash
in lysol immediately. Be careful to avoid the formation of air bubbles
between the film and the surface of the fixative. After the film has
floated on the surface for a few moments, pick it off with forceps and
immerse it completely, face upwards, in the fixative — allowing it to lie
thus on the bottom of the vessel until completely fixed. Use plenty of
fixative, and throw it away after use. Do not dilute the material too
much with saline solution — else the film will not adhere to the cover-
glass, but will float off and be lost. Films can, of course, be made on
slides instead of coverglasses, but this method is less convenient.)

For routine purposes — for fixing both active protozoa and cysts —

134 THE INTESTINAL PROTOZOA OF MAN

the following fixative is the most serviceable (so-called " Schaudinn's
solution," with acetic acid) :

Saturated solution of corrosive sublimate (HgCl2)

in distilled water ... ... ... ... 2 parts.

Absolute (or 96 per cent.) alcohol ... ... 1 part.

To every 100 c.c. of the mixture add 5 c.c. of glacial acetic acid.
(This fluid keeps indefinitely — notwithstanding statements to the
contrary.)

The film should be left in this fluid for 10 to 20 minutes — the longer
time being best for cysts. It is then transferred to 50 per cent,
alcohol, in another vessel ; rinsed rapidly in this, to remove most of
the fixative ; and then placed for at least 10 minutes— preferably longer
— in 70 per cent, alcohol to which a few drops of iodine solution have
been added. This is to remove the rest of the sublimate from the film,
before staining and mounting. (Don't forget that the film, after fixa-
tion, is soft and delicate, and must never be touched or scratched.
Films are most easily handled with fine forceps, with curved ends.
Never omit the iodine bath and never use a watery iodine solution. A
few drops of the iodine solution used in making temporary preparations
— described above — added to about 5 c.c. of 70 per cent, alcohol, answers
admirably. Although no sublimate crystals can be seen in the freshly
prepared film, they will make their appearance later unless the sublimate
is removed in this manner, and will ultimately ruin the preparation.)

It is advisable — if time is no object, and the best preparations are
required — to transfer the film from the iodine solution to strong
alcohol (70 — 90 per cent.), and to leave it to harden in this for a day
or two. (This prevents maceration or shrinkage during subsequent
manipulations.)

Many other good cytological fixatives can, of course, be used.
Bouin's fluid, Flemming's fluid, Zenker's fluid, and many others, give
excellent results with free organisms; but they often fail to penetrate
cysts properly, and cannot be recommended for routine purposes.

Staining may be accomplished successfully in a variety of ways.
We recommend Mayer's " Haemalum " for rapid diagnosis of cysts,
amoebae, etc., and one of the long iron-haematoxylin methods (such
as Heidenhain's) for more accurate work, when speed is not essential,
By this method the fiagella of flagellates can be stained, and nuclei and
other structures can be made to show their finer cytological detail —

THE DIAGNOSIS OF INTESTINAL PROTOZOAL INFECTIONS 1 35

neither of these requirements being fulfilled, as a rule, by the haemalum
method.

Mayer's "Haemalum" is best compounded as follows : —

Haematoxylin (crystals) ... ... ... 1 gm.

Distilled water ... ... ... ... 1 litre.

Dissolve and add : —

Potash alum ... ... ... ... ... 50 gm.

Sodium iodate (NaI03) ... ... ••• 0*2,,

When solution is complete, filter.

(This solution is ready for immediate use. It should be of a rich red
colour. It will not keep indefinitely; and when it turns brown and
precipitates, it is no longer fit for use. After staining, the solution may
be poured back into the bottle, and used again.)

The films to be stained are passed from the strong alcohol, through
descending grades of weaker alcohol, into distilled water (e.g., alcohol
70 per cent., 50 per cent., 30 per cent., distilled water. On no account
use tap-water.) They are then transferred to the staining fluid, and left
there for 5 to 20 minutes. (The longer times are better for cysts, which
are less readily permeable than unencysted organisms.) After staining,
the films, which now appear pinkish, are placed in running tap-water
till blue. (Put them film-side uppermost in a Petri dish containing
tap-water, and allow the tap to flow gently into the dish for about
5 minutes or so. If the water is not sufficiently alkaline, it may be
necessary to prolong the process, or to add a small amount of sodium
bicarbonate or other weak alkali.) They are then ready for mounting.*

The final stages consist simply in dehydrating gradually with
alcohol, clearing in xylol, and mounting in Canada balsam. (Pass the
coverglasses through ascending grades of alcohol — e.g., 30 per cent.,
50 per cent., 70 per cent., 90 per cent. — into absolute alcohol. Leave
in this for at least 5 minutes. Then transfer to a vessel containing
absolute alcohol and xylol, in equal parts. Leave 5 minutes. Then
transfer to pure xylol, when the preparation will clear almost immedi-
ately. This slow and gradual method prevents shrinkage and collapse
of cysts. To mount, place a drop of balsam — dissolved in xylol — in the
middle of a clean and dry slide ; then gently lower the coverglass —
taken from xylol — film-side downwards on to the drop, and press down

* If the films are found, on subsequent examination, to be overstained, they may
be differentiated to the required degree by means of a weak solution of acid or alum.

136 THE INTESTINAL PROTOZOA OF MAN

carefully. Do not use so much balsam that some of it runs on to the
back of the coverglass. Be careful not to introduce air bubbles under
the film, and not to let the film dry — by evaporation of the xylol —
before it is pressed home in the balsam. Harden the balsam, finally, by
putting the preparation in a warm but not too hot place — e.g., in the
incubator or on the imbedding bath — for a few hours.)

1 ron-h Hematoxylin staining is best carried out as follows. Transfer the
fixed films (as before described) to distilled water. Then mordant them
in a watery solution of iron alum (2*5 — 4 per cent.) for not less than
6 hours. (Overnight generally answers well.) Then rinse them in
distilled water, and place them in a o'5 per cent, ripened solution of
haematoxylin in distilled water. (Make the solution and put it in a flask,
plugged with cotton-wool, in a warm place — if possible in sunlight.
Shake from time to time. The solution is ''ripe" — i.e., the haematoxylin
is more or less oxidized to haematein — and ready for use, when it
becomes a good brown colour. This may require several weeks.) The
films should be left in this solution for 6 hours or more (up to 24).
They will then be overstained and black, and must now be rinsed in
distilled water and suitably differentiated by extracting the stain with the
iron alum solution (diluted to about 1 per cent.). This is the difficult
part of the process, and can only be learned by practice. During the
extraction of the stain, the film is removed from the alum solution,
rinsed in distilled water, and examined under the microscope. If still
overstained, it is put back in the alum, and the process repeated. When
the staining is satisfactory, the film is washed first in distilled water, then
in running tap-water for at least half an hour. It is then dehydrated
and mounted in the manner already described.

Staining can be accelerated by using alcoholic solutions (cf. Dobelf,
1914a), and by warming. (The beginner should master the other
method first.) It is to be remembered, however, that cyst-walls are
usually more permeable to watery than to alcoholic solutions ; and for
this reason various other methods of staining {e.g., with Weigert's iron-
haematoxylin,* paracarmine), though often useful, are not so suitable for
general use as those just described.

The appearance of the active protozoa or cysts when successfully

* This is a specially useful rapid stain for mucus containing numerous cells or
amoebae.

THE DIAGNOSIS OF INTESTINAL PROTOZOAL INFECTIONS 1 37

stained by the foregoing method may be gathered from the Plates
illustrating this volume. The appearance of stained cysts will be readily
understood if the reader will carefully compare the three panels of
Plate VIII. The same cyst, lying in exactly the same position, is here
shown* as it would appear (1) when alive, (2) when mounted in iodine
solution, and (3) after fixation and staining. Comparison of the figures,
with reference to the text, will, it is hoped, obviate the necessity of
entering into further detailed description and comparison of the various
cysts commonly seen in human faeces. The cysts of each organism
have already been described, and their comparison with one another
will be facilitated by the figures — which convey more information, if
carefully studied, than many pages of printed matter. Nevertheless,
the actual appearances of these cysts, and their correct determination,
can be learnt only by practical experience in the laboratory; and the
few figures which we are here able to give cannot claim to be more
than a small and imperfect sample of the almost infinite variety of cysts
and other objects which may be encountered in human faeces.

It is frequently desirable — or even necessary — to couuterstain films,
after staining them with haematoxylin by one of the foregoing methods.
This is best done with eosin, though any other plasma stain can, of
course, be used. (Stain the films to the required degree with a 1 per
cent, watery solution of eosin. If overstained, the excess of eosin can
be removed by prolonged washing in tap-water, or by dipping in 70 per
cent, alcohol containing a very small amount of orange G.)

Very pretty preparations of amoebae and cysts can be obtained by
Mann's staining method, as modified by one of us (C. D.). Films are
transferred — after fixation, etc. — to distilled water, and then placed for
some time (determined by trial — usually 4 to 12 hours) in Mann's stain,
prepared as follows :

Aqueous solution of methyl blue,f 1 per cent. ... 35 c.c.

Aqueous solution of eosin, 1 per cent. ... ... 45 c.c.

Distilled water ... ... ... ... ... 100 c.c.

They are then washed in distilled water, and differentiated in 70 per
cent, alcohol containing a little orange G. (A few drops of a saturated
solution added to 100 c.c. of 70 per cent, alcohol.) When differentiated

* See the remarks on this Plate in the Preface, p. vii.

t N.B., not methylene blue. The methylblue-eosin mixture keeps indefinitely, and
may be used over and over again.

I3& THE INTESTINAL PROTOZOA OF MAN

to the correct degree (control under microscope), they are dehydrated
and mounted in the usual way.

Innumerable other staining methods may, of course, be employed —
such as the various carmine and haematoxylin stains, etc. ; but the iron-
haematoxylin method should be mastered, as it is the only one whereby
satisfactory preparations showing the structure of flagellates can be
obtained. Borax carmine (especially if warmed, and acidulated with
hydrochloric or acetic acid) will sometimes stain cysts when all other
stains fail to penetrate their walls.

Glycogen can be preserved and stained in cysts — if permanent pre-
parations are required — by using Best's specific carmine stain for this
substance. (See Best, 1906.) Films should be fixed in Carnoy's fluid,*
in preference to sublimate-alcohol, though the latter can also be used.
They can be stained with Weigert's iron-haematoxylin or any other
alcoholic stain before the carmine process, if it is desired to show the
nuclei as well as the glycogen.

The technique of preparing sections of tissues infected with intes-
tinal protozoa hardly comes within the scope of the present work. For
detailed information the reader must consult the histological treatises
devoted to such subjects. We would only remark that for general
purposes excellent fixation of protozoa and tissues may be obtained
with Bouin'sf or Zenker's^ fluids, while any of the good cytological
stains may be employed. The technique of inoculating kittens or other
experimental animals with E. histolytica, or other protozoa, must also be
passed over here. Information on this subject will be found in the
work of Dale and Dobell (1917).

It may be added that the cultivation of the intestinal protozoa of
man is still too uncertain an achievement for the process to have any
value, at present, for diagnostic purposes. References to the successes
in this direction claimed by some workers, have already been made in
the descriptive chapters.

* Carnoy's Fluid: Absolute alcohol, 6 parts ; chloroform, 3 parts ; glacial acetic
acid, 1 part.

t Bourn's Fluid: Formol (40 per cent, formaldehyde), 25 parts ; picric acid (satur-
ated watery solution), 75 parts ; glacial acetic acid, 5 parts.

\ Zenker's Fluid: Potassium bichromate, 2*5 gm. ; sodium sulphate, 1 gm. ; mer-
curic chloride, 5 gm.; glacial acetic acid, 5 c.c. ; distilled water, 100 c.c.

the diagnosis of intestinal protozoal infections 1 39

Common Sources of Error in Diagnosis.

To deal with this subject adequately would require a whole book.
Human faeces may contain innumerable objects, and many of these
can be mistaken by the novice for protozoa or their cysts. Since Lamb)
(1859) first seriously attempted to describe and interpret the micro-
scopic constituents of stools, many works have appeared on this subject.
The recent contributions by Cammidge (1914) and Barthelemy (1917;
may be mentioned in this connexion. But up to the present there is
no work which deals exhaustively with the smaller particles which may
puzzle the protozoologist, and we cannot here attempt more than tht
briefest mention of the most noteworthy of these. A complete descrip-
tive catalogue is out of the question.

It is a wise counsel for the novice that he should never identify any
object found in faeces as a protozoon unless he sees it moving. Dead,
degenerate, and motionless specimens often cannot be identified with
certainty even by the expert. It is wise, moreover, when beginning,
never to identify any structure as an amoeba unless it puts out pseudo-
podia : and never to identify an amoeba, displaying such movements, as
E. histolytica unless it contains ingested red blood-corpuscles. (If the
beginner finds objects which he thinks are protozoa or their cysts, but
which do not agree exactly with the descriptions or figures, the proba-
bility is that he is mistaken.)

When active protozoa are found in a preparation, one should make
certain that they have not been introduced in the saline solution with
which the faeces have been diluted. To guard against this possibility,
the saline solution should be frequently sterilized by boiling, and, if
necessary, filtered also. This is especially important in hot countries,
and neglect of this precaution is a frequent source of error. It is sur-
prising how many organisms may make their appearance, and even
continue to live and multiply, in saline solution or the distilled water
used for preparing it. Further, if many active protozoa are found in a
stool more than 24 hours old,* it is highly probable that they are
coprozoic forms — not intestinal protozoa — which have developed in the
stool since it was passed. (See Chapter IX.)

Diarrhoeic or dysenteric stools present the greatest difficulties to the
beginner, on account of the numerous cellular elements, derived from

* In hot weather coprozoic flagellates may swarm in stools which are only a few
hours old.

14° THE INTESTINAL PROTOZOA OF MAN

the tissues of the intestine, contained in them. The difficulty arises
chiefly from the circumstance that these cells, when passed in the stool,
are usually in an advanced state of degeneration. Often they in no
way resemble the normal tissue-cells with which most medical men are
familiar.'*

Among the commoner cells which can be mistaken for dead pro-
tozoa or cysts we may specially mention the following : detached and
degenerating columnar epithelial cells and goblet cells — often present in
mucus from the gut wall, or isolated in the stool ; endothelial cells from
the blood-vessels in inflamed areas— sometimes containing red blood-
corpuscles and other inclusions, and thus apt to be mistaken for dead
specimens of E. histolytica ; squamous cells from the anal margin ;
leucocytes in pus, or scattered irregularly through the stool. Squamous
ceils, as seen in stools, often puzzle the beginner, owing to their large size
and their resemblance to some pictures of amoebae. Their outlines
are often irregular — "amoeboid" — and they possess a clearly visible
ring-like nucleus. These cells are usually present on the surface of
solid stools, but may be mixed with the faeces in soft or liquid speci-
mens. They can be readily distinguished by their centrally placed
nucleus, the small bright granules in their cytoplasm, their lack of
motility, and their shape — a flattened scale, not a rounded globule of
protoplasm, like a dead amoeba. (The shape can usually be made out
by tapping the coverglass, and so causing the cell to turn edgewise.)
Polymorphonuclear leucocytes should not give much trouble, as they
remain unchanged for a considerable time in stools. Owing to their
small size, however, and the apparent presence of several minute annular
nuclei in them, they can be mistaken for small cysts of E. histolytica —
especially when examined in iodine solution.

Worm eggs cannot easily be mistaken for protozoal cysts, owing to
their larger size (as a rule), their thick (often coloured and sculptured)
shells, and characteristic contents. (The ocular micrometer should be
freely used in studying doubtful objects, as their size often gives an
important clue to their identity.) Spores of certain Fungi may present
greater difficulties ; and large yeasts, fragments of moulds (especially in

* It may help the reader to appreciate the difficulties and sources of error if he
reads and studies the figures in the papers by Bartlett (1917), and Thomson and
Thomson (1916) : and then reads the criticism of their findings by Bahr and Willmore
(1918). The works by Wenyon and O'Connor (1917), and by Willmore and Shearman
(1918), may also be consulted in this connexion.

THE DIAGNOSIS OF INTESTINAL PROTOZOAL INFECTIONS 141

stale stools), and other colourless living vegetable structures are often
mistaken for protozoal cysts by beginners. (The veriest tiro may even
mistake oil drops and starch grains — and even air-bubbles — for cysts
of protozoa. Rounded homogeneous bodies, derived from the food, and
displaying little or no internal structure even when treated with iodine,
are common in stools, and should give rise to no confusion. But to
determine what some of these structures really are is another matter.;
It is impossible to discuss, or even mention, the thousand and one
objects— mostly animal and plant remains — of which human faeces are
usually composed. They can be learnt by practice only. Their identity
can often be guessed by careful inquiry into what the patient has
previously eaten, and the guess can then be verified by microscopic
examination of the food suspected and by experiment upon oneself.
The beginner can learn much by subjecting his own stools to frequent
and careful scrutiny — bearing in mind the various foods which he has
previously consumed.

The organism which is responsible for the largest proportion of
mistakes in diagnosis is probably Blastocystis hominis. This is a veget-
able organism, probably related to the Ascomycetes (Fungi), and occurs
in the intestine of nearly every human being. We give figures of a
typical specimen as it appears alive, in iodine solution, and after fixation
and staining (PI. VIII, 0',02,03). It consists of a thin layer of proto-
plasm, containing one or more minute nuclei and a variable number
of granules, surrounding a voluminous spherical mass of reserve
substance (of unknown chemical composition). Outside the proto-
plasm there is an extremely thin limiting membrane, and outside this
sometimes a gelatinous capsule. Dividing organisms, constricted into
an hour-glass figure, are commonly seen. The organism may have any
diameter from about 5 jjl to over 30 fx, but such large specimens are
very rare. The commonest sizes are from about 8^ to 14 fx. The
relative proportions of protoplasm and reserve-stuff in different indi-
viduals may show considerable variation. Usually the layer of proto-
plasm is very thin and the reserve mass very large — as in the figures.
Sometimes, however, there is a thick protoplasmic layer, and a small
mass of reserve material. Other peculiar forms (some of them possibly
distinct species) are also encountered.

Blastocystis may be found in the intestine of many animals besides
man. It has often been mistaken for the cyst of a protozoon — both in

I42 THE INTESTINAL PROTOZOA OF MAN

man and in other animals.* It is a source of trouble to inexperienced
workers, and everybody who has to examine human stools should make
himself thoroughly familiar with it.

Clinical Interpretation of the Protozoological Findings.

The protozoologist usually examines human faeces with a special
object in view. When he seeks for protozoa in a human stool, it is
seldom for the mere pleasure of studying these organisms. The stool
has usually been passed by a person who is suffering from some intes-
tinal disorder, and the ultimate aim of the examination is to ascertain
the "cause" of this disorder. In other words, the protozoological
diagnosis is but a contribution to a final medical diagnosis. From the
medical standpoint, therefore, the protozoological findings, in a given
case, have always to be considered in conjunction with the clinical
condition of a patient.

The correct clinical interpretation of the protozoological findings —
the correlation of the protozoological and the clinical diagnosis — is
obviously a matter of the greatest importance : for upon it the medical
diagnosis depends, and upon this will depend, in turn, the treatment and
cure of the patient. It is also a matter of immense magnitude. To
consider it adequately would lead us to discuss the differential diagnosis
of all intestinal diseases. Such a discussion cannot be attempted here ;
and the few remarks that we can make will therefore be little more than
notes.

In order to arrive at the correct interpretation of a given case, the

* Much work has already been done on this curious organism, but its complete life-
history has yet to be described. It was first noticed about the middle of last century,
and was at one time regarded as the " cause " of cholera. Since then it — or a related
species— has been frequently described and almost as frequently misunderstood. It
has already been figured as the cyst of an amoeba, of a flagellate, and as a coccidian,
in human stools. Prowazek (1904), and most of the German workers, regarded it
as the cyst of Trichomonas — an organism with which it has no connexion. More
recently Chatton (1917) has also supposed that it is a stage in the development of
a flagellate — having been deceived, apparently (as Prowazek was before him), by its
resemblance to the cysts of Prowazekella lacertae. Swellengrebel (1917a), on the
other hand, regards Blastocysts as a degenerative stage of various different intestinal
protozoa — in my opinion an equally untenable hypothesis. My own views are given
above, and are founded upon a study of Blastocystis in many different hosts — a study
extending over the last fifteen years, but of which the results are still for the most
part unpublished. The generic name Blastocystis was introduced by Alexeieff, who
has carefully studied the organism (see Alexeieff, 191 1, 1911a, 1917). With the views
expressed in his last publication I am essentially in agreement. I would merely note
that he regards the forms occurring in different animals as all belonging to the same
species — B. enterocola. I consider that there are at least several distinct species, and
prefer, provisionally, to distinguish that found in man as B. hominis — a name proposed
by Brumpt (1912). (CD.)

THE DIAGNOSIS OF INTESTINAL PROTOZOAL INFECTIONS 143

following points must always be carefully considered : (1) The clinical
condition of the patient. (2) The evidence derived from the macroscoj it
examination of the stools. (3) The protozoological evidence from Ihc
microscopic examination. And in addition to these, we must usually
consider (4) other evidence furnished by the bacteriological examination.)
and frequently also (5) the medical history of the patient.

We shall, for the sake of brevity, make a drastic simplification of the
foregoing programme by eliminating a number of complications which
can be entrusted to the common sense of the reader. In what follows
we shall assume that the fourth category — concomitant bacteriological
evidence — is negative and therefore negligible; and that no other
evidence of a like sort {e.g., serological or helminthological) has to be
taken into account — an ideal simplification which is rarely or never
realized in practice.

We can also simplify the discussion by arbitrary restrictions on the
protozoological side. We have already seen, in previous chapters, that
there is evidence to show that by no means all the protozoa of the
human bowel are pathogenic. All the flagellates, all the amoebae
except E. histolytica, possibly (or probably) all the coccidia, and all the
ciliates except Balantidium coli, may be regarded as harmless — at least
for present purposes. There is no sound evidence to incriminate them
as "causes" of any specific disease. Consequently, their clinical
significance will here be regarded as nil. If any of these organisms
should be discovered — in any stage of development — in the stools of
persons with intestinal disorders, their presence can be ignored by the
physician ; for they probably occur with equal frequency in persons with
no such disorders. The clinician may proceed with his diagnosis and
treatment as though no such discovery had been made."*

This leaves us with only two protozoa to be considered — E. histo-
lytica and Balantidium. The former, being much the commoner, is the
more important ; but what we have to say in the following paragraphs is
equally applicable to both, and it must be understood that when we now
speak of "parasites," we refer to these two organisms' — and these two
only. We shall illustrate our remarks by describing", with the utmost

* The propriety of such a procedure has been practically demonstrated over and over
again during the recent War. In Britain, at any rate, it was the rule, in the case of
military patients, to give a protozoological diagnosis of "negative" to all patients found
infected with any protozoon except E. histolytica or Balantidium.

144

THE INTESTINAL PROTOZOA OF MAN

brevity, three typical cases— from which the interpretation of inter-
mediate or atypical cases can be inferred. The selected types are
classified in terms of their clinical condition and the macroscopic
appearance of their stools.

Case I. An apparently healthy person, with formed and normal stools.
In such a person's stools no free (unencysted) parasites will be found.
If cysts are present, the person is a carrier of the parasite. For closer
diagnosis, we must ascertain his history.

If it is found that he has never suffered from dysentery or diarrhoea
(amoebic or balantidial*), he is a contact carrier. He has not suffered,
and probably will not suffer, from the presence of the parasites in his
gut. On the other hand, he may develop diarrhoea or dysentery — or, in
the case of E. histolytica, a liver abscess— at any time. The chances are
probably remote, but the physician must decide whether specific treat-
ment, to eradicate the infection, is advisable.

If the patient's history reveals the fact that he has previously suffered
from dysentery or diarrhoea (amoebic or balantidial), then he is a
convalescent carrier of the parasite. He has already shown that he is
sensitive to the presence of his parasites, and consequently he is liable to
a relapse at any time. Specific treatment,! to remove the parasites, is to
be recommended— even though the patient is, at the time, apparently in
perfect health.

Case II. A patient who is ill, with diarrhoeic stools. In the stools of
such a patient, we should expect to find free forms of the parasite,
probably with a more or less plentiful admixture of cysts. If the patient
is suffering from amoebic diarrhoea, precystic forms of E. histolytica will
be present in considerable numbers, while cysts of this amoeba may or
may not be present. If he is suffering from balantidial diarrhoea, free
ciliates will usually be plentiful. Such a patient obviously stands in
need of treatment.

Cases of this type often present great difficulty. A carrier can always
be made to pass free forms of the parasite which he harbours, and which

* In practice it will usually be found impossible, when a previous history of dysentery
or diarrhoea is elicited, to ascertain the causes of the disease. The physician will
usually have to base his decision upon probabilities — taking into consideration the
symptoms of the previous attacks, the place where they occurred, the patient's circum-
stances at the time, the effects of any treatment which he may have received, etc.

f This applies more particularly to E. histolytica — the specific treatment of Balmi-
tidium infections being still problematic (see p. 162).

THE DIAGNOSIS OF INTESTINAL PROTOZOAL INFECTIONS 145

may be doing him no appreciable harm, by any means (e.g., by a
purgative) which will cause him to empty his bowel. Accordingly, a
carrier of E. histolytica — to take an instance — will probably pass pre-
cystic amoebae, of this species, in his stools if he contracts diarrhoea
from any cause whatsoever. Consequently, an attack of diarrhoea, with
such organisms in the stools, does not necessarily justify a diagnosis of
amoebic diarrhoea or dysentery. To justify this diagnosis, other
possible causes must be ruled out. The diagnosis is probable if the
diarrhoea is persistent, and the amoebae are usually numerous. It is
practically certain if, in addition, the microscope reveals blood or pus
in the stools, and active forms of E. histolytica containing ingested red
blood-corpuscles are occasionally discoverable. The same applies,
mutatis mutandis, to Balantidiuni infections.

Case III. A patient who is ill, with dysenteric stools. In the stools of
such a patient, cysts will practically never be found. If active parasites,
containing ingested red blood-corpuscles, are present in the stools, a
diagnosis of amoebic or balantidial dysentery — as the case may be — is
justified.* Appropriate treatment is therefore necessary.

As a general rule, in a case such as this the parasites will be found in
abundance in the freshly passed stools; but they may, occasionally, be
difficult to discover. (If the stool is partly faecal, they should not be
looked for in this part, but in the flakes or streaks of bloody mucus
mixed with it. The faecal part may, however, contain cysts.)

It must be remembered that negative examinations may often be
made on positive cases : that is to say, an infected person does not
always pass his parasites in discoverable numbers in his stools. A
negative examination is no proof of non-infection. As a general rule,
a negative examination is of less value, as an index of non-infection, in
the case of a suspected carrier (Case 1, above) than in the case of a patient
displaying acute symptoms (Case 3). When a patient is suffering from
amoebic or balantidial dysentery, E. histolytica or Balantidiuni can
usually be found in his stools without much difficulty. On the other
hand, the stools of a healthy person must be carefully examined with

* We have assumed above that other concomitant causes of the condition have
been ruled out. It must be remembered, of course, that cases of dysentery due to the
presence of two pathogenic organisms simultaneously have been described. Such
"double dysenteries" must be extremely rare, however ; and even if dysentery bacilli
were isolated— for example — from the stools of the hypothetic patient here considered,
it would in no way invalidate the diagnosis of " amoebic dysentery " also.

146 THE INTESTINAL PROTOZOA OF MAN

negative results on at least 6 occasions before it can be said with
considerable probability that he is uninfected.*

No protozoologist will, of course, ever venture to diagnose a proto-
zoal infection without actually seeing and identifying the particular
organism in question. For example, the fact that a patient's condition
improved after the administration of emetine would not, in itself, justify
the inference that he harboured E. histolytica. Indirect methods such
as this — which are no more than the making of plausible guesses — can
have no place in protozoology. It is true that the stools may have a
characteristic look — in typical cases — which may enable one to con-
jecture the correct diagnosis. The macroscopic appearance of the
stools may sometimes enable one to say that the patient is probably
suffering from amoebic rather than bacillary dysentery (cf. Grail and
Hornus (1914), etc.); but amoebic dysentery cannot be diagnosed with
certainty without the aid of the microscope. Further, the microscopic
picture of the stools is, on the whole, clearly different in typical cases
of amoebic and bacillary dysentery. In the latter the cellular exudate
is richer, and contains more numerous leucocytes (cf. Wenyon and
O'Connor, 1 917 ; Bahr and Willmore, 1918 ; Willmore and Shearman,
1918) ; but to make a diagnosis of "amoebic dysentery" or " E.
histolytica" from the appearance of the cellular exudate alone — without
finding amoebae — would be a highly unscientific procedure.

These and other f indirect methods, which have sometimes been
advocated, may have their uses as clinical makeshifts : as protozoological
methods they are obviously worthless.

We may be allowed to conclude this chapter with some apt words
from an old writer on microscopy — words which are as true to-day as
they were when they were written, one hundred and eighty odd years

* The interpretation of negative examinations has been fully discussed elsewhere
by one of us (Dobell, 1917). Even more than 6 negative examinations may, of course,
be necessary ; and this appears to apply especially to Balantidimn infections — to judge
from Walker's (1913a) observations on monkeys.

t As a further example, it may be noted that some workers regard the finding of
Charcot- Leyden crystals in the stools as evidence of amoebic infection (cf. Acton, 1918).
We are not disposed to attach great importance to the presence of these crystals, and
will merely note that Barthelemy (1917) considers them to be particularly characteristic
of helminthic infections.

THE DIAGNOSIS OF INTESTINAL PROTOZOAL INFECTIONS 147

ago, and which contain wise counsels that no student of the Protoz

can ever afford to neglect :

11 Cautions in viewing Objects."

" Beware of determining and declaring your Opinion suddenly on
any Object; for Imagination often gets the Start of Judgment, and
makes People believe they see Things, which better Observations will
convince them could not possibly be seen : therefore assert nothing till
after repeated Experiments and Examinations in all Lights and in all
Positions.

"When you employ the Microscope, shake off all Prejudice, nor
harbour any favourite Opinions; for, if you do, 'tis not unlikely Fancy
will betray you into Error, and make you think you see what you would
wish to see.

" Remember that Truth alone is the Matter you are in search after ;
and if you have been mistaken, let not Vanity seduce you to persist in
your Mistake.

" Pass no Judgment upon Things over-extended by Force, or
contracted by Dryness, or in any Manner out of their natural State,
without making suitable Allowances."

— Henry Baker, The Microscope made
Easy. 1742. Chap. XV, p. 62.

148

CHAPTER VIII.

THE TREATMENT OF INTESTINAL PROTOZOAL
INFECTIONS.

We have now described the chief protozoa which live in the human
intestine ; and we have also considered very briefly their diagnosis and
the pathology and symptoms of the diseases which some of them may
play a part in producing. It still remains for us to say something about
the treatment of intestinal protozoal infections ; that is to say, about
the methods of removing these protozoa from the intestine, and so
curing a patient of the disease to which their presence may give rise.

In dealing with the subject of treatment, we shall confine our atten-
tion almost entirely to one aspect — namely, specific treatment. In a
work of the present character, dealing primarily with the protozoa
themselves, it is impossible to discuss the purely clinical aspects ; and
for information on this subject we must refer the reader to the ordinary
treatises which are devoted to medicine rather than to protozoology.
It will be understood, therefore, that when we now speak of treatment,
we refer primarily to specific treatment, directed towards the eradication
of infection.

We shall discuss, in turn, the treatment of infections with protozoa
belonging to each of the four great groups which we have hitherto con-
sidered. They will be taken severally and consecutively, because there
is no form of specific treatment which is applicable to intestinal
protozoa generally. W7ith some of them, such as the amoebae, great
advances have recently been made ; and as a result we can now
eradicate E. histolytica from the majority of infected persons with cer-
tainty. With most other protozoa, however, the problem is still
unsolved. We have no indication, indeed, of the line of attack which
we should adopt in attempting to dislodge them from their strong-
holds in the human body. Consequently, we shall be able to record
little but vain attempts at specific treatment in these cases.

The methods of treatment which have been already advocated, and
for which success has been claimed, are almost innumerable. Neverthe-

THE TREATMENT OF INTESTINAL PROTOZOAL INFECTIONS 1 49

less, but few of these have survived close scientific scrutiny; and in
the following pages we propose to consider chiefly those methods
which appear to be supported by evidence. Now the evidence n
sary to prove that a patient has been "cured" of a protozoal infection
is not easily obtained, and a "cure" is by no means so self-evident as
one might at first sight suppose. We shall preface the following notes
on treatment, therefore, with a few remarks regarding the evidence
which is requisite to prove that any particular mode of treatment has
been successful.

Let us take an imaginary case. We have a patient suffering from
amoebic dysentery — accurately determined by laboratory investigation
of his stools, which contain abundant specimens of active E. histolytica
amoebae, and are bacteriologically and otherwise "negative." We wish
to know whether a given drug X is a " cure " for the condition. The
patient is put to bed and properly tended, and appropriate doses of
the drug are administered. After a few days the patient recovers. His
stools gradually become normal, to the naked eye, and his health is
restored. In a week or two he is able to resume his ordinary work,
and is apparently " cured." Can we, on such evidence, say that the
drug X is a " cure " for amoebic dysentery ?

The answer to this question, on the evidence so far presented, is not
an affirmative — as is sometimes assumed — but in reality an emphatic
negative. There is no evidence whatever either (1) that the patient is
" cured," in the sense that his infection has been removed, or (2) that
the drug X has had anything to do with his clinical recovery. As
regards the first point, the disappearance of the infection can be proved
only by repeated microscopic examination of the stools, with con-
sistently negative results, for -a period of at least several weeks.
" Negative " results from naked-eye inspection of the stools, or even
a few " negative examinations " made with the microscope, mean
nothing ; for such negative evidence can often be elicited from
untreated cases harbouring many parasites in their intestines. As
regards the second point, it must be remembered that amoebic dysen-
tery is often "cured" by rest in bed and nursing. The attack may
pass off "spontaneously," without any other treatment. But in all
such cases the patient becomes a convalescent carrier of the parasite
(see p. 50). He undergoes clinical recovery, but remains infected and
liable to relapse at any time.

150 THE INTESTINAL PROTOZOA OF MAN

It is thus clear that we cannot say that the drug X has a specific
curative action until, in addition to the clinical recovery of the patient,
we have conclusive evidence, from adequate microscopic examination
of his stools after its administration, that he is no longer infected with
the parasite which caused the disease. (Spontaneous disappearance of
the parasites from the intestine has never yet been proved to occur after
they have once become established.) It is hardly necessary to add
that, for the evidence to carry conviction, there must be no possibility
that the original diagnosis was incorrect, and no question of the com-
petence of the protozoologist who made the negative examinations.

Although these requirements may appear self-evident, it is surprising
how frequently they have been ignored. Intestinal diseases due to
protozoa cannot be diagnosed, nor can their cure be guaranteed, on
clinical evidence alone. Consequently, all methods of treatment whose
claims to success are unsupported by expert and adequate proto-
zoological evidence, must be regarded with the gravest suspicion.

It is obviously of great importance, in considering the curative
efficacy of so-called " specifics " for intestinal infections, to ascertain
the proximate value of " negative examinations." An attempt to solve
this problem, with sufficient accuracy for practical purposes, has been
made by one of us (Dobell, 191 7), to whose paper the reader may be
referred. The results there reached have received support from sub-
sequent work, and need not be discussed in detail here. It will suffice
to notice the chief points of importance.* These are (1) that negative
protozoological examinations of the stools made during a course of
treatment are practically worthless as evidence of non-infection ; and
(2) that to prove that an infection has been removed by treatment, it
is necessary to make at least six negative examinations covering a period
of at least three weeks after the cessation of treatment. These require-
ments certainly represent an absolute minimum. Unless they have
been fulfilled it is too early to speak of a " cure " having been effected.
To arrive at certainty of cure it is necessary to exceed this minimum ;
and we now consider it desirable to keep all treated cases under proto-
zoological observation for a period of at least a month after treatment.

* The conclusions were based chiefly upon a special case — the treatment of
E. histolytica infection with emetine. There is good reason to believe, however, that
they are equally applicable to the results of treatment of other intestinal infections
with protozoa.

THE TREATMENT OF INTESTINAL PROTOZOAL INFECTIONS 1 = 1

If the stools remain consistently negative during this period — the
examinations being made every day, or every few day-, — the probability
is that the patient has been freed from his infection.

We shall now consider very briefly the chief results obtained in
attempts at specific treatment of the various intestinal protozoal infec-
tions of man, and we would ask the reader to bear in mind the points
which have just been noted. When we refer to doubtful or incon-
clusive results, we mean that they appear uncertain because they are
not supported by evidence such as we believe to be necessary. If the
reader will take the trouble to consult the original works themselves,
to which reference is made, he will find that the majority of "cures"
rest upon evidence which is far below the standard which we have
postulated as a minimum.

The Treatment of Amoebiasis.

In this section we shall deal almost entirely with the specific treat-
ment of primary or intestinal infection with E. histolytica. The opera-
tive treatment of liver abscess and secondary infections is beyond the
scope of the present work ; whilst the treatment of most other amoebic
infections is still problematic, and also, in practice, unimportant.

There are probably several chemical substances which, when
administered to an infected human being, are capable of eradicating
an intestinal infection with E. histolytica. By far the best known of
these, and the most thoroughly studied, is emetine — an alkaloid derived
from ipecacuanha. We shall begin with this, therefore, prefacing our
remarks with a few notes on ipecacuanha itself.

Ipecacuanha and its Alkaloids.— Ipecacuanha, formerly called
" Brazil Root," was introduced into Europe from South America in
the XVII century.*" It is the root of a Rubiaceous plant, Cephaelis
( =Psychotria —JJragoga) ipecacuanha, and was used as a native remedy
for "dysentery." It is now known that it has a curative action
in amoebic dysentery only, and that this action is due to the indirect
specific effect of some of its contained alkaloids upon E. histolytica.

* An interesting early account of the use of ipecacuanha for the " Bloody Flux "
■will be found in the following paper : " Of the Use of the Root Ipecacuanha, for Loose-
nesses, translated from a French Paper : With some Notes on the same, by Hans Sloane,
M.D." {Phil. Trans. Roy. Soc, xx, 69. 1698).

152 THE INTESTINAL PROTOZOA OF MAN

The most important of these alkaloids are Emetine, Cephaeline,
Psychotrine, and Methylpsychotrine.*

Emetine is a powerful gastro-intestinal irritant,! and has a re-
markable specific action upon E. histolytica in the human body, when
administered to the host. Vedder (1912), to whom we owe the revival
of its use in recent years, believed, from his experiments with free-
living amoebae, that emetine has a specific lethal action upon amoebae
generally. There is now good evidence, however, to show that it is
not a specially " amoebicidal " substance ; and that its action in eradi-
cating E. histolytica infections in man is due primarily to its effects
upon the host — not upon the parasites directly. (See Dale and Dobell,
1917.) The chief evidence for these conclusions is (1) that its derivatives,
and other substances, which are, in vitro, far more toxic than emetine
to E. histolytica, are inefficacious in eradicating human infections ; and
(2) that emetine will not eradicate an E. histolytica infection in the cat.J
Emetine thus has a specific action not merely upon a particular species
of amoeba, but upon that amoeba in a particular species of host.

A derivative of emetine, N-methylemetine, appears to resemble it
in its curative action, but is less toxic and less efficacious. § On the
other hand, the stereo-isomeride of emetine called z'soemetine (Pyman),
is comparatively non-toxic to man, but apparently of no value in
the treatment of E. histolytica infections. ||

Cephaeline is more toxic than emetine, but appears to have
similar curative properties.1I Psychotrine and METHYLPSYCHOTRINE
are comparatively non-toxic, and are therapeutically inactive.**

It appears probable that the toxic action of emetine and cephaeline
upon the intestinal mucosa of man is related in some way to their
therapeutic efficacy. Non-toxic derivatives, at all events, appear to

* See especially, on the chemistry of the ipecacuanha alkaloids, Carr and Pyman
(1914) and Pyman (1917, 1918).

t On the toxicity and pharmacology of emetine see especially Maurel (1914), Dale
(191 5), Balfour and Pyman (1916), Johnson and Murphy (1917), Walters, Baker, and
Koch (1917), Mayer (1919), Van den Branden (1919), Mattei (1920).

% As shown by Dale and Dobell (1917) and more recently by Mayer (1919). Mayer
claims some success in treating infected cats with a derivative called "Emetathylin "
(Karrer) : but his evidence appears inconclusive.

§ Cf. Low (1915), Stephens and Mackinnon (quoted by Dale and Dobell, 1917,
p. 450), Wenyon and O'Connor (1917).

|| Low (1918), and Low and Dobell (ined.).

^f Cf. Simon (i9i6),etc.
** On methylpsychotrine see Dale and Dobell (1917) and Jepps and Meakins (1917).

THE TREATMENT OF INTESTINAL PROTOZOAL INI LCI IONS J -3

be therapeutically inert. The exact mechanism by which emetine
acts upon li. histolytica in the body is, however, still a matter for
speculation.*

The mode of administration of emetine is a point of considerable
importance in treatment. The soluble salts of the alkaloid can be
administered by the mouthf or subcutaneously.* When given
orally they generally cause vomiting ; but given hypodermically in
equivalent therapeutic doses they do not, as a rule, give rise even to
nausea. Intravenous injection has been advocated,§ but emetine
appears to be more toxic when so given (Dale), and its therapeutic
efficacy does not seem to be enhanced. Treatment by intrarectal
injection of emetine (or ipecacuanha) has also been employed. |
Adsorption products of the ipecacuanha alkaloids, or of emetine
alone, with fuller's earth (" Alcresta ipecac," etc.) have found some
favour,! as they cause little or no vomiting. It appears probable,
however, that this is due to the contained emetine having been
rendered largely insoluble,** and consequently inactive. The results
of treatment with such compounds are, at all events, less satisfactory
than those which can be obtained by other methodsjt

Ipecacuanha itself is still regarded by some workers as superior to
emetine. Nevertheless, it appears to contain many unnecessary and
inactive ingredients, and its employment seems therefore less scientific
than that of its active alkaloids. In our opinion it should be regarded
as a substitute for emetine — when this is unobtainable — rather than
as a superior compound. It is more emetic, also, and less easily
administered.

The experience of the last few years has shown conclusively that
the success of emetine treatment depends upon giving adequate doses
in a suitable manner, and on prolonging the treatment for a sufficient
time. Small doses, given over short periods and intermittently, may

* The fate of emetine, when it enters the human body, is still not known with
certainty. It undoubtedly enters the blood-stream, and according to Mattei and
Ribon (1917) and Mattei (1920) the greater part of it appears to be eliminated in the
urine.

t Cf. Low (1913), Wenyon and O'Connor (1917), etc.

% This method was introduced by Rogers (1912).

§ Cf. Van den Branden and Dubois (191 5), Van den Branden (1919), etc.

I! See Lawson (19 18), Mayer (191 9). The results appear unsatisfactory.

IT Cf. Allan (19 16), etc.

** Cf. Sollmann (1919).

ft See Stephens and Mackinnon (1917) and Donaldson and McLean (191S).

154 THE INTESTINAL PROTOZOA OF MAN

appear to give successful results clinically. They practically never
suffice, however, to rid a patient of his infection. Even with larger
and continuous dosage, moreover, the method of administration is
important. It is now clear, for example, that hypodermic treatment
with emetine hydrochloride, in doses of i grain daily for 10 to 12
consecutive days, will not radically cure more than about a third of
the patients so treated.*

Two methods of administration have hitherto given the best results.
These are (1) oral administration of emetine in the form of its double
iodide with bismuth, and (2) administration of the hydrochloride
orally and hypodermically at the same time. We shall say a few
words about each of these methods.

(1) Emetine bismuthous iodide. Du Mez (1915) was the first to
suggest the employment of the double iodide of emetine and bismuth
for the treatment of amoebic dysentery. f He did not, however, make
trial of it himself. It was first tried, at the suggestion of Dale (1916),
by Maxwell and Paget} and Low and Dobell (1916). The results
obtained with this drug, when properly administered, have been
eminently satisfactory.! It has been subjected to more rigid tests

* See Dobell (1917), Wenyon and O'Connor (1917), etc. The more successful
results obtained by this method have invariably been supported by deficient protozoo-
logical control of the cases. A large body of evidence in support of the statement
made above has been obtained during the War.

t The double iodide of emetine and bismuth is formed by precipitation of soluble
emetine salts with Dragendorff's reagent. Precipitation with Mayer's reagent gives
an analogous compound, emetine mercuric iodide. Du Mez (1915) prepared both
these substances and suggested that they were worthy of trial in amoebic dysentery.
He appears to have been unaware, however, that the mercuric iodide had not only been
prepared and advocated for a similar purpose by Warden (1891), but that it had even
been tested clinically, with favourable results, by Tull Walsh (1891). Warden's
reasons for suggesting the use of this compound were, moreover, precisely the same
as those of Du Mez. Warden had satisfied himself that "the active remedial agent
[in ipecacuanha] is the emetine." And he says: "The most distressing feature
attending the treatment of dysentery with ipecacuanha is the deadly feeling of nausea
which usually supervenes after the administration of the drug. It seemed possible
that if the emetine could be prevented from being absorbed in the stomach, that nausea
might be allayed, or, perhaps, wholly prevented." " As is well known, Mayer's reagent
is employed as a precipitant for alkaloids from solutions acidulated with sulphuric acid ;
while the compound of the alkaloid with mercuric iodide is decomposed by alkalies.
Theoretically it is possible that an alkaloid in this form of combination would escape
decomposition, and hence absorption in the stomach, but be resolved into the free
alkaloid and mercuric iodide on coming into contact with the alkaline pancreatic juice."
It should be added that Warden's double iodide contained other alkaloids besides
emetine, and that it is uncertain how many of the patients successfully treated by Tull
Walsh were suffering from amoebic dysentery. The mercuric iodide has not been tried
in recent years, as it is more toxic than the bismuth compound.

% See Dale (1916) and Dobell (1917).

§ See Low and Dobell (1916), Dobell (1917), Jepps and Meakins (1917), Imrie and
Roche (1917), Lebceuf (1917), Low (1917), Dobell, Gettings, Jepps, and Stephens (1918),
Broc and Chatton (1918), etc., etc.

THE TREATMENT OF INTESTINAL PROTOZOAL INFECTIONS 1 55

than any other emetine compound, and has nevertheless given more
satisfactory results. We now possess conclusive proof of its curative
powers in many cases — some of the patients having been kept under
observation (clinical and protozoological) for several year-. The
failures which have been reported have probably been due, in most
cases, to mistakes in the method of administration.*

Since the method of administration is all-important, we may briefly
describe the correct method here. The details have been carefully
worked out, and various other methods tested, by Dale, Low, Dobell,
and other workers in England.

Emetine bismuthous iodide is an almost insoluble brick-red powder,
from which emetine is gradually liberated in the alkaline juices of the
intestine.f It is therefore important that the liberation of its emetine
should not be prevented by combining the drug with insoluble excipients
or coating it with substances which do not readily dissolve in the bowel.;:
It has been shown also that compression of the drug into a hard pill or
tablet interferes with its action. The drug is best administered pure, as
a loose powder enclosed in a hard gelatine capsule or paper cachet. It
should be obtained from a trustworthy firm, and be guaranteed to con-
tain not less than 26 per cent, of emetine (alkaloid). The dose should
be 3 grains daily, by the mouth, for 12 consecutive days. Shortening or
intermission of the course of treatment should not be permitted.
Administration of the double iodide in this way usually causes some
nausea, but this can generally be mitigated by giving a small dose of
opium previously (Tinct. Opii, 10-15 minims), and by giving the drug
after the patient has been put to bed — preferably at night, and not on
an empty stomach. It is best to give the double iodide in a single
dose of 3 grains, and not in separate doses of 1 grain thrice daily.

By the foregoing method, the patient receives, in all, 36 grains of the

* One of us (C. D.) has had numerous opportunities of verifying this statement.
The mistakes are too numerous to mention here, but have generally been due to
insufficient dosage, discontinuous treatment, and admixture of the drug with substances
which make it insoluble. A large number of published " failures " have been obtained
by methods which had already been shown, in the earliest papers published in this
country, to be inefficacious. It is remarkable, for example, how many failures have
been recorded as a result of a dosage which was shown, in the very earliest trials, to
be inadequate.

t See Du Mez (191 5), Dale (1916), Sollmann (1919), etc.

% For example, excipients such as vaseline, stearin, soap, and resin ointment should
not be used ; and keratin, salol, stearin, formolized gelatine, shellac, and other more or
less insoluble coatings, have all given unsatisfactory results in practice.

I56 THE INTESTINAL PROTOZOA OF MAN

double iodide in 12 days. This is usually sufficient to remove an infec-
tion with E. histolytica permanently, and does not as a rule give rise to
symptoms of emetine poisoning. Careful clinical control of all patients
during treatment is, of course, necessary. If, after treatment, the proto-
zoological examinations show that the patient is still infected, a further
course of treatment should be tried. It is necessary, in this case, to
prolong the treatment for a longer period or to administer a larger
quantity of emetine each day for a similar period. The patient should
therefore be given a double course of the double iodide (3 grains daily
for 24 consecutive days), or an ordinary 12-day course together with
emetine hydrochloride (i to 1 grain daily) hypodermically at the same
time.

(2) Combined oral and hypodermic administration of emetine hydro-
chloride, as advocated by Wenyon and O'Connor (1917), has also given
very satisfactory results in the treatment of E. histolytica infection. By
this method a larger quantity of emetine is given than by the double
iodide treatment. The dose should be 1 grain emetine hydrochloride
hypodermically combined with \ grain by the mouth — in a keratin-coated
tablet — every day for 12 consecutive days. The injection is best given
in the morning, and the oral dose after the patient has gone to bed for
the night.

Many modifications of the foregoing methods have been adopted —
occasionally with apparent success. Some workers still advocate
emetine hypodermically combined with ipecacuanha by the mouth —
simultaneously or after the hypodermic treatment. It is impossible
to discuss these various treatments here ; and we must refer the
reader to the original works themselves. Among these may be
specially mentioned* — in addition to those already cited — the papers
by Vedder (1914), Willets (1914), Jones (1915), Lyons (1915), Barlow
(1915a), Waddell, Banks, Watson, and King (1917), Savage and Young
(1917), Noc (1917), Lillie and Shepheard (1917), Watson-Wemyss
and Bentham (1918), MacAdam (1919), and Gunn and Savage (1919).
It may be added that emetine appears to be well borne by children.f

There is no evidence whatever to prove that there are emetine-
resistant strains of amoebae — as is often assumed. I There is, how-

* We by no means agree, of course, with all the views expressed by these writers.

+ Cf. Archibald (1914), De Buys (1914), Barlow (1914), etc.

\E.g-, Ravaut (1917), Ravaut and Krolunitski (1917), Mayer (1919).

THE TREATMENT OF INTESTINAL PROTOZOAL INFECTIONS 157

ever, considerable evidence to show that different human beings may
behave differently towards the drug ; and that when patients appear
to be incurable with emetine, this is because of their own constitu-
tion—not that of their amoebae.* There is also some evidence to
show that acute cases are more difficult to cure of their infections
than carriers, f

Although the majority of persons infected with E. histolytica can,
apparently, be radically cured of their infections by means of appro-
priate treatment with emetine, some few patients appear to be quite
unaffected by treatment with this alkaloid in any form. Such patients,
who are usually sufferers from subacute dysentery, seem to be con-
stituted like the experimentally infected cat — which appears to be
incurable with emetine (Dale and Dobell, 1917 ; Mayer, 1919). For
such patients some other treatment is necessary : and although no
other drug has yet been proved to be efficacious, successes have been
claimed for a number of substances. The most noteworthy of these
we shall now briefly mention, since some of them at least merit more
extensive trial.

" Chaparro amargosa." This is the Mexican name for a plant
called Castela Nicholsoni, belonging to the Simarubaceae. It has been
used with apparent success by Nixon (1914, 1915, 1916), Shepheard
and Lillie (1918), Sellards and Mclver (1918), and others, and appears
to be worthy of further trial. Another plant in the same family,
Simaruba itself, has also some apparent successes to its credit, and
has long been known as a " dysentery cure." It has recently been
favourably reported on by Yersin, Breaudat, and Lalung-Bonnaire
(1914), Shepheard and Lillie (1918), and Mayer (1919). " Kho-Sam,"
which is said to be prepared from the seeds of yet another Simaru-
baceous plant (Brucea sumatrana) has also been recommended as a
cure for amoebic dysentery (Menetrier and Brodin, 191 2 ; Galliard
and Brumpt, 1912 ; and others). It seems possible that all these
plants may contain a common principle of therapeutic value, but at
present no alkaloid or other very definite substance appears to have
been isolated from them. A crystalline bitter principle has been
obtained by Ewins from Chaparro, and a similar (or identical) one

* Cf. Dale and Dobell (1917), etc.

t Cf. Wenyon and O'Connor (1917), Savage and Young (1917), and others.

158 THE INTESTINAL PROTOZOA OF MAN

by Barger from Simaruba* — both of doubtful therapeutic action (cf.
Lillie and Shepheard, 1918).

SALVARSAN in various forms has had many advocates, as a " spe-
cific" for amoebic dysentery (see especially Ravaut and Krolunitski,
1915, 1916, 1917, etc.). At present we think there is little evidence
to show that this substance has a specific action upon E. histolytica
infections : and the fact that it usually appears necessary to administer
it together with emetine, in order to obtain successful results, prevents
one from drawing definite conclusions regarding its efricacy.f At
present we know of no single case in which it has been proved, by
adequately prolonged protozoological control, that an E. histolytica
infection has been eradicated by salvarsan treatment alone. Galyl
has been advocated by Fontoynont (1917), and Atoxyl (per os, com-
bined with emetine hypodermically) by Aime (19 17) : but the same
reservation must be made in regard to the results which they have
published.

Bismuth salts have been strongly advocated — especially by the
workers in Panama (cf. Deeks (1914), James (1918), and others).
Proofs of radical cure, by protozoological examination of the stools
for a sufficient period, appear, however, to be still wanting. In our
experience, bismuth salts alone have no specific action upon E. his-
tolytica : and we note that James (1918) now advises the giving of
bismuth not alone but combined with "emetine to the point of physio-
logical reaction."

Thorium salts have been tried by Frouin (1917), who records
apparently successful results in a case of amoebic dysentery which had
proved refractory to emetine treatment. J

Among other substances recently advocated we may mention Oil of
Chenopodium (Walker and Emrich, 1917 ; Barnes and Cort, 1918),
Adrenalin (Bayma, 1915, 19 17), Tannin, given hypodermically
(Hammacher, 1915), Benzyl benzoate (Haughwout, Lantin, and

* See Third Annual Report of the Medical Research Committee (London, 1917),
pp. 14, 15.

t Cf. also Noc (1916^), who finds that salvarsan cannot be regarded as "a real
specific for chronic intestinal amoebiasis." See also Willets ( 1 9 1 4) .

\ This treatment appears to merit further trial. The salt used by Frouin was thorium
sulphate, 4 to 6 grammes daily per os — in a cachet, with food. This treatment was con-
tinued for 9 days, and was supplemented during the last 4 days with a daily rectal
injection of 200 c.c. of a 2 per cent, solution of the same salt.

THE TREATMENT OF INTESTINAL PROTOZOAL INFECTION'S 1 59

Asuzano, 1919), and " Uzara." The last is a proprietory German drug,
said to be made from an East African plant (Asclepiadaceae).*

Although emetine— and possibly some other drugs — has so striking
an effect upon E. histolytica infections, it is somewhat remarkable that
it appears to have no action whatever upon infections with most of the
other intestinal amoebae. No matter how it be administered, emetine
will never eradicate an infection with E. coll or Endolimax nana ;f and
no other drug which has hitherto been tried appears to be capable of
dislodging these organisms from the human body. There is now
evidence to show, however, that emetine, whether given hypodermically
or orally, will remove infections with Iodamoeba butschlii.% This is the
only amoeba, other than E. histolytica, upon which emetine has been
shown to have any action. How emetine acts in this case is still a
mystery, since in its habits and habitat this organism resembles E. coll
and E. nana — which are unaffected by emetine — and not E. histolytica.

The Treatment of Flagellate Infections.

It appears probable, from the evidence at present available, that no
specific treatment for infection with any species of intestinal flagellate
has yet been discovered. This does not mean that claims to such
discoveries have not been made : but critical examination of these
claims shows clearly that — at least in most cases — they rest upon
standards of "cure" which are wholly inadequate.

The appearance of flagellates or their cysts in the stools of infected
persons is frequently very irregular. We have numerous records
showing that the stools of infected persons may be " negative," on
microscopic examination, for considerable periods of time : and this is
true of persons undergoing no treatment whatsoever. When " nega-
tive" examinations are made during or after a course of "specific"
treatment, therefore, they cannot be regarded as evidence of "cure"
unless they extend over a period much longer than any " negative
period " which may be observed in untreated cases. The figures pub-

* See Waldow and Giihne (1912), Seyfifert (1914), Wick (1914), and other German
workers, for further details.

f See Dobell (1916, 1917, 1919a, etc.), Wenyon and O'Connor (1917), and many
others.

t See Wenyon and O'Connor (1917), Dobell, Gettmgs, Jepps, and Stephens U9i8).
Dobell (1919a).

l6o THE INTESTINAL PROTOZOA OF. MAN

lishecl by one of us* for Giardia may be referred to in this con-
nexion.

Among the "specifics" for flagellate infection hitherto advocated
we may mention the following. Mayer (i9i4)and others have claimed
success in the treatment of Giardia infection with emetine. We have,
however, examined hundreds of patients infected with this flagellate, and
others, after treatment with emetine, in many different ways ; and we
can say with confidence that emetine has no effect whatsoever upon
infections with any of the common intestinal flagellates.f Another drug
which has been advocated strongly by some workers is methylene blue
(Castellani (1915), Barlow (1916), etc.) ; but in our experience it is also
without action upon any of the intestinal flagellates. Bismuth salts —
e.g., the salicylate — and various "intestinal antiseptics" such as salol,
cyllin, /3-naphthol, kerol, guaiacol, etc., have also all been equally useless.

Escomel (1913, 1914, 1919), in Peru, claims complete success in the
treatment of Trichomonas infections with turpentine. He also advocates
iodine per rectum. Turpentine with us has been worthless (for Giardia
and other flagellate infections), and this is also the experience of
Douglast with Trichomonas. Escomel (1917), it may be added, now
believes that there are "turpentine-resistant" strains of this flagellate
and finds that the same drug will cure bacillary dysentery in the same
region (Escomel, 1919a).

Recently several workers have recommended salvarsan§ as a specific
for Giardia infection. Ravaut and Krolunitski (1916) "cured" cases by
oral treatment with this drug, but Cade and Hollande (19 18) were
unsuccessful with this method, and apparently — from the results recorded
— equally unsuccessful when they gave the drug intravenously. They
remark that their results, as a whole, were " incomplete and variable."
More recently, Can" and Chandler (1920) have claimed success, but their
results are not supported by sufficient evidence. A number of workers
believe that they have been able to cure Giardia infections in laboratory
animals by means of salvarsan. Thus, Yakimoff, Wassilevski, and

* See Dobell and Low (1916) and Dobell (1917).

t Cf. Dobell (1916, 1917), Wenyon and O'Connor (1917), Dobell, Gettings, Jepps,
and Stephens (1918), etc.

% See Douglas, Colebrook, and Parry Morgan (1917), where his results are men-
tioned, but not described in detail. It may be noted that the doses used by Douglas
were very much larger than those advocated by Escomel.

§ It may be added that Barlow (1916) found this drug had no effect upon infections
with Trichomonas.

THE TREATMENT OF INTESTINAL PROTOZOAL INFECTIONS l6l

Zwietkoff (1917) claim to have cured mice of their infections, and Kofoid,
Boeck, Minnich, and Rogers (1919) report successful results in treating
rats. The evidence presented so far, however, appears inconclusive.
We have not ourselves observed any cases of cure by salvarsan in human
beings, and regard the reported "cures" with considerable scepticism:
and we may add that we have some evidence that salvarsan does not
cure Giardia infections in the rabbit. One of us (CD.), some years ago,
examined rabbits which had been used for testing various salvarsan
preparations, and found that they were all heavily infected with this
flagellate, even after fatal doses of the drug had been administered.
These observations appear significant, though they are not sufficiently
extensive to be conclusive.

Thymol has been advocated by several workers, and Barlow (1916)
found it the "most effective " of the drugs which he tried for Trichomonas
infection. In our experience it has appeared to be without action upon
all intestinal flagellates studied.

Other methods of treatment which have been advocated are too
numerous and too dubious to mention here. A perusal of the literature
on the subject leaves us with the impression — which our own experience
confirms — that nothing of any real value has yet been discovered which
can be regarded as a specific for the treatment of flagellate infections of
the intestine.*

The Treatment of Coccidiosis.

This subject may be dismissed in very few words. No substance has
yet been discovered which appears to have any action upon coccidial
infections of the human intestine — or, for that matter, upon coccidial
infections of any organ of any host. So far as we are aware, nobody
has yet made claim to the discovery of any " cure " for coccidiosis.

We will only add that emetine has already been tried, and shown to
have no value, in the treatment of human intestinal infections with Isospora
(Wenyon and O'Connor, 1917 ; Dobell, 1919; O'Connor, 1919). It
seems probable that it is equally useless for the treatment of Eimeria
infections (Dobell, 1919 ; Snijders, 1921). The recent observations of

* The "cures" described in numerous papers are also highly unsatisfactory from a
zoological standpoint. Many of them refer to "flagellate dysentery '' or "flagellate
diarrhoea," without specifying the protozoon concerned ; and a considerable number of
workers claim to have cured infections with " Cercomonasv {e.g., Chace and Tasker,
1917). It is impossible to discuss such works without more precise information.

II

J.62 THE INTESTINAL PROTOZOA OF MAN

Noc (1920) appear to indicate, further, that salvarsan and thymol are
inefficacious for the treatment of Isospora infections, though Noc himself
considers that they possess some efficacy (" une certaine emcacite ").

The Treatment of Balantidiosis.

Balantidiosis is still, unfortunately, a condition for which no really
specific treatment has been discovered. Many different drugs have been
tried, and successful results obtained with one or other of them have
been reported from time to time. But later workers have rarely been
able to confirm them. We shall here mention only a few of the
attempts at specific therapy — mostly recent, but for the most part not
particularly promising.

The older investigators tried quinine (1 in i,ooo, or 1 in 2,000),
iodine (1 in 10,000), silver nitrate (1 in 3,000), carbolic and salicylic acids,
naphthaline, and acetic acid and tannin — all administered rectally — in
their attempts to kill the parasites by direct antiseptic action. Successes
were occasionally claimed for one or other of these substances, but
more often they were found inefficacious. Quinine and calomel per os
were also largely tried, but on the whole were failures.*

Behrenroth (1913) believed that he had cured a patient by means of
de-emetinized ipecacuanha (30-60 pills, containing o'o6 gm. each, daily
for 10 days). Barlow (1915) recommends " alcresta ipecac." Axter-
Haberfeld (1915) thinks he effected a cure with emetine hydrochloride
(hypodermicaily — 0-03 gm. daily for 8 days). Tixier (19 19) also believes
that his patient was cured with emetine, though from the description it
seems improbable that the parasites were eradicated. Brenner (1919)
advocates ipecacuanha per os (powdered root — 1 gm. doses daily for
10-12 days). On the other hand, Dutcher (19 15), Lanzenberg (1918),
and most other recent workers, have found that emetine has no effect
upon Balantidium infections.

Barlow (19 15) has recommended methylene blue (2 grains, thrice
daily, for at least 4 days). Others have not found it of any use.
Dutcher (1915) was apparently successful with salvarsan, but Lanzenberg
(1918) was not. Labbe (1917) believes he cured a patient by means of
rectal injections of silver nitrate (followed by oxygenated water, com-
bined with calomel per os), but Lanzenberg (191 8) was unable to cure

For the older methods of treatment see especially Mitter (1891) and Strong (1904)-

THE TREATMENT OF INTESTINAL PROTOZOAL INFECTIONS 163

his patient by this method. Most other workers have had no sue
with silver nitrate, and the injections are usually extremely painful.
Mason (1919) appears to have had some success with oil of Chenopodium
(60 minims in half an ounce of olive oil, rectally). Lanzenberg (1918J
was unsuccessful with thymol, though it was found by Behrenroth (1913)
that dead balantidia were passed in the stools as long as this drug was
being administered.

Lanzenberg (1918), acting upon Brumpt's suggestions, has recently
"cured" a case with somewhat concentrated solutions of quinine,
administered per rectum (quinine hydrochloride 075 gm. in 300 c.c.
water). On the whole, this method seems to offer the best chances of
success at present. Rectal injections of quinine often appear to relieve
the symptoms of balantidial dysentery, and to reduce the number of
parasites, even when they do not effect a radical cure.

Haughwout, Domingo, and de Leon (1920) have recently tried
benzyl benzoate, and believe that they eradicated the parasites though
their patient died — apparently from other causes. Further trials of this
drug seem desirable.

Finally, it must be noted that Walker (1913) has tried the effects of
a number of substances on Balantidium directly, in vitro, in an attempt
to obtain indications for a specific method of treatment. He found
that ipecacuanha and emetine, arsenic and antimony compounds, and
various aniline dyes, appeared to have but little action on the parasite.
Mercury and silver salts, on the other hand, appeared to be " balanti-
dicidal " — the organic compounds appearing more potent than the
inorganic. It seems doubtful, however, whether experiments of this
sort will afford anv real indications for treatment.*

* Compare, for example, the observations of Dale and Dobell ( 1917) on E. histolytica.
In the case of this parasite, it seems clear that the relative toxicity of various substances
in vitro is no measure of their therapeutic efficacy in vivo. Analogous instances could
also be quoted.

164

CHAPTER IX.
THE COPROZOIC PROTOZOA OF HUMAN FAECES.

It has already been noted in the Introduction (p. 16) that there are
certain protozoa which are sometimes found in human faeces, but which
are not entozoic. Such organisms are suitably designated COPROZOIC
Protozoa. This name does not, of course, denote a natural group in
the zoological system, but merely refers to a habit of life common to a
number of organisms belonging to various groups.

The coprozoic forms which may be met with in human faeces are,
for the most part, forms which occur in nature in the faeces of other
animals also, and in organic infusions of various sorts. They belong to
the Rhizopoda and Mastigophora,* and only a few of them can be said
to be common. In this final chapter we shall notice merely the
commonest or most interesting organisms.

Coprozoic protozoa may gain access to faeces in two different ways.
As they are all free-living organisms, capable of living, as a rule, in
water or decomposing organic matter of many kinds, they may con-
taminate human excrement after it has been discharged from the body :
and if the conditions are suitable, and they find this material a favourable
culture medium, they may continue to live and multiply in it just as
they would in any other decomposing matter. On the other hand,
coprozoic protozoa frequently get into human faeces by another route.
Their cysts, carried by air, water, or other means, may be swallowed
by a human being with his food or drink. They then pass through
the alimentary canal with the food, and are finally discharged with the
stools. If they have thus survived the passage through the body, they
excyst in the deposited faeces and proceed to multiply in this material.
Such organisms are usually incapable of living in human faecal matter

* It is doubtful whether any truly coprozoic Ciliata occur in human faeces, though
free-living species of this group may sometimes get introduced accidentally. Cf. pp.
1 1 3-1 17 supra.

THE COPROZOIC PROTOZOA OF HUMAN FAECES 1 65

while it is still within the body — probably because the temperature is
too high and oxygen is lacking.*

This remarkable ability to pass, in the encysted state, safely through
the body of an animal, without undergoing any development, was long
an unrecognized property of some of the small free-living amoebae and
flagellates; and ignorance of it has led, in the past, to many mistakes.
It is now easy to understand how it is possible to find typically free-
living species of protozoa swarming in faeces shortly after leaving the
body — notwithstanding the fact that the faecal material may have been
carefully collected in sterile vessels and guarded from contamination
from outside. Although some of the older workers had reached correct
conclusions on this subject, f the facts were first put on a scientific
footing by the experiments of Walker and Sellards (19 13) with free-
living amoebae.

Many of the coprozoic amoebae and flagellates found in human
faeces have been described as human " parasites," and they have often
been named as "new species" owing to their identity with well-known
free-living forms having been overlooked. The literature on many of
these free-living forms — described as such — is also in a very confused
state at present, and bristles with mistakes and uncertainties of all sorts.
Consequently, it is by no means easy to deal with this subject accurately
and briefly. It is, in fact, quite impossible to attempt an exhaustive
survey of these organisms within the limits of one short chapter, and
the following few pages make no pretentions to completeness. It is
hoped, however, that they will serve as an accurate introduction to the
subject, and will enable the reader, desirous of pursuing it further, to
find his way to the more important work which has hitherto been
done.

(A) Coprozoic Rhizopods.

The commonest coprozoic Rhizopods found in human faeces are
the small amoebae commonly, but incorrectly, called " Umax amoebae,"
or " amoebae of the Umax group." Of these there are many species,
but their identification is difficult and their classification is at present
in a well-nigh hopeless muddle.

* This is inferred from their behaviour in cultures : e.g., Bodo candatus will not grow
at 370 C, or in the absence of free oxygen. (C. D.)

t For example some of the Italian workers — especially Casagrandi and Barbagallo
(i897«).

l66 THE INTESTINAL PROTOZOA OF MAN

The name "Amoeba Umax" was given by Dujardin (1841) to a fresh-
water "species" which is not now identifiable.* The most that can
be said about it is that it was certainly not any one of the forms which
are now generally called "Amoeba Umax;" since these are all very
small, and Dujardin's "species" is stated to have measured 100 jx by
30 fju. Instead, therefore, of attempting to fix this name upon any of
the different species which have since been described, it would be much
better to drop it altogether.

Many of the small free-living amoebae are so much alike in their
active amoeboid stages, that it is impossible, at present, to distinguish
them from one another by these stages alone. It is necessary to know
the whole life-history, or at least the chief stages. For purposes of
identification a knowledge of the following characters, at least, is
indispensable : (1) The structure and size of the free amoeboid form
(especially the finer details of nuclear structure) ; (2) all the chief stages
of nuclear division ; (3) the size and structure of the cysts (cyst-wall,
number of nuclei, inclusions — such as chromatoid bodies, etc.) ; (4)
other stages of development, if they occur — especially the presence or
absence of a flagellate form. Endless confusion has already been
caused by the renaming of species previously named — either through
ignorance of previous work or through failure to recognize a described
form owing to malobservation or misdescription ; by describing and
naming a few stages in the life-history, when other stages had already
been described and named ; and by introducing new specific names for
organisms which can never subsequently be identified — owing to the
author's omission to record (and often even to observe) any characters
of real systematic value.

A large number of free-living amoebae obtained from human stools
have already been observed, and some of them named — for example,
by Celli and Fiocca (1894), Musgrave and Clegg (1904), Walker and
Sellards (1913), Whitmore (1911^). The majority — probably all — of
these are not now identifiable with any certainty. The same is true,
unfortunately, of the greater number of the small species of free-living

* It is worthy of note — since it is usually overlooked— that Dujardin himself did
not profess to be able to distinguish his ''species" of Amoeba by any good specific
characters. His names were nearly all of uncertain application and doubtful validity.
He says himself (1841, pp. 231-2) that the characters which he employed for purposes
of classification ''are by no means true specific characters "; and he especially adds
that in his " enumeration " of various forms, under different names, " il est done Men
essentiel de ne pas voir une distinction d'especes." (C. D.)

THE COPROZOIC PROTOZOA OF HUMAN PAECE8 167

amoebae obtained from other sources. We have studied many species
during the last 15 years, but have been able to identify and name
but few. In the case of the amoebae from human stools we have
therefore selected three of the most certainly determinable species
which we have studied, and give them here — with sufficient detail for
their recognition by others — merely as types or examples of the forms
which may occur. The species selected belong to three different
genera — Dimastigamoeba Blochmann, 1895 (emend. Alexeieff, 1912c),
Hartmannella Alexeieff, 1912^ (= Hartmannia Alexeieff, 191 2), and
Sappiuia Dangeard, 1896 (emend. Alexeieff, 191212). These three genera
are now readily identifiable by their nuclear structure, nuclear division,
and the characters presented by their cysts. Dimastigamoeba is further
characterized by possessing a flagellate form.

These organisms will now be briefly described, and our account
of coprozoic rhizopods will then finish with a note on the interesting
shelled amoeba Clilamydophrys. Before giving descriptions of these
amoebae, however, a word may be said about their cultivation.

Cultivation. — Most of the small amoebae which live in water,
soil, infusions, faeces, etc., can be readily cultivated. Most of them
feed upon bacteria, and must therefore be cultivated together with
these micro-organisms — to serve as food. Much has been written on
this subject; but it will suffice to refer to the well-known works of
Musgrave and Clegg (1904), Walker (1911), Walker and Sellards (1913),
and Wtilker (191 1), where fuller references to the literature will be
found.*

The small coprozoic amoebae can be cultivated on solid media
(agar, etc.) or in liquids (hay infusion, dilute egg-albumin, etc.). One
of the most useful media is Walker's modification of Musgrave and
Clegg's " amoeba agar," prepared as follows :f

Agar ... ... ... .. 2*50 gm.

Sodium chloride ... ... o-oq „

Liebig's beef extract ... ... cos ,>

Normal sodium hydroxide solution 2-00 c.c.
Distilled water ... ... ... ioo'oo ,,

(Sterilize in autoclave. After sterilization, reaction approximately
neutral.)

* See especially the useful resume of Wiilker (191 1).
t See Walker and Sellards (1913), p. 265.

l68 THE INTESTINAL PROTOZOA OF MAN

Amoebae grow best on media containing plenty of water, or in
a moist atmosphere. For this reason it is a good plan, after the
inoculation of an agar plate with faeces or other material containing
amoebae, to invert the Petri dish and pour a little water in the lid.
In many liquid media — such as 5 per cent, egg-albumin solution —
amoebae often thrive wonderfully. It should be remembered that in
such cultures the organisms are usually present in the surface film
or on the sides and bottom of the vessel. (Amoebae — unless they
possess a free-swimming flagellate stage — can only creep on a more or
less firm surface. They are unable to swim in a liquid.) In old
cultures the amoebae encyst, but the cysts usually hatch readily on
transference to new medium. Cultures can thus be kept going
indefinitely ; or the cysts can be kept for months, or even years, and
used to prepare new cultures at any time by merely sowing them in
fresh medium.

(1) DlMASTlG AMOEBA GRUBERI (Schardinger) Alexeieff, 1912.

Chief synonyms :

Amoeba grub eri Schardinger, 1899.

Amoeba diplomitotica Aragao, 1909.

Amoeba punctata Dangeard, 1910.

Vahlkampfia punctata (Dangeard) Chatton & Lalung-Bonnaire, 1912.

Amoeba tachypodia Glaser, 191 2.

Naegleria punctata (Dangeard) Alexeieff, 1912.

Vahlkampfia soli Martin & Lewin, 1914.

Naegleria gruberi (Schardinger) Wilson, 1916.

Wasidewskla gruberi (Schardinger) Zulueta, 1917.

This amoeba is one of the most easily recognized of the species
which may occur coprozoically in human faeces, from which it was
first obtained by Schardinger (1899) in Vienna. It has often since
been studied — usually from soil — and almost as often renamed. The
foregoing list of probable synonyms is not complete, but indicates the
chief names under which the organism has previously been described..
The most detailed account which has yet appeared is that of Wilson
(1916), to whose work the reader is referred for a more complete
description than is here possible.

THE COPROZOIC PROTOZOA OF HUMAN FAECES I' 9

The active amoeba of this species (PI. IV, fig. 49) is small,
measuring as a rule from about 7/4 to 15/x in diameter when rounded.
Each animal possesses a single vesicular nucleus, about 3-4/x in
diameter, with a large central karyosome and rather sparse granules
of "peripheral chromatin" in the clear zone between it and the nuclear
membrane ; and each amoeba also has a single contractile vacuole,
formed by the fusion of several smaller ones. During locomotion the
amoeba usually displays several large pseudopodia, composed chiefly
of clear ectoplasm, at its anterior end. The endoplasm contains food
vacuoles enclosing ingested bacteria.

The NUCLEAR division of this species shows a number of very
characteristic mitotic figures — one of which (equatorial plate stage) is
shown in fig. 51* (PI. IV). The process has been studied in detail
by Glaser (191 2), Ford (1914), Wilson (1916), and others.

One of the most striking characters of the species is its ability, in
certain circumstances, to assume a free-swimming flagellate stage
(PI. IV, fig. 50). The amoeba contracts into an oval shape, and its
nucleus takes up a position at the more pointed anterior end. From
the anterior pole of the nucleus two long flagella develop, of equal
length and both directed forwards. They appear to grow out of
basal granules situated on the nuclear membrane. In these flagellate
forms the contractile vacuole always occupies a posterior position
(fig. 50). The amoebae can usually be made to assume the flagellate
condition by simply flooding the culture with an excess of water.
After a variable time the flagellate forms lose their flagella and again
become amoebae.

A similar flagellating amoeba has been described from human faeces
by Whitmore (1911a), and named by him Trimastigamocba pliilip-
pinensis. It appears to differ from D. gruberi only in having —
according to the description — 3 flagella instead of 2 in its flagellate
stages.

The CYSTS (PL IV, fig. 52) are spherical structures, measuring 8-i2yu,
in diameter — their average being about io/x. They are uninucleate, and
when first formed contain numerous rather large, spherical, deeply
staining chromatoid bodies. Their walls are double— the outer layer
being the thicker, and presenting a variable number (usually 3-8) of

* Note the "polar caps" of chromatin, and the persistence of the nuclear mem-
brane. Cf. fig. 54, of Hartmannella.

LJO THE INTESTINAL PROTOZOA OF MAN

pores, each of which is surrounded by a slight thickening of the cyst
wall.* The amoeba emerges through one of these pores during ex-
cystation, and the pores themselves are most clearly visible in empty
cysts. They are characteristic of this species.

D. gruberi appears to be one of the commonest species of the small
free-living amoebae. It probably occurs in soil and water almost every-
where, and is easily cultivable in hay and soil infusion, in diluted egg-
albumin, or on agar plates (see p. 167).

(2) Eartmannella hyalina (Dangeard) Alexeieff, 191 2.

Synonyms :

Amoeba hyalina Dangeard, 1900.

? Amoeba hyalina (Dangeard) Brodsky, 1910.

? Amoeba hyalina (Dangeard) Hartmann & Chagas, 1910.

The amoeba here described under the above name is not referable
to Dangeard's species " Amoeba" hyalina with absolute certainty. It is
also doubtful whether the organisms referred to the same species by
Brodsky (1910) and by Hartmann and Chagas (1910a) are identical
either with Dangeard's species or with ours. It is not improbable,
however, that all belong to the same species, since it is one which
appears to be common and widely distributed. As regards the generic
name there is more certainty, since the amoeba in question appears to
be undoubtedly a member of the genus originally named Hartmannia
by Alexeieff (1912) but subsequently changed by him to Hartmannella
(1912a) — the former name being preoccupied.f

It is probable that the organism obtained in cultures from liver-
abscess pus, air, and water by Wells, in India, and described by Liston
and Martin (1911) and Martin (191 1) as the "large amoeba from liver
abscesses," really belongs to this same species. It is also likely that it
is identical with one of the species of amoeba cultivated from human
faeces by Whitmore (1911a), and collectively designated by him "Amoeba
Umax subspecies M. II." The organism has also probably been obtained
from similar sources by others.

* Two of these pores are shown (in optical section) in the wall of the cyst depicted
in fig. 52.

t Alexeieff (1912a) has named H. hyali?ia Dang, as the type, but has not amended
the diagnosis by any adequate redescription of the actual organism. And it is still
doubtful to what animal the name was originally given — the observations of Dangeard
being far from complete. (C. D.)

THE COPROZOIC PROTOZOA OF HUMAN FAECES 1/1

This organism differs considerably from D. gruberi. The amoeboid
form is closely similar, but the method of nuclear division is entirely
different. Moreover, it possesses no flagellate stage,* and its cyst is
larger, and has a thick crinkled wall. (There are many other closely
related species with similar characters.)

The AMOEBA (PI. IV, fig. 53) is usually slightly larger than D. gruberi,
measuring from about 9 [x to 17 p in diameter when rounded. It posseses
a single contractile vacuole. Its nucleus is closely similar to that of
D. gruberi — and of most other small amoebae — and consists of a
spherical vesicle with a large central karyosome, and somewhat
abundant "peripheral chromatin" granules in the clear zone.

Multiplication occurs in the usual way by fission into two. The
stages of nuclear division are highly characteristic. The division is a
typical mitosis,-}- with the formation of a sharply pointed achromatic
spindle, and tiny spherical chromosomes (PL IV, fig. 54). The nuclear
membrane disappears during the process, and there are no " polar caps "
of chromatin, and no connecting chromatin strand is present in the
telophases — as in D. gruberi.

The cysts (PI. IV, fig. 55) are uninucleate, and double-walled. They
usually measure from io/a to 14/u. in diameter. The inner wall is thin
and smooth, the outer — when fully formed — very thick, wrinkled, and
brownish in colour, with no pores. Small spherical chromatoid bodies
are present in newly-formed cysts, and are sometimes very abundant.
As in other species, these bodies disappear in older cysts.

This species is readily cultivable on agar (see p. 167) and in many
other media.

It may be added that the process of "endogenous bud-formation"
described in this species (?) by Liston and Martin (191 1) has never been
observed by us : but we have seen the phenomenon so interpreted in
other species, and believe that the "internal buds" are merely small
amoebae of a different species which have been ingested as food. We
believe there is no good evidence of reproduction by internal budding
in any of the small amoebae.

* Numerous attempts to obtain flagellate forms by the methods successful with
D. gruberi have always been completely negative. (C. D.)

t I have studied all stages, but it is impossible to give a complete series of figures
here. (C. D.)

172 THE INTESTINAL PROTOZOA OF MAN

(3) Sappinia diploidea (Hartmann & Nagler) AJexeieff, 191 2.

Synonyms :

Amoeba diploidea Hartmann & Nagler, 1908.

Vahlkampfia diploidea (Hartmann & Nagler) Calkins, 191 2.

We follow Alexeieff (19120) in referring this very interesting amoeba
to Dangeard's genus Sappinia. Its generic designation is still, however,
open to question (cf. Chatton, 191 2). We have seen the organism but
rarely as a coprozoic inhabitant of human faeces, and it appears to occur
more commonly in the excrement of several other animals (lizard,
ox, etc.).

The amoebae (PI. IV, fig. 56) are of moderate size, measuring some
10-30//, when rounded and at rest. They usually display but slow
movements. Their distinctive characters are the possession of a com-
paratively thick, though smooth and hyaline, skin or pellicle — sometimes
more or less wrinkled, as in "Amoeba" verrucosa (or "A." terricola) —
and two nuclei. These nuclei are identical in structure, and usually
closely apposed. They are vesicular, and each contains a large central
karyosome surrounded by a clear zone containing " achromatic "
granules. A single contractile vacuole is present, but it pulsates very
slowly.

The life-cycle has been described by Hartmann and Nagler (1908)
and Nagler (1909), but certain points in it require further elucidation.
These authors obtained their material from the excrement of lizards.

Multiplication is effected by division into two — the two nuclei
undergoing mitosis simultaneously, side by side. The daughter in-
dividuals are thus binucleate from the moment of their birth (cf.
Dientamoeba, p. 37).

The cysts of this species are very remarkable structures (PL IV,
fig- 57)- Before encystation, two individuals come together ; and after
creeping round one another for some time, they form a single cyst in
common. Newly formed cysts thus always contain two individuals, in
close contact. The cysts themselves are spherical, with fairly thick but
uniform walls, and measure from about 1 2/ul to 18//, in diameter. According
to Hartmann and Nagler, a remarkable sexual process takes place inside
the cyst. The two nuclei first fuse in each individual, so that the cyst
comes to contain a pair of uninucleate amoebae. " Reduction "

THE COPROZOIC PROTOZOA OF HUMAN FAECES 173

phenomena are then said to occur, after which the two individuals fuse.
Only their cytoplasm fuses completely, however, their nuclei coming in
contact, but remaining separate. The cyst thus contains, at this final
stage, a single binucleate individual. When the cyst hatches later, this
individual emerges and begins life anew as the ordinary binucleate free
form. It will be noted that, if this account is correct, the nuclei of the
free forms must be regarded as unfused gamete nuclei from a previous
incomplete conjugation.

This account still requires confirmation, and we are by no means
certain, from our own observations, that the foregoing interpretation is
correct. It appears certain, however, that two binucleate individuals
enter into the formation of each cyst, and that only a single binucleate
form ultimately emerges from it.

Like the other coprozoic amoebae, S. diploidea is easily cultivable
on agar (p. 167).

(4) Chlamydophrys stercorea Cienkowski, 1876.
Synonyms :

Troglodytes zoster Gabriel, 1876.

Platoum stercoreum (Cienkowski) Butschli, 1880.

? Leydenia gemmipara Schaudinn, 1896.

Chlamydophrys is one of the shelled amoebae (Thalamophora or
Thecamoebae), and differs considerably from the naked rhizopods
previously described. We have never succeeded in finding this organism
in human faeces, though we have looked for it innumerable times : but
according to Schaudinn (1903) it is very common in this situation.
One of us has studied it, however, in the faeces of frogs and toads
(Dobell, 1909) — the figure here reproduced having been drawn from a
specimen found in the excrement of one of these animals (Bufo
vulgaris L.).

The organisms which we have studied (PI. V, fig. 96) possess oval
shells, measuring, in well-grown individuals, about 20 /x by 14^. The
shell itself is thin, white, and smooth, resembling porcelain. It has an
opening at its more pointed end, through which the protoplasm and
pseudopodia project in the living animal. The pseudopodia are filose
and sometimes branched, and serve to capture food. There is a single
large vesicular nucleus in the dense protoplasm at the opposite (closed)

174

THE INTESTINAL PROTOZOA OF MAN

end of the shell. It possesses a voluminous and deeply stainable
spherical karyosome. The protoplasm is much vacuolated towards
the more pointed end, and sometimes contains one or more contractile
vesicles.

In younger stages the animal is devoid of a shell, and closely
resembles the so-called " Umax " amoebae. It creeps about in an
amoeboid fashion, is able to encyst, and can probably reproduce by
fission in this form. The shelled forms multiply by the process of
" budding division " characteristic of shelled rhizopods generally. They
are also able to encyst — their cysts being uninucleate, and furnished
with very thick, irregular, and brownish or yellowish walls.

Schaudinn (1903) made some remarkable statements concerning the
life-history of Chlamydophrys, and briefly described its division, con-
jugation, etc. Figures of the various phases originally described were
published later in his posthumous works (Schaudinn, 191 1), but his
descriptions are still unconfirmed and not sufficiently detailed to carry
conviction. Some of his statements, indeed, are almost certainly in-
correct. He stated, for example, that it is necessary for the cysts to
pass through the intestine before they can hatch in human faeces, and
that sometimes they even hatch in the intestine, where the organisms
are able to live and multiply as naked amoebae. He claimed to have
found these amoebae in perfectly fresh human faeces, but nobody has
yet confirmed this observation,* and we have never succeeded in finding
them. It should be remembered, in this connexion, that Schaudinn
was not acquainted with several of the species of amoebae living in the
intestine of man, and held incorrect views about the development of
the two species which he did know.

But the most remarkable statement made by Schaudinn (1903) is
that " Leydenia gemmipara" is an abnormal amoeboid form of
Chlamydophrys which has gone astray in the peritoneal cavity. There
is good reason to believe, however, that "Leydenia," described by
Leyden and Schaudinn (1896), is not an amoeba at all. The "amoebae"
were probably cells belonging to the human body (cf. Dobell, 1919a).
At all events, no confirmation of Schaudinn's extraordinary assertion
has hitherto been forthcoming, and it is still unsupported by any
evidence.

* The "Chlamydophrys" amoebae found by Elmassian (1909) were probably
Endolimax nana. Cf. Dobell (1919a), p. 135.

THE COPROZOIC PROTOZOA OF HUMAN' FAECES 1 75

It should be noted that Schaudinn's posthumous figures of
Chlamydophrys differ in some respects from those of other workers.
The shape of the shell, for example, differs from that shown in our
figure (PI. V, fig. 96) — the shell, in Schaudinn's specimens, being drawn
out into a neck at the pointed end, with the margin of the opening
everted, so that it is flask-shaped rather than oval. The dimensions are
not stated. It thus seems not improbable that Schaudinn's form belongs
to a different species from that which we have studied.

(B) Coprozoic Flagellates.
(5) Bodo CAUDATUS (Dujardin) Stein, 1878.
Chief synonyms :

Amphimouas caudata Dujardin, 1841.

Bodo uriuarius Hassall, 1859.

Diplomastix caudata S. Kent, 1881.

Bodo asiaiicus Castellani & Chalmers, 1910.

Prowazekia cruzi Hartmann & Chagas, 1910.

Proivazekia weinbergi Mathis & Leger, 19 10.

Prowazekia asiatica (Castellani & Chalmers) Whitmore, 191 1.

Prowazekia javanensis Flu, 1912.

Prowazekia urinaria (Hassall) Sinton, 1912.

Prowazekia italica Sangiorgi & Ugdulena, 1916.

This is the commonest of all the coprozoic flagellates found in
human faeces. It is also very common in organic infusions of many
kinds. The organism named Bodo urinarius by Hassall (1859), and
found by him in human urine, almost certainly belongs to this species —
as is evident from the more recent account of it given by Sinton (191 2).*
Almost every worker who has studied this organism seems to have given
it a new name, so that the above list of probable synonyms is by no
means exhaustive. It may be added, however, that many of the
published accounts are not sufficiently precise for it to be possible to
identify the described organisms with absolute certainty.

The genus Bodo, originally proposed by Ehrenberg, has often proved
a puzzle to protozoologists ; but as a result of the work of Klebs (1892),

* Woodcock (1916) is of the same opinion.

176 THE INTESTINAL PROTOZOA OF MAN

Stiles (1902), Alexeieff (19116, 1911c, 1912c/, etc.), Kiihn (1915), and
others, it may now be regarded as definitively established. The following
are its distinctive characters : The organisms are all small, more or less
elongate or oval, and possess two flagella, both arising at the anterior
end — one directed forwards, the other trailed behind. There is a
vesicular nucleus, with a large central karyosome, near the middle of the
body. A small permanent mouth is present at the anterior end, and
near it is a minute contractile vacuole. Furthermore, at the anterior end
of the body, and closely associated with the roots of the flagella, there is
a conspicuous rounded and deeply stainable body. This structure is
usually called a " kinetonucleus," and is homologous with the structure
to which the same name is applied in the Trypanosomes (so-called
" blepharoplast " of German writers — though not a blepharoplast
proper). We consider that this structure is not a nucleus, but homo-
logous with those bodies in other flagellates — of doubtful function — to
which Janicki (1911) has given the name "parabasals." We shall adopt
the name "kinetoplast" proposed for it by Alexeieff (1917a). All species
of Bodo multiply by simple longitudinal fission, and form oval cysts
containing a single individual (as a rule).

B. caudatus displays the following features. The active flagellates
(PI. V, figs. 78-80) are polymorphic, and may be long and slender or of a
plump oval form. They vary much in size, but seldom exceed 18/j in
length.* In fixed and stained preparations they are usually much shorter
and more globular than when alive. (Cf. figs. 78 and 80.) The body is
usually pointed posteriorly during life, and is compressed laterally, so
that its general form is lanceolate or leaf-like. It is usually broadest at
the anterior end. At the anterior extremity there is a small snout-like
structure, which projects slightly over the small mouth aperture (fig. 78).
The contractile vacuole — seen as a clear spot in fig. 78 — is very minute,
and lies dorsal to the mouth. Food vacuoles, containing ingested
bacteria, are present in the protoplasm, chiefly towards the hind end of
the body (figs. 79, 80).

The nucleus is more or less central (figs. 78, 79), and has the typical
structure. The kinetoplast is oval, and lies at the anterior end — behind,
and dorsally to, the mouth. The two flagella are of unequal length, the
anteriorly directed one being of about the same length as the body,

* 11-19M according to Klebs (1892), 8-18 /j. according to Alexeieff (191 ic).

THE COPROZOIC PROTOZOA OK HUMAN FAECES 1 77

while the posteriorly directed one is much longer— often about twice as
long. The flagella arise from a pair of tiny blepharoplasts, situated
close to the anterior end of the kinetoplast, and lying side by side
(fig. 79). In this species the trailing flagellum is often adherent to the
body at the anterior end — a point first noted by Dujardin (1841).

The cysts of this species are small oval structures, with thin walls
(fig. 81). They measure 5-7 //, in length, and contain, as a rule, a single
nucleus and kinetoplast. When first formed the remains of the two
flagella can usually be made out within them also. Occasionally the
nucleus and kinetoplast divide, so that these two structures appear paired
inside the cyst. Small deeply stainable granules are also generally
present — sometimes in great abundance (cf. fig. 8i).

B. caudatus is easily cultivable in many liquid media (hay infusion,
etc.) or on agar plates (see p. 167). Like all the other species of the
genus which we have studied, it appears to be a strictly aerobic organism.
It is also unable to live long in cultures at 370 C. These two facts appear
to prove that it cannot live within the human body, and a number of
records of this animal — or other species of the genus — found living
" parasitically " in man appear to us, consequently, to be erroneous.
Abnormal forms — giants, dwarfs, amoeboid forms, etc. — sometimes
occur in old cultures.*

(6) Bodo ED ax Klebs, 1892.

This species of Bodo may also occur coprozoically in human faeces ;
but it is far less common than the preceding, from which it may be
distinguished by the following characters : —

The flagellates (PI. V, fig. 82) are typically slightly smaller
(6-14 //,, when alive), and are of a more regularly oval shape. As a rule
the body is not laterally compressed, and bulges on the dorsal (aboral)
surface. The flagella are approximately equal in length — the posterior
one being sometimes slightly longer — and are both considerably longer
than the body. The kinetoplast is massive and often almost spherical.
The "snout " is conspicuous. In most other characters B. edax closely
resembles B. caudatus. Its CYSTS are closely similar.

* A process of "fertilization'' has been described in " Prowasekia crust" (? = B.

caudatus) by Chagas and Torres (1916). But at present there seems to be no good
evidence — in this or any other paper — to prove that conjugation occurs in any species
of Bodo. Cf. also Woodcock (19 16).
12

178 THE INTESTINAL PROTOZOA OF MAN

This species has recently been well redescribed by Kiihn (1915), to
whose paper the reader may be referred for further details. It should
be noted that some of the names given on p. 175 as synonyms of
B. caudatus, may belong really to B. edax. The organism, for example,
called " Prowazekia cruzi " by Hartmann and Chagas (1910) may perhaps
have been the present species — not B. caudatus. In most of the pub-
lished descriptions of the various "species" of Bodo (= Prowazckia),
the characters requisite for accurate specific determination are not
sufficiently considered, and the identification of these forms is therefore
largely a matter of guesswork.

Possibly other species of Bodo also occur in human fasces ; but up
to the present we have not identified any but the two just described, nor
can we find conclusive evidence of the existence of any but these two in
the publications of other workers.

(7) Cercomonas longicauda Dujardin, 1841.
Synonyms :

? Cercomonas longicauda (Dujardin) Stein, 1878.
Cercobodo longicauda (Dujardin) Senn, 1900.
Cercomonas longicauda (Dujardin) Wenyon, 1910.
Cercomonas parva Hartmann & Chagas, 1910.
Cercomonas longicauda (Dujardin) Alexeieff, 191 1.

Flagellates belonging to the genus Cercomonas Dujardin, 1841, are
common in infusions, and occur occasionally in human faeces : but they
never live — so far as is known at present — within the human body.
Until recently there has been much doubt regarding the interpretation
of this generic name, and many of the species are still very difficult to
determine exactly.

All species of this genus (cf. PI. V, figs. 83, 84, 86, 87), are dis-
tinguishable by the following characters : The flagellates are all
small, of changeable " amoeboid " form, and possess a single anterior
nucleus with a large central karyosome. They possess, in addition,
two flagella having a very characteristic arrangement. Both arise from
minute blepharoplasts, placed side by side at the anterior pole of
the nucleus — the nuclear membrane being drawn out into a conical
process at this pole, with the flagella thus arising from its apex.
One flagellum is free, and directed forwards. The other is directed

THE COPROZOIC PROTOZOA OF HUMAN FAECES 179

backwards, and adheres for the greater part of its length to the surface
of the body — becoming free, as a rule, for only a short distance at the
hind end. A kinetoplast is not found in this genus.

Food, consisting chiefly of small bacteria, is ingested in an amoeboid
manner by the surface of the body — especially at the posterior end.
There is no permanent mouth, and no contractile vacuole has been
demonstrated. Ingested food is contained in the usual food vacuoles
in the cytoplasm.

Multiplication takes place by longitudinal fission, in the typical
flagellate manner.

The CYSTS are spherical and uninucleate, and contain numerous
brightly refractile granules which stain deeply with iron-haematoxylin.
They are able to survive desiccation (Wenyon, 1910a).

Cercomonads are easily cultivable in many liquid media, such as hay
infusion, and on agar plates such as are used for the cultivation of
amoebae (see p. 167). Wenyon (1910a) specially recommends "hay
infusion to which a small quantity of faeces has been added."

Cercomonas longicauda has been specially studied by Wenyon (1910a)
and Alexeieff (191 ib). The distinctive characters of this species are the
following: Length from about 5/x to 10 /x — or more, in greatly drawn-
out individuals. Anterior flagellum very long (about three times as long
as the body). Posterior flagellum much shorter, only slightly exceeding
the body in length. Karyosome relatively small. Cysts 4-6 p in dia-
meter. (See PI. V, figs. 83-85.)

(8) Cercomonas crassicauda Dujardin, 1841 {emend.).

This is another very common species of Cercomonas, and occurs
coprozoically — though in our experience less often than the preceding —
in human faeces. It has recently been carefully studied and described
(from infusions) by Alexeieff (191 16), and may be distinguished from
C. longicauda by the following characters (see PI. V, figs. 86-88) : Length
up to 10-14 /i. The two flagella short, and approximately equal in
length, being equal to, or only slightly longer than, the body.
Karyosome relatively large. Cysts usually 5-6 yu, in diameter.*

* According to Alexeieff (1911^) the cysts measure 9-iiM in diameter, but I have
never found such large cysts in my cultures of this species. His figures of the cysts of
C. longicauda, moreover (Alexeieff (1911^), figs. 6, 7, p. 513), are hardly recognizable as
those of a Cercomonas. (C. D.)

l8o THE INTESTINAL PROTOZOA OF MAN

Probably other species of the genus Cercomonas may also be found
occasionally leading a coprozoic life in human faeces; but up to the
present the foregoing are the only ones that we have been able to
identify.*

(9) Copromonas subtilis Dobell, 1908.

Synonyms :

? Monas pileatorum Perty, 1852.

1 Scytomonas pusilla Stein, 1878.

? Scytomonas pusilla (Stein) Klebs, 1892.

Copromonas major Berliner, 1909.

Scytomonas pusilla (Stein) Alexeieff, 191 1.

? Copromonas ruminantium Woodcock, 1916.

Scytomonas pusilla (Stein) Schiissler, 1917.

Under the above name a coprozoic flagellate was described some
years ago by one of us from the faeces of frogs and toads. A closely
similar — and probably identical — form occurs very rarely in human
faeces, and the organism will therefore be briefly described here.

There is still some doubt as to the correct name of this flagellate.
As was pointed out when the generic name Copromonas was introduced
(Dobell, 1908), the organism called Scytomonas by Stein (1878) is possibly
the same. But of this flagellate we have only Stein's crude figures —
unaccompanied by any proper description — and the identification is
there ore very questionable. However, Alexeieff (19116, 19126) and
Schiissler (1917) do not hesitate to assign Copromonas to the genus
Scytomonas, though they give no reasons for so doing. In our opinion
it is not now possible to ascertain what the organism really was to
which Stein gave the name " Scytomonas pusilla" If his figures really

* It should be noted that the foregoing descriptions do not agree in some points
with those of Woodcock (1916). This worker considers that C. longicauda and
C. crassicauda are the same species — a conclusion with which I can by no means agree.
It seems possible that his view is partly due to his having worked with a mixture of
species : but from a cytological point of view his figures leave much to be desired,
and I am not prepared to identify them precisely. I may also note that Woodcock
believes he has observed conjugation in " C. longicauda." I have not done so, and
consider — from the account published — that there is little or no evidence that conjuga-
tion occurs. The phenomenon observed by Woodcock appears rather to be an abor-
tive or regressive fission ; and the ultimate " encystation " appears to be merely the
rounding up of the degenerate product. I have observed such phenomena in several
other flagellates, and believe they have nothing to do with conjugation properly so-
called. (C. D.)

THE COPROZOIC PROTOZOA OF HUMAN FAECES l8l

depict the form which we call " Copromonas subtilis," then they are
incorrect in several details. In our view the genus Scytomonas is not
now identifiable, and should therefore be abolished. On the other
hand, it appears probable that the flagellate which Klebs (1892) called
"Scytomonas pusilla Stein" was a " Copromonas" : but how far Klebs
was justified in his identification is open to question, and his species was
apparently too small (4-8-6//,) to be C. subtilis. It seems probable that
the organism named Copromonas major by Berliner (1909) was really
C. subtilis, the distinctive features which he described being mostly due
— as is evident from the original description of C. subtilis, and the
more recent work of Schussler (1917) — to errors of interpretation. The
earliest account of a Copromonas is possibly that of Perty (1852), whose
similar flagellate was named Monas pileatorum.

Up to the present we have found this organism in human faeces on
only one occasion. The specimen containing it was sent to one of us
(CD.) by Mr. A. G. Thacker, and was obtained from a military patient
in the Kitchener Hospital, Brighton. The flagellates were easily culti-
vated on agar plates (see p. 167), and numerous cultures were made and
carefully studied. The most careful examination of living and fixed
and stained specimens has failed to reveal any constant structural
character* which enables us to distinguish this form from that occurring
in the faeces of frogs : but it should be mentioned that in old cultures
a number of very minute individuals made their appearance — a point
first observed by Mr. Thacker. These very small individuals were
never seen in the original cultures of C. subtilis from frogs. It is
possible — but we think improbable — that they belong to a distinct
species.

Copromonas subtilis (PI. V, fig. 91) is an oval, uniflagellate organism,
of relatively simple structure. Its length ranges from about 7 //. to 20 //,,
averaging usually about 15/*,: but the smallest forms, observed in
cultures, may measure as little as 4-5 //, (fig. 92). The body is subject
to little or no change of shape during life : and this is correlated with
the fact that the whole organism is invested with a relatively thick and
rigid pellicle. At the more pointed anterior end there is a small sub-
terminal aperture — the mouth — through which solid food is ingested.

* In the majority of the individuals cultivated from human faeces the nucleus
appears to lie slightly nearer to the anterior extremity than it does in specimens
from frog faeces. This character, however, is not constantly visible. (C. D.)

182 THE INTESTINAL PROTOZOA OF MAN

Extending backwards from the mouth, usually for rather more than
half the length of the body, and in a slightly spiral direction, is a
long narrow gullet. The posterior half of the body, which is rounded
terminally, usually contains conspicuous food-vacuoles, charged, for
the most part, with bacteria.

The single flagellum, whose length is rather greater than that of the
body, arises at the anterior extremity. It is fairly thick, and as it moves
as a rule but slowly — its lashing being particularly noticeable at its free
end — it is easily visible during life. The flagellum arises from a minute
blepharoplast situated in the wall of the gullet, and in close relation to
another structure— the reservoir — at the anterior end of the organism.
This reservoir is a clear vesicle, easily visible in the living animal. It
is not contractile, but has at its base a very small pulsating vacuole
which discharges its contents rhythmically into it.

The nucleus is single and vesicular, more or less centrally placed,
and contains a large central karyosome (fig. 91). It is bounded by a
delicate nuclear membrane, between which and the karyosome there is
a clear zone containing " achromatic " granules and crossed by radial
" linin " threads. There is no structure (rhizoplast) uniting the bleph-
aroplast to the nucleus, and no true centriole or centrosome is
demonstrable (contrary to the assertions of Berliner, 1909).

Multiplication takes place by simple longitudinal fission into two,
the splitting beginning at the anterior end, and passing gradually back-
wards. (See PI. V, fig. 93.) During this process the original flagellum
is drawn in ; the blepharoplast then divides into two ; and finally the
new flagella arise by outgrowth from the daughter blepharoplasts. The
nucleus divides by amitosis or a simple form of mitosis — the finer
details being difficult to make out.

This flagellate is one of the few in which conjugation has been
shown to occur (Dobell, 1908). Two individuals approach one another
and become united at their anterior ends (fig. 94) ; the union gradually
extending backwards until the organisms are completely fused. "Re-
duction " divisions of the nuclei occur during this process, and the
" reduced " nuclei finally fuse to form a single zygote nucleus. The
flagellum of one individual is drawn in during the act of fusion (fig. 94),
but the conjoined individuals continue to move actively throughout by
the aid of the one which persists. When fusion is complete, the zygote
may either become wholly remodelled into a single large flagellate —

THE COPROZOIC PROTOZOA OF HUMAN FAECES 1 83

which continues to lead an active life, and ultimately divides — or it
may encyst. Encystation also appears to take place without previous
conjugation.

The CYSTS (PI. V, fig. 95) are oval or rounded structures, with thin
walls and clear contents. They contain a single nucleus, and measure
about 7-8 fj, in diameter. On hatching, each cyst probably liberates a
single small monad.

For further details the reader may be referred to the accounts already
published — especially to the original description of the organism
(Dobell, 1908).

(io) Helkesimastix faecicola Woodcock & Lapage, 1915.

We refer to this species a minute coprozoic flagellate which we
have so far cultivated from only a single sample of human faeces. The
organism was found in a stale stool, several days old, and proved to
be cultivable on agar, on which it grew very rapidly. It is closely
similar to the form described from goat's faeces by Woodcock and
Lapage (1915).

The flagellate (PI. V, figs. 89, 90) is closely similar to a Cercomonas,
but differs in possessing no anterior flagellum. There is only one
flagellum, rooted at the anterior extremity, but which is directed back-
wards and adheres to the surface of the body, becoming free at the
posterior end. The nucleus is vesicular, with a central karyosome,
and lies at the anterior extremity. A minute contractile vacuole is
present in the middle or hinder part of the body.

The organism is usually more or less oval in shape, but somewhat
changeable — like a Cercomonas : but its anterior extremity, in front of
the nucleus, is usually rigid and pointed. During movement this end
is always in advance, and the flagellum is trailed behind. The organism
is very small, measuring usually only about 4-6 fi in length. The length
of the flagellum — from the point of origin, at the anterior end, to its
free tip — is about twice (according to Woodcock and Lapage 2^ to 3
times) that of the body. The flagellum appears to be attached to the
nucleus as in Cercomonas, but the exact insertion is very difficult to
make out, owing to the very small size of all the parts.

Multiplication is effected by simple longitudinal fission, but we
have not been able, as yet, to make out the finer details. Moreover we

1 84 THE INTESTINAL PROTOZOA OF MAN

have not been able to identify the cysts of this flagellate with certainty :
but according to Woodcock and Lapage (1915) they are spherical,
uninucleate, and measure from 3 fi to 3'5/z- in diameter.

The specimens found in human faeces, and those cultivated on
agar, live on bacteria. They ingest these in the hinder region of the
body — in the same way as a Cercomonas : and the ingested organisms
are easily seen in stained preparations (cf. figs. 89, 90). Woodcock and
Lapage, however, believed that their organisms did not take up solid
food. The dimensions of their flagellates, also, appear to be slightly
greater (6-7 yu.) than those of ours, and they observed a process of
"conjugation" which we have not encountered.* It is possible that
the form from human faeces belongs to a different species, but this
seems unlikely. Unfortunately Woodcock and Lapage have not pub-
lished a full description of the cytological characters of their organism,
their account being based chiefly upon a study of living specimens, in
which it is impossible to make out all the details.

(11) " Copromastix prowazeki" Aragao, 1916.

? Synonym :
Tetratricomastix intestinalis Sangiorgi, 19 17.

Under the above name a tetramastigine flagellate has recently
been described by Aragao (1916, 1916a). It was obtained in cultures^
made with egg-albumin (0*5 per cent.), from the faeces of a human
being and a frog :f and it is evident, from the description, that the
organism is a coprozoic form and not an inhabitant of the human
body.

The flagellate, 6- 1 8 /1, in length, is described as sub-triangular
in outline, and much attenuated at the pointed posterior end. At the
flattened anterior end four flagella, of equal length, arise from (?) a
single blepharoplast. The nucleus is vesicular, with a large central
karyosome, and lies near the anterior end. There is a short rhizo-
plast, attached to the blepharoplast but not to the nucleus. A mouth,

* The interpretation of the phenomena observed appears to be questionable. Cf.
what has been said concerning the " conjugation " of Cercomonas^ p. 180 footnote, supra.

tUp to the present I have never encountered this organism in cultures of human
faeces, nor in any of the very numerous cultures (egg-albumin and other media) which
I have made from the faeces of frogs and toads. (C. D.)

THE COPROZOIC PROTOZOA OF HUMAN FAECES 1 85

in the form of a short and straight cleft, is present at the anterior
end ; but it is stated that there are neither food vacuoles nor a con-
tractile vacuole in the cytoplasm. A few dividing- individuals have
been described and figured (Aragao, 1916a) but no cysts have yet
been discovered.

It appears almost certain, from the descriptions and figures, that
this organism really belongs to the genus Tetramitus Perty, 1852 : but
the previously described species of this genus require further investi-
gation. Consequently, while it is probable that " Copromastix " is a
synonym of Tetramitus, it is doubtful whether it belongs to any of the
species already known. Certain of Aragao's observations, moreover,
appear to be open to question. It would be remarkable, for example,
if his flagellate really possesses no contractile vacuole, and it is difficult
to believe that it can really possess a mouth but no food vacuoles.

Aragao found "Copromastix" in cultures of the faeces of only a
single human being, in Brazil ; and Leger (1918) states that he has
also once observed it in Guiana. No other workers appear to have
studied this organism, and further investigation of it — and, indeed, of
all the species of Tetramitus — is needed before a satisfactory classifi-
cation of these flagellates can be attempted.

An organism which appears to be, similarly, some species of
Tetramitus, has also been recently cultivated from human faeces by
Sangiorgi (1917). To this organism, which is possibly identical with
11 Copromastix," he has given the name " Tetratricomastix iutestiualis."
It is, at all events, probably a coprozoic species of Tetramitus and not
an intestinal flagellate ; but from the published description it is im-
possible to identify it more certainly.

(12) "TOXOBODO INTESTINALIS" Sangiorgi, 1917.

Sangiorgi (1917), in Italy, has recently described a "new" "intes-
tinal " flagellate from man, and given it the above name.

The organism in question was cultivated from human faeces, and
is almost certainly a coprozoic form, and not an intestinal inhabitant.
From the incomplete description published, it appears probable that it
is really a Spiromonas Perty, 1852.* Coprozoic species of this genus —

* Cf. also Saville Kent (1880), Woodcock (1916).

1 86 THE INTESTINAL PROTOZOA OF MAN

from goat dung — have recently been studied by Woodcock (1916).
The flagellates are small, elongate, and more or less spirally twisted
(" crescentic," according to Sangiorgi), and possess two free flagella —
both inserted at the anterior end, one recurrent, the other directed
forwards. The nucleus is central, and no kinetoplast is present.

We have not been able to study " Toxobodo" ourselves, and merely
note the foregoing points in order to call attention to the probability
that Spiromonas occurs in human faeces. We may also note that
another flagellate, recently found in the dung of a horse and the
excrement of a tortoise by Alexeieff (1918), and by him named
Alphamonas coprocola, probably belongs to the same genus. All these
organisms require further investigation.

187

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J3

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202 THE INTESTINAL PROTOZOA OF MAN

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204 THE INTESTINAL PROTOZOA OF MAN

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205

INDEX.

Abscess (Amoebic), cerebral, 41, 47, 52, 53,
57; hepatic, 41, 45, 52, 57, 144 (of cat,
56 ; of dog. 56 ; of monkey, 57) ; pulmonary,
41, 46, 52> 53 ; splenic, 47.

Adrenalin, for amoebiasis, 158.

Agar medium, for cultivation of amoebae,
etc., 167.

Alcresta ipecac, for amoebiasis, 153 ; for
balantidiosis, 162.

Alphamonas coprocola, 186.

Amebiasis (term), 4011.

Amoeba (genus), 4, 19, 38, 166 n.

Amoeba colt, 27.

— diploidea, 172.

— diplomitolica, 168.

— gruberi, 168.

— hyalina, 170.

— Umax, 31, 165, 166, 170, 174.

— proteus, 19.

— punctata, 168.

— tachypodia, 168.
Amoeba coli, 21.
felis, 21.

— — mitis, 27.

— dysenteriae, 21.

— intestini vulgaris, 27.

— urogenitalis, 47.

Amoebae (of Lewis and Cunningham), 2, 27.

Amoebae (intestinal) of man, 19-39 ; discovery,
2 ; genera and synonyms, 38, 39 ; key for
determination, 39.

Amoebaea (class), 5, 17, 19-39, 165-173.

Amoebiasis, 15, 16,40-57, 151-159 ; account
of, 40 sq ; aetiology, 40 sq ; definition, 40;
immunity, 54 ; in animals, 55 sq ; incuba-
tion period, 54 ; intestinal, 43, 49 sq ; mor-
bid anatomy, 42 sq, 57; parasitology, 48 sq;
pathogenesis, 40 sq ; pathology, 42 sq ; pri-
mary, 41, 43, 49 sq ; secondary, 41, 45 sq,
52 sq ; symptomatology, 49 sq ; term, 15,
16, 40; treatment, 151 sq ; urinary, 47.

Amoebic abscesses. See Abscess (Amoebic).

— diarrhoea, 41, 49, 51, 144.

— dysentery, 13, 41, 49, 51, 55, 148, 149,

150, 151 sq ; in cat, 56; in dog, 56; in

monkey, 57 ; treatment of, 151 sq. See
also Amoebiasis.
Amoebic hepatitis, 41, 45, 52.

— liver abscess. See Abscess, hepatic.
Amphituonas caudata, 175.
Apparatus necessary for diagnosis. 127 sq.
Atoxyl, for amoebiasis, 158.
Azure-chloroform stain, for diagnosis, 132.

Balantidial diarrhoea, 122, 144. See also
Balantidiosis.

— dysentery, 13, 119, 122, 145 sq. See also

Balantidiosis.

Balantidicidal substances, 163.

Balantidiosis, 15, 1 18-124, 162-163; account
of, Il8 sq ; aetiology, 1 18 sq ; definition,
118; distribution, 119; in animals, 122 sq ;
incidence, 119; morbid anatomy, 119 sq ;
pathogenesis, 118; pathology, 119 sq ;
symptomatology, 122 sq ; term, 15, 118;
treatment, 162 sq.

Balantidium (genu>), 5, 17, 106, 107, 114,
117, 118, 122, 123.

Balantidium coli, 2, 5, 10, 13, 15, 17, 9210
107-110, in, 113, 116, 117, 11S, 119, 120,
121, 122, 123, 143, 144, 145, 146, 162,
163 ; account of, 107 sqj acquisition of infec-
tion, no, 118 sq, 123 sq ; budding, no;
cilia, 108 ; ciliate, described, 107 sq ; con-
jugation, no; cysts, no; discovery, 2,
107 ; division, 109 ; experimental iufection,
123, 124; habitat, 109, 118 sq ; nuclei,
108; nutrition, 109, 120; sporulation, no ;
synonyms, 107 ; vacuoles, 108.

giganteum, 116.

sp. Albanense, 117.

variety Hondurense, 117.

— giganteum, 116 n.

— minutum, 5, 17, 1 11- 11 2, 1 13, 11511, nS;
description, III sq.

var. iialicum, 112.

Benzyl benzoate, for amoebiasis, 158 ; for

balantidiosis, 163.
Best's carmine stain, 138.
Bibliographic note, 18.

206

INDEX

Bismuth salts, for amoebiasis, 158 ; for flagel-
late infections, 160.

Blastocystis (genus), 69, 141, 142 n.

Blastocysts enterocola, 142 n.

■ — hominis, 37, 141-142.

Blood-count, in amoebiasis, 51, 52 ; in balan-
tidiosis, 122.

Bodo (genus), 59, 175, 176, 178.

Bodo asialicus, 175.

— caudatus, 165 n, 175-177, 178; cultivation,
165 n, 177; description, 175 sq ; synonyms,

175-

— edax, 177-17S.

— intestinalis, 59.

— urinarius, 175.

Borax carmine, for cysts, 138.
Bouin's fluid (formula), 138 n.
Brucea sumatrana, 157.

Carmine stains, 138.

Carnoy's fluid (formula), 138 n.

Carriers, of Balantidium, 1 18, 122, 144 sq ;

of E. histolytica, 49 sq, 57, 144 ; contact,

50 ; convalescent, 50.
Castela Nicholsoni, 157.
Cat, amoebic liver abscess of, 48 n, %6 ;

Balantidium in, I24n ; E. histolytica in,

56, 57 ; Giardia in, 92.
Cautions in viewing objects (Baker), 147.
Cebus caraya, flagellate of, 80.
Cells mistaken for protozoa, 140.
Cellular exudate, in diagnosis, 146.
Cephaeline, 152.
Cephaelis ipecacuanha, 15 1.
Cercobodo longicauda, 178.
Cercomonad A, 65, 69 n.

— B, 70, 71-

Cercomonas (genus), 58, 59, 65, 66 n, 71, 72,

86, 87, 161 n, 178-180, 183, 184.
Cercomonas coli hominis, 65.

— crassicauda, 179, 180 n.

— davainei, 70, 72.

— hominis, 65.

A, 2, 65, 70, 71, 72.

B, 2, 65, 71, 72.

— intestinalis, 58, 59, 70, 71.

— longicauda, 178-179, 180 n.

— obliqua, 65, 72.
— parva, 178.

— sp. I, 70.

— sp. 2, 65.

Cerebral Amoebic Abscess. See Abscess,

cerebral.
Chaparro amargosa, for amoebiasis, 157.
Charcot-Leyden crystals, 24 n, 146 n.
Chenopodium, oil of, for amoebiasis, 158 ; for

balantidiosis, 163.
Chilodon (genus), 114.

Chilodon dentalus, 1 14.

— uncinatus, 114.

Chilomastix (genus), 5, 17, 65, 87, 88 ;

synonyms, 87.
Chilomastix caulleryi, 73 n, 74 n.

— davainei, 71, 72,

— hominis, 72 n.

— mesnili, 2, 5, 14, 17, 65, 66, 69, 70-
78, 79, 80, 88, 117; blepharoplasts, 73
sq ; cultivation, 76 ; cysts, 76 sq ; dis-
covery, 2, 71 ; division, 76 ; flagella, 74 ;
flagellate, described, 72 sq ; habitat, 76 ;
mouth, 73, 74; neuromotor system, 75;
nomenclature, 71, 72; nucleus, 73; nutri-
tion, 74 ; parabasal and parastyle, 75 ;
synonyms, 70.

Chlamydophrys stercorea, 167, 173-175 ', des-
cription, 173 sq ; synonyms, 173.

Chromatoid bodies, of E. coli, 29 ; of E.
histolytica, 24.

Chromidial bodies, 24.

Chromosome cycle in coccidia, 95.

Cilia, 4.

Ciliata (class), 5, 17, 106, 164 n.

Ciliate dysentery, 119.

Ciliates, 106-124; doubtful, 113 sq; key for
determination, 1 17; life-cycle, 106.

Ciliophora, 4, 5, 17, 106.

Cimaenomonas (genus), 86.

Classification of Protozoa, 3 sq, 17.

Clinical interpretation of findings, 142 sq.

Coccidia, 2, 5, 9, 10, 13, 15, 17, 94-105 ;
classification, 97 ; discovery, 2, 98 ; key for
determination, 102 ; life-cycle, 94 sq.

Coccidies intestinales, 98.

Coccidiomorpha, 94.

Coccidiosis, account of, 102 sq ; intestinal,
102 ; term, 15, 16 ; treatment of, 161 sq.

Coccidium (genus), 97.

Cocciaium bigenmium, 98.

var, homznis, 98.

— hominis, 98.

— perforans, 98.
Collection of material, 125 sq.
Colpoda cucullus, 1 15-
Commensalism (term), 13.
Concentration methods, for cysts, 132.
Contact carrier (term), 50.
Convalescent carrier (term), 50.
Copromaslix (genus), 185.
Copro?nastix prowazeki, 184 sq.
Copromonas (genus), 180 sq.
Copromonas major, 180, 18 1.

— 7-uminantium, 180.

— subtilis, 180-183; conjugation, 182 ; cysts,

183 ; description, 180 sq ; division, 182 ;

synonyms, 180.
Coprophilic (term), 16.
Coprozoa, 16.

INDEX

207

Coprozoic protozoa, 16, 164-186 ; flagellates, |
J39 n, 17S-186; rhizopods, 165-175.

Counterstains, 137.

Counting methods, for cysts, 133.

Coverglasses, 128.

Cryptosporidia in, 102.

Crystalloid bodies, 24.

Cultivation of Balantidium, 117, 121 ; of
Chilomastix, 76 ; of coprozoic protozoa, 167
sq ; of Trichomonas, 69, 70.

Cure, definition of, 149 sq.

Cyathomastix (genus), 72, 76, 87.

Cyathomaslix ho minis, 71.

Cyclidium (genus), 116 n.

Cyst-carrier (term), 7, 50.

Cysts of intestinal protozoa (general), 6 sq.

Cylospermiutn hominis, 98.

Diagnosis, 125-147 ; common errors in, 139.
Diarrhoea, amoebic, 41, 49, 51, 144, 145 ;

balanlidial, 119, 122, 144, 145; flagellate,

89, 90.
Dicercomonas (genus), 86, 87.
Dicercomonas {Dimor plats') muris, 58.

— soudanensis, 80, 82.
Dientamoeba (genus), 5, 17, 39.
Dientamoeba fragilis, 5, 17,36-38, 39, 172;

amoeba, 36 ; cysts, 38; division, 37 ; move-
ments, 36 ; nuclei, 37.

Difdmus (genus), 72, 87.

Difdmus tunensis, 71.

Dimastigamoeba (genus), 167.

Dimastigamoeba gruberi, 168- 1 70, 1 7 1 ;
amoeba, 169 ; cultivation, 170; cysts, 169 ;
division, 169; flagellate form, 169.

Dimorphus (genus or subgenus), 86.

Diplocercomonas (genus), 82, 83, 84, 87.

Diplocercomonas soudanensis, 80, 82.

Diplomastix caudata, 175.

Diplospora (genus), 97.

Discovery of intestinal protozoa, I.

Disease (term), 13, 15.

Dissemination (general), 7 sq.

Distribution, geographical (general), 9sq.

Dog, E. histolytica in, 56.

Double iodide. See Emetine bismuthous
iodide.

Doubtful ciliates, 113-117.

Duration of E. histolytica infections, 53.

Dysentery, amoebic, 13, 41, 49, 51, 52, 55,
145 ; in cats, 56 ; in dogs, 56 ; in monkeys,
57; treatment of, 149 sq, 151-159.

— , balantidial, 13, 119, 122, 145; ia monkeys,
124 ; treatment of, 162 sq.

— , ciliate, 119.

Eimeria (genus), 5, 16, 17,97, ioo, 102, 104,
105, 161.

Eimeria falcifoi'mis, 100.

— oxyphila, ioo.

Eimtria oxyspora, 5, 17, 100-101,102,104;
description, 100 gq ; o-'^y-t-, 100 sq ;
treatment, 161.

— snijdersi, 5, 17, 101-102, 104, 161.

— s;j., from human liver, 103.

— stiedae, 98, 103.

— wenyoni, 5, 17, 100, 102, 104 ; description,

100.

— zilrtii 102, 103.
Eimeria (Coccidium), 100.
Embadomonas (genus), 5, 17, 79, 87, 88;

synonyms, 87.
Embadomonas inteslinalis, 5, 17, 78-80,88;

cysts, 79; discovery, 78; division, 79;

flagellate, described, 79 sq ; synonyms, 78.
Emetathylin, 152 n.
Emetine, alkaloid, 152 sq; administration,

*53; properties, 152; toxicity, 152.

— bismuthous iodide, for amoebiasis, 154; ad-

ministration, 154-156; history, 154, 154m

— hydrochloride, for amoebiasis, 154, 156;

administration, 154, 156; for balan-
tidiosis, 162; for coccidiosis, 161; for
flagellate infections, 160.

— mercuric iodide, 154 n.
Endameba (genus), 38.
Endamoeba (genus), 38.
Endamoeba nana, 33.

Endolimax (genus), 5, 17, 33 n, 38, 39;

synonyms, 38.
Endolimax inteslinalis ', 3 1 .

— kueneni, 57 n.

— nana, 5, 17, 31-33, 36, 39, 78, 85 n,
159, 174 n ; amoeba, 31; cysts, 32; division,
32 ; nucleus, 31 ; nutrition, 31 ; races, 33 ;
synonyms, 31.

— pileonncleatus , 33, 36 n.

— williamsi, 33.
Endothelial cells, 44, 140.
Enlameba (genus), 38.

Etitamoeba (genus), 5, 17, 38, 39 ; synonyms,

38.
Entamoeba africana, 23 n.

— brasiliensis, zr, 27.

— butschlii, 33.

— coli, 2, 5, 9, II, 13, 14, 17, 27-30, 33, 34,

36, 39. 57> 76, 159; amoeba, 27 sq ;
autogamy, 30 ; conjugation, 28 ; cysts,
29 sq ; degeneration, 28; discovery, 2;
division, 28; encystation, 29; excysta-
tion, 30 ; movements, 28 ; multiplication,
28 ; nucleus, 27 ; nutrition, 27 ; pre-
cystic forms, 29 ; races, 30 ; sexual
dimorphism, 30 ; synonyms, 27.

— dysenieriae, 21.

— hartmanni, 21, 25.

— histolytica, 2, 5, 9, 10, 11, 13, 17, 21-
26, 27, 28, 29, 30, 33, 36, 39, 40-57, 78,
118, 119, 120, 126, 127, 138, 139, 140, 143-

208

INDEX

146, 148, 150, 151, 152, 153, 156, 157, 158
159, 16311 ; amoeboid form, 21 ; autogamy
25 ; cysts, 23 sq ; degeneration, 26 ; dis
covery, 2, 21; divUion, 22; encystation
23 ; cxcystation, 25 ; geographical dis
tribution, 9, 54, 55 ; habitat, 41 sq
movements, 22; nucleus, 21; nutrition
22, 41 sq ; pathogenesis, 40 sq ; precystic
forms, 23; races, 24 sq; reproduction, 22
sexuality, 26 ; spore-formation, 26 ; super
nucleate cysts, 26 ; synonyms, 21 ; viru
lence, 54. See also Amoebiasis.
Entamoeba hominis, 27.

— minuta, 21, 23.

— minutissima, 21, 25.

— nana, 31.

— ranarum, 91 n.

— tenuis, 21, 25.

— tetragena, 21, 23 n.

— undnlans, 65, 69.

— willianni, 27, 30, 36.

Enteromonas (genus), 5, 17, 80-83, 84, 85.

87, 88 ; synonyms, 87 ; in rabbit, 85.
Enteromotias bengalensis, 80, 81.

— hominis, 5, 17, 80-85, 88 ; cysts, 84 ; divi-

sion, 84 ; flageilaie, described, 83 sq ;

nomenclature, 80 sq ; synonyms, 80.
Enloplasma (t;enu-), 116, 117.
Entozoa (term), 12.
Eosin, as counterstain, 137 ; for diagnosis,

Eosin-iodine stain, 131 ; formula, 131 n.
Errors, common, in diagnosis, 139 sq.
Euglena, 4.

Eutrichomaslix (genus), 81, 87.
Examination of stools, 127 sq ; macroscopic,

127, 144, 146; microscopic, 127 sq, 144 sq.
Examinations, negative, I45, 146 n, 150.
Experimental infection of man, with Balan-

tidium, 123, 124; with E. histolytica, 54.

Fanapepea (genus), 72, 75, 87.

Fanapepea intestinalis, 71, 75.

Fertilization in coccidia, 96.

Fixation of films, 133 sq.

Fiagella, 4.

Flagellata (class), 5, 17, 58-93, 175-1S6.

Flagellate diarrhoea or dysentery, 89 sq ;

treatment of, 159 sq.
Flagellate infections, lesions described in, 90,

91 ; treatment of, 159 sq.

Flagellates, attempts to infect animals with,

92 sq ; coprozoic, 175-186; intestinal, 58-

93 ; key for determination of, 88 ; patho-
genicity of, discussed, 89 sq ; synonyms
and homonyms of genera of, 85, 87.

Fkgellosis, intestinal, 15, 89 sq ; account of,

89-93 '< term, 15 ; treatment of, 159 sq.
Fries, as spreaders of infection, 8, 9.

Food-robbers (term), 14.

Free forms of protozoa (general), 6 sq.

Free-living amoebae (James), 31.

Galyl, for amoebiasis, 158.

Genera of amoebae, 38, 39 ; of ciliates, 106 ;

of coccidia, 97 ; of flagellates, 86, 87.
Geographical distribution (general), 9 sq.
Giardia (genus), 5, 17, 59 n, 86, 88, 92 ;

synonyms, 86.
Giardia enterica, 58, 59.

— intestinalis, 1, 5, 9, II, 14, 15, 17, 28,

58-65. 7i» 76, 88, 91, 92, 93, 160, 161 ;
axostyles, to, 61, 62; conjugation, 64;
cysts, 63 sq ; discovery, I, 59; division,
62, 63 ; encystation, 63 ; excystation, 65 ;
flagella, 60, 61, 62 ; flagellate, described,
59 sq; habitat, 62 ; nuclei, 60 ; nutrition,
62 ; parabasal bodies, 60 ; pathogenicity,
89 sq ; synonyms, 58 ; treatment, 160 sq.

— lamblia, 58.

— maris, 63 n, 92 sq, 161.
Giardiasis (term), 15.

Glycogen, in cysts of Chilomastix, 76 ; of E.

coli, 29; of E. histolytica, 24; of E. nana,

32 ; of Giardia, 65 ; of /. biitschiii, 35 ;

staining of, 130, 138.
Gregarinida, 94.
Guinea-pig, E. histolytica in, 56 ; Giardia in,

92 ; Trichomonas in, 69 n, 70, 92.

Haemalum (formula), 135 ; method of stain-
ing with, 135.

Haemosporidia, 94.

Hartmannella (genus), 167, 170.

Hartmannella hyalina, 1 70-171 ; description
and synonyms, 170.

Hartmaruria (genus), 167, 170.

Heikesimaslix faecicola, 183-184.

Hepatic abscess (amoebic). See Abscess,
htpatic.

Hepatitis, amoebic, 41, 45, 52.

Heterotricha, 106.

Hexamastix (genus), 68 n, 86.

Hexamastix Ardin Delteili, 65, 68.

Hexamita (genus), 59, 86.

Hexamila duodenalis, 92 n.

Historic note, 1 sq.

Holophrya coli, 107.

Host (term), 12.

Humidity, necessary for survival and dispersal
of cysts, 9.

I. cysts, 33.

Illumination, 128, 131.

Incidence of infection (general), 11 sq.

Indirect methods of diagnosis, 146.

Infection, 6. See also Amoebiasis, Balan-

tidiosis, Coccidiosis, Flagellosis.
Infusoria, 106. See Ciliata, Ciliates.

INDEX

209

Interpretation, clinical, of protozoological
findings, 142 sq.

Iodamocba (genus), 5, 17, 39, 57 n; synonyms,
39-

lodamoeba bulschlii, 5, 17, 33-36. 39, 57 n,
159 ; amoeba, 33 sq ; cysts, 34 sq ; divi-
sion, 34 ; nucleus, 34 ; nutrition, 34 ; pre-
cystic amoebae, 34 ; races, 36 ; synonyms,
33 ; treatment, 159.

Iodine cysts, 33.

— solution, for diagnosis, 130 ;

— , treatment of flagellate infections with, 160.

Ipecacuanha and its alkaloids, 151 sq ; for
amoebiasis, 151, 153 ; for balantidiosis,
162.

Iron-haematoxylin staining methods, 136.

/foemetine, 152.

Isospora (genus), 5, 16, 17, 97,98, 102, 104,
105.

Isospora bigemina, 98.

— hominis, 5, 17, 28, 98-99, 102, 104, 105,

161, 162; discovery, 98; oocysts de-
scribed, 98 sq ; synonyms, 98 ; treat-
ment, 161 sq.

— rivoltae, 98.

Key to genera and species of amoebae, 39 ;

of ciliates, 117; of coccidia, 102; of

flagellates, 88.
Kho-sam, for amoebiasis, 157.
Kinetoplast (term), 176.

Lamblia (genus), 86 ; (subgenus) 59 n.

Lamblia intestinalis, 58.

Lambliasis (tetm), 15.

Ltucophrys coli, 107.

Leydenia gemmipara, 173, 174.

Life-histories (general), 6 sq.

Liver abscess. See Abscess, hepatic.

Liver, Eimeria of human, 103.

Lophomonas, 68 n.

Loschia (genus), 38.

Loschia colt, 27.

— histolytica, 21.

— (Viereckia) tetragena, 21.

Macrostoma (genus), 87.

Macros toma tnesnili, 70, 71.

Mann's stain, 137.

Mastigophora, 4, 5, 17, 58 sq, 164.

Media, culture, for amoebae, etc., 167, 16S.

Megastoma (genus), 86.

Megasloma entericum, 58.

— intesiinale, 58.
Merozoite (teim), 95.
Metazoa (definition), 3.
Methylblue-eosin stain (Mann), 137.
Methylemetine, for amoebiasis, 152,

Methylene blue, for balantidiosis, 162 ; for
flagellate infection, 160.

— violet and methyl violet stain, lot dia-
gnosis, 132.

Methylpsychotriie, 152.
Micrometer, 128, 140.
Monas pileatorum, 180, 181.
Monocercomonas (genus), 80, 81, 86, 87.
Monocercomonas Ziominis, 65, 70, 71.
Monocystis, 4.

Monkeys, amoebae of, 57 ; Balantidium of,
107, 118, 123.

Naegleria gruberi, 168.

— punctata, 168.

Negative examinations, 145, 166 n, 150.

Neutral red, for diagnosis, 131, 132.

Neosporidia, 94.

Non-cellular (term), 3.

Nyclotherus (genus), 5, 17, 106, 115 n, 116

118.
Nyctotherus africamis, 115.

— /aba, 5, 17, in n, 112, 113, 115 n, 118 ;
description, 112 sq.

— giganieus, 116.

Octomitus ho minis, 80, 85.
Oocyst (term), 96.

Paramaecium (?) coli, 107.

Paramecium (genus), 4, 106, 107.

Paramecium cauJalum, 107.

Parasite (term), 12, 13, 14.

Parasitism (term), 13.

Pentatrichomonas (genus or subgenus), 68, 86,.

88 n, 91.
Pentatrichomonas bengalensis, 65, 68 n.
Permanent preparations, making of, 133 sq.
Phagedaenic skin ulcers, amoebae in, 47.
Pig, Balantidium in, 107, 109 n, 123, 124 \

lodamoeba in, 36 n, 57 n.
Plagioto??ia coli, 107.
Platoum stercoreum, 173.
Poneramoeba (genus), 38.
Postage of specimens, regulations concerning,

126 n.
Preparations, making of, 12S sq ; fresh, 128,

129; iodine, 130; permanent, 133 sq.
Proctamoeba (genus), 38.
Protozoa, classification of, 3 sq ; definition,

3 ; synopsis of intestinal P. of Man, 17.
Prowazekella lacertae, 142 n.
Prowazekia (genus) = Bodo, q. v.
Prowazekia asiatica, 175.

— cruzi, 175, 177 n, 17S.

— italica, 175.

— javanensis, 175.

— tirinaria, 175.

— weinbergi, 175.

14

2IO

INDEX

Pseudolimax, 33.

Pseudopodia, 4, 19.

Psorospermien, 98.

Psychotria ipecacuanha, 151 •

Psychotrine, 152.

Purgatives, use of, in collecting material, 126.

Quinine, for balantidiosis, 162, 163.

Rabbit, E. histolytica in, 56 ; Enteromonas
of, 85 ; Giardia in, 92, 161.

Rat, E. histolytica in, 56 ; Giardia in, 92, 161.

Relation of intestinal protozoa to man, 12 sq.

Rodents, Giardia of, 63 n, 92, 161 ; Tricho-
monas of, 69 n, 92.

Rhizopoda, 4, 5, 17, 19 sq, 164; coprozoic,
165 sq.

Rubin-iodine stain, 131.

Saenolophus (genus), 86.

Saline solution, for diagnosis, 129, 139.

Salvarsan, for amoebiasis, 158; for balan-
tidiosis, 163 ; for coccidiosis, 162 ; for
flagellate infections, 160, 161.

Sappinia (genus), 167, 172.

Sappinia diploidea, 172, 173; cultivation, 173;
description, 172 sq; synonyms, 172.

Saprophytic (term), 14.

Saprozoic (term), 14.

Schaudinn's solution (formula), 134.

Schizogony (term), 95.

Schizont (term), 95.

Scytomonas (genus), 180, 181.

Scytomonas pusilla, 180, 181.

Sections, preparation of, 138.

Selection of specimens for diagnosis, 126 sq.

Sigmoidoscope, for collecting material, 126.

Silver nitrate, for balantidiosis, 162.

Simaruba, for amoebiasis, 157.

Small amoeba (Wenyon), 31.

Sources of error in diagnosis, 139 sq.

Sphaerita, in E. nana, 33.

Spherical bodies (Wenyon), 33.

Spiromonas (genus), 185-6.

Spore (term), 96.

Sporoblast (term), 96.

Sporocyst (term), 96.

Sporogony (term), 97.

Sporozoa, 4, 5, 17, 94 sq.

Sporozoite (term), 96.

Sputum, Balantidium in, 121.

Squamous cells, 140.

Staining methods, 134 sq.

Stools, collection of, 125 sq ; examination of,
127 sq ; postage of, 126 n.

Sublimate-alcohol fixative, 134.
Supernucleate cysts, of E. coli, 30 ; of E.
histolytica, 26; of E. nana, 32 ; of /. b'ut-
schlii, 35.
Symbiosis (term), 13.

Table of chief intestinal protozoa ot man, 17.
Tannin, for amoebiasis, 158.
Tetrachilomastix (subgenus), 75 n.
Tetramitus (genus), 71, 87, 185.
Tetramitus mesnili, 71.
Tetratrichomonas (genus or subgenus), 68, 86,

88 n.
Tetratricomaslix mtestinalis, 184, 185.
Thalamophora, 173.
Thecamoebae, 173.
Thorium salts, for amoebiasis, 158.
Thymol, for balantidiosis, 163 ; for coccidi-
osis, 162; enema, for collecting material,
126 ; for flagellate infections, 161.
Tissues, fixation of, 138.
Toxins of intestinal protozoa, 14.
loxobodo (genus), 186.
Toxobodo intestinalis, 185, 186.
Treatment, of intestinal protozoal infections,
148-163 ; of amoebiasis, 151 sq ; of balan-
tidiosis, 162 sq ; of coccidiosis, 161 sq ; of
flagellate infections, 159 sq.
Tricercomonas (genus), 81, 82, 83, 84, 85, 87.
Tricercomonas intestinalis, 80, 81.
Trichomastix (genus), 81, 87; cultivation of,

70.
Trichomastix hominis, 80, 81.
Trichomonas (genus), 5, 17, 65, 71, 72, 86,

87, 88, 92, 142 n ; synonyms, 86.
Trichomonas batrachorum., 69 n.

— buccalis, 70.

— caviae, 69 n, 70.

— hominis, 2, 5, 14, 17, 28, 65-70, 71, 72,

78, 88, 50, 91, 160, 161 ; amoeboid
forms, 66, 69 ; axostyle, 67 ; cultivation,
69, 70 ; cysts, 69 ; discovery, 2, 65 ;
division, 69 ; flagella, 67, 68 ; flagellate,
described, 66 sq ; nucleus, 66 ; nutrition,
68, 70, 91 ; synonyms, 65 ; treatment,
160, 161; undu'ating membrane, 67;
varieties, 68 n.

— intestinalis, 65, 70, 71.

— obliqua, 72 n.

— vaginalis, 68 n, 70.
Trichomoniasis (term), 15.
Tcichomonosis (term), 15.
Trico-monas (genus), 86.
Tricomonas confusa, 65.
Trimastigamoeba philippinensis, 169.
Tritrichomonas (genus or subgenus), 68 n, 85.

88 n.
Troglodytes zoster, 173.
Tubes for collection of material, 126.
Turpentine, for flagellate infections, 160.

Unicellular (term), 3.

Uragoga ipecacuanha, 151.

Urine, amoebae in, 47 ; ciliates in, 121.

Uronema (genus), 116 n.

INDEX

Uronema catt datum, 116.

— marinum, 116 n.
Uzara, for amoebiasis, 159.

Vahlkampjia (genus), 38.
Vahlkampfia diploidea, 172.

— nana, 31.

— punctata, 168.

— soli, 168.

Viereckia (genus or subgenus), 3S

Volutin, in E. nana cysts, 32; in /. bUtschlli
cysts, 35.

Wasielewskia gruberi, 168.
#&r&a (genus), 78, 79 n, 8o n, 87.

Was/da intestinaHs, 78.
— wenyoni, 80.

Zenker's fluid (formula), 138 n.

PLATE II.

PLATE II.
All drawings were made from fixed and stained specimens. Magnification 2,000 diameters

throughout. Fixation, sublimate-alcohol — unless otherwise stated : staining as indicated. (After

Dobell (1919a), but slightly reduced.)

Figs. I — 16. Entamoeba histolytica.

Fig. I. Active large form, containing 3 red blood-coipuscles. From stool of a case of amoebic
dysentery. (Stained Weigert's iron-haematoxylin and eosin.)

F;gs. 2 — 7. Successive stages in riivision. From specimens in sections of ulcers in large intestine
of experimentally infected kitten. (Fixed in Bouin's fluid, and stained in various ways.)

Figs. 8, 9. Precystic amoebae, belonging to strains forming large and small cysts respectively.
(Fig. 8, Mann's stain : fig. 9, haemalum.)

Figs. 10, 11, 12. Uninucleate, binucleate, and quadrinucleate cysts respectively: from same case
as fig. 8. Strain forming cysts with mean diameter of 13'5/i. (Mann's stain.)

f'S I3- Quadrinucleate cyst belonging to a strain with cysts measuring 1 5 ^ in average diameter.
(Haemalum.)

Figs. 14, 15, 16. Uninucleate, binucleate, and quadrinucleate cysts respectively — belonging to a
strain producing cysts with an average diameter of 6'6/u. (Haemalum.)
Figs. 17 — 26. Entamoeba coli.

Fig. 17. Large active amoeba, Irom human stool. (Heidenhain's iron-haematoxylin and eosin.)

Fig. 18. Precystic amoeba. Note small size, and freedom from food inclusions. (Mann's stain.)

Figs. 19 — 22. Successive stages in development of cysts, which contain I, 2, 4, and 8 nuclei
respectively. (Figs. 19, 20, Mann's stain ; fig. 21, Bouin's fluid and alcoholic ferric-
chloride iron-haematein ; fig. 22, Heidenhain's iron-haematoxylin.)

Fig. 23. Very small 8-nucleate cyst of E. coli. (Haemalum and eosin.)

Fig. 24. 8-nucleate cyst, containing filamentar chromatoid bodies. (Haemalum.)

Fig. 25. 8-nucleate cyst, containing a sheaf of spicular chromatoids. (Haemalum.)

Fig. 26. Very large cyst, containing 16 nuclei. (Haemalum.)

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PLATE III.
The left half of the Plate (Fig. 27) illustrates the microscopic appearance of the lesions in
Amoebiasis (E. histolytica infection).

The right half (Fig. 28) illustrates the size-relations of the cysts of E. histolytica belonging to
four different races.

Fig. 27. (A) Section of an early intestinal ulcer, with the amoebae in and upon the mucous
membrane, which they have partly destroyed. Magnification 90 diameters.

(B) Section of a later and deeper ulcer, showing the amoebae invading the submucous
tissue. Magnification 90 diameters.

(C) More highly magnified portion of the base of the ulcer shown in (B). The amoebae
are here seen in contact with the healthy submucous tissue — with the destroyed tissue in
the cavity of the ulcer in their train, above and to the right. Magnification 450 diameters.

(D) Part of a section through the periphery of an amoebic liver-abscess. Above,
healthy liver tissue : below, and in contact with it, amoebae and necrotic tissue in the
abscess cavity. Magnification 450 diameters.

AH these figures are drawn from sections of experimentally produced lesions in kittens. The
material was fixed in Bouin's fluid : figs. (A) and (D) stained with acid fuchsin and picro-indigo-
carmine, figs. (B) and (C) Mann's stain.

[From The Practice of Medicine in the Tropic s.~\
Fig. 28. These drawings illustrate the differences in the dimensions of the cysts of E. histolytica
— belonging to four different strains of the parasite — from four different human infections
(Cases H. 8, H. 7, E. 42, B. 1). They show in parallel columns ten cysts from each of
these cases — taken at random from fixed and stained preparations, and outlined with the
camera lucida. The drawings were made at a magnification of 2,500 diameters, and have
been reduced to the size here shown in the process of reproduction. (Only the outlines of
the cysts and nuclei are shown, and their chromatoid bodies — in black— when present.)

The remaining figures are outlines, drawn in the same way, and to the same scale, of
fixed and stained amoebae of E. histolytica. E. h. (1), two individuals (containing red
corpuscles) from a case of acute amoebic dysentery — belonging to a strain forming cysts
similar in size to those of Case E. 42. Fig. E. h. (2), two precystic amoebae belonging to
a similar strain. Fig. E. h. (3), precystic amoebae belonging to a strain with cysts similar
in size to those of Case H. 8.

[After Dobell and Jepps (1918).]

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PLATE III.
B.1.

Fig. 27.

PLATE IV.
All figures, unless otherwise indicated, drawn from specimens fixed with sublimate-alcohol
and stained with Heidenhain's iron-haematoxylin and eosin. Magnification 2,000 diameters
throughout.

Figs. 29 — 48. Intestinal amoebae.
Figs. 29—39. Enciolimax nana.
Figs. 29 — 32. Four ordinary individuals, showing various common types of nuclear structure.
Figs. 33, 34. Two individuals parasitized by Sphaeriia. (Fig. 34 stained haemalum.)
Figs. 35> 36, 37- Three successive stages in development of cysts — containing I, 2, and 4 nuclei

respectively.
Fig. 38. Mature 4-nucleate cyst containing filamentar and granular inclusions.
Fig- 39- Supernucleate cyst, containing 8 nuclei. (Haemalum.)

Figs. 40 — 42. Dientamoeba fragilis.
Figs. 40, 41 1 Two ordinary binucleate individuals.
Fig. 42. A uninucleate specimen.

Figs. 43 — 48. lodamoeba butschlii.
Figs. 43, 44. Two ordinary amoeboid individuals.
Fig. 45. Precystic amoeba.
Fig. 46. An organism just encysting.

Figs. 47, 48. Typical cysts— fig. 48 a very irregular specimen, such as is commonly seen in this
species. (Haemalum and eosin.)

Figs. 49 — 57. COPROZOIC AMOEBAE, FROM HUMAN FAECES.

Fig. 49. Dimastigamoeba gruberi, amoeboid form.

Fig. 50. D. gruberi, free-swimming flagellate form.

Fig. 51. Stage in division (equatorial plate) of amoeboid form of D. gruberi.

Fig. 52. Cyst of D. gritberi.

Fig. 53. Hartmannella hyahna, ordinary amoeba.

Fig. 54. Stage in division (equatorial plate) of H. hyalina.

Fig- 55- Cyst of H. hyalina.

Fig. 56. Sappinia diploidea, ordinary individual. (Note the two large nuclei, in apposition.)

Fig. 57. Newly formed cyst of 5. diploidea, containing two individuals.

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All drawings made from fixed and stained specimens, unless otherwise indicated. Fixation,
sublimate-alcohol : staining, Heidenhain's iron-haematoxylin, usually combined with eosin.
Magnification 2,000 diameters throughout.

Figs. 58—77. Intestinal Flagellates.
Figs. 58 — 61. Giardia intestinalis. (Fixation : Bouin's fluid.)
P'ig. 58. Active flagellate, ventral view.

F'g- 59- Similar flagellate, in profile (ventral surface to right, dorsal to left of figure).
Fig. 60. Binucleate cyst.
Fig. 61. Quadrinucleate cyst — later stage of development.

Figs. 62 — 68. Enteromonas hominis.
Fig. 62. Active flagellate ; typical form, with 4 flagella— 3 free, and : recurrent and adherent to

the body (" Iricercomonas" of Wenyon and O'Connor).
Fig. 63. Form in which the lecurrent flagellum is not clearly visible (" Enteromonas" of
Fonseca).

Fig. 64. Form in which only 2 anterior flagella are visible (" Diplocercomonas" of Chalmers and
Pekkola).

Fig. 65. Typical form, showing 2 blepharoplasts.

Figs. 66—68. Uninucleate, binucleate, and quadrinucleate (mature) cysts, respectively.

Figs. 69 — 71. Trichomonas hominis.
Fig. 69. Small individual, with 3 anterior flagella.
-Fig. 70. Large individual, 3 anterior flagella (" Trilrichomonas").
Fig. 71. Individual with 4 anterior flagella (" Tetratrichomonas ").

Figs. 72, 73. Embadomonas inlestinalis.
■Fig. 72. Active flagellate.
Fig. 73. Cyst.

FiS?s- 74—77- Chilomastix mesnili.
Fig. 74. Active flagellate, ventral view.
Fig. 75. Smaller individual, from right side.
Fig. 76. Individual seen antero-ventrally— to show the arrangement of blepharoplasts and organs

arising from them.
Fig. 77. Mature cyst. (Fixation : Bouin's fluid.)

Figs. 78—95- Cophozoic FLAGELLATES from human faeces.
Figs. 78—81. Bodo caudatus.
Fig. 78. Living organism— unstained.

Figs. 79, 80. Stained specimens. (Fixation : alcoholic picro-acetic.)
Fig. 81. Cyst, stained specimen.

Fig. 82. Bodo edax, active flagellate.
Figs. 83—85. Cercomonas longicauda.
Fig. 83. Living flagellate, creeping. Unstained.
T"ig. 84. Stained specimen.
Fig. 85. Cyst— living and unstained.

Figs. 86 — 88. Cercomonas crassicauda. l

Figs. 86, 87. Active flagellates (stained alcoholic iron-haematein).
Fig. 88. Cyst (stained as preceding).

Figs. 89, 90. Helkesimaslix faecicola, 2 flagellates.
Figs. 91—95. Copromonas subtilis.
Fig. 91. Ordinary flagellate.
Fig. 92. Dwarf form, from cultuie.
Fig. 93. Stage in longitudinal division.
Fig. 94. Early stage of conjugation.
Fig. 95. Cyst.

Fig. 96. Chlamydophrys stercorea.

^;s:s sia SfSs!>udopodia projecting through the she"

PLATE V.

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72

PLATE VI.

PLATE VI.
All drawings represent living and unstained specimens. Magnification 2,000 diameters
throughout.

Figs. 97 — 102. Isospora hominis.
Fig. 97. Oocyst with unsegmented protoplasm, as usually passed in stools.
Fig. 98. Later stage ; nucleus divided into two.
Fig. 99. Later stage ; protoplasm segmented into two sporoblasts.

Fig. 100. Fully developed oocyst, containing two spores— each containing four sporozoites.
Figs. 101, 102. Degenerate oocysts, which have failed to develop.

Fig. 103. Eimeria oxyspora.
A ripe oocyst, containing four fully-formed spores.

Fig. 104. Eimeria wenyoni.
A ripe oocyst, containing four fully-formed spores. (After Wenyon, 1915.)

Fig. 105. Eimeria snijdersi.
Ripe oocyst, with four fully-developed spores. (Combined from figures and specimens of
Dr. E. P. Snijders.)

PLATE VII.

PLATE VII.

Fig. 106. Balantidiitm coll. Active ciliate, semidiagrammatic. Living specimen, seen from
left side.

N. = meganucleus.
n. = micronucleus.
c.v.i = anterior contractile vacuole.
c.v.2 = posterior contractile vacuole,
f.v. = food vacuole,
mo. = mouth.
Magnification 2,000 diameters. (The sketch was
a P'R-)
Fig. 107. Balantidiitm mimtlnm. x 2,000. (Dr

description.) Ventral view.
Fig. 108. Nyctotherus faba. x 2,000. (Drawing

description.) From left side.
Fig. 109. Balantidiitm coli. x 1,000. Specimen from stool of a human case of Balantidiosis.

Fixed sublimate-alcohol, stained Heidenhain's iron-haematoxylin.
Fig. no. Balantidiitm coli. Cyst, x 1,000. Living; from faeces of pig.

Fig. ill. Part of the periphery of a Balantidial Ulcer: colon' of human case of balantidiosis.
x 50. (Section stained iron-haematoxylin and orange G.) Above and to the right, the
cavity of the ulcer, filled with necrotic tissue : below and to the left, numerous balamidia
in the submucous tissue.
[Figs. 109-III from The Practice of Medicine in the Tropics.']

made from an individual in the faeces of
wing made from Schaudinn's figures and
from Schaudinn's figures and

109

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PLATE VIII.

Semi-diagrammatic figures of the CYSTS OF the chief intestinal protozoa of man.
These figures have been made as aids to diagnosis. They are not drawn from actual specimens,
but are not "diagrammatic" in the sense that they are unlike the objects which they are
intended to depict. On the contrary, they have been drawn to look as much like the actual
objects as possible. (Cf. Preface, p. vii.) Magnification 2,000 diameters throughout.

The left-hand panel of the Plate shows the cysts as they appear when alive and

UNSTAINED.

The middle panel shows the same cysts as they would appear when mounted and
examined in iodine solution.

The right-hand panel shows the same cysts as they would appear when fixed and

STAINED WITH IRON-HAEMATOXYLIN.

Each cyst is labelled with the same letter throughout, but is distinguished by a different
index number (1, 2, or 3) on each panel of the plate. Fig. A, for example, is marked A1, A2, A3,
according as it represents the same cyst alive (A1), in iodine (A2), or after fixation and staining
(A3). The cysts are shown lying in the same position in each figure, so that they can be
readily compared.

Figs. A, B, C. l-nucleate, 2-nucleate, and 4-nucleate cysts respectively of Entamoeba histolytica

— a strain with cysts ca. I2,u in diameter.
Figs. D, E. i-nucleate and 4-nucleate cysts of E. histolytica— -strain with small cysts, ca. 7-5^

in diameter.
Fig. F. Mature (l-nucleate) cyst of Iodamoeba biitschlii.
Figs. G, H, I. i-nucleate, 2-nucleate, and 4-nucleate cysts respectively of Endolimax nana.

(H is a cyst containing a lump of glycogen.)
Fig. J. Mature (i-nucleate) cyst of Chilomastix mesnili.
Figs. K, L, M, N. i-nucleate, 2-nucleate, 4-nucleate, and 8-nucleate cysts respectively of

Entamoeba coli.
Fig. O. A specimen of Blastocystis hominis — for comparison.
Fig. P. A 4-nucleate cyst of Giardia intestinalis.

PLATE VIII.

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