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U. S. : MT OF AGRICULTURE,

BURKAF ov CHEMISTRY— BULLETIN No. 14&

\N ILKY. CHIBP or BUBKAV.

RECAP

IPTE TOXTOTTY OF CAFFEIN:

AN EXl^ERIMENTAL STUDY

().\ I'il'FERENT SPEClfes OF ANIMALS.

BY

WHiLLLM S.\LANT,

Chief rharniucologicnl Lnfjoralonj, D-iviMon of Drugs ,

AND

J. B. RIEGER,

Assistant f^- ,-"'-'

"'^i^^l^^^

GOVERNMENT PRINTING OPPIOE.

ja^SiiXi

^a35)

Columbm ®nitJers(ttp
intljeCttpoflfttigork

College of ^fjpsiciansf anb ^urgeonsf
Hifararp

1ksik-<1 April 1, 1'J12.

U. S. DEPARTMENT OE AGRICULTURE.

BUREAU OF CHEMISTRY— BULLETIN No. 148.

H. w. WILKY, t;HiKF OK Bureau.

THE TOXICITY OF CAFFEIN:

AN EXPERIMENTAL STUDY

ON DIFFERENT SPECIES OF ANIMALS.

WILLIA.M SALAXT,

Chief Pharmacological Laboratory, Division of Drugs,

AND

J. B. RIEGER,

Assistant Chemist.

WASHINGTON:

GOVERNMENT PRINTING OPPIOE.

1912.

LEHER OF TRANSMITTAL,

U. S. Department of Agriculture,

Bureau of Chemistry,
Washington, D. C, November 1 4, 1911.
Sir: I have the honor to submit for your approval a manuscript
on the toxicity of caffein, which is the first of a series of reports to
be made by Dr. Salant on the pharmacology of this drug; the con-
clusions here reported are, therefore, in some particulars to be
regarded as tentative. The data obtained are primarily of use in the
execution of the food and drugs act, but are capable of much broader
apphcation.

Acknowledgment is made of the assistance rendered by Dr. John
R. Mohler, Cliief of the Pathological Division, Bureau of Animal
Industry, and his assistants, in performing the autopsies recorded in
this report. I recommend the publication of the manuscript as
Bulletin No. 148 of the Bureau of Chemistry.
Respectfully,

H. W. Wiley, Chief.
Hon. James Wilson,

Secretary of Agriculture.

nPHIS PUBLICATION may be pro-

-*- cured from the Superintendent of

Doctunente, Government Printing Office

Washinglon, D. C, at 15 cents per copy

CONTENTS.

Pago.

Tiilroduction 5

Historical review of the literature on the toxicity of caffein 9

Acute caffein intoxication 18

Experiments on rabbitH 18

Subcutaneous injection 18

Administration by mouth 2G

Injection into the peritoneal cavity 28

Intramuscular injection 33

Intravenous injection 37

Summary 42

Experiments on guinea pigs 43

Subcutaneous injection 43

Injection into the peritoneal cavity 47

Administration by mouth . . 49

Summary ' 52

Experiments on cats 53

Subcutaneous injection 53

Injection into the peritoneal cavity 56

Administration by mouth 57

Summary 59

Experiments on dogs 60

Administration by mouth 60

Subcutaneous injection 60

Experiments on puppies 61

Summary 62

Chronic caffein intoxication 63

Experiments on rabbits 63

Experiments on dogs 75

Discussion of results 91

General summary and conclusions 95

Bibliography 97

3

THE TOXICITY OF CAFFEIN.

INTRODUCTION.

Comparative physiology lias established the fundamental fact that
some properties are common to all forms of living matter. But the
same method of inquiry has also led to the recognition of marked
differences in the physic^logical processes of various species of animals.
Among tlie most important investigations which contributed to the
knowledge of such variation of function are the studies in comparative
metabolism. It is now recognized that metabolism is in some
resj^ects cpiite different in herbivora and in carnivora. Some forms
of oxidation are much greater in the rabbit than in cats and dogs.
Nuclein metabolism presents important differences in the rabbit and in
man, while the mode of neutralizing acid in the body may be cited as
another variation in the metabohsm of these forms. Perhaps the
most striking examples of differences in the metabolism of different
organisms is furnished by the results of studies on the fate of certain
poisons introduced into the body.

The classical experiments of Bunge and Schmiedeberg^^ '^on the syn-
thesis of hippuric acid are of interest in this regard. It will be recalled
that in the dog the synthesis takes place in the kidney ; the rabbit is able
to form hippuric acid in the liver as well as in the kidney, while frogs
can synthesize hippuric acid even when both of these organs have been
removed or excluded from the circulation. Observations on the fate
of some of the alcohols of tlie fatty acid series have likewise s]lo^^^l that
these substances maybe combined with glycuronic acid in some animals
but not in others. According to Thierfelder and Von Mering, ^* ter-
tiary alcohols are combined in tliis manner in the rabbit but not in the
dog. According to Neubauer,®^ the primary and secondary alcohols
are so combined in the dog as well as in tlie rabbit, but to a greater
degree in the latter.

Pohl '^ found that amyl alcohol is largely eliminated by the lungs in
the cat and in the dog. The protocols of liis experiments show that
65 per cent of the alcohol given these animals was thus recovered,
while he recovered only 22 per cent of this substance in the expired
air of the rabbit. Examination of me urine showed the ])resence of
glycuronic acid. Hofmeister's ^^ work with tellurium in the dog is of

a The small Tigures refer to the bibliography at the end of this bulletin.

6 THE TOXICITY OF CAFFEIN.

interest in this connection. He made the important discovery that
some animals possess the power of methylation as well as of demethyl-
ation. Abderhalden and Brahm's ^ experiments with pyridin show
that the same is true of young dogs when on a meat diet. His experi-
ments on rabbits with this substance were negative.

The metabohsm of oaffein and theobromin furnisli another illustra-
tion of differences in the physiological mechanism of animals. Al-
though the substances foutid in the urine of man, dog, and rabbit after
the administration of caffein and theobromin were the same, the quan-
tities varied considerably. According to Krtiger and Schmidt," over
14 per cent of the theobromin introduced into the rabbit is eliminated
as 7-methyl xanthin in the urine. The dog eliminates only about 0.67
per cent. On the other hand, the amount of tri-methyl xanthin elimi-
nated was only 3 per cent in the dog and not quite 1 per cent in the
rabbit.

It appears, therefore, from studies in comparative metabolism,
whether endogenous or exogenous, that well-marked physiologic and
chemical differences exist in various species of animals. That phar-
macological action may likewise vary in different species of animals
is shown by the following investigations. According to Guinard,^^
who made an exhaustive study of morphin, the reaction to this alka-
loid varies in different forms of life, both qualitatively and quanti-
tatively. He established its narcotic effect in the dog, rabbit, guinea
pig, white mice, and rats, while for the cat, horse, ox, sheep, hog, and
goat it is, on the contrary, a stimulant. Moreover, there is no evi-
dence of cerebral effect. The stimulating effect of morphin on the
nervous system in some animals was also observed by Noe ^^ in experi-
ments with this substance on the hedgehog.

Guinard ^^- ^° has also shown that morphin has no narcotic effect in
the marmot, although this animal is very sensitive to the drug. Two
milligrams per kilo were found to be a surely fatal dose for this animal.
His experiments on the comparative toxicity of morphin ^" ^^ show a
considerable range of variation in different species. Thus the fatal
dose for the dog was found to be 0.65 per kilo, while 7 mg per kilo is
the fatal dose for the horse. About twice the amount is fatal for the
ox and 0.2 mg per kilo kills the pig. Experiments with other drugs has
shown that a considerable range of variation in resistance exists in
animals of different species.

Noe's "•'' studies on the comparative toxicity of chloral brought out
the interesting fact that the rabbit is more resistant to it than the
hedgehog and the latter more resistant than the guinea pig. Per-
haps the most striking example of a difference in reaction of the
same substance in widely different species is that furnished by
apocodein, quinin, and yohimbin. According to Gunn^^ these sub-

INTRODUCTION. 7

stances have been found to cause vasodilation in warm-blooded
animals, but they constrict the blood vessels of the frog.

Experiments with upomorjihin likewise show that the reaction to
this substance varies in dillVrent species of animals. The resistance
of the cat to this drug is, accortling to Guinard,^' ten times greater than
that of the dog, and the latter is more sensitive than the rabbit to
the ciystalline form of apomorphin when given intravenously.
According to Robert *■' amygdalin is without effect on dogs, but it
is poisonous to rabbits. Lapicque *" found that the toxicity of
curara varies in different species of frogs, the dose required to pro-
duce paralysis in Rana esculenta being three times greater than in
Bufo vulgaris. Weir Mitchell ^° pointed out long ago that turtles
stand enormous doses of curara. Sclimiedeberg's experiments with
cafTein on Rana temporaria and Rana esculenta (and more recently
those of Jacobi and Golowinski ^^ with caffein, theobromin, and
theophyllin) are also of interest in this connection. These experi-
menters observed well-marked differences of reaction to methyl-
xanthins in these closely allied forms.

Experiments with quinin have shown that the action of this sub-
stance differs in some animals. It causes a fall of temperature imme-
diately after its administration in the guinea pig, but frequently
produces, at first, a rise of temperature, followed by an unimportant
fall, in rabbits, dogs, and man.

The numerous investigations which have been carried out on the
effect of atoxyl within recent years have contributed much to the
comparative pharmacology of this substance. Although the symp-
toms and organic changes produced by this substance in a variety of
animals present no great differences, the resistance of some has been
found to vary; according to Koster**' it is more toxic for dogs than
for rabbits. A number of other substances have been found by
various experimenters to vary in toxicity for dift'erent species of
animals. Cantharadin, phenol, atropin, and strychnin may be men-
tioned as illustrations.

Pharmacological studies on lower forms of life have also revealed
marked variations in the effect of some poisons. Observations made
by Danilewski/^ with hydrochinone indicate that solutions of 1 to
100 or 200 are toxic to Celentrates, causing paralysis in these organ-
isms. Echinoderms are killed within one or two hours in 1 to 1,000
or 2,000 solution, while in Vermes even weaker solutions cause
tetanus and finally paralysis. The experiments of Drzewina^® with
potassium cyanid are also interesting in this connection. Teleosts
placed in 100 cc of sea water containing twentieth-normal potassium
cyanid showed signs of asphyxia and died in 10 to 20 minutes.
Actinia placed in a solution of sea water containing five times as
much potassium cyanid were active on the thirteenth day of the

8 THE TOXICITY OF CAFFEIN.

experiment. Similar results were obtained with other marine
organisms.

From these data it is evident that the toxicity of a substance may
vary considerably in different forms of life. It has been shown also
by some investigations cited by Salant^^ that the action of drugs
may be modified by different conditions in the environment as well
as in the subject of the experiment. The recognition of the import-
ance of these factors in determining pharmacological action has con-
tributed much to the elucidation of the mechanism by which drugs
and other substances produce physiological effects in the body. More-
over, such knowledge has often enhanced the therapeutic value of
pharmaco-dynamic agents and has frequently served to avert effects
of an undesirable character in man and domestic animals. The results
obtained in one species of animals under a particular condition do not
admit, therefore, of universal application. Furthermore, the nature
of the action of a drug can only be partly learned from the manifes-
tation of its acute effects. Equally important, therefore, especially in
studies on toxicity, are the changes produced in chronic intoxication.

That the acute effects of a substance can hardly be considered a
correct estimate of its toxicity is shown by the evidence obtained in
experiments on tolerance and cumulative action of drugs; for the
toxicity of a substance may diminish when the substance is given
steadily for a long time if the body acquires tolerance for it. Arsenic,
morpliin, and cannabis indica may be cited as illustrations of drugs,
the toxicity of wliich decreases with repeated doses, wliile digitalis
and lead show a tendency to increased toxicity when similarly
administered. Moreover the acute and chronic effects are sometimes
qualitatively different. According to Igersheimer *^ the symptoms
in acute atoxyl intoxication are nausea, vomiting, and diarrhea.
These symptoms are absent in clironic intoxication, in wliich trophic
disturbances of the skin and inflammation of the mucous membranes
were the effects produced. That the acute action of atoxyl differs
from the chronic effects was likewise shown by experiments on ani-
mals. The studies of von Anrep ^ on cln-onic atropin intoxication
are of interest in tliis connection, as he found that after 10 to 15
injections of atropin there is no manifestation of symptoms such as
is observed in acute intoxication, while the effects on the circulation
are also less marked, the acceleration of the pulse being less than
after the same dose in a normal subject not accustomed to its use.
Wlien the administration of atropin is continued for a longer time
its usual effects on the pulse disappear altogether; there is, on the
contrary a decreased frequency of the pulse. If atropin has been
administered for from two to three weeks, respiration is likewise
affected.

HISTORICAL REVIEW. 9

mSTORICAI REVIEW OF THE LITERATURE ON THE TOXICITY

OF CAFFEIN.

CafFein was discovered in 1820 by Runge," Pelletier,"' and Robi-
quet '* and was first analyzed by Dumas and Pellctier,^" but its
exact percentixge composition was detemiined by Pfaff and Liebig,
71. 72 ^vhile to Herzog *^' " belongs the cre<lit of having esta])lished
that it is basic. Strecker ^- prepared caffein synthetically by lieating
theobromin silver and methyl iodid in a closed tube for 24 hours.
Soon after its discovery in coffee Oudry " reported the presence of
a substance in tea wliich he called "thein." Its identity with cafTein
was established 15 years later by Jol)st ""^ and also by Mulder. ^-' ®^
According to Brill/^ Mulder (1838) was also the first to perform
experiments with caffein on animals. After the administration of
one-half grain to a j^regnant rabbit he observed loss of appetite and
ky}:)hosis. The rabbit aborted but recovered from the effects of
caffein. It has since been made the subject of numerous investiga-
tions which were carried out on a variety of animals. Observations
with caffein were also made on the human subject. About four
years after Mulder pubhslied his results, Lehmann *^ (1842) rei)orted
experiments on a number of people who were given caffein. The
administration of fi-om 2 to 10 gi'ains of the alkaloid was followed bv
headache, palpitation of the heart, increased frequency and irregu-
larity of the pulse, tinnitus aurium, photopsia, insomnia, and even
dehrium. Similar experiments reported by Frerichs " (1846) indi-
cate that in doses of 25 grains it may induce severe symptoms about
15 minutes after its administration. He also observed circulatory as
well as nerv'ous symptoms and vomiting.

According to Albers - (1852), 4.5 grains of caffein citrate injected
subcutaneously into the thigh of a rabbit was soon followed by dimin-
islied motion and tremors of the operated thigh. Other symptoms
reported were spasms of the facial muscles, increased resj)iratory
movements, and mental confusion. Of interest in this connection
are tlie experiments of Cogswell^^ (1852) on frogs. He concluded that
in point of destructive action on the tissues, caffein is far superior
to morphin and may be compared to stryclmin and coniin, its action
on the nervous system he beheved to be principally confined to the
effect on the brain and spinal cord.

Lehmann" (1853) observed increased frequenc}^ of heart action
after the acUninistration of 4 grains, wliich were given with a normal
diet to an adult man. Wlien the dose was doubled the frequency of
the pulse was stiU more increased, heart action became stronger, and
tremors and confusion of thought with excitement of the imagination
made their appearance. There was also an increased desire to
niicturate.

10 THE TOXICITY OF CAFFEIN".

Stuhlmann and Falck ^^ (1857) were the first to make a study of
the toxicity of caffein on animals of different species. The adminis-
tration of 0.5 gram of caffein subcutaneously or per rectum in rabbits
induced tremors, tonic and clonic convulsions, paralysis, and increased
frequency of respiration at first followed by violent dyspnoea. On
autopsy he noticed congestion of the organs and in two of the three
rabbits experimented upon punctiform hemorrhages of the brain with
congestion of the meninges were found. In the other rabbit anemia
of the brain was observed. Experiments on cats were carried out
by subcutaneous, intravenous, and rectal injections. The symptoms
observed after the administration of 0.5 -to 0.7 gram of caffein were
the same as in rabbits except that the cats developed diarrhea when
caffein was given and no anatomic lesions were found on autopsy.
The effect of caffein on dogs indicated that in subjects of medium
weight a dose of 0.5 gram given by mouth might produce restlessness
and increased frequency of respiration, while the injection of the
same amount intravenously into such animals may cause death.
Large, full-growm dogs, however, survived an intravenous injection
of 2 grams of caffein, showing symptoms of incoordination, salivation,
and frequent defecation. These investigators also made observations
on caffein, using pigeons and other birds; 0.5 to 0.1 gram introduced
into the stomach caused vomiting, diarrhea, tonic, but more fre-
quently clonic, convulsions, incoordination, tremors, paresis, and
paralysis.

In a few, but not in all of the birds, there was at first increased
frequency of respiration followed by dyspnoea and circulatory dis-
turbances. These amounts of caffein proved fatal in all of the experi-
ments on birds. Inflammation of the intestinal mucosa and conges-
tion of the meninges were the only changes found on autopsy.
Stuhlmann and Falck also studied the effects of caffein on fishes and
toads. Mitscherlich ""^ (1858) fed 0.4 gram of caffein with bread to a
rabbit and noticed lowered temperature, fatigue, convulsions, first
increased then decreased frequency of respiration, and on autopsy
congestion of all the viscera. He also reported observations on two
frogs, one of which was given one-sixteenth of a grain of caffein in a
pill with bread. It was administered to the other frog in aqueous
solution, but the mode of administration was not published. The
symptoms observed were in the main the same as in rabbits. In
pigeons 0.125 gram introduced into the stomach caused severe vomit-
ing, muscular incoordination, tonic rigidity of the limbs, and retrac-
tion of the head. Respiration was increased in frequency. Death
followed within 3 hours and 15 minutes.

From a series of experiments on frogs wliich Hoppe '^ carried out
(1 858) by applying one-fourtli of a grain of caffein to the muscles of
the back, he concluded that caffein causes paralysis of the nerves,

HISTORICAL REVIEW. 11

spinal cord, and brain, sensation being paralyzed before movement.
The injurious action of caffein proceeds, according to Hoppo, from
the spinal cord. This was based on experiments on two frogs, Rana
esculevta, in which the right h'g was am])utat(Ml, the nerve being left
intact, while the nerve of the other leg was hgated. At the end of
30 minutes paralysis was more marked on the right than on the left
side. In anotlicr frog of the same species he resected the femoral
nerva on the right side; about 1^ hours after the administration of
cafTcin convulsions were observed. The left leg was rigid, but the
right was relaxed.

Voit ^' (1860) ligated the vessels of the right lower extremity, cut
the nerves of the left leg, and introduced a few drops of cafTein
solution into the stomach. Shortly afterwards tetanus of the rig] it
leg occurred on toucldng the back of the animal; the left leg was
motionless. Later the entire body exliibited tetanic convulsions.
From this and similar experiments Voit concluded that cafFein acts
first and principally on the central nervous sj^stem, and that cafFein
is also poisonous to nerve and muscle fibers, as they die when a solution
of caffein is applied to them. The action of caffein, according to
Voit, is similar in great part to that of strychnin. The effect on the
blood vessels is particularly interesting, as Voit observed dilatation
of the vessels, due as he thought to muscular paralysis, and also trans-
udation and congestion of the capillaries.

Kurzak ^^ (1860) made a study of the comparative toxicity of
caffein in frogs and rabbits and came to the conclusion tliat the lethal
dose for frogs is about one-seventh of that for rabbits. Caffein
citrate in the form of crystals was administered in both cases by
mouth. The doses given to frogs were 1 to 1..5 grains. lie observed
convulsions and increased respiratory activity at first; after one hour
respiration diminislied and voluntary muscular activity disappeared.
Even on the second day convulsions were sometimes noticed. Death
occurred at the end of the first or second day. Experiments on
only two rabbits were reported, 0.8 gram of cafFein citrate causing
the death of one at the end of 13 hours. The symptoms noticed were
the same practically as in frogs, but it is interesting to observe that
ecchymosis of the mucous membranes of the stomach near the cardia
was the only lesion found on autopsy. Several experiments made
on different days on the other rabbit inchoated that the toxic
dose exceeded 0.5 gram, while smaller doses caused but very mild
symptoms.

According to Gentilhomme " (1867), after cafFein the reflexes are at
first diminished and then disappear altogether. Death is produced
by stiffness and immobility of all the muscles, particularly of the
muscles of respiration, thus causing asphyxia. He furthermore held
that caffein has no effect on cardiac or smooth muscle fiber, its action

12 THE TOXICITY OF CAFFEIN.

being specific on voluntary muscle fiber, contractions of which he
observed under the microscope, thus differing completely from strych-
nin, which is a nerve poison.

These observations seemed to be confirmed by Pratt '•* (1868), who
reported that the isolated posterior extremities and muscle fibers of
the toad placed in a solution of caffein (1 grain to a wineglassful of
water) for three minutes were contracted, while controls placed in
distilled water were relaxed. This experiment is, of course, defective,
as normal salt solution should have been used in both cases. ^'\nien
the muscular fibers previously immersed in caffein solution were
placed under the microscope violent contractions were observed.
The same author administered from 2 to 18 grains at a dose to five
healthy young men. After the administration of 12 grains he noticed
mental anguish, tremors of the hands and arms, and insomnia.
Doses under 5 grains had no marked effect except a diminution in the
frequency of the pulse and wakefulness.

About the same time Amory * (1868) published the results of his
Studies on the toxicity of caffein in cats, dogs, rabbits, and pigeons.
In all cases very large doses were introduced directly into the stomach
by means of a temporary gastric fistula. Ten grains given in meat
to a dog caused restlessness, but no other symptoms. Doses of 30
grains and above were invariably fatal. Seventy-three grains given
to a cat caused death within 20 minutes.

From observations on frogs, guinea pigs, rabbits, and on one dog,
Leven ^^ (1868) concluded that caffein which he gave in the form of
the citrate in doses of 10 mg to frogs, from 150 to 200 mg to guinea
pigs, and three to four times the latter amount to rabbits, stimulates
the central nervous system and the voluntary, cardiac, and smooth
muscles. He found that 0.9 gram caffein was fatal for a rabbit when
injected subcutaneously, while 1 gram of the citrate was not toxic
for a dog of medium size. Caffein applied directly to muscle fiber
causes tetanus and destroys muscular contractility, while a nerve
fiber similarly treated loses its irritability.

According to Johansen *■* (1869), caffein acts directly on the mus-
cular fiber. After the subcutaneous injection of 0.02 gram of caft'ein
into frogs, he observed contraction of the muscles at the site of injec-
tion, then contraction of the anterior extremities, and finally the
posterior extremities become rigid and extended. Johansen obsei-ved
muscular rigidity after caffein, even after curara was injected, or after
ligating the vessels, or cutting the nerves which supply the muscles.
He also observed that large doses of caffein diminish muscular irrita-
bility. When cardiac muscle was poisoned with caffein, microscopical
examination showed that the striations disappeared. Johansen also
states that reflexes disappear after caffein poisoning. He never
observed tetanus in frogs, but reported tonic and clonic convulsions a.s

HISTORICAL REVIEW. 13

a result of cafTeiii poisoning in mammals. Somewhat dilTercnt cd'ccts
of caffein in frogs were obsei-ved by Buclihcim and Eisenmengor ^*
(1870). After the injection of 2 per cent of the citrate the frogs soon
become inactive. lie also observed muscular twitching of the
extremities, which gradually increased, with rigidity of the muscles
and opisthotonos, while respiration became slow and superficial,
finally stopping altogether.

Aubert " (1872) studied the toxicity of caffein in man and other
animals. After the ingestion of 0.36 gram, he obsei-vcd dizziness,
but doses of 0.12 and 0.24 gram were without any apparent effect.
On the other hand, a dose of 0.5 gram of caffein was followed by
increased frequency of the pulse, which soon disappeared. After one
hour he noticed dizziness and trembling of the hands, which likewise
passed away soon. The injection of 0.16 gram of a 2 per cent solution
of cad'ein into the jugular vein of a rabbit weighing 1,090 grams
caused tetanus and death in two and one-half minutes, and 0.12 gram
injected into a rabbit weighing 980 grams caused death in one minute.
Much larger doses could be borne, however, when artificial respiration
was resorted to. A dog which was given 3 grams of caflein survived
when artificial respiration was performed. Aubert reports, on the
other hand, a similar experiment with 0.25 gram of caffein which
terminated fatally.

That caffein may give rise to different effects in various species of
animals was observed for the first time by Bennett." lie studied its
action on frogs, mice, rabbits, and cats, and attempted to determine
the minimum fatal dose in rabbits and cats. He also reported experi-
ments with tliein. In his first communication on the subject he
states that the administration of thein to rabbits first increased and
then diminished the frequency of respiration, while the pulse was
decreased in frequency. Caffein, which he apparently thought was
different from thein, caused increased frequency of respiration, while
the pulse was markedly retarded after a preliminary acceleration.
He also noticed congestion of the ears, muscular incoordination,
tetanus, paralysis, diminished reflexes, and contraction of the pupils.
Bennett reported the minimum fatal dose of caffein for a rabbit weigh-
ing 3.25 pounds as being 5.25-5.5 grains. The symptoms in cats
after the administration of toxic doses of thein or of caffein were
groat excitement, paralysis alternating with convulsions, and profuse
salivation. The mmimum fatal dose for a cat weighing 5 pounds
was, accordmg to Bennett, 6 grains of caffein and 5.5 grains of theia*
Only one experiment on a mouse is reported; the administration of
0.1 grain proved fatal. The symptoms were the same as those
observed in cats and rab])its after the admmistration of caffein. The
experiments on frogs indicate that the symptoms were about the
same as those previously described in the case of warm-blooded ani-

14 THE TOXICITY OP CAFFEIN.

mals except that the reflexes are almost completely lost after the sub-
cutaneous injection of doses of one-sixteenth to one- twelfth of a grain.
The latter dose was fatal for frogs. It would be of interest to know
the comparative toxicity of caffein to frogs and mammals, but unfor-
tunately the weights were not reported.

Schmiedeberg '^ (1874) noticed that the administration of 20 mg of
caffein to frogs weighing about 45 grams was followed, in Rana escu-
lenta, in about 25 minutes, by increased reflexes, 7 minutes later
by tetanus. Several attacks occurred, but tonic spasms were never
observed. On the contrary, when the same amount of caffein was
given to Rana temporaria weighing 45 grams he noticed a marked
diminution of the reflexes and tonic rigidity of the muscles after 23
minutes ; the reflexes were greatly increased, however, about 24 hours
later. The frogs were under observation for three days, and although
symptoms were still present at the end of this time in the subjects of
both species tetanus was never observed in Rana temporaria.

Peretti's '"^ (1875) studies on the effects of caffein were confined
chiefly to observations on dogs. He also made observations on a
few rabbits and reported an experiment on one cat to which he admin-
istered, by subcutaneous injection, 0.18 gram of caffein per kilo and'
noticed increased frequency in lachrymation and crying. The cat
was found dead the next day. The subcutaneous injection of a rabbit
in which artificial respiration was instituted with 0.36 gram of caffein
per kilo proved fatal soon after the injection without any manifesta-
tion of symptoms. Small doses of caffein, 0.1 gram, given to a rabbit
weighing 3,670 grams, failed to produce any visible effects. Doses
under 0.1 gram per Idlo Hkewise failed to induce any symptoms in
dogs. When 0.1 gram of caffein per kilo was given by mouth or sub-
cutaneously it was followed by restlessness, salivation, rigidity of
hind legs, and vomiting. In both instances the dogs recovered. The
symptoms were more severe when the dose was increased to 0.185
gram per kilo, but even in this case the dog recovered. A dose of 0.2
gram per kilo, however, proved fatal.

Henneguy ^^ (1875) experimented on three frogs to which he gave
0.01 gram of caffein citrate subcutaneously. He observed mild stim-
ulation of the nervous system and of the muscles, as well as increased
cardiac activity. Later, voluntary movement and respiration disap-
peared and sensations diminished, but convulsions of the extremities
appeared. Cardiac activity was then diminished, the heart being
finally arrested in systole. Since the motor nerves retained their irri-
tability even after the reflexes disappeared, he concluded that the
loss of motion was due to the action of caffein on the nerve centers.

Binz " (1878) reported experiments on dogs and also made some
observations on man with caffein. The subcutaneous injections of
0.2 gram caffein may prove fatal to dogs, although some survive such

HISTORICAL REVIEW. 15

a (lose. TJio toxic dose in man varies from 0.5 to 1.5 grams. Dis-
turbance of the circiilation, such as palpitation of the heart and full-
ness of pulse, restlessnass, and diarrhea were the symptoms he
observed.

Extensive investi^rations on the action of caffein were carried out
by Leblond^" (1883), who studied its effect on the circulation in man
and lower animals, and its toxicity in the lower animals alone. Five
to twenty centigrams of caffein and 0.06 to 0.25 gram of salicylate of
soda were dissolved and injected into the muscles of the thigh of
young guinea pigs weighing a little over 300 grams. In the three
experiments reported the death of the animals occurred after 23 min-
utes, 40 minutes, and 1 hour and 20 minutes. Symptoms appeared
in from 10 to 15 minutes after the injection of caffein. Incoordination
of movements, convulsions, both tonic and clonic, opisthotonos,
tremors, increased frequency of respiration, ataxia, paralysis were
the symptoms observed. It is worthy of note that the appearance
of paresis preceded the convulsions. Diminished sensation was
reported in one pig, but no sensory disturbances nor reflexes had been
observed in the other. Two rabbits, one of wliich received 0.5 and
the other about 0.3 gram of caffein per kilo with equal parts of sali-
cylate of soda, were injected subcutaneously into the thigh. Dimin-
ished sensation, paresis of the posterior extremities, hyperexeita-
bUity, convulsions, opisthotonos, dilation of the veins of the ear were
observed. Death followed in 1 hour and 23 minutes in one rabbit
and in 3 hours and 7 minutes in the other.

Filehne " (1886) experimented with caffein on Rana esculenta and
Bana temporaria. The subcutaneous injection of 7 mg of caffein into
Rana esculenta caused tetanus, while 50 mg given by mouth caused
tonic spasms. He further stated that the difference between Rana
esculenta and Rana temporaria as regards the reaction to caffein was
one of degree only.

Amat ^ (1889) reported experiments on three guinea pigs, in which
0.4 to 0.5 gram per kilo injected subcutaneous!}^ proved fatal ^vithin
38 and 44 minutes. One guinea pig which received 0.1 gram of
caffein per kilo survived. The symptoms observed in the two fatal
cases were gcnei-al muscular rigidity and convulsions.

Parisot ^^ (1890) made a study of the toxicity of caffein on different
species of animals. Unlike most of his predecessors, however, he
reported, at least in some cases, the weight of the animals on which he
worked. iVfter the subcutaneous and intramuscular injections of
from 5 to 20 mg of caffein into Ranu temporaria weighing from 14 to 16
grams, he noticed increased irritability at first; later, a loss of reflexes,
inabihty to use the nmscles, complete muscular rigidity resembhng
rigor mortis, and also cessation of heart action. The effect of caffein
})roduced in the green frog was analogous to that observed in

16 THE TOXICITY OF CAFFEIN.

strychnin poisoning. Parisot found, however, that muscular rigidity
developed, although very gradually, also in the green frog, but it set
in much later than in frogs of the other species and without super-
seding -the clonic convulsions. According to Parisot, the muscular
rigidity after cafl'ein persists after the destruction of the brain and
spinal cord, thus showing that it is not of nervous origin. He further
emphasized the difference in the behavior of these two species of frogs
toward caffein by stating that he never observed tetanic convulsions
in the red frog. His experiments also indicate that the green frog is
more resistant to caffein than Rana temp'oraria, as the same doses
which are fatal for the latter were only toxic for Rana esculenta.
The number of experiments, however, is too few to justify a positive
conclusion on this point. Parisot also made some experiments on
turtles. The results he obtained show that caffein is at least as toxic
for these animals as for the frogs he experimented upon, 0.33 gram
per kilo (carapace not included in weight) having proved fatal within
24 hours. Two experiments on one pigeon were also reported by the
same observer; two doses of 0.06 gram per kilo given at an interval
of four hours caused mental depression and muscular rigidity, but the
pigeon survived.

Experiments with caffein on the human subject made by Parisot
showed that man is far more susceptible to this substance than the
other animals he investigated. After the ingestion of 0.3 gram of
caffein symptoms of intoxication pointing to cerebral disturbance
appeared, which became more marked when the size of the doses was
increased.

It will be noticed that the nature of the action of caffein, whether it
is a nerve or a muscle poison, formed the subject of several investiga-
tions. Binz " (1890) brought forward additional evidence in support
of the view that caffein acts primarily on the ganglion cells, and not on
the muscle directly. This he has shown by injecting 0.5 gram into
each of two rabbits after cutting the sciatic nerve on one side ; in one
case he also resected the obdurator and crural nerves on the same side.
Clonic spasms developed in both subjects soon after caffein was given,
but in each rabbit the side operated upon remained paralyzed.
Baldi ^ (1891) studied the action of caffein on Rana esculenta. After
injecting from 4 to 20 mg tetanus, such as observed in strychnin
pois(ming, was noticed. Frohner ^^ (1892) made observations on the
comparative toxicity of caffein in domesticated animals. After the
administration of 5 grams of caffein sodium salicylate by mouth to a
dog weighing 10 kilos, he noticed salivation, restlessness, vomiting,
and convulsions as in strychnin poisoning. Death occurred three
hours after the drug wasgiven. On autopsyhe noticed mild inflamma-
tion of the mucous membranes of the stomach and intestines and
edema of the lungs; the heart was in diastole. A dose of 2 grams of

HISTORICAL REVIEW. 17

cafTein sodium salicylate given to the same animal subcutaneously two
days previously provoked only very slight symptoms. The sub-
cutaneous injection of 10 grams of the same preparation into a pig
weighing 30 kilos caused death in two and a half hours, with the pro-
duction of symptoms of disturbance of the nervous system and of
gastrointestinal irritation. The same dose per kilo of body weight
given to a goat likewise caused death in two and a half hours after its
administration. P^xammation on autopsy revealed inflammation of
the gastrointestinal tract. Similar lesions were found in a horse
killed by 100 grams of calTein, in which he also noticed hemorrhage
of the mucosa in the fundus of the stomach.

Gourewitch ^* (1907) conducted experiments with caffein on
rabbits, pigeons, and wliite rats. It appears from his protocol that
single doses of about 0.2 to 0.25 gram caffein per kilo given subcuta-
neously proved to be fatal. He states, however, that the resistance
to caffein was markedly diminished, when its administration was
repeated daily, for much smaller amounts sufficed to cause death in
these animals. A dose of 120 mg of caffein per kilo proved fatal after
the third injection. When the dose was increased to 170 mg per kilo,
the animal succumbed to the effects of caffein after the second injec-
tion. His experiments on the other animals do not indicate the
degree of resistance to caffein, since the weights for some were n<H
given while for the others no attempt was made to determine the
minimum toxic or fatal dose.

Maurel ^'^ (1907) studied the influence of different methods of
administration on the toxicity of caffein on frogs and rabbits. He
determined the minimum toxic and lethal doses of caffein hydro-
bromid which he employed in 1 to 2 per cent solutions. He concluded
from his experiments that the toxicity of caffein when given by
mouth is twice as great for the frog as for the rabbit.

More recently Hale •^' carried out a number of experiments on guinea
])igs in which he determined the toxicity of caffein given in the form
of the citrate and made into a pill with mucilage of acacia and arrow-
root starch. After the pill was dried it was fed to the animal, due
precaution being taken that none of it was lost during feeding.
From experiments on guinea pigs which received doses of ().;? to 0.6
gram caffein citrate, the following data have been reported: Tliree
decigrams per kilo given to one pig was not fatal. Of three pigs
which received 0.4 per kilo, one died and two survived. Exactly
the same results were obtained in three others which received 0.5 per
kilo. Two guinea pigs, which received 0.55 and 0.6 per kilo each,
died after 15 and 7 hours, respectively, while another animal survived
a dose of 0.45 per kilo.

18594°— Bull. 14&— 12 2

18 THE TOXICITY OF CAFFEIN.

This review of the Hterature on the toxicity of caffein, although
bearing evidence of considerable investigation and extending over
three-quarters of a century, i? largely qualitative in character. It
appears from the experiments that the main object of the investiga-
tions was to ascertain the nature of the action of caffein, whether it
is a muscle or a nerve poison. The comparative toxicity in different
species of animals by the accurate determination of the toxic and
fatal doses received but little attention. To fill the gap in our
knowledge of the toxic effects of caffein, the present investigation
was undertaken. This, it will be seen, proved to be a most laborious
task, because in the large number of experiments careful observations
showed that individuals of the same species varied considerably in
their reaction to the drug. Numerous other factors, as will be shown,
were also found to play an important part in the determination of the
toxicity of caffein.

ACUTE CAFFEIN INTOXICATION.

The object of these experiments was to determine the resistance
to caffein in various species of animals and by various methods of
administration. Caffein was therefore given by mouth and injected
subcutaneously into the peritoneal cavity, into the muscles, and in-
travenously. As far as could be judged by appearance, healthy ani-
mals were selected for the subjects of the experiments, but as it is
impossible to diagnose with any degree of accuracy the condition of
the animal while it is alive, post mortem examinations were resorted
to in many cases in which the issue of the experiment was fatal.
Since the age of the animal may modify toxicity full grown, as well
as young, animals were employed for these experiments; diet, race,
and season also play an important part in determining the toxicity
of a drug and these factors were also taken into account in the present
investigation.

EXPERIMENTS ON RABBITS.

Animals of different varieties were used and were given caffein by all of the methods
indicated in the preceding paragraph. Some of the rabbits employed in these experi-
ments received oats, others received a diet exclusively of carrots for several days or weeks
previous to the administration of caffein. The experiments were conducted at all sea-
sons of the year.

SUBCUTANEOUS INJECTION.

From a study of the literature on the toxicity of caffein it seemed that about 150 mg
per kilo is probably the lethal dose for the rabbit when the drug is injected subcuta-
neously. Preliminary observations were therefore carried out wilh such a dose, but
it was found, on the contrary, that this amount per kilo was hardly sufficient to induce
symptoms in the great majority of cases.

ACUTE INTOXICATION — RABBITS. 19

Series A.
(Doses of 147 to 107 inK of cafloln per kilo were employod in these experiments.]

Rabbit 3S2. Bclgicin hare, female. Weight, 1,070 grains. Diet, oats.

March 25: 8.5 cc 2 per cent caffein (158 mg per kilo) injected subculaneously at
2.15 p. m.; 4 p. in., reflexes increased; 5.45 p. m., increases of reflexes still more
marked .

March 2(;: Rabbit looked normal; no symptom.s observed.
Rabbit. 1^1. Belgian hare, female. Weight, 1,170 grams. Diet, oaLs.

March 25: 2.15 p. m., 9 cc 2 per rout caffein (153 mg per kilo) injected subcutane-
ously; 4 p. m., reflexes increa.sed; 5.45 p. ni., condition the same.

March 2(j: Rabbit looks normal; no symptoms observed.
Rabbit 3JS. Belgian hare, female. Weight, 1,300 grams. Diet, oats.

March 25: 9 cc 2 percent caffein injected subcutaneously (1-50 mg per kilo); 4 p. m.,
reflexes increased; 5.45 p. m., reflexes increased but not markedly.

March 26: No symptoms; rabbit looks normal.
Rabbit 322. White female. Weight, 1,065 grams. Diet, oats.

March 17: 8 cc 2 per cent caffein (150 mg per kilo) injected subculaneoiisly at 11.55
a. m.; 12. .55 p. m., reflexes increased, but no tetanus nor any oilier symptoms.

March 18: Rabbit running around in cage; condition apparently normal.

March 25: Condition of rabbit good.
Rabbit 217. White. Weight, 1,355 grams. Diet, oats.

October 29: 10 cc 2 per cent caffein (147 mg per kilo) injected subcutaneously at
1.51 p. m. 5.15 p. m., rabbit alive; survived.
Rabbit 219. Maltese. Weight, 1,S20 grams. Diet, oats.

October 29: 14 cc 2 per cent caffein injected subcutaneously at 1.40 p. m. (153 mg
per kilo); 5.15, rabbit alive; survived.
Rabbit 194. White female. Weight, 1,490 grams. Diet, oats.

October 14: 13 cc 2 per cent caffein (174 mg per kilo) injected subcutaneously;
increased reflexes and tremors were observed.

October 15: Condition of rabbit good; no symj^toms.
Rabbit 191. Brotvn male. Weight, 1,915 grains. Diet, oats.

October 14: 16 cc 2 per cent caffein (167 mg per kilo) injected subcutaneously;
reflexes increased and tremors present.

October 15: Condition of rabbit good.

A study of this series shows that about 150 mg of caffein per kilo caused increased
reflexes within one to two hours after injection. ^Vhen the dose was increased, as
in rabbits 194 and 191, the symptoms were more pronounced; 150 mg per kilo may
be regarded as the minimum dose which produces symptoms of nervous irritability
Avhen caffein is injected subcutaneously. Experiments with larger doses were there-
fore carried out in order to determine the minimum fatal dose.

Series B.

Approximately 0.2 gram of caffein per kilo was employed in these experiments.
Diet and raie as possible factors which may influence the toxicity of caffein were
made the subject of study in these experiments which were divided into two groups
as shown in the table, page 25.

Rabbit 95. Gray and ivhite male. Weight, 1,478 grams. Diet, oats.

February 27: 11.30 a. m., 15 cc 2 per cent caffein (210 mg per kilo) injected sub-
cutaneously; 2.20 p. m., no symptcms, tremors observed when handled, but not
marked, reflexes slightly increased, no muscular rigidity nor any other symptoms;
2.45 p. m., rabbit suddenly became very restless, jumped off the table, and had
convulsions; 3.45 p. m., rabbit died, rigor mortis set in almost immediately after
death.

Rabbit 96. Gray and white male. Weight, 1,585 grams. Diet, oats.

February 27 :_ 16 cc 2 per cent caffein (200 mg per kilo) injected subcutaneously
at 3.40 p. m.; increased reflexes observed about one hour after caffein was injected,
but no other symptoms.

February 28: Rabbit found dead.
Rabbit 112. Bla/^h female. Weight, 875 grams. Diet, oats.

March 18: 9 cc 2 per cent caffein (205 mg per kilo) injected subcutaneously at
3 p. m.; 3.30 p. m., rabbit became restless, reflexes were increased, tremors were

20 THE TOXICITY OF CAFFEIN.

observed, but no other symptoms; 4.15 p. m., rabbit had tremors, was handled but
this failed to induce tetanus, 10 minutes later tetanus of short duration with recovery
occuri'ed .

March 19: 9 a. m., found dead.
Rabbit 119. Yellow ivhite female. Weight, 1,060 grams. Diet, oats.

April 17: 10 cc 2 per cent cafferu (188 mg per kilo) injected subcutaneously at
2.10 p. m.

April 18: Rabbit found dead.
Rabbit 195. White female. Weight, 1,309 grams. Diet, carrots, since October 7.

October 14: 13 cc 2 per cent caffein (0.2 gram per kilo) injected subcutaneously at
11.15 a. m.; 2.25 p. m., rabbit had convulsions and died. Note: Ulceration of
rectum was noticed.
Rabbit 208. Gray. Weight, 1,068 grams. Diet, carrots, October 7-15, inclusive.

October 15: 10 cc 2 per cent caffein injected subcutaneously at 11 a. m.; 1 p. m.,
increased reflexes and tremors observed; 3.45 p. m., tremors were marked when
rabbit was handled.

October 16: Rabbit found dead. Note: Looked poorly nourished.
Rabbit 247. Belgian hare, female. Weight, 1,295 grams. Diet, oats last 10 days before
expenment.

November 10: 11 a. m., urine obtained from the bladder was acid to litmus and
did not contain sugar or albumen, 13 cc 2 per cent caffein was injected subcutaneously;
1.30 p. m., 15 cc urine obtained was markedly alkaline to litmus and reduced Feh-
ling's solution; 2.30 p. m., reduction of urine considerable, marked tremors observed
but no tetanus.

November 11: 10.30 a. m., 95 cc urine collected gave moderate reduction of Feh-
ling's solution, no symptoms, condition of rabbit seemed to be good.
Rabbit 248. Belgian hare, female. Weight, 1,305 grams. Diet, oats the last 10 days
before the experiment.

November 10: 11 a. m., urine markedly acid to litmus, no albumen, no sugar;
13 cc 2 per cent caffein injected subcutaneously; 1.30 p. m., urine was slightly alka-
line to litmus, no reduction of Fehling's solution; 2 p. m., reflexes increased; 2.30
p. m., 2 cc urine obtained from bladder, sugar abundant; 4.45 p. m., reflexes in-
creased as before, but no tetanus.

November 11: 10.30 a. m., m'ine collected showed slight reduction of Fehling's
solution; otherwise condition of rabbit was good; rabbit did not show any effects
of caffein.

Rabbit 337. Belgian hare. Weight, 1,040 grams. Diet, carrots, March 31 to April 6,
inclusive.

April 6: 3 p. m., 11 cc 2 per cent caffein injected subcutaneously in the back
(0.211 per kilo); 4.30 p. m., reflexes much exaggerated.

April 7: 8.15 a. m.; condition good, no symptoms. ,

Rabbit 336. Belgian hare. Weight, 1,040 grams. Diet, carrots, March 31 to April 6,
inclusive.

April 6: 3 p. m., 11 cc 2 per cent caffein injected subcutaneously into tissues of
the back.

April 7: 8.15 a. m., no symptoms, condition good.

Although symptoms appeared in rabbits of Group I (see table, page 25) about the
same time after the administration of caffein as in the rabbits of the preceding series
all of them terminated fatally 2 J hours to 24 hours after its administration. Two
of these rabbits (Nos. 195 and 208) were fed carrots for several days before the injec-
tion of caffein, the others were fed oats. Since symptoms and death appeared in
these two rabbits about the same time as in the rest of this group it may be concluded
that caffein is not less toxic when carrots are fed than when oats form the exclusive
diet. But since rabbit No. 208 was poorly nourished and ulceration of the rectum
was observed in No. 195 it is quite possible that caffein might be less toxic in
normal rabbits on this diet. This was tested in rabbits Nos. 336 and 337, both of
which seemed to be free from abnormality and were well nourished. Since these
rabbits survived and manifested mild symptoms only of intoxication it would eeem
that a carrot diet decreases the toxicity of caffein.

It was suggested, however, that another factor might be the cause of the greater
resistance to caffein in these two rabbits, namely, race. This was tested in rabbits 247
and 248, both Belgian hares. Since the toxicity of caffein in these two rabbits was the

ACUTE INTOXICATION — RABBITS. 21

same aa in Noa. 336 and 337, diet as a factor in acute caffein intoxication may be diw-
regarded. The greater resistance to caffein of these four rabbits is in all ])robability
due, therefore, to a difference of race. This suggestion gained additional support
from the experiments of the next series.

Series C.

The object of these experiments was to determine the minimum fatal dose for the
gray rabbit and to obtain addit ional evidence as to the toxicity of caffein in the several
varieties of rabbits. Eight experiments were performed, in which from 230 to 252 mg
per kilo were given. The white rabbits, three in number, received 250, 242, and 238
mg per kilo. All the others (which were Belgian hares) received from 236 to 252 mg
per kilo. Two of the white rabbits were fed carrots for one week preceding the injec-
tion of caffein. The other was fed oats. Three of the Belgian hares were on a diet
of oats, two were fed carrots the week before the experiment with caffein.

Rabbit 122. While, female. Weight, 2,060 grams. Diet, oats.

April 14: 25 cc of 2 per cent caffein (250 mg per kilo) in aqueous solution injected
Bubcutaneously in the back at 1.35 p. m.; 4.30 p. m., tremors, reflexes increased,
condition otlierwise good.

April lO: 9 a. m., found dead in cage. Autopsy: Liver deeply congested; kidneys
congested in cortex and medulla; stomach showed small hemorrhagic areas, perforating
ulcers in pyloric portion; small intestine petechiated on mucosa; lungs and spleen
normal.
Rabbit 234. White, female. Weight, 1,650 gram^. Diet, November 2-9, carrots.

November 9: 10.45 a. m., 20 cc 2 per cent caffein (242 mg per kilo) administered
subcutaneously.

November 10: 9 p. m., found dead.

Rabbit 335. Gray hare, female. Weight, 1,170 grams. Diet, March 31 to April 7,
carrots. f

April 7: 9.30 a. m., 14 cc 2 per cent caffein solution (240 m^ per kilo) injected sub-
cutaneously in the back; 10.30, reflexes much increased, rabbit is extremely sensitive.

April 8: 9 a. m., found dead. Autopsy: Liver was congested and contained several
coccidiosis nodules; stomach distended with rather dry food mass; mucosa exhibited
mild catarrhal inflammation; mucosa of intestines also slightly inflamed.
Rabbit 249. Belgian hare, female. Weight, 1,185 grams. Diet, oats.

November 11: Urine, 5 cc, from bladder acid to litmus, no sugar, no albumin; 11.50
a. m., 14 cc 2 per cent caffein (236 mg per kilo) administered subcutaneously; 3.45
p. m., reflexes increased, hyperaeathesia marked, but no tetanus, even when handled;
30 cc urine collected at 4 p. m., reduction of Fehling's solution considerable.

November 12: 10 a. m., 8 cc urine collected, reduction heavy, only a few cubic
centimeters obtained from bladder, did not contain any sugar, general condition of
rabbit good, no symptom of caffein intoxication.
Rabbit 321. Yellow, female. Weight, 1,135 grams. Diet, oats.

March 16, 1910: 11.50 a. m., 14 cc 2 per cent caffein (246 mg per kilo) injected sub-
cutaneously in the back; 2 p. m., reflexes increased, is very sensitive, started to run
when put on floor, no handling except what was required for removal and return to
cage, feces soft.

March 17: 9.30 a. m., condition good, rabbit put on floor, gait normal, but does not
care to walk.

March 18: 9 a. m., walks around when put on floor, appetite good, condition seems
to be normal.

March 25: 11 a. m., rabbit still alive, condition good.
Rabbit 250. Belgian hare, female. Weight, 1,4S5 grams. Diet, oats at least two days
before the experiment.

November 11: 11 a. m., urine obtained from bladder acid to litmus, no albumin,
no sugar; 11.10 a. m., 18 cc, 2 per cent caffein (252 mg per kilo); 3.45 p.m., reflexes and
hyperaesthesia, no tetanus; 4 p. m., 60 cc urine, marked reduction of Fehling's solution.

November 12: 10 a. m., condition of rabbit good, no symptoms of caffein intoxication,
80 cc urine collected, sugar considerable, only a few cubic centimeters of urine obtained
from bladder, no reduction of Fehling's solution.

22 THE TOXICITY OF CAFFEIN.

Rabbit SS4- Belgian hare, female. Weight, 1,270 grams. Diet, carrots, March SI to
April 7.

April 7: 9.30 a. m., 15 cc 2 per cent caffein (240 mg per kilo) injected subcutane-
ously in the back; 10.30 a. m., reflexes much increased, rabbit extremely sensitive.

April 8:9 a. m., condition good, no symptoms.
Rabbit 233. White, male. Weight, 1,675 grams. Diet, carrots, November 2 to 9.

November 9: 10.50 a. m., 20 cc 2 per cent caffein (238 mg per kilo) injected subcuta-
neously, no symptoms observed until 5 p.m., when increased reflexes and hypersesthe-
sia were noticed, but no tetanus.

November 10: 9 a. m., paralysis of posterior extremities; died at 1 p. m.

Analysis of the results obtained in the experiments of this series and inspection of
Table I, page 25, show that all four of the rabbits which survived doses of 236 to 252 mg
of caffein per kilo were Belgian hares. Of the four which died one only was a Belgian
hare. The other three were white rabbits. Two of these were fed oats; the other two
received carrots during seven days preceding the administration of caffein. This diet
does not seem to be a factor, therefore, in the toxicity of caffein. Moreover, it may
be observed that rabbit No. 122, which was fed oats, died after receiAdng 250 mg per
kilo, while rabbit No. 250 received the same diet and survived the same dose of caffein
per kilo.

Experiments 234 and 334 offer another illustration that the toxicity of caffein is not
dependent upon diet, since both rabbits were fed carrots, but the same dose of caffein
caused only symptoms in one while it proved fatal to the other. It is evident, there-
fore, that the difference in resistance to caffein shown in these experiments is in all
probability due to race, the Belgian hare being more resistant to caffein than rabbits
of other varieties. Rabbit No. 335 seems to be an exception, but the post-mortem
examination showed the presence of coccidiosis of the liver. As will be shown later,
wherever this condition prevailed even smaller doses of caffein proved fatal.

Series D.

To obtain additional evidence regarding the resistance of the various races of rabbits
to caffein and to ascertain the smallest dose which is surely fatal to the gray rabbit or
Belgian hare was the object of this series of experiments. The diet in all cases con-
sisted of oats, which was given ad libitum excepting to rabbit No. 235, which received
carrots for one week previous to the injection of caffein. The doses administered
ranged from 267 to 300 mg per kilo and were administered to different varieties of adult
rabbits.

Rabbit 253. Brown and black, male. Weight, 1,600 grams. Diet, oats, November 9 to 12.

November 12: 11.30 a. m., urine from bladder acid, no albumen, no sugar; 11.35
a. m., 22 cc 2 per cent caffein (275 mg per kilo) injected subcutaneously; 11.45 a. m.,
rabbit jumped off the table, had convulsions, retraction of head and opisthotonos,
general tremors, anterior extremities stretched out, posterior extremities almost
normal, frequent twitchings; died at 12.15 p. m.
Rabbit 252. Black, female. Weight, 1,335 grams. Diet, oats, November 9 to 12.

November 12: 11.30 a. m., 18 cc 2 per cent caffein (270 mg per kilo) injected
subcutaneously. Urine obtained from bladder before injection, acid, no albumen,
no sugar, color normal, tremors and great excitement noticed about 12 noon; 4.30
p. m., when handled, showed unusual restlessness and excitement followed by con-
vulsions with opisthotonos; occasional twitching, condition bad. Died 4.35 p. m.
Rabbit 327. White, female. Weight, 820 grams. Diet, oats, March S to 16.

March 16: 11.45 a. m., 12 cc 2 per cent caffein (292 mg per kilo) injected subcu-
taneously in the back; 2 p. m., found dead, but was still warm. Autopsy: Hemor-
rhagic area at point of injection into spinal muscles; subcutaneous abdominal region
exhibited a large area of cheesy purulent material; liver and spleen were engorged;
bladder filled; intestines normal.
Rabbit 340. While and brown male. Weight, 1,465 gravis. Diet, oats.

March 30: 3.20 p. m., 20 cc of 2 per cent caffein (273 mg per kilo) injected subcu-
taneously in back.

March 31: 9 a. m., found dead.

ACUTE TNTOXICATlON — RABBITS. 23

Rabbit 341. White and brown. Weight, 1,4W grams. Diet, oats

March 'M): 3.20 p. m., 20 cc 2 per cent caflein (270 nii: per kilo) injected snbcu-
tanoously in back; 4.40 p. m., found in dyin^ condition, had convulsions; 4.45 p. ni.,
dead.
Rabbit S'26. White, male. Weight, 1,64.') grams. Diet, oats, March 8 to 16.

March IG, 1!)10: 12 noon, 20 cc 2 per cent caffein (243 mg per kilo) injected aubcu
taneously in the back; 2 p. m., tremors marked, hypersensitive, started to run when
put on floor; rabbit was not handled any more than was required for his removal from
and return to ca>:e.

March 17: !».30 a. m., tremors still present and marked, otherwise general condition
good; no other symptoms.

March IS: 9.30 a. m., no appetite, tremors still present, general condition poor;
died about 2 p. m.
Rabbit '235. Belgian hare, male. Weight, 1,870 grains. Diet, carrots, November 2 to 9.

November 10: 11.05 a. m., 25 cc 2 per cent canein (2G7 mg per kilo) injected subcu-
taneously; reflexes increased and tremors, but no tetanus observed; found dead next
morning.
Rabbit 316. Belgian hare, female. Weight, 860 grams. Diet, oats, March 8 to 16.

March 16, 1910: 11.40 a. m., 12 cc 2 per cent caffein (267 mg per kilo) injected sub-
cutaneously in the back; 2.15 p. m., reflexes somewhat increased, but not markedly
so; walked when put on floor; gait clumsy and slow; tremors of head observed; 2.35
p. m., rabbit l}"ing in his cage, posterior extremities extended and rigid, anterior
extremities flexed, head retracted; is still breathing; occasional spasms observed.
Kabbit died at 3 p. m. Autopsy: No lesion at point of injection in dorsal spinal
muscles; liver and spleen engorged; intestines injected; other organs apparently
normal.
Rabbit 395. Belgian hare, male. Weight, 1,410 grams.

August 18: 1 p. m., 20 cc 2 per cent caffein (2S3 mg per kilo) injected subcutaneously
in the back; 4 p. m., reflexes markedly increased; 5 p. m., reflexes about the same,
but no tetanus.

August 19, 9.15 a. m.: Reflexes increased markedly.

August 21, weight, 1,215 grams. Given 275 mg per kilo of caffein; no symptoms
observed.

August 23, found dead. Autopsy: Liver greatly engorged; stomach fairly well dis-
tended and mucous membrane in a slightly inflammatory condition; contents of
small intestine li(juid in nature, but walla of same appeared normal; other organs
nonnal in appearance.
Rabbit 396. Belgian hare, female. Weight, 1.475 grams. Diet, oats.

August 18: 1 p. m., 20 cc 2 per cent caffein (272 mg per kilo) injected subcutaneously
in the back; 4 p. m., reflexes increased markedly; 5 p. m., reflexes increased markedly
but no tetanus.

August 15: 10.30 a. m., reflexes still increased very markedly; rabbit jumps when
touched.

August 21: Weight, 1,245 grams. Injected subcutaneously 275 mg of caffein per
kilo; reflexes increased, posterior extremities stiff over hour later.

August 22: 9 a. m.. found dead. Autopsy: Thoracic organs normal in appearance;
stomach distended and mucous membrane affected with a catarrhal inflammation;
contents of stomach were covered with a shiny mucus; contents of small intestine
liquid in nature and bile stained; liver showea a coccidial infestation; kidneys and
spleen normal in appearance.
Rabbit 397. Belgian hare, male. Weight, 1,375 grams. Diet, oats.

August 19: 10.30 a. m., 20 cc 2 per cent caffein (290 mg per kilo) injected subcu
taneously in the back.

August 22: 9 a. m., found dead. Autopsy: Stomach distended with ingesta;
mucous membrane exhibited a catarrhal inflammation with excessive secretions;
major portion of intestines showed a condition similar to that of stomach, contents
consisting mainly of a shiny mucus; liver enlarged; other organs apparently normal.
Rabbit 398, Belgian hare, female. Weight, 1,570 grams. Diet, oats.

August 19: 10. 30 a. m. , 23 cc 2 per cent caffein (293 mg per kilo) injected subcutane-
ously in the back; 4 p. m., found dead. Autopsy: Thoracic organs seemingly normal;
mucous membrane of stomuch exbibited a catarrhal inflammation generally; large
intestines somewhat impacted but walls appeared normal; other organs normal.
Rabbit 399, Belgian hare, male. Weight, 1,725 grams. Diet, oat^.

August 19: 10.30 a. m., 26 cc 2 per cent caffein (300 mg per kilo) injected subcutane-
ously in the back; found dead at 4.30 p. m. Autopsy: Lungs slightly congested; liver

24 THE TOXICITY OF CAFFEIN".

engorged and friable; gall cyst well filled; stomach exhibited catarrhal gastritis; injec-
tion of mesenteries and intestines; kidney showed marked cortical congestion.

The results of the experiments of this series likewise indicate that the Belgian
hare is more resistant to caffein than the rabbits of other varieties. Thus, of the four
gray rabbits (Nos. 235, 316, 395, and 396), which received 267 to 283 mg of caffein per
kilo, two died and two lived, « one of which, 396, showed the presence of coccidiosis
of the liver. On the other hand it will be observed that the black and white rabbits
which received from 270 to 275 mg of caffein per kilo all died from the effects of the
drug; one within 1 hour and 25 minutes and another within 50 hours after the admin-
istration of the caffein, while Ko. 340 died in the night. Fiuthermore it will be noted
that of the last three rabbits of this series, which were Belgian hares and received
290, 293, and 300 mg of caffein, two died six hours after the injection, while the other.
No. 397, lived three days. The minimum fatal dose of caffein for Belgian hares is,
therefore, about 290 to 300 mg per kilo when injected subcutaneously, which is about
50 per cent greater than for rabbits of other varieties.

Series E.

It was shown in series A that 0.15 caffein per kilo caused symptoms of intoxication.
Before concluding, however, that this is the smallest dose which causes symptoms of
poisoning, a number of experiments were performed with smaller doses. It was
found that in the great majority of cases 0.1 caffein per kilo may cause diiiresis,
but no ners^ous or muscular symptoms. In some rabbits, however, even such a dose
proved fatal. Post-mortem examinations in these cases showed the presence of.
coccidiosis of the liver, and it will be recalled that similar observations were made
before. It is quite possible, therefore, that coccidiosis of the liver is an important
factor in decreasing the resistance to caffein. Experiment 551 (p. 25) shows that
other conditions may likewise increase the toxicity of caffein.

Rabbit 325. White, female. Weight, 1,065 grams. Diet, oats.

March 17: 11 a. m., 6 cc 2 per cent (112 mgper kilo) caffein injected subcutaneously
in the back. About 5 cc of urine squeezed out from bladder before injecting caffein.

March 17: 1 p. m., hind legs crossed and stretched out, front legs also extended;
rabbit lying stretched out on her belly.

March 17: 5.40 p. m., rabbit still alive, condition somewhat improved.

March 18: 9 a. m., found dead, stiff and cold. Autopsy: Hemorrhagic area at point
of inoculation; subcutaneous region of both thighs presented a hemorrhagic infiltra-
tion of the tissues; liver contained lesions of coccidiosis; other organs apparently
normal.
Rabbit 330. Belgian hare, female. Weight, 933 grams; poorly nourished.

March 18: 3.35 p. m., 5 cc 2 per cent caffein (107 mg per kilo) injected into subcu-
taneous tissues in the back; 5.30 p. m., no symptoms.

March 19: 9 a. m., no symptoms.

March 25: Weight, 825 grams.
Rabbit 329. Belgian hare, male. Weight, 775 grams; poorly nourished. Received
March 18.

March 18: 3.30 p. m., 4 cc 2 per cent caffein (103 mg per kilo) injected into sub-
cutaneous tissues in the back; 5.30 p. m., no symptoms.

March 19: 9 a. m., no symptoms.

March 25: Rabbit alive in good condition; weight, 825 grams.
Rabbit 320. Black, male. Weight, 1,040 grams. Diet, oats.

March 17: 11 a. m., 6 cc 2 per cent caffein (115 mg per kilo) injected subcutaneously
in the back; only a few drops of urine oV^tained from bladder before injecting caffein;
1p.m., rabbit very restless; ran away when placed on floor; cried when touched with
a piece of paper; no tremors observed, but rabbit became exhausted and was unable
to walk; legs extended out; after running for about a minute dyspnoea was very
marked, but rabbit soon raised himself on his legs; 5.40 p. m., rabbit up on his legs.

a Survived first dose.

ACUTE INTOXICATION — RABBITS.

25

March 18: 9 a. m., found dead, but still warm. Autopsy: Lungs studded with
small grayish white nodules, adhesions to eoslal pleura; j)robably lesions of coccidiosis;
liver studded with coccidiosis nodules. Hemorrhages at point of inoculation.
Rabbit, 551. Gray, female. Weight, January 26, 1,650 grams. Diet, oats; fed 20 cc of
25 per cent alcohol daily from January 26-Sl.

January 3i: Weight, 1,450 grams; 10.20 a. ra., temperature 101.0°; 10.45, a. m.,
temperature 101.6°; received 7 cc 2 per cent caffein subcutaneously into back; 11.15
a. m., convulsions of short duration; raised himself on posterior legs, anterior legs
wide apart; 4.10 p. m., looked normal, not hypersensitive; 4.30 p. m., condition
seemed to be good.

February 1: 9 a. m., found dead, was alive at 5.30 p. m. of previous day. Autopsy:
Lesions found involved thoracic cavity maiidy; lungs were hepatizecl and a fibre
plastic exudate caused them to adhere to costal pleura; liver engorged and appeared
fatty; no marked lesions affecting digestive tract, a slight catarrh of stomach being
the oTdy noticeable feature; kidneys and spleen normal.

Table 1. — SuhctUaneous injections of caffein — rabbits.

SERIES A.

No.

Weight.

Caffein
per
kilo

Appearance of symp-
toms in—

Duration oflifc

Diet.

Remarks.

332

Grams.
1,070
1,170
1,200
1,065
1,355
1,820
1,490
1,915

Mg.

158
153
150
150
147
153
174
167

1 hour 45 minutes

. do

Oals

...do

"%o.

331

do

328

do

do

...do

Do.

322

do

...do

White.

217

do

...do

Do.

219

do

...do

Maltese.

194

do

...do

White.

191

do

...do

Light brown.

SERIES B, GROUP I.

95

1,478

210

96

1,585

200

112

875

205

119

1,060

188

195

1,300

200

208

1,068

188

2 hours 50 minutes.

1 hour

30 minutes

2 hours.

3 hours 10 minutes.

About 18 hours

do

do

3 hours 10 minutes.
About 24 hours

Oats

..do

...do

..do

Carrots ..
..do

White.
Gray white.
Black.

Yellow white.
White.
Gray.

SERIES B, GROUP II.

''47

1,295
1..305
1,040
1.045

200
200
211
211

2 5 hours ...

Survived

Oats

...do

Gray.
Do.

'MS

3 hours

do

3'17

1.5 hours

do

Carrots. . .
...do

Do.

■<?6

..do

do

Do.

SERIES C.

122

2,060

250

234

1,650

242

335

1,170

240

249

1,185

236

321

1,135

246

250

1,435

252

334

1,270

240

'233

1,675

238

2 hours 55 minutes . . .

Ihour

4 hours

2 hours 10 minutes.
4 hours 35 minutes.
1 hour

238 6 hours 10 minutes .

1.5 days

About 24 hours.

do

Survived

do

do

.do.

26 hours do

Oats

Carrots...

..do

Oats

..do

..do

Carrots. . .

White.

Do.
Gray coccidiosis.
Gray.
Yellow.
Gray.

Do.
White.

2G

THE TOXICITY OF GAFFEIlSr.

Table 1. — Subcutaneous injections of caffein — rabbits — Continued.
SERIFS D.

Caffein

No.

Weight.

per
kilo.

Grama.

Mg.

253

1,600

275

252

1,335

270

327

820

292

340

1.465

273

341

1,450

270

32(5

1,645

243

235

1,875

267

31(5

860

267

395

1,410

283

395

1,215

275

■Am

1,475

272

396

1,245

275

397

1,375

290

39«

1,570

203

399

1, 725

300

Appearance of symp-
toms in—

Duration of life.

Diet.

Remarks.

10 minutes.
30 minutes.

2 hours.

2 hours 45 minutes.

3 hours

do

do

Ihour

35 minutes

4 hours 55 mmutes .

2 hours 15 minutes.

About 18 hours

1 liour 25 minutes..

50 hours

20 hours

3 hours 20 minutes.

Survived

About 2 days

Survived

About 18 hours

3 days

5.5 hours

6 hours

Oats...
...do...
...do...
...do...
...do...
...do...
Carrots.
Oats...

Oats.
..do.
..do.
..do.
..do.
..do.

Brovs^n and black.

Black.

Wliite.

White and brown.

Do.
White.
Gray.

1)0.

Do.
Do.
Do.
Do.
Do.
Do.
Do.

SERIES E.

S-'o

1,065

935

775

1,040

1,450

112
107
103
115
100

2 hours

Less than 22 hours

Survived

Oats

White female.

330

None

Gray.

T'9

.do

.do

Gray male.
Black male.

r>{\

2 hours

46 hours

Oats

...do

I'll

30 minutes

Less than 24 hours

Gray female.

ADMINISTRATION BY MOUTH.

These experiments were carried out on two varieties of rabbits, the white and the
gray. The diet consisted chiefly of oats, but in a few cases carrots formed the exclusive
diet. Food and water were given ad libitum. A 2 per cent solution of caffein was
administered through a stomach tube. Since the resistance to most drugs is com-
monly supposed to be greater when given by mouth than when administered by any
other path, doses of 175 to 200 mg per kilo were fed in a series of preliminary experi-
ments, all of which were performed on gray rabbits weighing from 865 to 1,135 grams,
and which were fed carrots for several days previous to the experiment. Three of the
rabbits survived, two mthout showing any symptoms; in the other case paralysis of
the posterior extremities was observed five hours after he received caffein and he was
found dead the next morning. Unfortunately no autopsy was performed. The low
resistance to caffein of this animal was probably due to some abnormal condition which
developed about the time of the experiment, since this rabbit received 325 mg of
caffein per kilo two weeks previously and increased reflexes only were observed as a
result of this treatment. Hence 200 mg of caffein per kilo can not be considered the
toxic dose when fed by mouth. In the following experiments larger doses were
therefore given.

Series A.

Rabbit 24S. Belgian hare. Weight, 1,170 grams. Diet, oats.

November 17: 1.20 p. m., 19.5 cc 2 per cent caffein (330 mg per kilo) administered
by the mouth; 4.30 p. m., somewhat hypersensitive.

November 19: No symptoms; at 9 a. m., urine collected, no reduction of Fehling's
solution; rabbit survived .

Rabbit 241. White male. Weight, 1,-380 grams. Diet, oats.

November 17: 1.15 p. m., 20 cc 2 per cent caffein (290 mg per kilo) administered
by the mouth; 4.30 p. m., some hypersensitiveness, but no other symptoms.

November 18: 9 a. m., urine collected, no reduction of Fehling's solution; no
eymptoms; rabbit Burvived.

ACUTE INTOXICATION — RABBITS. 27

liubbit 249. Belgian hare. Weiffhl, 890 grams. Diet, oats.

Noveinher 17: I.IW p. in., 14.5 rr 2 por ctMit futfein (325 mg per kilo) administered ;
4.30 p. Ml., hyporsouHitiveiiws; 110 oLluT Hyiiiptom.s.

November 18: 10 a. in., no Hymptdni.s; nriiu' collected, no reduction; rabbit sur-
vived.

Series H.

The object of these experiments was to (let(!rmine tlio minimum fatal ditse of caffein
in the two varieties of rabbits, the white ami the K'li.V- AH of the animals selected
were api)roximately of the same weij^ht.

liubbit J.i9. Belgian hare, male. Weight, 9.>V5 grams. Diet, outs.

November lit: 1 p. m., 17 cc 2 j)er cent callVin (3G3 mg per kilo) adminiHlcrcil ])y
mouth, followed by 10 cc of 0.9 j)er cent salt solution.

November 20: Urine examined, no sugar found, no symptom noticed at any time
after injection.
Rabbit '254. Belgian hare, female. Weight, 975 grams. Diet, oats.

November 1!): 4.05 p. m., 18 cc 2 per cent callein (3(ji) mg per kilo) administered by
mouth, followed by 10 cc of 0.9 per cent salt solution.

November 20: 9 a. m., rabbit found dead.
Rabbit 267. White. Weight, 1,050 grams. Diet, oats.

November 23: 12.10 p. m., IS cc 2 per cent caffein (342 mg per kilo) given by mouth,
followed by ISccsalt solution; 1 p. m., increased reflexes, tremors marked but no teta-
nus; 1.0")]). m., rabbit stretched on abdomen, posterior exlremiti(!H in extended position
and paralyzi'd, soon after clonic spasms set in, which recurred about every minute;
1.1 I p. m., tetanus and death. Aulopsij: Liver showed fatty degeneration; slight in-
flammation of stomach and intestines; other organs normal.
Rabbit 268. White. Weight 1,1 UO grams. Diet, outs.

November 23: 20 cc 2 per cent caffein (3G3 mg per kilo) administered by mouth, fol-
lowed by 20 cc salt solution; 1.15 p. m., somewhat hypensensitive; 4.30 p. m., tremors
fairly marked, no urine ])assed, about 2 cc of bloody looking urine obtained from blad-
der, which contained albumen and a considerable amount of glycogen; rabbit died.
Rabbit 419, Belgian hare, male. Weight, 1,600 grams. Diet, oats.

September 2(5: 10 a. m., 28 cc 2 per cent caffein (350 mg per kilo) given by mouth;
reflexes increased at 4 ]). m.; 6 p. m., reflexes still increased, no other symptoms.

September 27: 9 a. m., found dead. Autopsy: Lungs, liver, and kidneys congested;
other organs normal.
Rabbit 420. Belgian hare, male. Weight, 1,250 grams. Diet, oats.

September 2(i: 10 a. m., 22 cc 2 per cent caffein (352 mg per kilo) given by mouth;
11.35 a. m., convulsions; 12 noon, found dead. Autopsy: Liver showed very extensive
coccidiosis; no other lesions.
Rabbit 421. Belgian hare, male. Weight, 1,485 grams. Diet, oats.

Sejitember 2t): 10 a. m., 20 cc 2 per cent caffein (351 mg per kilo) administered by
mouth; 4 p. m., reflexes increased; 6 p. m., reflexes as before, no tetanus observed.

September 27: 9 a. m., rabbit found dead. Autopsy: Congestion of lungs and kid-
neys; liver congested and slightly fatty.
Rabbit 424. White^male. Weight, 1,295 grams. Diet, oats.

September 2G: 2 p. m., 19 cc 2 per cent caffein (293 mg per kilo) administered by
mouth; 4 p. m., reflexes increasetl, no other symptoms; 6 p. m., no change since 4 p. m.

September 27: 12 noon, convulsions and death. Autopsy: Congestion of the lungs;
no other lesions.
Rabbit 4iS. White, male. Weight, 1,205 grams. Diet, oats.

September 20: 2 p. m., 18 cc 2 per cent caffein administered by mouth; 4 p. m.,
reflexes increased, no tetanus; 6 p. m., condition unchanged since 4 p. m.

September 27: 9 a. m., found dead. Autopsy: Lungs liver, and kidneys congested ;
other organs normal.
Rabbit 422. White, male. Weight, 1,440 grams. Diet, oats.

September 2(j: 2 p. m., 21 cc 2 per cent caffein (291 mg per kilo) given by mouth;
reflexes increased at 4 p. m.

September 27: 3 p. m., alive, no symptoms; 4 p. m., convulsions with recovery, this
was soon followed by a violent attack of tetanus, which lasted about one minute and
was succeeded by paralysis; rabbit died at 4.30. Autopsy: Liver slightly congested;
a small portion of the intestine showed congestion and edema; other organs normal.

28

THE TOXICITY OF CAFFEIN.

A study of these experiments shows also considerable variation in the toxicity of
caffein when given by mouth. In some cases a dose of 300 mg per kilo, and even less,
caused death, as in rabbits 423 and 424. In other rabbits, however, approximately the
same doses of caffein produced increased reflexes only. The same symptoms were pro-
duced in Nos. 248 and 249 after the administration of 325-330 mg of caffein per kilo,
while another rabbit (No. 239) sur\dved a dose of 363 mg per kilo. That this is excep-
tional, however, appears from the result of the following experiments on rabbits
Nos. 419, 420, and 421, all of which died after receiving 350 mg of caffein per kilo, and
rabbits 267 and 268, to which doses of 363 and 342 mg, respectively, per kilo proved
fatal. It will be observed further that the gray rabbits are more resistant to caffein
than the white animals, as 350 mg per kilo was the smallest fatal dose for rabbits 419,
420, and 421, all of which were gray rabbits, while a dose of 290 mg per kilo was fatal
for some of the white rabbits. Again, it will be noticed that of the two gray rabbits,
Nos. 254 and 239, which received the largest doses in these experiments, namely, 369
and 363 mg, respectively, one survived. The largest doses given to the white rabbits
were 363 and 342 mg caffein per kilo. Both of these died from the effects of the drug.
It may be concluded, therefore, that the minimum toxic dose for the gray rabbit is
about 325 mg of caffein per kilo, and the minimum fatal dose is at least 350 mg per kilo.
It is to be remarked in this connection that post-mortem examination showed ex-
tensive coccidiosis in rabbit 420 and fatty liver in No. 421, while the macroscopical
examination of the organs of Nos. 424 and 423 failed to show the presence of such
abnormalities. Since, as was observed in the section on subcutaneous injection and
elsewhere in this investigation, pathological changes are apt to decrease the resistance
to caffein, it is quite possible that 350 mg per kilo is not the minimum fatal dose for
the normal rabbit. Indeed, the experiment on rabbit 239 lends support to this
view, thus furnishing additional evidence of difference in the resistance to caffein
in the two varieties of rabbits.

Table 2. — Administration of caffein by mouth.
SERIES A.

Rab-
bit
No.

Weight.

Caffein
per kilo.

Symptoms.

Duration of life.

Diet.

Remarks.

248

Grams.

1,170

1,380

890

Mg.
330
290
325

3 hours 10 minutes

Survived

Oats

...do...-

Gray.

241

do

White male.

249

do

...do....

Gray male.

SERIES B.

239

935

363

254

975

369

207

1,050

342

268

1,100

363

419

1,600

350

420

1,250

352

421

1,485

351

424

1.295

293

423

1,205

300

422

1,440

291

50 minutes.

6 hours

1 hour 35 minutes.
6 hours

2 hours

do

do

Survived

About 2 days...

1 hour 4 minutes

About 3 hours

Less than 24 hours

2 hours

Less than 24 hours

22 hours

Less than 19 hours
2i hours

INJECTION INTO THE PERITONEAL CAVITY.

In a number of experiments caffein was introduced into the peritoneal cavity.
Rabbits of different varieties receiving a diet of oats or carrots were employed for this
purpose; food and water were given ad libitum. The minimum doses required to
induce symptoms or cause death in these animals were determined; tests with caffein
were also made on young rabbits in order to study the influence of age on the Resistance
to this substance. The results are shown in the following experiments:

ACUTE INTOXICATION — BABBITS. 29

Series A.

In this series large dosea were administered, apjiniximatinK ()..S Kram per kilo.

RdbhitJt. Grnij female. Weight, 1,659 grams.

January 20: 2.20 p. m., 25 cc aqueous solution 2 per cent caffein (300 ni^ |)er kilo)
were injected into the peritoneal cavity; 3.45 p. m., when doora of cage were opened
rabbit had spasm of short duration.

January 21 : Rabbit found dead.
Rabbit 7 J. Gray and white. Weight, 1,402 grams.

January 21: 11.17 a. m., 20.2 vv (acjueoiis solution) of 2 per cent caffein (300 mg
per kilo) injected into i)eritoneal cavity from burette; 11.25 a. m., paralysis; 11.30
a. ni., rabbit had convulsion when picked up from the floor, followed by several
epasms later; 11.35 a. m., typical tetanus; 12.30 noon, found dead.
Rabbit 61. Black female. Weight, 2,14-3 grains.

January 19: 40 cc 2 per cent caffein, aqueous solution (300 mg per kilo), injected
into peritoneal cavity Ironi burette; tetanus when about 30 rr were injected; when
removed from holder, repeated and vi«jlent convulsions, terminating in death.

Series B.

The object of these experiments was to determine the minimum lethal dose; 0.2 to
0.15 gram of caffein per kilo was injected into the rabbits of this series.

Rabbit 69. White female. Weight, 1,714 grams.

January 20: 10.15 a. m., (i cc 2 per cent caffein, aqueous solution, injected into
peritoneal cavity. No symptoms, under observation for 45 minutes, rabbit defecated
rather copiously; feces were soft; 11 a. m., 6 cc 2 per cent caffein, aqueous solution,
injec-ted into peritoneal cavity, no symptoms, under observation for 40 minutes; 11.40,
6 cc 2 per cent caffein injected into peritoneal cavity; 11.45, rabbit is restless, reflexes
increased.
Rabbit 70. Gray and white female. Weight, 1,487 grams.

January 20: 1.30 p. m., 15 cc 2 per cent aqueous solution of caffein (0.2 gram per
kilo) injected into the peritoneal cavity; 2.20 p. m., no symptoms.

January 30: About 2 p. m. rabbit died.

February 1: Autopsy: Cirrhosis of the liver; enteritis of small intestines; stomach
and kidneys normal.
Rabbit 93. Maltese, male. Weight, 1,197 grams.

March 2: 11.30 a. m., 12 cc of 2 per cent caffein (200 mg per kilo) injected into
peritoneal cavity; 11.35 a. m., while being released from holder, tetanus occurred,
repeated attacks later, clonic convulsions with tonic rigidity of posterior extremities
during the attacks as well as during intervals, anterior extremities were relaxed during
the intervals between the attacks, opisthotonos of cervical region but kyphosis in
lumbar region were observed, no salivation nor dilatation of the pupils; 2 p. m.,
rabbit died.

Rabbit 92. Yellow female. Weight, 1,388 grams.

February 25, 4.15 p. m., 14 cc 2 per cent caffein (0.2 gram per kilo) injected into
peritoneal cavity; 4.20 p. m., restlessness and increased reflexes, rabbit found stretched
out in cage, but raised himself on his legs again; 4.45, general tremor when touched.

February 26: 9 a. m., rabbit found dead. Autopsy: Hemorrhage into abdominal
muscles at site of injection; hemorrhage also in walls of stomach opposite similar
spot in abdominal wall.
Rabbit, 309. Belgian hare, female. Weight, 1,. 500 grams. Diet, oats.

March 2: 2.05 p. m., 2per cent caffein solution (0.2 gram per kilo) injected into
peritoneal cavity; 2.25 p. m., found dead, no urine found in bladder.
Rabbit 307. Belgian hare, female. Weight, 1,320 grams. Diet, oats.

March 2: 12 noon, urine obtained from bladder, clear amber colored, no albumin,
no reduction; 12.06 p. m., 10 cc of 2 per cent caffein (0.151 gram per kilo) injected
into peritoneal cavity; 1.30 p. m., rabbit ])laced on floor, runs around but anterior and
posterior extremities soon extended, in tonic condition; 2.25 p. m., reflexes increased,
paralysis of extremities, dyspnoea; 4.50 p. m., about 100 cc urine collected, no
albumin, reduction of Fchling's solution moderate.

March 3: 9.30 a. m., posterior extremities extended and rigid, anterior extremities
paralyzed, respiration less frequent and deeper than normal. Rabbit died at 11.50
a. m.; urine collected since 4.50 p. m. previous day gave very heavy reduction of
Fehling's solution. Autopsy: Animal in good condition; in the left axillary region

30 THE TOXICITY OF CAFFEIN.

was observed a hemorrhage into the subcutaneous and muscular tissue of that region.
The ventral portion of the large colon, in contact with the ventral abdominal wall,
showed a hemorrhagic area about one-half inch in length, such as might be produced
by a puncture or bruise of the colon through the abdominal wall. A small portion
of the small intestine adjacent to the colon was affected in a similar manner. All
internal organs were apparently normal.
Rabbit 308. Belgian hare, female. Weight, 1,350 grams. Diet, oats.

March 2: 11.45 a. m., urine obtained from bladder, no albumen, no reduction;
11.50 a. m., 10 cc 2 per cent caffein (0.15 gram per kilo) injected into peritoneal cav-
ity; 1.30 p. m., not very active, no abnormal symptoms otherwise; 3. 30 p. m., rabbit
looked depressed, made very little attempt to move about, remained in one position
most of the time when placed on floor; 4.30 p. m., 180 cc m-ine collected, no albumen,
reduction of Fehling's solution moderate.

March 3: 9.30 a. m., rabbit looks normal, is able to walk but is easily fatigued when
made to walk about or when placed on his side, followed by paralysis of anterior
extremities, posterior extremities apparently normal, about 90 cc of urine collected
at noon was free from albumen, did not reduce Fehling's solution.

March 4: 11 a. m., lying on his side in cage, anterior extremities limp, posterior
extremities extended and rigid, is in dying condition.

March 5: 9 a. m., found dead. Autopsy: Liver engorged; spleen congested, but
not enlarged; kidneys, some congestion in cortex; stomach filled, mucosa thickened
and easily pulled off; petechial hemorrhages on serosa of colon.

Series C.

The experiments of this series were made to determine the minimum toxic dose.
Rabbit 295. Belgian hare, female. Weight, 1,205 grams. Diet, carrots.

March 1: 10.40 a. m., 6 cc 2 per cent caffein (0.1 gram per kilo) injected into peri-
toneal ca^^ty; about 2 cc of urine obtained before injecting caffein; 2 p. m, 100 cc
urine, bloody in appearance, collected, a moderate quantity of albumen present, no
reduction; 3.40 p. m., no symptoms.

March 4: 2 p. m., rabbit looks well.
Rabbit 293. Belgian hare, female. Weight, 1,605 grams. Diet, carrots.

March 1: Urine from bladder clear, alkaline; 11.55 a. m., 8 cc 2 per cent caffein
(0.1 gram per kilo) injected into peritoneal cavity; 3 p. m., 90 cc urine normal in color
collected, no albumen, no reduction; 3.40 p. m., no symptoms.

March 4: 1.15 p. m., rabbit looks normal.
Rabbit 292. Belgian hare, male. Weight, 1,595 grams Diet, carrots.

March 1: 10.10 a. m., 8 cc 2 per cent caffein (0.1 gram per kilo) solution injected
into peritoneal cavity; 10.40 a. m., rabbit lu-inated, reflexes increased, but no other
symptoms; 10.50 a. m., no urine obtained from bladder; 2 p. m., 105 cc of clear pale
urine collected; no albumen, no reduction; 3.40 p. m., no symptoms.

March 4: 2 p. m., rabbit looks well, mine collected, did not contain sugar.
Rabbit 298. Belgian hare, female. Weight, 1,205 grams. Diet, carrots.

March 1: 4.06 p. m.,' 7.5 cc 2 per cent caffein solution (0.125 gram per kilo) iiijected
into peritoneal cavity, urine obtained from bladder immediately after injection, no
albumen, no reduction; 5.30 p. m., reflexes increased, rabbit was able to run around,
but became paralyzed soon; 5.40 p. m., rabbit is again able to run arouud.

March 3: 10 a,, m., anterior extremities paralyzed, is able to use posterior exkemi-
ties.

March 4: 1 p. m., rabbit looks normal.
Rabbit 223. Belgian hare, male. Weight, 1,165 grams. Di£t, carrots.

March 1: 3.50 p. m., urine obtained from bladder clear, amber colored, no albumeii,
no sugar; 3.52 p. m., 7.5 cc 2 per cent caffein (125 mg per kilo) injected into peri-
toneal cavity; 5.40 p. m., rabbit makes little attempt to run when put on the floor,
weakness of extremities marked.

March 4: 1.15 p. m., rabbit normal.

Series D.

The object of the experiments of this series was to study the effect of age on the
resistance to caffein. Half-grown rabbits were, therefore, used in the following experi-
ments.
Rabbit 310. Belgian hare, female. Weight, 880 gr&Tns. Diet, oats.

March 2: 3.25 p. m., 9 cc 2 per cent caffein (0.2 gram per kilo) injected into peri-
toneal cavity.

ACUTE INTOXICATION — RABBITS. 31

March 3: 9.30 a. m., no symptoms, rabbit looks normal.

March 4: II a. m., posterior extremities abductetl, walked when placed on the
fl(K)r, made no attempt to change attitude when placed on it.s side, remained some
time in this position.

March 5: 9 a. m., found dead. Autopsy: Liver showed areas of degeneration;
kidneys cong&^tion and petechial hemorrhage on cortex; small and large intestines,
inflammation marked; bladder distended.
Rabbit 75. Gray arid irhite, female. Weight, 842 grains.

January 25: 3 p. m., 8.5 cc 2 per cent caffein solution (0.2 gram per kilo) injected
into peritoneal cavity; 3.15 p. m., anterior extremities weak and reflexes increased.

January 27: Rabbit paralyzed but is able to turn over when placed on back.
Rabbit 74. Gray and uhite, female. Weight, 692 grams.

January 25: 3 p. m., 7 cc 2 per cent caffein (0.2 gram per kilo) solution injected
into |>eritoneal cavity; 3.15 p. m., reflexes increased and anterior extremities paralyzed.

January 27: Rabbit recovered and is able to walk about in the room.
Rabbit S 1 2, maltese, female. Weight, 740 gn.m^. Diet, oats.

March 3: 11.47 a. m., urine obtained from bladder, appearance normal, no albumen,
no reduction of Fehling's solution; 1 1.50 a. m., 7.5 cc 2 per cent caffein (0.2 gram per
kilo) injected into peritoneal cavity; 2.30 p. m. anterior extremities paralyzed, pos-
terior extremities rigid and extended; 5 p. m. (about), rabbit died.
Rabbit 311. Belgian hare, female. Weight, 6-50 grams. Diet, oats.

March 3: 11.26 a. m., lu-ine obtained from bladder normal in appearance, albumen
considerable, reduction of Fehling's solution none; 11.27 a. m., 6 cc 2 per cent caffein
Bolution (0.2 gram per kilo) injected into peritoneal cavity; 2.30 p. m., rabbit seemed
to be normal, no symptoms had developed; urine collected contained a large amount
of sugar, reduction was very heavy, but no albumen was found.

March 4: 11 a. m., condition good, moves about when put on floor; gait, normal.
Rabbit 78. Yelloiv and uhite. Weight 659 grams.

January 26: 1.30 p. m., 8.5 cc 2 per cent caffein (250 mg per kilo) injected into
peritoneal cavity, under obser\-ation the rest of the afternoon, no symptoms.

January 27: 4 p. m.. no sj-mptoms developed.
Rabbit S17. Belgian hare, female. Weight 635 gravis. Diet oafs.

March 15: 10.35 a. m., 8 cc 2 per cent caffein (0. 252 gram per kilo) injected into
peritoneal cavity; 12 noon, marked abduction of hind legs, was unable to walk after
a little exertion, rabbit died between 12.30 and 12.50 p. m. Autopsy. Right lung
hepatized and showed adhesions to costal and mediastinal pleura; liver studded
with nodules of coccidiosis; spleen congested; stomach tilled, mucosa normal; intes-
tines injected: colon hemorrhagic on serosa in ventral region, near point of injection;
kidneys normal.
Rabbit 323. White, female. Weight 820 grams. Diet oats.

Jklarch 15: 10.45 a. m., 10 cc 2 j^er cent caffein (250 mg per kilo) injected into peri-
toneal cavity; 12 noon, reflexes increased, hind legs abducted but is able to walk,
BjTnptoras are mild: 1.40 p. m., tremors, weakness, and abduction of head and legs
much more marked than at 12 noon.

March 16: Condition good.

March 17: Condition good, recovery apparently complete.

Since the experiments of Series A, which were intended as preliminary tests, have
shown that 0.3 gram of caffein per kilo when introduced into the peritoneal cavity is
rapidly absorbed and is fatal, much smaller (ioses were employed in subsequent
trials with the drug. This is shown in series B, which may be divided into two
groups. Group I, consisting of rabbits 69, 70, 92, 93, and 309, which received 0.2
gram of caffein per kilo, and Group II, Nos. 307 and 308, into which 0.15 gram of
caffein per kilo was injected. Three rabbits of Group I (Nos. 92, 93, 309) died from
the effects of caffein; rabbit 309 twenty minutes after injection, and rabbits Nos. 92
and 93, twenty hoiu-s and two and one-half hoiu-s. respectively, after the administration
[Of caffein. In both of these rabbits svanptoms appeared within five minutes after the
injections were made. Rabbits 69 and 70, it will be noticed, survived the same
amount of caffein in proportion to body weight as was given to the other members of
this group. Increased peristalsis and the distribution of the dose may account for the
greater resistance of rabbit No. 69. The case of rabbit No. 70 is evidently one of ex-
ceptional resistance to caffein, since both the rabbits of Group II died from the effects

32

THE TOXICITY OF CAFFEIN.

of a much smaller dose, namely, 0. 15 gram of caff ein per kilo. Moreover, macroscopical
examination at the autopsy of Nos. 307 and 308 failed to show any lesions which might
tend to lessen the resistance to caff ein.

That a dose of 0.15 gram per kilo is therefore in all probability the minimum fatal
dose for the rabbit when injected into the peritoneal cavity appears from the results
of the experiments in series C, in which smaller doses, 0.125 gram of caffein per kilo
caused mild symptoms only, while 0.1 gram per kilo rarely induced any symptoms.
It may be remarked that the rabbits of series C were fed carrots while rabbits Nos. 307
and 308 received oats. Their- resistance to caffein may be different, but, as was
pointed out in the earlier part of this investigation, diet does not seem to influence the
toxicity of the single dose of caffein. Doses of 150 and of 100 to 125 mg per kilo, when
injected into the peritoneal cavity, may be considered, respectively, as the minimum
fatal and minimum toxic doses for the gray rabbit. Analysis of the experiments in
series D shows much greater resistance to caffein than in the other rabbits which
received it intraperitoneally. Thus, after the administration of 0.2 gram per kilo to
each of five rabbits, no effect was observed in two cases (Nos. 310, 311), while in two
others (Nos. 74, 75) symptoms developed, but they survived. Only one rabbit, No-
312, died from the effects of this dose; the autopsy showed the presence of degenera-
tion of the liver and petechial hemorrhages on the cortex of the kidneys in the case of
No. 310, which was probably the cause of death rather than the caffein.

Two decigrams of caffein can not be considered, therefore, the fatal dose for rabbits.
This is further corroborated by the results obtained in experiments Avith larger doses.
Rabbit 78, which received 257 mg per kilo, failed to show any symptoms. The same
amount in proportion to body weight in No. 323 caused mild symptoms only, while
the rapid death of rabbit No. 317 after the same dose of caffein may be explained by the
lesion found at autopsy, thus affording additional evidence that disease may decrease
the resistance to caffein. It will be observed that all the members of this series were
young rabbits and, as will be shown later, young animals of other species are likewise
more resistant to caffein than adult animals. Similar results were obtained by von'
Anrep, Avho observed that atropin is less toxic in young than in full-grown animals.

Observations were also made on the diuretic effect of caffein when injected into the
peritoneal cavity. The results shown in the following table indicates the stimulating
effect on renal secretion whether the diet consisted of oats or of carrots. The urine of
some rabbits contained moderate amounts of sugar after from 0.2 to 0.15 gram of caffein
per kilo was given; albumen was observed in one case, but in none of the others. In
rabbit No. 311 albumin was found before the injection of caffein, but none in the urine
which was collected three hours after caffein was injected.

Effect of caffein on renal secretion.

No.

Weight.

Caffein
per kilo.

Urine.

Time.

Diet.

307

Grams.
1,320
1,.305
1,205

1,605
1,595

Gram.
0.150
.150
.100

.100
.100

cc.
100
180
100

90
105

1.5 liours

do

2 hours 20 min-

utes.

3 hours

4 hours

Oats.

308

Do.

295

Carrots.

293 . ....

Do.

292

Do.

Note.— The amount pf urine secreted in three hours by control rabbits, on a carrot diet, varied between
.3.5 and .50 cc, the average weight of the animals being a little above 1,600 grams. The secretion of urine
on an oat diet was much less for an equal period of time.

ACUTE INTOXICATION — RABBITS.

33

Table 3. — Intraperitoneal injections.
SERIES A.

No.

Weight.

C'aflein
per kilo.

Time of appearance of
symptoms.

Duration of life.

Remarks.

71

Grams.
1,659
2,113
1,402

Oram.
0.3
.3
.3

24 hours

Gray.
Black.

61

At the end of injection . .
1.25 hour

72

Gray and white.

SERIES B, group:.

70

1,4S7
1,492

1,492
1,388
1,500

0.2

.2

.2
.2

10 (lavs

Gray and white.
Maltese; given second

93

2.') hours

69

About 5 minutes

Survived

dose after 3 days, died
2.5 hours later.
White.

92

24 hours

Yellow.

309

20 minutes

Belgian; oats.

SERIES B, GROUP II.

0.15
.15

3 hours and 40 minutes.
1 hour 24 minutes

About 2.5 days.
24 hours

Belgian; oats.
Do.

SERIES C.

223
293
295
292
298

1,16.5

0.125

1,605

.1

1.205

.1

1,595

.1

1,205

.125

2 hours.

1.5 hours.

Survived.

do...

do...

do...

do...

Belgian; carrots.

Do".
Do.
Do.

SERIES D.

310

311

312

78

75

74

317

323

880

0.2

650

.2

740

.2

659

.257

842

.2

C.92

.2

63.1

.252

820

.25

2 days 1

40 minutes ,

15 minutes ,

do

do

1 hour 25 minutes .
1 hour 15 minutes ,

About 2.5 days'.

Survived

4.5 hours

Survived

do

do

About 2 hours . . .
Survived

Belgian; oats.

Do.
Maltese; oats.
Yellow and white; oats.
Gray and white.

Belgian; oats.
White; oats.

> Not due to caflfein.

INTRAMUSCTJIiAR INJECTION.

Well-fed rabbits, which received a diet exclusively of oats, were used for these
experiments. The injections were made into the lumbar or into the gluteal muscles.

Series A.

In this series the caffein was injected into the gluteal muscles.

Rabbit 284. Brotcn and white, female. Weight, 1,100 grams.

December 14: 2 p. m., 11 cc 2 per cent caffein injected into the gluteal muscles
(0.2 gram per kilo), under observation until 5 p. ni., had frequent convulsions; at
5 p. m. in a comatose condition. Rabbit was found dead the next morning.
Rabbit 2S6, while and black, female. Weight, 1,31.5 grams.

December 15: 2.30 p. m., 13 cc 2 per cent caffein injected into the gluteal muscles
(0.1977 gram per kilo), tremors and increased reflexes observed during the next two
hours, but no other symptoms.

December 17: Rabbit alive.

18594°— Bull. 148—12 3

34 THE TOXICITY OF CAFFEIN.

Rabbit 2S5, yelloiv and tvhite, female. Weight, 1,385 grams.

December 14: 10.15 a. m., 14 cc 2 per cent caffein injected into the gluteal muscles
(0.2 gram per kilo), general tremors, but no convulsions observed. Rabbit survived.

December 17 : Rabbit still alive.
Rabbit 287. Belgian hare, female. Weight, 1,140 grams.

December 15: 2.15 p.m., lice of 2 per cent caffein injected into the gluteal muscles;
2.30 p. m., tonic contractions of posterior limbs. Paralysis and death at 2.40 p.m.

Series B.

In series B the caffein was injected into the lumbar muscles.

Rabbit 307. Belgian hare, female. Weight, 1,175 grams.

February 16: 11.05 a. m., 8 cc 2 per cent caffein injected (0.136 gram per kilo) into
the lumbar muscles; under observation until 4 p. m., no symptoms; 4 p.m., allowed
to walk on the floor; after walking a short distance loss of coordination and paralysis
of posterior extremities; 5.20 p. m., found dead.
Rabbit 306. Belgian hare, female. Weight, 1,860 grams.

February 16: 11 a. m., 12.5 cc 2 per cent caffein injected into the lumbar muscles;
12 noon, no symptoms; 2 p. m., walked about 10 feet, exhaustion and paralysis;
3p.m. found dead.

Rabbit 181. Belgian hare. Weight, 1,230 grams. (Was experimented on some
time previously.)

February 16: 10.55 a. m., 8 cc 2 per cent caffein injected into the lumbar muscles;
(0.130 gram per kilo); 12 noon, no symptoms; 2 p. m., no symptoms; 3 p. m., put on
the floor, walked about 10 feet and was exhausted, posterior extremities paralyzed;
4 p. m., found dead.

Series C.

In the fall of the same year additional experiments were carried out with doses
ranging from 100 to 200 milligrams of caffein per kilo, which were injected into the
lumbar muscles. The results are given in the following abbreviated protocols:

Rabbit 425. Belgian hare. Weight 1,520 grams.

September 27: 10.30 a. m., 7.5 cc 2 per cent caffein injected into the lumbar mus-
cles; 2 p. m., reflexes increased.

September 28: Rabbit normal.

October 5: Weight, 1,620 grams; 2.50 p. m., 10 cc 2 per cent caffein injected into
lumbar muscles; 3.05 p. m., reflexes increased.

October 13: Weight, 1,520 grams; 10.30 a. m., 10 cc 2 per cent caffein (131 mg per
kilo) injected; 11 a. m., no symptoms; 11.30 a. m., reflexes much increased.

October 14: Alive, no symptoms.
Rabbit 426. Belgian hare, female. Weight, 1,425 grams.

September 27 : 7 cc 2 per cent caffein injected into the lumbar muscles at 10.30 a. m.;
2 p. m., reflexes increased.

September 28: Rabbit normal.

October 5: Weight, 1,425 grams; 2.55 p.m., 9 cc 2 per cent caffein injected into lum-
bar muscles; 3.05 p. m., reflexes increased.

October 13: Weight, 1,405 grams; 10.30 a. m., 10 cc 2 per cent caffein (142 mg per
kilo) injected; 11 a. m., no symptoms; 11.30 a. m., reflexes increased.

October 14: Rabbit alive, no symptoms.
Rabbit 427. Belgian hare, female. Weight, 1,780 grams.

September 27: 9 cc 2 per cent caffein injected into the lumbar muscles; 2 p. m.,
reflexes increased.

September 28: Rabbit normal.

October 5: Weight, 1, 850 grams; 3 p. m., 11.5 cc 2 per cent caffein injected into
lumbar muscles; 3.10 p. m., reflexes increased.

October 13: Weight, 1,830 grams; 10.40 a. m., 14 cc 2 per cent caffein (153 mg per
kilo) injected into lumbar muscles; 11 a. m., no symptoms; 11.30 a. m., reflexes
increased.

October 14: Rabbit alive, no symptoms.
Rabbit 453. Belgian hare, male. Weight, 1,160 grams.

October 12: 3.45 p. m., 11.5 cc 2 per cent caffein in aqueous solution injected into
lumbar muscles; 4.15 p. m., reflexes increased; 4.30 p. m., paralyzed.

ACUTE INTOXICATION — RABBITS. 35

October 13: 9 a. m., found dead. Autopsy: Gastric mucosa hemorrhagic; liver
darkened; other organs normal.
Rabbit 45'} . Belgian hire, gray, female. Weight, 1,185 grams.

October 12: ;i.:iO p. m., 11.5 cc 2 per cent caffein injected into the lumbar muscles;
4 p. m., reflexes increased.

October 13: Rabbit weighed 1,070 grams, no symptom of caffein poisoning, rcflcxea
normal; 10.30 a. m., 10 cc 2 per cent caffein injected into the lumbar muscles; 11.30
a. m., jumped off the tiible, had attack of convulsions and died. Autopsy: Findings
same as in No. 453.
Babbit 428. Belgian hare, gray, male. Weight, 1,650 grams.

October 5: 4 p. m., 14.8 cc 2 percent caffein (0.18 gram per kilo) injected into the
lumbar muscles.

October G: Found dead.
Rabbit 429. Belgian hare, male. Weight, 1,. 340 grams.

October 5: 4 p. m., 13.5 cc 2 per cent caffein (0.2 gram per kilo) injected into lum-
bar muscles.

October 8: Rabbit found dead.

Series D.

Further experimenks making injections into both the lumbar and the gluteal muscles,
were made in this series.

Rabbit 577. Gray male. Weight, 1,380 grams.

February 14: 3 p. m. 14 cc 2 per cent caffein injected into the gluteal muscles of

' the right side; 3.10 p. m., restless, jumped off the table and walked about, reflexes

increased; 3.45 p. m., passed 30 cc clear, straw-colored urine; 4.45 p. m., allowed to

walk about, ran across the room, about 20 feet, looked tired, stretched himself out on

the floor, then raised himself and walked about showing no disturbance of gait.

February 15: 9 a. m., found dead.
Rabbit 578. Gray, female. Weight, 1,670 gram^.

February 14: 3.05 p. m., 18 cc 2 per cent caffein solution injected into the gluteal
muscles of the right side; 3.15 reflexes increased, but not restless; 5 p. m., allowed to
walk about, no symptoms observed.

February 15: Found dead.
Rabbit 579. White and gray, male. Weight, 1,490 grams.

February 14: 3.15 p. m., 15 cc 2 per cent caffein solution injected into the gluteal
muscles of the right side, put in cage; 3.30 p. m., reflexes increased; 5 p. m., taken
out of cage and allowed to walk across the room, no special symptoms noticed.

February 23: Still alive.
Rabbit 580. Gray male. Weight, 1,510 gram^.

February 14: 3.35 p. m., 15 cc 2 per cent caffein solution injected into lumbar
muscles.

February 23: Still alive, in good condition.
Rabbit 581. Gray female. Weight, 1,680 grams.

February 14: 3.45 p. m., 17 cc 2 per cent caffein solution injected into the lumbar
muscles of the right side; 4 p. m., reflexes increased; 4.15 p. m., jumped off the table
and had wild convulsions, became very restless, walked about the laboratory; 4.25
p. m., had convulsions occasionally; 4.30 p. m., extremities extended and quite rigid;
4.35 p. m., convulsions and death.
Rabbit 582. Gray male. Weight, 1,870 grams.

February 14: 4.15 p. m., 18 cc 2 per cent caffein solution injected into the lumbar
muscles of right side; 5 p. m., reflexes increased; walked about in the room, then
rested; 5.15 p. m., had short spasm when handled.

February 23: Alive; good condition.

The data presented in these experiments show that the toxicity of caffein when
injected into the muscles of the lumbar regions is the same as when injected into the
gluteal muscles. The rabbits of series A received approximately 0.2 gram caffein per
kilo and two died as a result of this treatment. The other two sur\'ived but symptoms
of caffein intoxication were observed.

In series B smaller doses proved fatal, from which it would appear that caffein is
more toxic when injected into the lumbar muscles. Further observation?, however,
failed to corroborate the results obtained in this series. Thus, in series C, 130 to 150

36

THE TOXICITY OF CAFFEIN.

mg of caifein per kilo injected into the lumbar muscles produced mild symptoms only.
Experiments with larger doses showed that 0.180 gram caffein per kilo may cause
death. It will be noticed, on the other hand, that rabbit No. 455 survived a dose of
0.2 gram per kilo. New experiments were therefore carried out in which the same
amounts of caffein in proportion to the weight of the animals were injected into the
lumbar muscles as into the gluteal muscles. As shown in the experiments of series D,
one rabbit (No. 581) died shortly after caffein was injected into the lumbar muscles;
two recovered. Two of the three which received injections into the gluteal muscles
were found dead the next day; one recovered. Post-mortem examination failed to
indicate the presence of any abnormalities. The rate of absorption of caffein from
the gluteal and from the lumbar muscles seems to be, therefore, the same, or not to
differ very much . The observations of Auer and Meltzer'' are of interest in this con-
nection. According to their investigations adrenalin is more rapidly absorbed from
the lumbar than from the gluteal muscles. This is in all probability due to the greater
delicacy of the test they employed (since they judged the rate of absorption by the
effect of adrenalin on blood pressure) as well as to the much greater activity of the
substance.

Table 4. — Intramuscular injections.

SERIES A.

No.

Weight.

Caffein
per
kilo.

Symptoms
after—

Duration of life.

Site of in-
jection.

Remarks.

284
286

Grams.
1,100
1,315

1,38.5
1,140

Gram.

0.200
.1977
.200
.210

3 hours

2hoiu-s

Less than 20 hours...

Gluteal...
...do

White and brown female.
White and black female.

285

do

...do

Yellow and white female.

287

15 minutes

25 minutes

...do

Gray female.

SERIES B.

307

30fi

1,175

i,8eo

1,230

0.136
.134
.130

5 hours

3 hours

4 hours

6 hours, 20 minutes...
4 hours

Lumbar...
...do

Grayfemale.
Gray.

1S1

...do

SERIES C.

425

1,520
1,405
1,830
1,160
1,185
1,6.50
1,340

0.131
.142
. 153
.200
.200
.180
.200

1 hour

30 minutes

50 minutes

30 minutes

do

Survived

Lumbar...
...do

Gray.

426

do

Grayfemalo.

427

do

...do

453
455

Less than 20 hours. . .
Survived

...do

...do

Gray male.
Gray female.

428

Le.ss than 20 hours. . .
do

...do

...do

Gray male.

429

Do.

SERIES D.

577

1,380

0.200

578

1,070

.210

579

1,490

.200

.580

1,510

.200

581

1,080

.200

582

1,870

.192

10 minutes

do

15 minutes

15 minutes
45 minutes

Less than 18 hours. . .

do

Survived

do

50 minutes

Survived

Gluteal..

..do

..do

Lumbar.

..do

..do

Gray male.

White and gray male.
Gray male.

iDo.

Do.

Examination of Table 4 shows that 14 rabbits received from 180 to 210 mg caffein
per kilo. The appearance of symptoms in these rabbits varied considerably. In
some increased reflexes could be noticed in 10 to 15 minutes after the injection of
caffein; in others it was delayed 2 or 3 hours. It might be added that the onset of
symptoms occurred in many cases very soon after the administration of the drug —
on an average about 10 to 30 minutes after the drug was injected. After smaller

ACUTE INTOXICATION — RABBITS. 37

doses were administered by iujectioii into the lumbar muscles the appearance of
symptoms was delayed several hours in some cawes. The duration of life in thtjse 14
rabbits varied considerably. Eight of them died within 1 to 20 hours; six survived.
About 0.2 gram caffein per kilo may be regarded as the minimum fatal dose, while
the minim um toxic dose is somewhere between 130 and 150 mg per kilo.

INTRAVENOUS INJECTION.

These experiments were carried out on well-fed, full-grown gray rabbits. The diet
for several days preceding the experiments consisted of oats or carrots, which were given
ad libitum. The injections were made into the ear veins from a burette or by means
of a syringe, the temperature of the caffein solution being about 40° C. Attention
was also directed to the effect of the rate of injection and of the concentration on the
toxicity. The minimum toxic as well as lethal doses were determined as shown in
the following experiments.

Series A.

In these experiments the rate of injection was about 1 cc of 2 per cent caffein solution
per minute.
Rabbit 194. While, female. Weight, 1,310 grams.

October 19: Injected 7.5 cc 2 per cent solution caffein (115 mg per kilo) into the ear
vein. Rabbit showed stiffness; paralysis of extremities appeared soon after. ^f Rabbit
survived.
Rabbit 556. Gray, female. Weight, 1,635 grams.

January 31: 2 p. m., 11 cc 2 per cent caffein (134 mg per kilo) injected into ear vein,
in about 11 minutes; 2.10 p. m., convulsions, rabbit remained lying on its side; during
the rest of the hour it had convulsions occasionally; 3.20 p. m., convulsions and died.
Rabbit did not urinate after the injection of caffein.
Rabbit 657. Gray, female. Weight, 1,.5S0 grams.

January 31: 2.30 to 2.37 p. m., 7 cc 2 per cent caffein injected from the burette at
the rate of 1 cc per minute; 2.37 p. m., flow of liquid ceased, veins were engorged and
bled freely, injection was continued by means of a sjTinge; 2 cc 2 per cent caffein
injected in two minutes; injections discontinued as convulsions appeared; 2.50 ]). m.,
rabbit raised itself but fell over; 3.10 p. m., rabbit assumed normal attitude, walked
about the floor without manifesting any signs of the effects of caffein; 4.30 p. m.,
walked about, gait normal, condition seemed to be good.

February 1: 2 p. m., condition good, appetite good, total amount of caffein injected,
9 cc 2 per cent solution, or 114 mg per kilo.
Rabbit 558. Gray, female. Weight, 1,590 grams.

January 31: 3 p. m., given 8 cc 2 per cent caffein in eight minutes; 3.10 p. m.,
violent conAoilsions ; 3.20 p. m., rabbit was stretched out on his abdomen, extremities
extended, urinated; 4.30 p. m., looked normal; was able to walk about.

February 1: 2 p. m., condition good, appetite good.
Rabbit 292. Belgian hare, male. Weight, 1,770 gram^.

February 18: 4.26 to 4.39 p. m., 12.5 cc warm caffein solution (0.141 gram per kilo)
injected into ear vein, convulsion followed when this quantity was injected, tonic
rigidity of limbs followed soon after; 4.52 p. m., condition unchanged, rabbit on floor,
limbs stretched out, and lying on abdomen.

Rabbit 294. Belgian hare, female. Weight, 1,350 grams. Carrot diet for about 10 days
before the experiment.

February 19: 12.20 p. m., 5 cc 2 per cent caffein (74 mg per kilo) injected into
ear vein in five minutes, edema of the ear, other ear used, 3.5 cc injected in 10 min-
utes, repeated convulsions; 1.25 p. m., rabbit still alive, frequent attacks of convul-
sions; 2.30 p. m., found dead. Total amount injected in 15 minutes, 8.5 cc, or 0.126
gram per kilo.

It will be observed in the preceding experiments that symptoms of severe intoxi-
cation were present in all of the six rabbits, but only two of these (Nos. 294 and 556)
died from the effects of caffein. Of those which survived, three received doses of

a Time of Injection Inadvertently omitted, but was probably not slower than In the other cases of this
series.

38 THE TOXICITY OF CAFFEIN.

100 to 114 mg caffein per kilo, and another (No. 292) received 141 mg of caffein per
kilo. The death of rabbits Nos. 294 and 556 may be regarded therefore as a case of
exceptionally low resistance to caffein.

Series B.

Doses of 160 to 200 mg caffein per kilo were employed in these experiments. The
rate of injection was 1 cc per minute, with the exception of Experiment 254, in
which 10.8 cc 2 per cent caffein were introduced in 17 minutes and 25 seconds.
Rabbit 562. Gray female. Weight, 1,650 grams. Diet, oats.

February 1: Injection began at 3 p. m., injected 10 cc in 12 minutes; 3.01 p. m.
to 3.09 p. m., 3 cc injected, convulsions; 3.09 p. m. to 3.14 p. m., 3 cc injected, fol-
lowed by violent convulsions, marked opisthotonos; 4.30 p. m., rabbit died; total
quantity injected, 16 cc.
Rabbit 561. Gray female. Weight, 1,450 grams. Diet, oats.

February 1: Injection began at 11.40 a. m.; 11.48, rabbit struggled, 7 cc 2 per cent
caffein injected; 11.50, convulsions, 10 cc 2 per cent caffein total amount injected;
11.55 a. m., injections stopped; injections resumed 11.58, violent convulsions, injec-
tions discontinued, total quantity received, 14.5 cc 2 per cent caffein solution; 1.30
p. m., found dead, did not m-inate, 25 cc urine found in the bladder.
Rabbit 560. Gray male. Weight, 1,620 grarris. Diet, oats.

February 1: Injection began 11 a. m.; 11.10 a. m., 7 cc 2 per cent caffein injected,
rabbit struggled; 1 cc was injected during the next three minutes, rabbit struggled
but there were no convulsions, injection stopped; resumed at 11.15 a. m. and
continued 10 minutes, 8 cc 2 per cent caffein introduced during this time; total
amount caffein injected, 16 cc; reflexes markedly increased; 12 noon, tetanic con-
vulsions off and on until 2 p. m., then remained stretched out on abdomen, extremi-
ties extended.

February 2: 9 a. m., found dead.
Rabbit 559. Gray female. Weight, 1,875 grams. Diet, oats.

January 31: 4 p. m., convulsions after injection of 9 cc 2 per cent caffein in 14
minutes; 4.08 p. m., convulsions after injection of 7 cc caffein in 8 minues; 4.10 to
4.12 p. m., injected 2 cc more, rabbit lying stretched out on abdomen, extremities
extended; total amount of caffein injected, 18 cc (190 mg per kilo).

February 1: 2 p. m., condition good, walked about, appetite good, passed 155 cc
dark, reddish-brown urine since 5.30 p. m. previous day.
Rabbit 279. Gray and white female. Weight, 1,S20 grams.

February 24: 10.09 a. m., 6 cc 2 per cent caffein passed rapidly into jugular vein;
10.15 a. m., involuntary twitching of muscles of legs, but no other symptoms; 10.23
to 10.26, 3 cc of 2 per cent caffein injected; 10.27 to 10.28, 2 cc 2 per cent caffein
injected, convulsions; 10.29, convulsions stopped; 10.32, convulsions; 11 a. m., rab-
bit lying on its side, anterior extremities paralyzed, posterior extremities contracted,
no clonic convulsions, breathed deeper and more slowly than normal; 11.10 a. m.,
rabbit died, had no convulsions immediately before death; amount of caffein injected,
11 cc 2 per cent solution, or 0.166 gram per kilo.
Rabbit 254. Belgian hare, female. Weight, 1,285 grams. Diet, oats.

November 12: 1.30J to 1.47f p. m., received 10.8 cc 2 per cent caffein from burette
into ear vein, after injection of 6.2 cc dyspnoea, 6.7 cc struggling, convulsions; at
1.50^ p. m., released from holder, paralysis especially marked in the anterior extremi-
ties; 1.50 p. m., recovered, survived; total amount injected^ 10.8 cc 2 per cent
caffein in 17 minutes and 25 seconds, or 0.16 gram caffein per kilo.
Rabbit 255. Belgian hare, male. Weight, 1,105 grams. Diet, oats.

November 12: 2.311 to 2.35i p. m., received 3.7 cc; from 2.37^ to 2.46J- p. m., 5 cc
injected; after injection of 6.1 cc convulsions followed by dyspnoea, then contin-
uous struggling; when 8.3 cc were injected rabbit had another convulsion; 2.47 p. m.,
tonic contraction of anterior extremities; amount injected, 8.7 cc (158 mg per kilo)
in 15 minutes and 35 seconds.
Rabbit 567. Gray female. Diet, oats.

February 6: Injection began at 4.11 p. m.; 4.18, convulsions after injection of
5 cc 2 per cent caffein; 4.21, convulsion after total injection of 8 cc; 4.24 p. m., injec-
tion resumed and 2 cc more introduced; 4.28 p. m., convulsions, injected 2 cc more;
total caffein injected, 12 cc, or 162 mg per kilo; 4.40 p. m., rabbit paralyzed in pos-
terior extremities; 5 p. m., found dead.

ACUTE INTOXICATION — RABBITS. 39

In the eight experimentH compriHinp soricH B nibbit.s Noh. oG7, 254, 279, and 255,
which may be dcHignuted as Group II, received doHcs of lfj2, IfJO, IGG, and 158 mg,
respectively. Nos. 5(>2, oGl, 5(50, and 559, which may be designated as Group I,
received about 200 nig caffein per kilo. In Group II, which received the smaller
doses, one (No. 254) survived. This may be regarded aH exceptional, since, a.s was
shown in the experiments of the preceding series, even smaller doses may be fatal.
About IGO mg ])or kilo is, therefore, the smallest surely fatal dose. Thus might be
regarded aa a contradiction of the results obtained for rabbit No. 559, but it will be
noticed that in this Ciise diuresis was very marked. The results of experiments
Nos. 294 and 255 are of interest in this connection, since they indicate that a moderate
difference in the rate of injection is without any effect on the toxicity of caffein.
The greater resistance to caffein of rabbit No. 559 is in all probability due, therefore,
to increased diuresis.

Series C.

In these experiments the minimum toxic dose was determined. The conditions
were the same as in the experiments of the other series.

Rabbit 29S. Belgian hare, female. Weight, 1,610 grams. Diet, oats.

February IS: 3.40 to 3.43 p. m., 4 cc 2 per cent warm caffein solution injected into
ear vein, convulsions when 3 cc were injected, repeated attacks; 4 p. m., raised itself
on legs, but fell over immediately and lay stretched on abdomen.

February 19: 9 a. m., rabbit looked normal, apparently recovered.
Rabbit 227. White male. Weight, 2,320 grams.

October 26: 3.29} to 3.37^ p. m., injected into ear from burette G.7 cc 2 per cent
caffein, no symptoms; experiment discontinued; survived.
Rabbit 563. Gray female. Weight, 1,650 grams. Diet, oats.

February G: Injection began at 1.02 p. m., injected 3.5 cc 2 per cent caffein (42 mg
per kilo) in four minutes, O.G cc more Avithin the next two and one-half minutes, total
amount injected 4.1 cc; 1.10 p. m., hypersensitive, some disturbance of muscular
coordination; restlessness; 1.35. p m., reflexes decreased, urinated and walked about,
gait normal. Under observation for several days; no symptoms noted.
Rabbit 564. Gray female. Weight, 1,515 grams.

February 6: Injection began at 1.26 p. m., 3.5 cc 2 per cent caffein (46 mg per kilo)
injected at the rate of 1 cc per minute; 1.30 p. m., reflexes increa.sed; 1.34 p. m.,
marked paresis of the extremities, rabbit stretched out on abdomen, legs abducted
and partly extended, able to hop about but gait disturbed, no untoward symptoms
noticed, under observation for several days after experiment.
Rabbit 565. Gray female. Weight, 1,. 545 grains. Diet, oats.

February G: Started to inject at 3.40 p. m., received 2.5 cc 2 per cent cafTein intra-
venously in two minutes or 32 mg per kilo, under observation all afternoon, no
symptoms.

Rabbit 566. Gray female. Weight, 1,900 gram^. Diet oats.

February G: Injection began at 3.05 p. m., received 3 cc 2 per cent caffein intra-
venously in three minutes or 31 mg per kilo, no symptoms observed.

These experiments show that a dose of about 50 mg per kilo when injected intra-
venously produces mild symptoms, such as increased reflexes. In the four experi-
ments with this amount of caffein these effects were observed in each case. In the
experiments in which smaller quantities, 30 mg per kilo, were given intravenously
there was no manifestation of symptoms. A dose not over 50 mg per kilo may, there-
fore, be regarded as the minimum toxic dose when injected intravenously under the
conditions stated .

Series D.

A 0.5 per cent caffein solution was used in these experiments in order to test the
effect of concentration on its toxicity; the rate of injection was 1 cc per minute.
Rabbit 569. Gray male. Weight, 1,475 grams. Diet, oats.

February 6: 11.50 a. m. to 12.01 p. ni., injected 10 cc 0.5 per cent caffein; 12.03
to 12.12 p m., injected 10 cc of 0.5 per cent caffein; 12.13 to 12.26 p. m., injected

40 THE TOXICITY OF CAFFEIN".

10 cc of 0.5 per cent caffein, total amount injected, 30 cc; 12.20, passed 35 cc of urine;
12.30, increased reflexes, but no convulsions; 4 p. m., reflexes increased.

February 11: Alive, condition good.
Rabbit 574- Gray female. Weight, 1,555 grams. Diet, oats.

February 8: 10.25 to 10.33 a. m., injected 4 cc of 0.5 per cent caffein in salt solution,
injection discontinued for five minutes; 10.38 to 11.10, injected 30 cc, total amount
of caffein solution received, 34 cc; 11.55 a. m., very sensitive; reflexes markedly
increased.

I February 9: Alive, condition good.
Rabbit 571. Gray female. Weight, 1,530 grams. Diet, oats.

February 7: Injection 3.18 to 3.50 p. m., received 30 cc in 32 minutes, not hyper-
sensitive; 3.55, restlessness and weakness of extremities; 4.10 p. m., control of ante-
rior extremities impaired, distinctly paretic but tried to walk about, died the same
afternoon.
Rabbit 568. Gray male. Weight, 1,605 grams. Diet, oats.

February 7: Injection 10.53 to 11.01 a. m., injected 10 cc 0.5 per cent caffein; 11.03,
injection resumed after two minutes interval; 11.14, received 10 cc 0.5 per cent
caffein intravenously in 11 minutes; 11.16, injection resumed; 11.35, received 12 cc
0.5 per cent caffein, total amount of caffein solution received, 32 cc; 12.30 p. m.,
urinated 14 cc of bloody urine; 12.55 p. m., convulsions and death a few minutes later.
Autopsy showed congestion of viscera, but no other lesions.
Rabbit 570. Gray female. Weight, 1,225 grams. Diet, oats.

February 7: 2.06 to 2.35 p. m., injected 24.5 cc 0.5 per cent caffein, reflexes increased
but no convulsions, paresis especially marked in the anterior extremities; 3 p. m.,
passed xuine which was normal in appearance, reflexes not increased but rabbit was
weak.

February 9: Found dead. Autopsy: Liver, spleen, and kidneys congested; large
intestines hemorrhagic; omentum congested and showed the presence of small caseous
nodules; liver showed adhesion to diaphragm; viscera presented the appearance of
intraabdominal infection.

I Of the five rabbits of this series three died as a result of the administration of caffein.
The other two which survived showed mild symptoms only, such as increased reflexes,
but no evidence of severe poisoning such as was observed after the injection of the
same doses of caffein in series A when a 2 per cent solution of caffein was injected.
Convulsions were noticed in one case only (No. 568); paresis in two cases (Nos. 570
and 571). The nervous symptoms even in this group, therefore, were much milder
than in series A. The percentage of death, however, was greater than in series A, in
which the concentration of caffein was four times as great. It is quite probable that
the strain on the heart due to the sudden increase in volume of the blood and its dilu-
tion might be an important factor in increasing the toxicity of caffein. It is conceiv-
able that doses just sufficiently large to depress the normal heart may cause paralysis
of an already overstrained organ.

Series E.

In the two experiments of this series the rate of injection as a possible factor influ-
encing the toxicity of caffein was tested. A 2 per cent caffein solution was injected
at the rate of 1 cc in two and one-half to three minutes.

Rabbit 572. Gray male. Weight, 1,770 grams. Diet, oats.

February 8: Injection began at 3 p. m., discontinued at 3.37 p. m., and resumed at
3.38 p. m. ; rabbitwas restless; injection finished at 3.52 p. m. Total quantity received,
17.4 cc 2 i^er cent caffein intravenously in 52 minutes; struggled intermittently during
the injection; anterior legs paralyzed.

February 9: Found dead.
Rabbit 57.3. Gray male. Weight, 1,810 grams. Diet, oats.

Februarys: Started to inject at 1.35 and discontinued at 2.27 p. m.; received 18 cc
2 per cent caffein intravenously in 52 minutes; reflexes markedly increased soon
after; 2.45, passed bloody urine; 4.30 p. m. reflexes increased; no other symptoms.

February 9: 9 a. m., found dead.

It will be observed that some retardation of the onset of symptoms was caused by
slower injection, but the final result was the same as when liie injections were made

ACUTE INTOXICATION — RABBITS.

41

more rapidly. It is ciiiito probable, therefore, that a much slower rate of injection
may lessen considerably the toxicity of caffein.

From the re.'^ults of the experiraenta by intravenous injection summarized in the
table, it appears that tlie niiuinuim toxic dose for rabbits of a 2 per cent caffein solu-
tion, injected at the rate of 1 cc per minute, is about 50 mg per kilo. Twice the dose
induces severe symptoms and may be fatal; 1(50 mg per kilo are surely fatal. If the
rate of injection is diminished, the toxit-ity of caffein is lessened, but this effect is
not marked unless the injections are very slow. Dilution of the caffein solution sup-
presses to some extent the nervous symptoms, but the toxicity, on the contrary, eeema
to be increased.

Table 5. — Intravenous injecticms.

SERIES X.

No.

Weipht.

Caftcia
per
kilo.

Symptoms.

Duration of life.

Diet.

Remarks.

1f)4

Orams.
1,310
1,635
1,580
1,590
1,770
1,350

Mg.
114
134
114
100
141
126

Present...
10 minutes
Present...
...do

Survived

Oats

...do

Mfi

20 minutes

Gray female.

f\M

Survived

..do

558

do

.do.. ..

Do.

■X)->

...do

do

...do

Do.

1<»4

...do

10 minutes

Carrots

Do.

SERIES B, GROUP I.

w

1.650
1,450
1,620
1,875

200
200
200
190

1 J hours

Oats

.do

Gray female.

5til

do

5ti0

Present...
...do

Less than 24 hours

.do .

Do.

."vSq

Survived

...do

Do.

SERIES B, GROUP II.

?7<»

1,320
1,285

166
160
162
158

1 hour

Gray and white female.
Grayfemale.

?54

Survived

Oats

.567

?'>.5

Died

SERIES C.

M?

1,610
2,320
1,650
1,515
1,545
1,900

500
570
500
460
320
310

Present. . .
None

Survived

Oats

Gray female.

??7

do

56.{

Present. . .
...do

do

.do

Grayfemale.

.')fi4

do

.S65

None

do

.do . .

Do.

566

...do

do

...do

Do.

SERIES D.

<m

1,475
1,5.55
1,530
1,605
1,225

100
112
100
100
100

Present...
...do

Survived

Oats

do

Gray male.
Grayfemale.

.574

.. ..do

.571

...do

About 2 hours

...do

.56,S

20 minutes

.do

.570

. .do

"Do

SERIES E.

.572

1,770
1,810

200
200

Present..

. About 24 hours

Oats

.do .

fiV.I

do

i ■

42 THE TOXICITY OF CAFFEIN".

SUMMARY.

The results of the experiments on rabbits show considerable variation in the toxicity
of the single dose. Individuals differed so widely in their resistance to this drug
that the same experiments had to be repeated many times with each method of ad-
ministration before satisfactoiy conclusions could be drawn. This is strikingly
illustrated in the experiments by intravenous injection in which a dose of nearly 0.2
gram per kilo was not fatal. Similar instances of exceptional resistance or of sensi-
tiveness to caffein were observed when it was given in other ways. A comparison
of the toxicity of caffein administered by different methods in this investigation
shows well-marked differences in its activity, although they are not quite so striking
as similar experiments with other alkaloids reported by several observers. The tox-
icity of caffein in these experiments on the rabbit indicates that it is greatest when
given by vein and least when given by mouth. The ratio of the minimum toxic
doses by these two methods of introduction of caffein was about 7.1; the relation of
the miaimum fatal dose was about 3.1. The toxicity when given subcutaneously is
about 15 to 20 per cant greater than when given by mouth. The difference between
the intramuscular and subcutaneous injection is even more marked. The toxicity
of caffein when injected into the muscles is about midway between that adminis-
tered by the subcutaneous and intraperitoneal routes, and is about half that injected
intravenously. Meltzer and Auer, ** who experimented with a number of drugs
found that the intramuscular method of administration is as effective as the intravenous,
fluorescin formiag the only exception according to their observations. In the experi-
ments of Sollman and Brown *^ with ergot, the effect was quite different from those
obtained by Meltzer and Auer ^^ with the drugs they used. It is quite possible that
the result obtained with ergot is merely illustrative of a difference in the behavior of
various substances in this regard. This appears probable on account of the difference
in the rate of absorption for various substances. Thus, according to Achard, Gaillard,
and Ribot (Compt. rend. Soc. biol., 1907, 62: 90), absorption from the peritoneal
cavity varies with the concentration of the solution and the size of the molecule. The
smaller the molecule and the greater the concentration the more rapid the absorp-
tion. That the rate of absorption from the intramuscular tissues is unequal and
varies for different substances appears from the experiments of Meltzer and Auer. ^^
The difference was very striking between intramuscular and subcutaneous adminis-
tration of curara or adrenalin; the results were somewhat different with morphin and
with fluorescin. As shown in their protocols, the onset of the symptoms after the
intramuscular injection of morphin was sooner than after subcutaneous injection,
but in time the difference diminishes and disappears altogether. The absorption of
fluorescin is much faster when the intramuscular path is used than when given sub-
cutaneously, but the writers state that the rate falls far behind that of the intravenous
administration. The difference in toxicity we observed between feeding by mouth
and subcutaneous injection, although distinct, was not very great. It was much
less than Maurel ^^ obtained with the hydrobromid of caffein in the rabbit. Whether
this difference between his results and ours is due to the use of the pure alkaloid in ';
our experiments and the hydrobromid employed by Maurel can not be stated at <
present with any degree of accuracy. It is hoped that the work in progress in the
laboratory will throw some light on the subject in the near future. But Maurel's ""
experiments show that various substances behave differently in this regard. Thus
the toxicity of strychnin, he states, is three times as great when given subcutane-
ously as when given by mouth and six times that of the minimum fatal dose by vein.
It may be remarked, however, that examination of his data shows that his doses are
much too large for the rabbit. In experiments with other drugs little or no difference
between the two modes of administration was noticed. Thus, digitalin was but
slightly more active when given subcutaneously than by mouth, while the toxicity
of emetin hydrochlorid was just the same, whichever one of these methods of Intro-

ACUTE INTOXICATiaN GUINEA PIGS. 43

ducing the subatance was used. Differences in the toxicity of substances have also
been observed betweeu subcutaneous and iutruvenijurf modes of administration,
but here, too, the differtjucvs for vatious substances wore unequal.

EXPERIMENTS ON GUINEA PIGS.

The toxicity of caffein was studied in a large number of individuals. The experi-
ments were conducted on fuU-j^rown animals and were carried out at different seasons
of the year in a variety of ways. Special attention was given to di-it aa a poasible
factor influencing resistance to caffein, and the effect of different modes of adminis-
tration on toxicity. Some animals were therefore fed oats, some carrots, others re-
ceived both hay and oats. Caffein was introduced subcutaneously, intraperitoneally,
and by mouth.

SUBCUTANEOUS INJECTION.

Series A.

Preliminary experiraentd carried out on three guinea pigs, which received 360,
300, and 290 mg of caffein per kilo subcutaneously have shown that such doses were
rapidly fatal. Two of the animals were seized with convulsions half an hour after
the introduction of caffein and died during the attack. The other had tetanus two
minutes after the injection of caffein. Repeated attacks followed, which terminated
in the death of the animal two and a half hours later. The fatal and toxic doses must
therefore be considerably under 0.3 gram of caffein per kilo when introduced by this
path and smaller doses were therefore injected. The results are shown in the experi-
ments of the next series.

Series B.

Experiments with 2 decigrams per kilo constituted this series.
Guinea pig 20. Female. Weight, 497 grams. Diet, oats.

April 2: 5 cc 2 per cent caffein injected subcutaneously at 11.30 a. m.; 1.50 p. m.,
epasm of short duration. Died at 3 p. m., three and one-naif hours after injection.
Guinea pig S8. Brovm male. Weight, 570 gram^. Diet, carrots and oats week previous
to injection.

February 11: 3.50 p. m., 6 cc 2 per cent caffein injected subcutaneously in back
(210 mg per kilo); 4.15, reflexes increased, had convulsion of short duration when
disturbed; 4.45 p. m., on handling, repeated convulsion and paralysis; 5 p. m., guinea
pig l>"ing on his side, respiration difficult and labored.

February 11: 5.05 p. m., guinea pig found dead, 2 hours and 15 minutes after
injection.

Guinea pig 37. Male. Weight, 820 grains. Diet, carrots and oats during week pre-
ceding the injection ofcafein.

February 11: 3.35 p. m., 8.5 cc 2 per cent caffein injected subcutaneously in the
back; 5 p. m., pig very sensitive, anterior extremities paralyzed when handled, fre-
quent spasms of posterior extremities, no symptoms noticed before 5 p. m., although
watched all the time; 5.05 p. m., guinea pig on his legs and looked normal. No attack
on handling.

February 12: 9 a. m., found dead; died within 18 hours.
Guinea pig l.L Female. Weight, 61S grams. Diet, oats.

March 29: 2.45, 6 cc 2 per cent caffein injected subcutaneously (0.194 grams per
kilo).

March 30: Died at 4 p. m., 25 hours after injection.
Guinea pig 36. Male. Weight, 850 grams. Fed oafs and carrots for one week previous
to injection.

February 11: 3.30 p. m., 8.5 cc 2 per cent caffein injected subcutaneously into
back; 5 p. m., somewhat more sensitive than normal, no other symptoms, no effect
on handling; 5.05 p. m., no symptoms.

February 12: 9 a. m., found dead, about 18 hours after injection.

The results of these experiments, as observed in five guinea pigs, indicate that
two decigrams of caffein per kilo of animal produce svTmptoms within a half to about
two and a quarter hours after injection. Death followed iu two guinea pigs 70 minutes

44 THE TOXICITY OP CAFFEIN.

to 1 hour after the first manifestations of symptoms. Two others died during the
night, while one lived 25 hours after the injection of caffein. Even 2 decigrams
caffein per kilo weight might therefore be fatal to the guinea pig. Experiments
carried out later have shown, however, that the resistance to caffein is appreciably
greater in some guinea pigs. This is indicated by the following experiments, in which
doses of 0.2 to 0.24 gram caffein per kilo were administered by the same path.

Series C.

Guinea pig 66. Yellow and dark brown male. Weight, 510 grams. Diet, oats.

October 4: 5 cc 2 per cent caffein (0.2 gram per kilo) injected subcutaneously in
the back at 3 p. m.; 5 p. m., no symptoms.

October 5: 9 a. m., alive; condition good.

October 9: Found dead. Autopsy: Congestion of liver, kidney, and small intestine.
Guinea pig 65. White and black male. Weight, 510 grams. Diet, oats.

October 4: 5 cc 2 per cent caffein (0.2 gram per kilo) injected subcutaneously in
the back at 3 p. m.; 5 p. m., no symptoms.

October 5:9 a. m., condition good.
Guinea pig 60. White and gray female. Weight, 320 grams. Diet, oats.

October 3: 2.25 p. m., 3.5 cc 2 per cent caffein ((0.219 gram per kilo) injected sub-
cutaneously in the back; 3.40 p. m., convulsion with recovery; 3.50 p. m., frequent
spasms with paralysis, especially of anterior extremities; 5.30 p. m., tetanus when
removed from cage and put on floor.

October 4: 8.50 a. m., found dead. Autopsy: Congestion of small intestines, limgs,
liver.
Guinea pig 57. White and gray female. Weight, 350 grams. Diet, oats.

October 3: 2.15 p. m., 3.5 cc 2 per cent caffein injected subcutaneously in the back
(0.2 gram per kilo); 3.40 p. m., convulsions with recovery; 5.30 p. m., no marked
symptoms.

October 4: 8.50 a. m., alive, active.

October 6: Found dead at 9 a. m. Autopsy: Congestion of lungs and liver; kidneys
petechiated; severe gastro-enteritis.
Guinea pig 68. Yellow male. Weight, 785 grams. Diet, oats.

October 6: 11.35 a. m., 7.8 cc 2 per cent caffein (0.2 gram per kilo) injected subcu-
taneously; 12 noon, reflexes increased markedly; 4.20 p. m., reflexes the same as at
12 noon.

October 7: 9 a. m., dead. Autopsy: Limgs congested; liver congested and fatty;
spleen congested, kidney showed hemorrhagic spots; gastric mucosa necrotic; small
portion of small intestine inflamed.
Guinea pig 69. White male. Weight, 585 grams. Diet, oats.

October 6: 11.40 a. m., 5.8 cc 2 per cent caffein injected subcutaneously; 12 noon,
reflexes increased, but not as much as in No. 68; 4.20 p. m., guinea pig hypersensitive,
reflexes increased more than at 12 noon.

October 7:9 a. m., alive.

October 15: 9 a. m., found dead.
Guinea pig 61. Brown and black female. Weight, 330 grams. Diet, oats.

October 3 : 4 p. m.^ 4 cc 2 per cent caffein (240 mg per kilo) injected subcutaneously;
5.30 p. m., reflexes increased; runs, but drags posterior extremities.

October 4: 8.50 a. m., found dead.
Guinea pig 62. White, yellow, and black female. Weight, 335 grams. Diet, oats.

October 3: 4.05 p. m., 4 cc 2 per cent caffein (238 mg per kilo) injected subcu-
taneously in the back; 5 p. m., convulsions; 5.20 p. m., convulsions, alternating with
paralysis of anterior and posterior extremities.

October 4: 8.50 a. m., found dead.
Guinea pig 10. White and brown male. Weight, 545 grams. Diet, oats.

October 7: 3 p. m., 6.5 cc 2 per cent caffein (238 mg per kilo) aqueous solution
injected subcutaneously; 3.50 p. m., reflexes increased.

October 9: 9 a. m., found dead.
Guinea pig 71. Br ovm and white male. Weight, 540 grams. Diet, oats.

October 7: 3 p. m., 6.5 cc 2 per cent caffein solution (0.24 gram per kilo) injected
subcutaneously; 3.45 p. m., reflexes increased, tetanus.

October 9: 9 a. ui., found dead.

ACUTE INTOXICATION — GUINEA PIGS. 45

Guinea pig 72. Brown and white male. Weipht, .560 grams. Diet, oats.

October 7: 3 p. m., 6.5 cc 2 per cent caffein (0.232 gram per kilo) aoueous solution
administered by subcutaneous injection; 3.35 p. m., reflexen increa.><eu.

October 10: found dead. Autopsy: Nos. 70, 71, 72 showed congestion of organs.

The reaction to caffein in the e.xperimcnta of this series (C) showed considerable
variation. Tiie appearance of symptoms, as well as the final outcome of the experi-
ments, differed markedly in a number of cases, notwithstanding the fact that tho
conditions were the same; thus the administration of 0.2 gram per kilo to guinea
pigs, all of which received the same diet, induced no symptoms in two of the animals
(Nos. 66 and 65), while marked symptoms were observed in the other four; in two
of these tho symptoms appeared in one hour and a quarter after injection, and in two
others (No.-<. 68 and 69), mild symptoms only appeared in 20 or 25 minutes. Tlie
last two were under observation for 4 hours longer, but there was no visible change
in their condition. The duration of life in all of these guinea pigs, as indicated in
the table, likewise varied. Two (Nos. 60 and 68) died during the night after they
received caffein, one survived (No. 65), and three others (Nos. 57, 66, and 69) lived
2J, 5, and 9 days, respectively. Experiments with larger doses likewise showed
differences in the behavior of these animals toward caffein, but they were not quite
80 marked. As shown in the table, symptoms appeared in from 35 minutes to 1 .5 hours
after injection. The duration of life was less than 1 day in two pigs, about twice as
long in two others, and in one case between 2 and 3 days.

A comparison made with results obtained in the preceding series shows a striking
difference in the resistance to caffein. As 2 decigrams per kilo proved more rapidly
fatal to the guinea pig than the larger doses employed in the later experiments, this
difference in the resistance to caffein may be due to several factors. As pointed out
in the experiments on rabbits, age might be an important factor influencing the
toxicity of caffein. Unfortunately, no accurate data were available on the age of the
guinea pigs, but they were all apparently full grown, although they differed in weight
considerably. The difference in their ages was in all probability not ver>' great.
Moreover, it will be observed that the resistance in series B and C differed in animals
of approximately the same weight. This is evident on comparing experiments Nos.
20, 38, and 13 of series B with Nos. 65, 66, and 69 of the next series. Again, further
inspection and analysis of these tables show no difference in the toxicity, although
there may be considerable difference in the weight, from which it may be concluded
that the animals were of about the same age or that this plays no part in the resistance
to caffein in the guinea pig.

Diet is another factor which should be taken into consideration in this connection.
The recent work of Ilunt^' indicates that this may influence the resistance of animals
to some poisons. Our experiments, however, fail to show any difference in the toxicity
of the caffein in guinea pigs, whether fed oats, carrots, or both, for different results were
obtained on the same diet, and there seemed to be little or no difference in the toxicity
of caffein when the diet was different. Other explanations suggest themselves to
account for the results obtained. Seasonal changes have been assigned by a number
of investigators as a cause of variation in the resistance to drugs. According to Focke,-*
frogs are more susceptible to digitalis in the spring than in the summer, while Mosch-
kowitsch ** and Edmunds -' reported the very opposite results. Schmiedeberg's ^
obsers-ations on strophantin in frogs were in harmony with those of Edmimds -^ and
Moschkowitsch."^ Similar results were reported with guinea pigs. Harrington's ^*
experiments indicate that stimulation of the vagus is less effective from October to
January than from February to April, when they are also much more susceptible to
operative procedure. Hunt found that the resistance of guinea pigs to aceto nitril is
about twice as great in the summer months as it is in January and February.

Race might also be thought of as an important factor in this connection. Since the
guinea pigs used at different seasons of the year were of several varieties, there is no

46 THE TOXICITY OF CAFFEIN.

reason to suppose, however, that the varieties experimented upon in the summer
were more resistant than those used in the winter and spring. It is highly probable,
therefore, that the greater resistance to caffein of the guinea pigs of series C than those
of series B was due to seasonal variation.

Doses of 0.20 to 0.24 gram caffein per kilo weight, therefore, may be regarded as the
minimum fatal dose for the guinea pig, depending upon the season. Since 0.2 gram
per kilo proved to be rapidly fatal in series B, this quantity was perhaps not the
minimum fatal dose for the guinea pig at the season during which the experiments
were made. Additional tests with smaller doses were therefore carried out during
February and March. The results are shown in series D.

Series D.

Guinea pig 49. Male. Weight, 510 grams. Diet, oats Jor 1 month previous to experi-
ment.

March 17: 3 p. m., 4 cc 2 per cent caffein (0.16 gram per kilo) were injected sub-
cutaneously; 4.40 p. m., reflexes increased; 5.40 p. m., no symptoms.

March IS: 9 a. m., found dead, died in less than 18 hom-s. Autopsy: Hemorrhage
into abdominal cavity; liver and spleen unduly congested; intestines injected;
hemorrhagic area at point of injection.

Guinea pig 40. Male. Weight, 630 grams. Diet, oats and carrots one week previous to
injection.

February 12: 11 a. m., 5 cc 2 per cent caffein (0.158 gram per kilo) injected subcu-
taneously into back.

February 13: 1 p. m., still alive.

February 14: 9 a. m., found dead.
Guinea pig 45. Female. Weight, 435 gram^. Diet, oats for about one mxjnth previous to
injection.

March 17: 3 p. m., 3.5 cc of 2 per cent caffein injected subcutaneously in the back
(0.160 gram per kilo); 4.35 p. m., no symptoms; 5.40 p m., no symptoms.
Guinea pig 39. Male. Weight, 820 grams. Diet, oats and carrots.

February 12: 11 a. m., 6 cc (0.15 gram per kilo) 2 per cent caffein injected subcu-
taneously in back.

February 14: 9 a. m., alive; seemed to be in good condition; found dead at 1 p. m.
Guinea pig 41. Weight, 660 grams. Diet, oats and carrots one vjeek previous to injection-

February 12: 11 a. m., 5 cc (0.15 gram per kilo) 2 per cent caffein injected subcu"
taneously.

February 14: 2 p. m., pig alive; apparently normal.

February 18: Guinea pig still alive and apparently in good condition.
Guinea pig 46. Female. Weight, 470 grants. Diet, oats about one month previous to
experiment.

March 17 : 3.15 p. m., 4 cc (0.170 gram per kilo) 2 per cent caffein injected into back
subcutaneously; 4.35 p. m., reflexes increased, tremors on handling marked; 5.40 p.
m., no change, symptoms about as before.

March 18: 2.30 p. m., no symptoms.

The experiments of this series (D) likewise showed a considerable difference in the
resistance of the individual guinea pigs. Nos. 41, 45, and 46 survived; the rest of
the pigs died within 18 hours to 2 days after the administration of caffein. Since an
autopsy was held on one only, it is impossible to assign a cause for the variation in the
toxicity of caffein in these guinea pigs, as the diet and the other conditions under
which the experiments were conducted were the same. It was found in the experi-
ments on cats and rabbits that the presence of morbid processes tends to increase the
toxicity of caffein. The observations of Ophiils'^° are of interest in this connection.
He found spontaneous lesions of the kidney and liver in a large proportion of guinea
pigs examined. The greater susceptibility to caffein of guinea pigs Nos. 39, 40, 49,
is probably due therefore to some pathological change which increased its toxicity.
About 0.2 to 0.24 gram per kilo may therefore be regarded as the minimum lethal
dose for the normal guinea pig when caffein is introduced subcutaneously, the mini-
mum toxic dose being about 150-160 mg per kilo.

ACUTE INTOXICATION^ — GUINEA PIGS. 47

Exp>eriments were also conducted to determine the largest dose which does not pro-
duce any vi^^iblo effects. In a number of tests \vith from 100 to 120 mg caffein per
kilo (series E, see Table 6, p. 51) no manifestation of nervous or muscular disturbance
nor any departure from the normal in respiratory activity was observed. Such
quantities may be regarded as the largest doses which are surely safe for these animals.
It is qnito possible, therefore, that the greater variation in the toxicity of caffein
observed in these exi)eriments is due to morbid conditions. Moreover, there is some
evidence that caffein increases the toxicity of certain poisons, as shown by Hale'" for
acetanilid. Is it not possible that caffein may similarly be affected by poisons cir-
culating within the body? Indeed the recent work of Loeb ^' makes this supposition
highly probable. This investigator found that caffein and adrenalin injected together
produce myocarditis in the rabbit. It ia conceivable that the combined action of
caffein and some preexisting poison may cause changes which terminate in the death
of the animal. The delayed death of guinea pigs after the administration of caffein
observed in this and other series may probably be accounted for in this way.

Experiment 57 lends some support to this view. The condition of the kidneys and
the presence of a severe gastro-enteritis are sufficient to account for the death of this
case. Again the frequent association of gastro-enteritis and congestion of the organs
in caffein intoxication iound in different animals makes it highly probable that these
lesions were caused by caffein.

INJECTION INTO THE PERITONEAL. CAVITT.

The experiments were carried out with different doses. All the guinea pigs in
this series were kept on a uniform diet, consisting of oats . Most of them were of average
size and there were no wide variations in their weights. The experiments of series A
with the smallest doses were conducted in March and April; all the other experiments
it will be noticed were made in October.

Series A.

Guinea pig 41- Weight, 700 grams. Diet, oats.

April 1: 3.30 p. m., 4.5 cc 2 per cent caffein (130 mg per kilo) injected into peri-
toneal cavity. 5.35 p. m., symptoms present but no tetanus.

April 2: Found dead about 2 p. m., duration of life about 22 hours. Autopsy:
Subcutaneous hemorrhage at the point of inoculation; serious exudate on visceral
and parietal peritoneum with marked inflammation of peritoneum; portions of
intestines showed slight enteritis.

Guinea pig 49. Male. Weight, 370 grams. Diet, oats.

April 1: 3.15 p. m., 2.5 cc 2 percent caffein (135 mg per kilo) injected into the peri-
toneal cavity; 5.30 p. m., symptoms present; reflexes increased, but no tetanus.
Guinea pig survived.
Guinea pig 47. Female. Weight, 550 grams. Diet, oats since about Fehruary 4-

March 17: 3.30 p. m., 3.5 cc 2 per cent caffein (127 mg per kilo) injected into peri-
toneal cavity; 4.35 p. m., increased irritability present, but not marked; 5.40 p. m.,
symptoms about the same as before.

March 18: 2.30 p. m., condition good; no symptoms. Survived.
Guinea pig ,50. Female. Weight, 290 grams. Diet, oats.

April 1: 3.30 p. m., 2 cc 2 per cent caffein (138 mg per kilo) injected into peritoneal
ca\'ity; 5.35 p. m., symptoms present; reflexes much increased, but no tetanus.
Survived.

Series B.

Guinea pig 51. Yellow female . Weight, 415 grams.

October 1: 9.50 a. m., 3 cc (144 mg per Idlo) 2 per cent caffein injected into peri-
toneal cavity; 4.30 p. m., no symptoms, although under observation all day.

October 3: 2 p. m., alive.
Guinea pig 52. White male. Weight, 450 grams.

October 1: 9.45 a. m., 3.5 cc, 2 per cent caffein (155 mg per kilo), injected into
peritoneal cavity; 4.30 p. m., no symptoms developed since injection.

October 3: 2 p. m., auve.

48 THE TOXICITY OF CAFFEIN.

Guinea pig 53. Brown and rvhite male. Weight, 490 grams.

October 1: 9.45 a. m., 4 cc, 2 per cent caffein (163 mg per kilo), injected into peri-
toneal cavity; 4.30 p. m., no symptoms developed since injection.

October 3: 2 p. m., alive.

October 8: Found dead. Autopsy: Congestion of lungs, spleen, liver, kidneys, and
small intestines.

Series C.

Guinea pig 59. Gray and white. Weight, 375 grams. Di£t, oats.

October 3: 2 p. m., 3.75 cc (0.2 gram per kilo) injected into peritoneal cavity; 2.15
p. m., reflexes increased but not markedly; 4 p. m., reflexes still more increased;
no other symptoms; 5.30 p. m., no symptoms.

October 4: 8.50 a. m., guinea pig alive and active.
Guinea pig 58. Brown and ivhite. Weight, 380 grams. Diet, oats.

October 3: 2 p. m., 3.8 cc caffein (0.2 gram per kilo), 2 per cent solution, injected
into peritoneal cavity; 2.10 p. m., bind legs extended, then tetanus; attack lasted a
few seconds, after which pig raised himself on his legs, but reflexes remained much
exaggerated; 4 p. m. to 5.30 p. m., no symptoms of caffein intoxication.

October 4: 8.50 a. m., guinea pig alive and active.
Guinea pig 56. Gray and white male. Weight, 440 grams. Diet, oats.

October 1: 11.30 a. m., received 4.6 cc of 2 per cent caffein solution (0.2 gram per
kilo) into abdominal cavity; 11.45 a. m., stiffness and rigidity of posterior extremi-
ties, reflexes increased; 12.30 p. m., hind legs paralyzed, reflexes increased; 4.35
p. m., no symptoms, guinea pig in good condition.

October 3: Still alive, in good condition.

October 14: Died. Autopsy: Anterior lobe of right lung hepatized. Small portion
of small intestine edematous. Other organs normal.
Guinea pig 55. White and yellow vnale. Weight, 690 grams. Diet, oats.

October 1: 11.30 a. m., received 6.5 cc of 2 per cent solution caffein (188 mg per
kilo) into peritoneal cavity; 11.40 a. m., stiffness in all extremities, reflexes markedly
increased; 12.30p. m., reflexes increased, anterior and posterior extremities paralyzed;
3 p. m., found dead.

Series D.

Guinea pig 67. Gray and yellow male. Weight, 330 grams. Diet, oats.

October 5: 11.25 a. m., 4 cc of 2 per cent caffein injected into peritoneal cavity
(240 mg per kilo); 11.30 a. m., tetanus — survived, convulsions off and on. Death
at 2.55 p. m. Autopsy: Severe gastroenteritis; kidney petechiated; congestion of
lungs and liver.
Guinea pig 63. Gray and white male. Weight, 340 grams. Diet, oats.

October 5: 11.20 a. m., 4 cc of 2 per cent caffein (235 mg per kilo) injected into
peritoneal cavity.

October 14: Alive and in good condition.
Guinea pig 64. Brown and black female. Weight, 305 grams.

October 5: 11.35 a. m., 3.8 cc 2 per cent solution caffein (250 mg per kilo) injected
into peritoneal cavity; 11.40 a. m., tetanus — survived, convulsions off and on, died
at 4.15 p. m. Autoj)sy: Findings exactly the same as in No. 67.

Examination of the results of the experiments by intraperitoneal injections showed
that 0.2 gram caffein per kilo was toxic in two guinea pigs (Nos. 59 and 58). Severe
symptoms were observed within 15 minutes in No. 56 and within one hour in No.
55 after the administration of approximately the same dose of caffein. One of these
died within three and one-half hours; the other. No. 56, made a good recovery from
the acute effects. This amount of caffein may be regarded, therefore, as the mini.
mum toxic dose for the guinea pig when injected into the peritoneal cavity. This
ia corroborated by the experiments of series B in which smaller doses failed to show
any muscular, nervous, or respiratory symptoms, nor were there any after effects
noticed, as all of them survived and were kept under observation for some time.
The guinea pigs of series A, however, seem to contradict these results. It will be
remarked that appreciably smaller doses induced symptoms in all of them, and one
case terminated fatally. The seasonal variation, as already pointed out, is in all
probability likewise responsible for the difference in the resistance between the

ACUTE INTOXICATION GUINEA PIGS. 49

guinea piga of series A and B. Testa were made also to determine the minimum
fatal dose. For this purpose the experiments of series D were performed. The
resistance of No. 63 in this series is quite striking. We are unable to explain such
a discrepancy in the results obtained under practically uniform conditions. The
minimum fatal dose of caffein, when injected into the peritoneal cavity, Ls therefore
about 240 to 250 milligrams per kilo. These amounts, it will be observed, were
rapidly fatal, in striking contrast to the results obtained when such doeea were injected
Bubcutaneously. This is probably due to a better absorption from the peritoneal
cavity than from the subcutaneous tissues.

ADMINISTRATION BY MOUTH.

All the guinea pigs in these experiments were kept on a diet of hay and oats and
were of large size. The tests were made with different doses of caffein in order to
determine the limits of toxicity when the drug was administered by mouth.
Guinea pig 12Q. White and black male. Weight, 855 grams. Diet, oats and hay.

June 6: 2.20 p. m., 12 cc of 2 per cent caffein (0.28 gram per kilo) by mouth; 3
p. m., reflexes increased; 5 p. m., reflexes still more increased; no other sj-mptoms.

June 7: 9 a. m., found dead; guinea pig passed 75cc urine, which was almost color-
less. Autopsi/: Heart and blood vessels injected; lungs congested; small intestines
congested; other organs apparently normal.
Guinea pig ISO. Black and brown male. Weight, 800 grams. Diet, oats and hay.

June 6: 2.30 p. m., 12 cc of 2 per cent caffein (0.3 gram per kilo) administered by
mouth; 3 p. m., reflexes increased; 5 p. m., increase of reflexes greater than at 3
p. m.

June 7: 9 a. m., found dead; only a few cubic centimeters of urine passed since
4 p. m. Autopsy: Heart and blood vessels injected; lungs congested; small intes-
tines congested slightly.
Guinea pig l.U. White and yellow male. Weight, 860 grams. Diet, oats and hay .

June 6: 2.40 p. m., 12 cc 2 per cent caffein administered by mouth; 3 p. m., reflexes
increased; 5 p. m., reflexes still more marked.

June 7: 9 a. m., found dead, pig passed about 5 cc urine since 4 p. m. of previous day.
Autopsy: Same as in No. 130.
Guinea pig 136. White and black male. Weight, 1,000 grams. Diet, oats and hay.

June 9: 4 p. m., 7.5 cc 2 per cent caffein solution injected subcutaneously into the
back; 4.50 p. m., reflexes increased.

June 10: 9.30 a. m., more sensitive than normal guinea pigs, but reflexes not quite so
marked as at 5 p. m. previous day, about 15 cc urine passed since caffein was injected,
reduction of Fehling's solution considerable, no albumin.

June 13: Alivo and in good condition. Appetite good. (Note. — Parallel test with
urine from two guinea pigs which did not receive caffein failed to show reduction of
Fehling's solution.)
Guinea pig 137. White and broun male. Weight, 925 grams. Diet, oats and hay.

June 9: 4 p. m., 7 cc 2 per cent solution caffein injected subcutaneously; 4.50 p. m.,
reflexes increased.

June 10: Reflexes less marked than at 5 p. m. previous day, but is more sensitive
than normal guinea pig, about 10 cc urine passed since injection of caffein, moderate
amount of reduction of Fehling's solution.

June 13: Guinea pig alive, appetite good, condition good.

June 16: 9 a. ra., found dead.
Guinea pig 135. White and black male. Weight, 955 grams. Diet, hay and oats.

June 9: 3 p. m., 7.5 cc 2 per cent caffein solution given by mouth through stomach
tube; 4.50 p. m., reflexes increased.

June 10 : Keflexes less than on prex-ious day and less marked than in No. 136, a few
cubic centimeters dirty brown urine collected but could not be tested for reduction.

June 13: Condition good, appetite good.

June 16: 9 a. m., found dead.
Guinea pig 134. White and brown male. Weight, 740 grams. Diet, hay and oats.

June 9: 2.55 p. m., 6 cc warm 2 per cent caffein solution given by mouth through
stomach tube; 4.50 p. m., reflexes increased.

18594°— Bull. 148—12 4

50 THE TOXICITY OF CAFFEIN.

June 10: 9.30 a. m., reflexes much lesa than day before, increase slight, a few cubic
centiraeters of urine passed since injection of caffein, looked brown and dirty, could
not be tested for reducing substances.

June 13: Guinea pig alive, appetite good, condition good.

June 14: 9 a. m., found dead.
Guinea pig 128. White and black male. Weight, 1,075 grams. Diet, hay and oats.

June 7: 10 a. m., 11 cc 2 per cent caffein by mouth through stomach tube; 11.10
a. m., no symptoms, no urine passed; 1 p. m., increased reflexes, about 15 cc (esti-
mated) lu-ine passed; 4 p. m., reflexes increased, still more urine passed (about 20 cc);
4.50 p. m., tetanus, frequent attacks, then paralysis and death at 4.58 p. m. Autopsy:
Lungs congested; blood vessels of heart injected; intestines slightly congested; fatty
liver.
Guinea pig 126. White and gray male. Weight, 980 grams. Diet, oats and hay.

June 7: 9.40 a. m., 9.8 cc 2 per cent caffein given by mouth through stomach tube;
10 a. m., no symptoms; 11.10 a. m., no m'ine passed, reflexes increased; 1 p. m., more
sensitive than before; 4 p. m., increase of reflexes more marked, no urine passed; 4.45
p. m., about 15 cc urine collected; 5 p. m., no change.

June 8: 9 a. m., reflexes about the same as 5 p. m. previous day, no urine passed
since 4.45 p. m. previous day, considerable reduction of Fehling's solution, much more
than ui'ine of guinea pig No. 127; 11.05 a. m., convulsions; 12 noon, still alive and
stretched out on abdomen; died at 1 p. m. Autopsy: Lungs badly congested; heart
and blood vessels injected; blood vessels of kidney and of small intestines injected;
liver engorged with blood; a few necrotic spots in stomach.
Guinea pig 127 . White,hlach, and brown male. Weight, 760 grams. Diet, oats and hay.

June 7: 9.50 a. m., 7.6 cc 2percentcaffeinby mouth through stomach tube; 10 a. m.,
no symptoms; 11.10 a. m., reflexes increased, no urine passed; 1 p. m., very sensitive;
4 p. m., sensitiveness increased, about 20 cc xudne passed; 5 p. m., no change.

June 8:9 a. m., reflexes about the same as 5 p. m. previous day; 9.30 a. m., guinea
pig passed 30 cc urine since he received caffein, urine showed a moderate amount of
reduction; 12 noon, convulsions; died at 2.30 p. m. Autopsy: Lungs congested;
blood vessels of heart and of intestines injected; numerous necrotic spots in stomach;
other organs apparently normal.

Examination of the protocols shows that the absorption of caffein from the gastro-
intestinal canal was quite rapid, symptoms having been observed as early as 20 min-
utes after its introduction. The duration of life, it will be remarked, varied with the
size of the dose. When approximately 3 decigrams per kilo were fed, all the animals
died in the night. They lived, therefore, less than 18 hours. Two decigrams per kilo
were likewise fatal, but the duration of life was longer. To decide whether or not this
is the smallest fatal dose, smaller amounts were fed. It seemed at first that about 150
mg per kilo was the smallest toxic dose, and about 200 mg per kilo the minimum fatal
dose. Macroscopic examination of the organs, however, threw some doubt on this
supposition, for well-marked lesions were noticed in all of the guinea pigs which
received 0.2 gram per kilo. It is quite possible, therefore, that the minimum fatal
dose may be somewhat higher, as we have reason to believe that, at least in some patho-
logic conditions, the susceptibility to caffein is increased. The presence of fatty
changes in the liver of No. 128 and the rapid death in this case lends especial support
to this view. Hence, the minimum fatal dose is probably greater than 0.2 gram per
kilo for the normal guinea pig. The doses employed for the tests on guinea pigs Nos.
129, 130, and 131 may be considered therefore the minimum fatal dose for these animals.
It will be also remarked that macroscopical examination of the organs of these animals
failed to reveal the presence of severe lesions. That the minimum toxic dose is prob-
ably much smaller than 0.28 gram per kilo is indicated by the experiments on guinea
pigs Nos. 135 and 134, in which 0.15 gram caffein per kilo induced mild symptoms
in from two to three horns. Both of these, however, and also No. 137 died io\xr to six
days after the drug was fed. As already pointed out, caffein may be a factor in the
delayed death of guinea pigs which received moderate doses of it. That this suppo-
sition may also be true for guinea pigs Nos. 134, 135, and 137 is indeed made probable
by the observation that after moderate amounts of caffein symptoms may persist in
the guinea pig for about 24 hours, and also by the fact that the secretion of urine in

ACUTE INTOXICATION GUINEA PIGS.

51

these animals was very scanty, as shown in the preceding record of the experiraenta;
this means slow elimination of caffein and iLs produrta of decomposition. It is con-
ceivable that the presence of toxic amounts of caffein in the body for a considerable
length of time would induce changes that ultimately lead to the death of the animal
or that morbid processes are set up by the combined action of caffein and some pre-
existing poinon. Since some guinea pigs, however, survived the doses indicated, it
is more probable that such changes would be brought about by caffein in the presence
of a preexisting poison. The death of these pigs, and also of No. 137 several days later,
is difficult to account for on any other theory -than the one suggested. Were it not for
the fact that controls, that is, animals of the same lot which had not received caffein
survived all of the experimental animals, changed conditions of environment or acci-
dent might be considered the cause of death in the guinea pigs of the last series.

Table 6. — Subcutaneous injection of guinea pigs.
SERIES A.

Num-
ber of
pig-

Weight.

Callein
per
kilo.

.\ppearance of
symptoms.

Duration of life.

Diet.

Month.

Remarks.

18

Grams.
500
548
442

Gram.

0.300

.290

.360

2 minutes

2 hours 40 minutes..
30 minutes

Carrots

Oats

March

...do

Female.

15

Do.

14

15 minutes..

..do

.do

.do

Do.

SERIES B.

497

0.200

570

.210

820

.200

618

.194

850

.200

2 hours 20 minutes.

25 minutes

1 hour 25 minutes. ,

1 hour 30 minutes.

3 hours 30 minutes.
2 hours 15 minutes.
Less than 18 hours.

25 hours.
18 hours.

Oats

Carrots

Carrots and

oats.

Oats

Carrots and

oats.

April

February
..do

March

February

Female.
Male.
Do.

Female.
Male.

SERIES C.

510

0.200

510

.200

320

.219

3.50

.200

785

.200

585

.200

330

.240

335

.238

545

.238

540

.240

560

.232

None

do

1 hour 15 minutes.

do

25 minutes

20 minutes

1 hour 30 minutes.

1 hour

50 minutes

45 minutes

35 minutes

5 days

Survived

Within 18 hours....

About 2i days

Less than 22 hours.

9 days

Less than 24 hours.

do

About 2 days

do

About 3 days

Oats

do

do

do

do

do

do

do

do

do

do

October.

..do

..do

..do

..do

..do

..do

..do

..do

..do

..do

Male.

Do.
Female.

Do.
Male.

Do.
Female.

Do.
Male.

Do.

Do.

SERIES D.

49

510
630

435

820

660
470

0.160
.158

.160
,150

.150
.170

1 hour 40 minutes..

Less than 18 hours. . .
Less than 2 days

Survived

Oats

March

February .

March

February .

...do

Male.

40

Oats and
carrots.

Oats

Oats and

carrots.
do

Do.

45

None

Female.

39

2 days

Male.

41

Survived

46

1 hour 20 minutes. .

do

Oats(?)

March

Female.

SERIES E.

19

556
4C)0
430
5:55
330
520

0.100
.120
.116
.112
.100
.100

Survived

Oats

do

April

February .
...do

42

None

.do

43

do

do

do

do

44

do

do

...do

97

do

do

do

November
...do

98

do

About 3 days

Carrots

52

THE TOXICITY OF CAFFEIN".

Table 7. — Injection into peritoneal cavity; guinea pigs.

SERIES A.

Num-
ber of
pig-

Weight.

Caflein
per
kilo.

Appearance of
symptoms.

Duration of life.

Diet.

Month.

Remarks.

41

Grams.
700
370
550
290

Gram.

0.130

.135

.127

.138

2 hours

22 hours

Oats

do

April

.do

Male

49

2 hours 15 minutes.
1 hour

Survived

Do.

47

do

do

March

April

50

do

.do

Do

SERIES B.

415

0.144

450

.155

490

.163

None..

do.

do.

Survived.

do....

do....

Oats . . .
....do.
....do.

October.

..do

..do

SERIES C.

375

0.200

380

.200

440

.200

690

.188

15 minutes.

10 minutes.
15 minutes.
1 hour

Survived.

do

14 days

3 hours 30 minutes. .

Oats.

...do.
...do.
...do.

October. .

.do.
.do.
.do.

Table 8. — Caffein by mouth; guinea pigs.
SERIES J.

SERIES D.

67

330
340
305

0.240
.235
.250

5 minntps

30 minutes.

Oats

.do

October. . .
.do

Male.

63

Survived.

Do.

64

25 minutes

4 hours 40 minutes. . .

do

...do

Female.

Caflein

Weight.

per

kilo.

Grams.

Gram.

855

0.280

800

.300

800

.280

955

. 150

740

.KM

925

.1.50

1,000

.150

980

.200

760

.200

1,075

.200

Appearance of
symptoms.

Duration of life.

Diet.

Month.

40 minutes

.30 minutes

20 minutes

1 hour 50 minutes.

3 hours

SO minutes

do

20 minutes

1 hour

3 hours

Less than 8 hours. .
Less than 18 hours.

do

6 days

4 days

6 days •.■.-.

Survived

27 hours

28 hours

7 hours

Hay and oats

do

....do

do

do

....do

....do

....do

....do

....do

June .
...do..

..do..
...do..

..do..
...do..

..do..
...do..

..do..

..do..

' Subcutaneous injection for comparison.

SUMMARY.

A survey of the results obtained in experiments on guineapigs shows that the mode
of introduction of caffein exerts but little influence on its toxicity. On careful analy-
sis it will be observed that the rate of absorption after the administration of caffein by
mouth, subcutaneously, or intraperitoneally is about the same for the time of appear-
ance of symptoms. The persistence of the symptoms of caffein intoxication observed
in these experiments for 24 hours after administration points to slow elimination,
which may be expected, owing to the fact that the guinea pigs passed but little urine
and caffein is not diuretic for these animals. The prolonged presence of caffein
in the body probably exerts a harmful influence or after effect, which may account

ACUTE INTOXICATION CATS. 53

for tho delayed death of annw animals many days after a single dose of caffein was given.
Among the factors which undoubtedly influence toxicity, season should be considered,
while tho presence of a diseased condition undoubtedly tends to decrease the resist-
ance of the guinea pig to caffein. Diet was without any influence on the toxicity of
the single dose of caffein.

EXPERIMENTS ON CATS.

These experiments were performed on well-fed animals which were kept under
observation for several days before the testa with caffein were made. The diet con-
sisted of meat exdu.sively. In some cases tho urine was examined for albumin and
sugar before caffein was given. No test.s ^\^th caffein were made if large amount.s of
albumin were found. It may be remarked that sugar was never found in cats before;
the administration of caffein, but that considi'rablo amounts of it were found in some
cases after it was givi-n. Studies by various modes of administration were made, by
subcutaneous injection, intraperitoneally, or by mouth. Attention waa also directed
to the resistance to caffein in young cats, several experiments on kittens being made
with this object in view.

SUBCTTTANEOTTS IXJECTION.

Rost stated that caffein is eliminated in the urine unchanged after its introductinn
into the body and that the amounts found varied with different species of animals.
In the rabbit the amount eliminated was about 21 per cent; in the dog about 8 per cent ;
and in the cat somewhat less than 2.5 per cent. It would appear, therefore, that the
cat decomposes caffein more readily than the rabbit or dog; its resistance consequently
ought to be greater than that of the other animals. Moderately large doses were accord-
ingly employed in the preliminary experiments (series A), but the results obtained, as
shown in the protocols, indicated that caffein is fully as toxic fur the cat as for the
rabbit or dog. The doses were then decreased and experiments were performed in
order to ascertain the smallest toxic as well as the smallest fatal dose.

Series A

Three decigrams of caffein per kilo were administered in these experiments. The
results are shown in the following protocols:

Cat 4- Black and white. Weight, 1,440 grams.

May 26: 10.05 a. m., 22 cc 2 per cent caffein (0.3 gram per kilo) injected subcuta-
neously; 11.10 a. m., copious salivation, cat irritable, muscular stiffness present, but
no tetanus; 11.45 a. m., cat restless, convulsions, attacks of short duration, no paralysis
observed after the convulsions, pupils dilated; 4.45 p. m., cat quiet, slight paralysis
present.

May 27: Cat exhausted.

May 28: Found dead.
Cat 5. Black and ivhite male. Weight, 1,396 grams.

June 3: 10 a. m., 21 cc of 2 per cent caffein (0.3 gram per kilo) injected subcuta-
neously; 12 noon, found dead.

Although there was considerable difference in the duration of life following the
injection of the same dose of caffein per kilo, the final outcome was the same, as both
cats died from the effects of the drug. One died within 2 hours and the other lived
more than 30 hours after its administration. Three decigrams of caffein per kilo is,
therefore, surely fatal to these animals. Tests made with smaller doses are shown in
the following experiments:

Series B.

In these experiments the doses employed ranged between 0.20 and 0.25 gram caffein
per kilo.

54 THE TOXICITY OF CAPFEIN".

Cat 3. Black and wMte female. Weight, 2,854 grams. Well fed.

June 4: 10.30 a. m., 35 cc 2 per cent caffein (0.25 gram per kilo) injected subcuta-
neously; 11 a. m., found dead.

Cat 6. Black and tuhite. Weight, 1,645 grams.

June 3: 20 cc 2 per cent caffein (0.243 gram per kilo) injected subcutaneously at 3
p. m., cat grew very irritable in a few minutes; about 4. p. m. reflexes decidedly
increased; 5 p. m., cat paralyzed.

June 4: Cat found dead.
Cat 8. Weight, 1,735 grams.

October 7: 4 p. m., 22 cc 2 per cent caffein (0.25 gram per kilo) injected subcuta-
neously in the back; 4.30 p. m., cat irritable, salivation profuse, convulsions; died at
5.30 p. m. ; no urine passed after caffein was given.
Cat 9. Weight, 1,960 grams.

October 7: 3.45 p. m., 25 cc 2 per cent caffein (0.25 gram per kilo) injected subcuta-
neously in the back; 4.45 p. m., cat very irritable, repeated attacks of convulsions,
salivation copious; died at 5.30 p. m.; cat did not urinate after injection of caffein.
Cat 12. Striped kitten. Weight, 1,185 grams.

October 9: Urine examined, no albumin, no sugar; 1.45 p. m., 12 cc 2 per cent
caffein administered; 5 p. m., cat alive, no symptoms except salivation and general
irritability. ..

October 10: 10.30 a. m., found dead. About 15 cc urine collected, but no examina-
tion made.
Cat 14- Black. Weight, 1,855 graTns. >

October 8: 1.40 p. m., 18.5 cc 2 per cent caffein (0.2 gram per kilo); 3 p. m., cat
became restless about 10 minutes after caffein was injected; cried persistently and
moved about in cage, no convulsions, cat urinated about 15 cc, cat defecated.

October 9: 9 a. m., cat found dead in cage. Urine gave very heavy reduction of
Fehling's solution (much more than was obtained from urine of rabbits); 20 cc urine
analyzed contained 4.65 per cent sugar. Autopsy: Lungs deeply congested; liver
marked fatty infiltration and degeneration; spleen normal; kidneys pale and anemic;
intestines normal; stomach normal.
Cat 15. Striped. Weight, 2,145 gram^.

October 8: 2 p. m., 22 cc (0.2 gram per kilo) 2 per cent caffein injected subcutane-
ously; 2.30 p. m., cat irritable, restless, trying to get out of cage, crying persistently;
2.40, convulsions lasting about two minutes, then cat raised itself and made attempts
to get out of cage, no salivation, cat vuinated about 10 cc and defecated.

October 9:9 a. m., cat found dead in cage, about 10 cc of urine contained enormous
quantities of sugar. Autopsy: Lungs severely congested; liver showed marked fatty
degeneration; spleen normal; kidneys slightly pale and anemic; intestines mildly con-
gested; stomach normal.
Cat 19. White. Weight, 1,100 grams.

October 20: 13 cc of 2 per cent caffein (0.236 gram per kilo). About 15 minutes
later cat became irritable, reflexes increased, persistent crying, stiffness of extremities,
diarrhea present; 4.30 p. m., stiffness of muscles, coordination much disturbed, walked
with great difficulty; 4.30 p. m., no new symptoms, persistent crying continued.

October 21: Found dead.
Cat 20. White kitten. Weight, 790 grams.

October 20: 11.35 a. m., 10 cc 2 per cent caffein (0.25 gram per kilo) given subcu-
taneously; 12 noon, convulsions followed by paralysis; 1.30 p. m., still breathing,
apparently in comatose condition, lay on its side, dyspnoea, profuse salivation; 4 p. m.,
convulsions and death.

The results of the experiments of series B show that a dose of even 0.2 caffein per kilo
is very toxic for the cat. Symptoms appeared in one animal 40 minutes after the injec-
tion of caffein. Some of them were found dead 18 hours after injection, which means that
the duration of life was probably a great deal less since there was evidence that they
had been dead for some time. Death occurred quite soon after larger doses were
injected. Cat No. 3 died 30 minutes after it received caffein. The amounts employed
in these experiments can not be considered therefore as the minimum fatal doses.
Smaller doses were then tried, as shown in the experiments of the next series.

ACUTE INTOXICATION — CATS. 55

Series V.

Experimenta were performed on five cats which received from MO to 155 mg per kilo,
as follows:

Cat 24. Striped. Weight, 1,. MO grams.

October 25: 10 a. m., 50 cc urine, albumin moderate amount — no sugar; 10 cc caffein
injected subcutaneously at 12 noon; 12.80, irritable, cried persistently, no appetite;
4 p. m., no convulsions, but persistent crying.

October 27 : Cat was still alive.
Cat 17. Weight, 2,030 grams.

October 12: 9.30 a. m., G5 cc urine collected; more than a trace of albumin present,
no reduction of Fehling's solution; 3 p. m., 20 cc 2 per cent caffein (150 mg per kilo)
injected subcutaneously; 3.15 p. m., irritable and restless.

October l.'i: 9 a. m., about 15 cc urine collected, reduction of Fehling'a solution
marked; osazone test also positive.
Cat 23. Black and white. Weight, J, 645 grams.

October 25: 10 a. m., 140 cc urine collected (since October 23), small amount of
albumin present, no sugar.

October 27: 9 a. m., no albumin; no sugar in urine; 11.50 a. m., 12.5 cc caffein injected
subcutaneously (0.15 gram per kilo); 1 p. m., convulsions and death.

Cat 7. Striped kitten. Weight, 1,285 grams.

October 11: Urine collected, no albumin, no sugar; 9.50 a. m., 10 cc 2 per cent caf-
fein injected subcutaneously in the back; 10.10, violent convulsions lasting about 30
seconds; 10.20, convulsions of shorter duration; 10.30 convulsions; 10.35, convulsions
lasting a few seconds; urine passed about 10.20, contained a moderate amount of albu-
min, but there was no reduction of Fehling's solution; 10.45, profuse salivation and
paralysis; died about 10.50.
Cat 39. Yelloiv. Weight, 2,285 grams.

April 13: 2.40 p. m., 16 cc 2 per cent caffein (0.14 gram per kilo) injected subcu-
taneously in the back; 3.45 p. m., cat died.

Of the five experiments of this series three died after doses of 140, 150, and 155 mg
per kilo. The other two showed symptoms of toxicity, but survived a dose of 150 mg
per kilo which indicated that the minimum fatal dose was probably reached. To test
this supposition smaller doses were administered, as shown in the following experi-
ments.

Series D.

Ten cats were used for this series of experiments, and the doses administered varied
between 103 and 139 mg per kilo. The results shown in the appended table (p. — ) in-
dicate that about 120 to 140 mgof caffein per kilo may induce mild symptoms in some
cases. The conclusion may be safely drawn therefore that 150 mg per kilo is approxi-
mately the minimum fatal dose for the cat when the drug is given subcutaneously.
That smaller doses are, however, by no means to be regarded as always safe is shown in
the follo^ving experiments.

Series E.

Cat 4S. Weight, 3,225 grams. «

September 14: 10.20 a. m., 20 cc 2 per cent caffein (0.124gram per kilo) injected into
the back; 11 a. m., tetanus and death. Autopsy: Lungs congested; liver congested
and showed hemorrhagic spots in capsules and fatty degeneration; kidneys slightly
congested; other organs normal.
Cat 48. Black female. Weight, 3,050 grams.

September 14: 18 cc 2 per cent caffein (0.118 gram per kilo) injected subcutaneously
in the back; 10.30 a. m., violent convulsions and death. Autopsy: Lungs congested in
spots showing numerous petechia; liver congested; spleen congested; other organs
normal.

The diminished resistance to caffein of cats Nos. 43 and 48 might be due to the
pathologic changes found on autopsy, for evidence is not wanting that the toxicity

oCat probably old; had been in the laboratory for several weeks before the experiment. Gained in
weight 175 grams.

56 THE TOXICITY OF CAFFEIN.

of drugs might be greatly altered under pathological conditions. Hunt*" has Bhown
that resistance to acetonitril is considerably diminished in chi-onic alcoholism. This
Beems to be true also of other di'Ugs imder abnormal conditions. Smaller doses of
atropiu"^ are required in lead poisoning than under jaormal conditions to produce
the same results. The following experiment is of interest in this connection, for in
this case a much smaller dose than was given in experiments Nos. 43 and 48 produced
the typical symptoms of caffein poisoning and proved to be fatal.

Cat 47, black and white male. Weight, 4,220 grams.

September 15: Received sub cutaneously 18 cc 2 per cent oaffeia (0.084 gram per
kilo) ; no symptoms observed for about six hours.

September 16: No symptoms.

September 17: Weight, 4,250 grams; injected 18 cc 2 per cent caffein (0.084 gram
per kilo); tetanus and death after two hours. Autopsy: Severe hemorrhagic pneu-
monia; kidneys pale, other organs normal.

Since two controls survived the same dose in proportion to the body weight of the
animal without showing any symptoms, the assumption is justified that the lower
resistance to caffein was due to the presence of pneumonia, thus affording additional
support to the view that the toxicity of caffein may be increased in disease.

INJECTION INTO THE PERITONEAL CAVITY. >

These experiments were carried out on full-grown and on young subjects. As in
previous experiments, doses of different sizes were employed. A dose of 0.2 gram
per kilo was tried first an(>then reduced gradually to 0.1 gram per kilo.

Cat 10. Female. Weight, 2,970 grams.

October 9, 1909: 1.30 p. m., 30 cc 2 per cent caffein (0.2 gram per kilo) injected
into the peritoneal cavity; urine examined for albumin and sugar, negative; cat
found dead at 2.30 p. m. No urine in the bladder.
Cat 16. Black female. Weight, 2,420 grams.

October 9, 1910: Urine examined for albumin and sugar, negative; 2.30 p. m., 22 cc
2 per cent caffein (0.183 gram per kilo) injected into the peritoneal cavity; foimd
dead at 3 p. m.
Cat 99. Well-fed gray female. Weight, 3 kilos.

Jime 22, 1911: 3.40 p. m., 15 cc 2 per cent caffein injected into peritoneal cavity;
salivation and marked irritability within one hour after injection.

June 24: Alive, appetite good.
Cat 98. Well-fed black male. Weight, 4,100 grams.

June 22: 3.45 p. m., 20.5 cc 2 per cent caffein (0.1 gram per kilo) injected into
peritoneal cavity; very irritable a few minutes after injection, no other symptoms.

Jime 24: No symptoms, appetite good.
Cat 93. Black and white. Weight, 1,450 grams.

June 22: 3 p. m., 30 cc 2 per cent caffein (0.137 gram per kilo) injected into peri-
toneal cavity; salivation, no other symptoms; under observation imtil 6 p. m.

June 23: 9 a. m., no m-ine, cat showed no symptoms.

Jime 24: 9 a. m., no symptoms, took nourishment as usual.
Cat 87. Well-fed white female. Weight, 2,615 grams.

Jime 23: 2.45 p. m., 19 cc 2 per cent caffein (0.145 gram per kilo) injected into peri-
toneal cavity; became irritable and restless.

June 24: 9 a. m., no symptoms, took nourishment as usual.
Cat 97. Gray. Age, 3 months. Weight, 500 grams. Diet, meat.

June 24: 2.25 p. m., 5 cc 2 per cent caffein (0.2 gram per kilo) injected into peri-
toneal cavity; 4 p. m., no symptoms.

June 29: Died.
Cat 96. Gray and white. Age, 3 months. Weight, 575 grams. Diet, meat.

June 24: 2.20 p. m., 4 cc 2 per cent caffein (0.139 gram per kilo) injected into peri-
toneal ca^dty; 3.55 p. m,, no symptoms.

June 30: Died.
Cat 95. Black. Age, about 3 months. Weight, 860 grams. Diet, meat.

Jime 24: 10.15 a. m., 8.6 cc 2 per cent caffein injected into peritoneal cavity, sali-
vation immediately after injection; 10.25, convulsions and paralysis; died 10.45 a. m.
Autopsy: Macroscopical examination of the organs, negative.

ACUTE INTOXICATION — CATS, 57

Cat 94. Black and white. Weight, 790 yrains. Aye, about d months. Diet, meat.

June 24: 10 a. m., 8 cc 2 per cent caffein injected into peritoneal cavity; 4 p. m.,
under continual observation since injection, cat very irritable, respiration more rapid
than normal, diarrhea present.

Examination of the above protocols show that a dose of 2 decigrams per kilo was
fatal within one hour to one cat and that a somewhat smaller dose killed another
individual in 30 minutes. Amounts under 0.15 gram per kilo were just sufficient to
induce mild symptoms, such as increased irritability and salivation, Avhich disap-
peared within a few hoiu^. In no case were the effects noticeable on the following
day. The experiments on yomig kittens are especially interesting, as they proved,
contrary to expectation, to be distinctly more resistant than full grown individuals.
The death of Nos. 97 and 96 \vithin five and six days, respectively, can not be ascribed
to caffein, since some of the controls also died. Moreover, it will be remarked in
this connection that no symptoms appeared in three of the four yomig kittens after
the administration of a dose which was rapidly fatal to adult cats. The rapid death
of No. 95 after the same dose forms an exception which can not be accounted for, as
macroscopical examination at autopsy proved negative.

ADMINISTRATION BY MOUTH.

Two decigrams per kilo were given at first, but it was found that this amount was
surely fatal. The dose was therefore reduced to 0.125 gram per kilo. In all of these
experiments caffein was given by means of a soft rubber patheter slipped over the
stem of a funnel which served as a stomach tube. A 2 per cent aqueous solution was
used throughout these tests except in one case in which caffein was given mixed
with the food.

Cat 92. Black and ivhite female. Weight, 1,750 grams.

June 10: 12.05 p. m., 14 cc 2 per cent caffein (0.16 gram per kilo) given by mouth;
cat was quiet when tied on holder, struggled only a little when tube was put into
stomach; 12.30 p. m., cat vomited, no other symptoms.

Jime 13: Condition good, appetite good.
Cat 87. White female. Weight, 2,620 grams. Diet, meat.

June 5: 2.15 p. m., 20 cc 2 per cent caffein (0.15 gram per kilo) solution admin-
istered by mouth through stomach tube; 2.30 p. m., cat irritable, but no other symp-
toms; 5 p. m., condition about the same, except that it was more irritable and showed
some stiffness of the extremities.

June 13: Alive and in good condition, appetite good, not irritable.
Cat 91. White female. Weight, 3,050 grams.

Jime 10 : 12 noon, 23 cc (0. 15 gram per kilo) of 2 per cent caffein administered by mouth,
cat struggled violently; 1.30, salivation; 1.40 p. m., convulsions; died at 2 p. m.
Autopsy: Congestion of limgs, liver, and spleen; heart vessels injected; other organs
normal.
Cat 88. Black and ivhite female. Weight, 3,260 grams. Diet, m^at.

June 5: 2.20 p. m., 25 cc of 2 per cent caffein (0.15 gram per kilo) given by mouth;
2.45 p. m., cat irritable, no other symptoms (cat did not vomit after the administrdtion
of caffem); 4 p. m., cat found dead. Autopsy: Liver very much congested; heart
contracted; body was still warm at the time of autopsy.
Cat 90. White and yellow female. Weight, 2.685 grams. Diet, meat.

June 5: 3.15 p. m., 27 cc of 2 per cent caffein (0.2 gram per kilo) given by mouth
through stomach tube, about half an hour later cat became irritable and began to
salivate; at 4.30 p. m. salivation became more marked, dyspnoea was well developed,
and the cat was quite restless and had tremors; 5 p. m., short spasms of posterior
extremities, but lay quietly in the cage most of the tmie; 5.20 p. m., con\Tilsions of
short duration and death, muscular relaxation followed immediately after convulsions,
no vomiting, diarrhea observed after administration of cafl'ein, and cat passed about
10 cc of urine.

June 6: 9 a. m., found dead.
Cat 89. White and black female. Weight, 2,860 grams. Diet, meat.

June 5: 3.15 p. m., 28.6 cc (0.2 gram per kilo) of 2 per cent caffein given by mouth
through stomach tube, no vomiting observed, nor any other symptoms; 3.30, found
dead. Autopsy: Organs normal; liver congested.

58

THE TOXICITY OF CAFPEIN".

Cat 82. Gray female. March S, weight 2,450 grams; June 6, weight 2,750 grams. Diet,
150 grams of vieat daily.

June 7 : Giveu 0.4125 gram of caffein in 150 grams of meat, did not eat.

June 8: Given 0.4125 gram of caffein in 150 grams of meat, refused to eat.

June 9: Given 150 grams of meat without caffein, ate all of it.

June 10: No food given.

June 11: No food given.

June 12: Given 0.4125 gram caffein in 150 grams of meat (150 mg per kilo), ate all
of it.

June 13: Found dead. Autopsy: Lungs congested, liver congested; other organs
apparently normal.
Cat 100. Gray female. Weight, 2,740 grams. Diet, vieat.

July 17 : 3 p. m. , 17 cc of 2 per cent cafiein (124 mg per kUo) given by mouth through
stomach tube at 3.20 p. m. ; 5 p. m., very irritable, but no other symptoms.

July 18: Under observation all day, no symptoms.
Cat 93. Black and white female. Weight, 1,640 grams.

July 17: 3.30 p. m., 10 cc (0.125 gram per kilo) of 2 per cent caffein given by mouth
through stomach tube.

July 18: Under observation all day, no symptoms.

From the results of the experiments of this series it appears that 0.15 gram\caffein
per kilo may be fatal within a few hours after its administration, even if the drug is
mixed with a moderate amount of meat. Experiments 87 and 92 show, however, that
this amount may be borne by some individuals without any serious consequences, as
the cats were under observation for some time after they received caffein, and no
untoward symptoms were noticed in either of them during this time. It may be
remarked that cat No. 92 vomited shortly after it received caffein. It is practically
certain, therefore, that this amount of caffein in proportion to the weight of the animal
will in the great majority of cases prove fatal, and perhaps in a smaller percentage of
individuals it is surely toxic if it does not escape absorption. Smaller doses may
cause irritability in some individuals, but symptoms referable to nervous symptoms
of muscles were absent, as in experiments Nos. 93 and 100. The minimum fatal dose
of caffein for the cat when given by mouth is, therefore, 0.15 gram per kilo.

Table 9. — Subcutaneous injection; cats.

SERIES A.

Num-
ber.

Weight.

Caflein
per kilo.

Symptoms.

Duration of life.

4

Grams.
1,440
1,396

Gram.
0.30

.30

65 minutes

Over 29 hours.

5

About 2 hours.

SERIES B.

3

2,854

0.25

6

1,645

.243

8

1,735

.25

9

1,900

.25

12

1,185

.20

14

1,8.55

.20

1.5

2,145

.20

10

1,100

.236

20

790

.25

Few minutes

30 minutes

1 hour

3 hours

1 hour 20 minutes

40 miautes

15 minutes

SERIES C.

30 minutes.

1 hour 30 minutes.

1 hour.

1 hour 45 miautes.

Less than 18 hours.

Do.

Do.

Do.
4 hours 30 minutes.

24

1,300
2, (;20
1,045
1,285
2,285

0. 153
.15
.15
.155
.14

1 hour

Survived.

17

15 m inutes

Do.

23

1 hour 10 minutes.

7

20 minutes

1 hour.

j9

65 minutes.

ACUTE INTOXICATION — CATS.

59

Table 9. — Subcutaneous injection; cats — Continued.
SERIES D.

Num.
ber-

Weight.

Caffein
per kilo.

Symptoms.

Duration of life.

13

Orama.
730
1,165
965
1,605
1,625
2,335
2,710
1,785
2,315
2,325

Oram.
0. i;w

.138
.103
.125
.125
.128
.129
.123
.112
.120

Restlessness

21

None

25

do

26

do

27

do

28

do

40

do

Do.

41

do

Do.

42

do

Do.

38

Mild

SERIES E.i

3,225
3,050
4,220
4,250

0. 124
.118
.084
.084

40 minutes.
Died soon after.
Survived.
2 hours.

Pathological conditions. * Two days after first injection.

Table 10. — Injections into peritoneal cavity; cats.

Num-
ber.

Weight.

Caffein
per kilo.

Symptoms.

Duration of life.

99

Qrams.

3,000

4,100

1,450

2,615

505

575

860

790

2,970

2,420

Oram.
0.100
.100
.137
.145
.200
.139
.200
.200
.200
.183

Mild

Survived.
Do.
Do.
Do.

5 days.

6 days.

30 minutes.
Survived.
1 hour.
30 minutes.

98

do.i

93

Very mild

87

..do

97

None

96

..do .

95

15 minutes

94

10

16

1 In few minutes.
Table 11. — Administration of caffein by mouth; cats.

No.

Weight.

Caffein
per kilo.

Symptoms.

Duration of life.

91

Qrams.
3,050
3,260
1,750
2,620
2,685
2,860
2,450
2,740
1,640

Oram.
0.15
.15
.16
.15
.20
.20
.15
.124
.125

1 hour 40 minutes

2 hours.

88

1 hour 40 minutes.

92

2") minutes

Survived.

87

3 hours

Do.

90

1 hoiu" 15 minutes

Loss than 18 hours.

89

75 minutes.

82

Less than 24 hours.

100

1 hour 40 minutes

Survived.

93

Do.

SUMMARY.

The toxicity of caffein in cats is shown to be the same when given by mouth as
when injected subcutaneously, the minimum fatal doses in both cases being 0.15
gram per kilo. When introduced by the intraperitoneal route, caffein is, on the
contrary, distinctly less toxic. After the administration of 0.137 and 0.145 gram

60 THE TOXICITY OF CAFFEIN".

caffein per kilo (Nos. 93 and S7) salivation in one cat (No. 93) and initability and
muscular stiffness in the other were the only effects noticed. These symptoms were
no longer observed the next day and the cats appeared to be perfectly normal. Experi-
ments vrith larger doses indicate that the minimum fatal dose by this method of
administration is about 0.2 gram per kilo.

EXPERIMENTS ON DOGS.

The experiments were carried out on well-fed adult dogs and on puppies, kept
imder observation for some time before the drug was administered. Only those
manifesting no signs of abnormality were used for these tests. Caffein was given by
mouth mixed with 10 to 20 grams of meat, or eubcutaneously in 2 per cent aqueous
solution. The young animals received caffein dissolved in milk. The determination
of the minimum toxic or fatal doses when the drug was fed presented considerable
difficulty, as in many instances the ingestion of the drug was closely followed by
vomiting. , >

ADMINISTRATION BY MOUTH.

«.
Series A.

The effective dose in these experiments showed considerable variation. One dog
(No. 38) died after a dose of 0.12 gram caffein per kilo, while some subjects survived
doses of 0.2 and 0.23 gram per kilo. In the 12 experiments given in Table 12, page 62,
it will be noticed that from 0.12 to 0.152 gram per kilo proved fatal to three dogs,
while thi-ee others sm-\T.ved the same amounts in proportion to the body weight. The
results were the same with larger doses. It may be observed in this connection that
in the case of the five dogs in which vomiting was noticed some time during the 24
hotirs following the administration of caffein, four suj-\dved. No. 38 being the exception.
The greater toxicity of caffein in this case is in all probabihty due to some morbid
process, the presence of which was indicated by the high temperature of this subject.

That vomiting may avert a fatal issue after larger doses of caffein is made fm-ther
probable by experiment on dog No. 48, for which, in the absence of vomiting, a dose of
0.2 gram of caffein per kilo proved fatal. On this supposition the discrepancy in the
results obtained in this series may be readily explained. The smallest doses which
proved fatal in these experiments were 0.145 and 0.152 gram per kilo. No. 38, which
died from a dose of 0.12gi-am per kilo, may be considered as an exception, as this subject
was not normal. Experiments with caffein on dogs were made at various other times
in this laboratory but failed to show that smaller doses of caffein, even when vomiting
did not occur after its administration, were fatal, although toxic effects were observed.
The conclusion is therefore justified that the minimum fatal dose of caffein for the
normal dog is about 0.15 gram per kilo when given by mouth.

subcutaneous injection.

Series B.

To determine the toxicity of caffein more accurately, especially for comparison
with animals of other species, the subcutaneous method of administration was also
used. The injections were made with a syringe of 20 cc capacity, the contents of
which were introduced into contiguous areas. The results of experiments on six
dogs indicate that approximately 150 to 160 mg per kilo is the minimum fatal dose,
since such doses proved fatal to two out of the three animals receiving this amount,
while three others which received doses of from 143 to 160 mg per kilo survived.

ACUTE INTOXICATION — DOGS. 61

HXPBRIMENTS ON PUPPIES.

Series C.

In these experiments the resistance of young growing puppies to caffein was studied.
Caffein waf< given by mouth to all the subjects except one, to which it was administered
Bubcutancously. The protocols, only a few of which are given, and the tabulated
data of the experiments (p. 62) show that the age of the animal has a decided
influence on the toxicity of caffein.

Doa 11. Weight, 1,260 grams.

August 2: At 10 a. m. given 12.5 cc of 2 per cent of caffein through stomach tube;
2 p. m., had con\'ulsions, diarrhea, salivation, and stiffness of limbs.

August 3: Found dead 9 a. m. Autopsij: Thoracic \iscera apparently normal;
stomach immensely distended and filled with a white, cheesy ma.ss and some fluid;
round worms plentiful in stomach and small intestine; mucosa of entire intestine
congested; contents of lower intestine congested; liver pale; spleen flabby; kidney
congested.
Dog 10. Weight, 1.650 grams.

July 26: 9.30 a. m., 29 cc of 2 per cent caffein added to 60 cc of milk offered, but
refused, and was therefore fed by mouth through stomach tube; 10.25 a. m., no
symptoms; 11.30 a. m., restlessness, extremities stiff, post, extremities spread apart,
dog shows well-marked symptoms of caffein poisoning; 12.10 p. m., symptoms more
severe, extremities extended and spread out, is hing flat on belly so that nose touches
floor of the cage; 12.40 p. m., found dead; was alive at 12.10 p. m. Autopsy: Lungs
showed hemorrhagic foci in all lobes; heart apparently normal; liver fatty; stomach
and intestines filled with roimd worms; spleen and kidney apparently normal.
Dog 9. Weight, S,000 grams.

July 25: 350 mg caffein per kilo; 5 p.m., lying down most of the time, occasionally
walks about in stall; restlessness present, but not marked; 5.30 p. m., vomit which
looked frothy and mucilaginous noticed on the floor of the stal'; no meat particles
noticed in vomit, though seiirched for; whines occasionally.

July 26: 9 a. m., looks well; no signs of the effect of caffein given the day previous.
Dog S. YeUow female. Weight, 3,100 grams.

July 22: 10.50 a. m., received 1.1 grams of caffein in 10 grams of meat (354 mg caffein
per kilo); 3 p. m., vomited mucus; gait clumsy; refused to eat; continually drinking
water; vor>' restless; 4 p. m., conv-ulsions set in at 3.55 p. m.; tonic rigidity of the
posterior extremities; profuse salivation; conxnilsions were both tonic and clonic in
character, and resembled those seen in rabbits in caff'ein intoxication; a striking
feature was the duration of the spasm, which began at 3.55 p. m. and kept up for more
than two hours.

July 23: Found dead at 9 a. m.

The data recorded in the table and in the protocols of the experiments of series C
show that four out of the seven animals experimented upon died in less than 24 hours
after caffein was fed ; three of these received 300 to 354 mg caffein per kilo, and one
received 200 mg caft'ein per kilo. No. 8 vomited four hours after caffein was given.
No vomiting was obser\-ed in the other three dogs. From 0.300 to 0.350 gram of
caffein per kilo may be regarded, therefore, as surely fatal to young gi-owing puppies.
That this is in all probability the minimum lethal dose appears from the following
experiments: No. 9, which received 350 mg per kilo, vomited one hour after and
survived, which indicates that some of it was probably not absorbed. The amount
which entered the circulation was therefore less than 350 mg per kilo. Since No. 15,
which received 250 mg caffein subcutaneously, likewise survived, the probabilities
are that 300 to 350 mg per kilo were the minimum fatal doses for these animals. More-
over, No. 12, which received 200 mg caffein per kilo, sur\'ived, no vomiting ha\'ing
been obsers'ed. The case of No. 11, in which the same amount of caffein in proportion
to body weight proved fatal, may be explained perhaps by the findings of the autopsy.

The results obtained in these experiments justify the conclusion that young growing
dogs can stand larger doses of caffein than full-grown and older dogs.

Attention may also be called here to the difference in the sjTnptom? produced by
caffein in very young and in adult dogs. It was often noticed in these experimenta

62

THE TOXICITY OF CAPFEIN".

that the symptoms in older subjects when given toxic doses of caffein set in rather
abruptly and ended in instantaneous death. We failed to observe this phenomenon
after the administration of large amounts of caffein to very young dogs, in which tonic
and clonic convulsions alternating with paresis were observed. These symptoms set
in rather gradually and lasted several hours (see experiment No. 8), resembling the
rabbit in this regard.

SUMMARY.

The toxicity of caffein for adult dogs is about the same, whether given by mouth
or injected subcutaneously. The resistance of puppies to caffein is much greater than
that of adults.

Table 12. — Administration by mouth; dogs. {Series A.)

No.

Weight.

Caffein
per kilo.

Results.

Remarks.

47

Kilos.
13.60
12.75
7.95
13.60
6.50

23.10

11.50
12.00

13.40
13.15
14.50

10.30

Gram.
0.144
.200
.200
.147
.230

.120

.174
.200

.200
.152
.120

.145

Vomiting observed.

"15

do

Stiffness of muscles; no other symptoms.

56
52

Found dead next day. .
Survived

57

do

Vomited after 1 hour; convulsions after 1 hour and 45

39

....do

minutes.
Increased frequency of respiration, thirst, loss of appe-

48

do

tite, vomited rest of day when he drank water, sali-
vation, restlessness, passed feces frequently.
Vomiting observed.

48
54

Found dead next day. .

No vomiting observed. Second dose was given 8 days

after first.
Vomiting observed.

Symptoms after 1§ hours: Dog had a temperature of

49
3S

Foxmd dead next day. .
do

IS

.do

104° F. before caffein was given; vomited 3 hours
after caffein was fed.

Table 13. — Subcutaneous injection; dogs. (Series B.)

No.

Weight.

Caffein
per kilo.

Results.

Remarks.

62

Kilos.

9.30
14.00
12.00
14.00

7.20

14.60

Gram.
0.161
.160
.1.50
.150
.160

.143

Survived

Restlessness and vomiting one-half hour after injection.

61A
63

Found dead next day. .
Survived

Restlessness 1 hour after injection.

64

do

Restlessness and thirst 45 minutes after injection.

59
61

Died 1 hour and 20
minutes after injec-
tion.

Marked restlessness, but no convulsion.
Symptoms observed in li hours.

Table 14. — Administration by mouth to puppies. (Series C.)

No.

Weight.

Caffein
per kilo.

Result.

Remarks.

8
9

Kilos.
3.10

3.15

1.60
1.26
1.28
1.20
3.50

Gram.
0.354

.3.50

.350
.200
.200
.250
.300

Found dead ncXt day .
Survived

Vomited in 4 hours after feeding; restlessness, loss of
appetite, thirst, incoordination of muscles, con%nil-
sions.

Muscular incoordination and stiffness, restlessness,

10
11

Died in 3 hours

Found dead next day .
Sunnved

vomited 1 hour after caffein was given.
Convulsion; no vomiting.
Salivation; convulsions.
No svmptoms.

15
10

do........

Died in 1 hour

Subcutaneous injection.

Convulsions 45 minutes after caffein was fed.

CHRONIC INTOXICATION — RABBITS. 63

CHRONIC CAFFEIN INTOXICATION.

The object of tliis study was to ascertain the effect of repeated
dosage when caffein was given daily or at longer intervals. The
experiments were tried on rabbits and on dogs. As in the experi-
ments on acute intoxication, the animals were under observation for
some time in the laboratory before the administration of caffein
was begun in order to ascertain the presence or absence of abnor-
mality. The relation of diet to toxicity received some attention,
but the question was not studied exliaustively in the present inves-
tigation.

EXPERIMENTS ON RABBITS.

Full-grown adult as well aa young rabbits were employed. The diet consisted
either of carrots or of oats; water was given ad libitum. The rabbits were kept in
metal cages in a well-lighted and well-ventilated room. Unnecessary handling or
any other procedure tending to fatigue or to cause discomfort to the animals was
very carefully avoided, since we had found that such treatment was likely to decrease
the resistance of the rabbit to caffein. The caffein was administered by feeding by
mouth and through a stomach tube, or by the subcutaneous method. In a good many
cases it was given daily, in some at longer intervals.

Series A.

The experiments of this series formed a preliminary study for the purpose of testing
the effect of moderate doses. One decigram of caffein per kilo was given daily for
several days; when administered at longer intervals the dose was increased to 150 to
200 mg per kilo. It was found that the smaller doses did not produce any symptoms;
even the weights of the animals were not influenced. Doses of medium size given on
two successive days were likewise without any noticeable effect (Nos. 182, 183, 123,
101). When a third dose of this size was given within 48 or 24 hours it proved fatal
(Nos. 123, 182, and 183). Exceptionally, however, moderately large doses (for rabbits)
may be given for three consecutive days without fatal issue, as in rabbit No. 101.
When given at intervals of two to three days, larger doses, as may be seen from the
protocols, can be administered without causing acute death (Nos. 173, 181, 201).

The results of the tests of this series point to the absence of any accumulation and
to the possible elimination of moderate doses of caffein and its products of decom-
position within 24 hours or thereabouts. 'WTien the doses are larger the time of its
elimination is apparently longer, as shown by the fact that repetitions of the dose the
next day may be fatal, but when a longer interval is allowed it may be given without
causing death. It will be observed that only one rabbit of this series 8ur\-ived, but
it was extremely emaciated. This condition has been observed in a number of cases
after caffein had been given for several days. Even when the drug was Avithdrawn
the animals continued to lose weight. This may be explained by the condition of
the gastro-intestinal canal as found at autopsy. The presence of inflammation of the
mucous membrane of the stomach and intestines, with ulceration of the mucous mem-
brane of the pylorus in one of the rabbits (No. 173) of the series, in all probability
caused diminution or loss of appetite, which of itself would tend to cause loss of flesh
and strength and finally death. Protocols of the experiments follow.

64

THE TOXICITY OF CAFFEIN.

Rabbit 173. Carrots ivere fed from October 1 to 18 and oats for the remainder of the experi- '
ment.

Date.

Weight.

Caflein
per kilo.

Date.

Weight.

Caffein
per kilo.

Oct. 9

Grams.
1,980
1.905
1,930

Oram.
0.141
.190
.207

Oct. 16

Grams.
2,005
1,845
1,740

Gram.
0.220

Oct. 11

Oct. 18

Oct. 13

Oct. 20 . .

230

October 21: Paralysis of posterior extremities.

October 22: 9 a. m., found dead.

The urine was examined before and after the administration of caffein. No symp-
toms were observed after the administration of caffein (5 doses in 11 days), nor was
albumen or sugar found in the urine after any of the experiments on this rabbit.
Autoj}sy: Pyloric mucosa exhibited several ulcers; small intestines showed slight
inflammation; liver deeply congested; kidneys showed marked inflammation of cortex;
other organs practically normal.

Rabbit 181. Diet, carrots September 29-October 17, then oats.

Date.

Weight.

Cafieln
per kilo.

Date.

Weight.

Caffein
per kilo.

Oct. 4

Grams.
1,425
1,450
1,270
1,210
1,375
1,305

Gram.
0.105
.100
.100
.100
.130
.153

Oct. 11

Grams.
1,370
1,385
1,345
1,030
1,230
1,215

Gram.
0 175

Oct. 5

Oct. 13

.180

Oct. 6

Oct. 16

200

Oct. 7

1 Oct. 17

Oct. 8

Oct. 18

Oct. 9

Oct. 20

Rabbit was markedly emaciated and weak,
urine as a result of caffein feeding.

Rabbit 182. Diet of carrots from September 29.
Received caffein subcutaneously as follows:

No albumen or sugar found in the

Date.

Weight.

Caffein
per kUo.

Date.

Weight.

Caffein
per kilo.

Oct. 4

Grams.
1,765
1,880
1,750

Gram.
0.100
.100

.100

Oct. 8

Grams.
1,685

Gram.
.135

Oct. 5

Oct. 9

.150

Oct. 6

Oct. 11

1,605

.174

Oct. 7

1,710 -100

October 12: 11 a. m., 23 hom's after caffein was given, convulsions with recovery;
rabbit died at 1.30 p. m. No sugar was found in the urine at any time after the
administration of caffein. Albumen was present only in one specimen.

Rabbit 183. Diet of carrots from September 29.
Received caffein subcutaneously as follows:

Date.

Weight.

Caffein
per kilo.

Date.

Weight.

Caflein
per kilo.

Oct. 4

Grams.
1,.385
1,400
1,385
1,240

Gram.

0.100

.100

.100

.122

Oct. 8

Grams.
1,310
1,390
1,390

Oram.
0.153

Oct. 5

Oct 9 ...

.142

Oct. 6

Oct. 11

.187

Oct. 7

October 12: 9 a. m., found dead,
sample contained sugar.

No albumen was found in the urine. Only one

CHRONIC INTOXICATION RABBITS.

65

Rabbit 12.3. ^Vh^te, female. Diet, oats.

Received caffein subcutaneously as follow.s:

Date.

Apr. 14
Apr. 16
Apr. 17

Weight.

Orams.
2,350
2,250
2,325

Caffein
per kilo.

Grams.
42
90
80

Date.

Apr. 20
Apr. 21
Apr. 22

Weight.

Grams.
2,126
1,965
1,876

Caflein
per kilo.

Orams.
141
152
160

Rabbit died 30 minutes after last injection of caffein. Autopsy: Stomach exhibited
marked inflammation of mucosa. Slight enteritis. Liver and kidneys were deeply
congested and dark colored.

Rabbit No. 101, white male. Diet, oats.
Received caffein subcutaneously as follows:

Date.

Weight.

Caffein
per kilo.

Date.

Weight.

Caffein
per kilo.

Mar. IS

Grams.
2,025
1,970
2,009
1,855
1,738

Gram.
0.100
.100
.100
.100
.114

Mar. 24

Grams.
1,815
1,830
1,710
1,734
1,000

Gram.
0.166

Mar. 19

Mar. 25

.185

Mar. 20

Mar. 26

.176

Mar. 22

Mar. 29

.219

Mar. 23

Apr. 1

.224

April 5: Found dead. Autopsy: Marked inflammation of gastric mucosa. Con-
siderable enteritis affecting the whole extent of the intestines; liver congested and
friable; kidneys deeply congested in cortical and medullary portions; spleen con-
gested, but of normal size; lungs and heart normal.

Four days, 0.1 per kilo; 10 doses in 14 days.
Rabbit 201. Diet of carrots begun October 1; October 19, oats.

Subcutaneous injections as follows:

Date.

Weight.

Caffein
per kilo.

Date.

Weight.

Caflein
per kilo.

Oct. 9

Orams.

1,000

1,015

1,005

Gram.
0. 150

. ISO
.187

Oct. 16

Grami.

1,005

850

890

Gram.
0.225

Oct. 11...
Oct. 13...

Oct. IS..
Oct. 20..

.111

Under observation six hours October 20; no symptoms.

October 23: Died; was much emaciated but did not show any sjinptoms; emaciation
set in when caffein was withdrawn; urine never contained sugar or albumen; symp-
toms observed after second dose only.

Series B.

The question whether caffein is cumulative in the rabbit, suggested in the preceding
experiments, was the subject of further investigation in Series B. Caffein was given
by mouth or subcutaneously. Carrots formed the exclusive diet, a measured amount
being given. The rabbits were kept under observation for two weeks, except
Nos. 370 and 373, records of which were made only for four days before the administra-
tion of caffein was begun. Caffein was given by mouth in experiments of Groups I
and III. Rabbits 292, 293, and 29-5 received daily 20 cc water by mouth for four days
previous to the administration of caffein, while in the rabbits of Group II the caffein
treatment was preceded by the injection of 0.8 per cent salt solution subcutaneously.
The object in both cases was to ascertain whether or not the method of the adminis-
tration of caffein has any influence on the animal, but observation made from day to
18594°— Bull. 148—12 5

66 THE TOXICITY OF CAFFEI:N-.

day failed to show any effect of such treatment. About 1 decigram of caffein per
kilo was administered daily, with occasional intermissions. Later in the com'se of
the experiment the doses were increased, 0.15 gram per kilo being the maximum dose
given. Rabbit 293 died after the third dose with symptoms of typical caffein poison-
ing. The administration of the same dose of caffein was continued 10 days longer in
Nos. 292 and 295. It was omitted on the seventh, fourteenth, and fifteenth days of
the experiment. On the eighteenth day of the experiment the dose was increased to
150 mg per kilo and was repeated 2 days later. No. 295 was found dead the next
day. No. 292 survived. Rabbits 313 and 315 may be considered together, as they
were treated alike in every respect. The initial dose of 100 mg caffein per kilo was
finally increased to 122 mg. After the twelfth dose the emaciation was well marked
and the rabbits were very weak. No. 313 was found dead 2 days, and No. 315
3 days, after the last dose of caffein was given. It should be remarked in this con-
nection that symptoms of caffein poisoning were never observed in these rabbits.
Death was not due, therefore, primarily to caffein, but the rapid loss of flesh and
strength observed during the last few days suggests that it was due to malnutrition
apparently brought about by caffein.

The results obtained by subcutaneous injection of caffein are given in the table
as Group II. The initial dose of 100 mg per kilo was injected daily. No. 298 died
after the second dose. Nos. 223 and 296 received this amount daily for 6 days.
An intermission of 2 days followed, at the end of which the same dose was given
again. The next day it was increased to 150 mg per kilo, but no effect was observed ;
48 hours later this dose was repeated. No. 223 was found dead, but its mate survived.
Symptoms of acute caffein intoxication were not observed in any of these rabbits.
It would seem, therefore, that caffein is not cumulative. This supposition, however,
appears somewhat contradictory in view of the fact that out of the eight rabbits of
this series six died, nor could any cause of death be ascribed other than caffein. Also
the first results of Experiments 293, 370, and 373 might be considered as indicat-
ing that cumulation, though to a moderate extent, does take place, since in these
cases reflexes developed after the drug was given for some time. But this view is
contradicted by the results of Experiment 371, in which 150 mg per kilo given 5
days after the daily dosage of caffein was suspended likewise caused increased reflexes.
Cumulation, therefore, does not account for the effects noted in the other rabbit. It
will be observed that rabbit No. 370, as well as Nos. 371 and 373, had diarrhea for
several days. It is quite possible that the weakened condition rendered the rabbits
more sensitive to the action of the drug. This is made highly probable by the obser-
vations recorded in the experiments on acute intoxication with caffein in which
death occurred after small doses. In such cases some pathological condition was
often disclosed by the autopsy. The results of this series corroborate, therefore, those
of Series A, and indicate again the absence of cumulative action. The results ob-
tained are in all probability due to malnutrition and other conditions brought about
by congestion of the viscera and consequent injury to the gastro-intestinal canal.

CHRONIC INTOXICATION RABBITS. 67

Table 16. — Chronic caffcin intoxication of rabbits; Series B on cumulation.

i

1 (

^roup 1.

1

Group II,

Group

III.

Data.

1

1

1

No. 292.

No. 293.

No. 295.

No. 296.

No. 223.

No. 298.

No. 315.

No. 313.

Diet (grams carrots in 2 days)

; 1,000

1,000

975

930

905

880

355

300

f'afTein administered (cc) and weight

1

Lrrams):

(

1

Mar.5

I i,4i6
/ •

1,470

1,015

1,040

1,070

955

770

770

Mar. 7

\ 1,415
/

1,3G0

1,140

1,090

1,095

1,000

715

690

Mar.O

■ \ 1,350

1,270

1,070

1,000

1,055

1,005

655

665

Mar. 11

■{ i.sos

f

1,465

1,190

1,230

1,285

1,250

755

760

Mar. 10

■\ i,580
/ - •■

1,460

1,230

1,165

1,170

1,145

730

745

Mar. 17

■\ 1,515

1,415

1,080

1,040

1,115

1,105

720

685

Mar. 19

■\ 1,565

1,570

1.280

1,195

1,235

1,220

710

7:«

•{ 1.585

7
1,530

6
1,265

4
755

4

Mar.21

1,150

1,215

1.260

700

-{ 1.440

7

6

(')

(')

(')

4

4

Mar. 22

1,315

1,175

1,100

1.045

1,150

675

635

■{ 1,335

7

G

(')

(')

(')

4

4

1,140

1.110

1,145

1.190

1,230

715

700

•{ 1.310

6

(')

(')

(')

4

4

Mar. 24

(-)

1,090

1,115

1,170

1,250

680

650

Mar.2o

• { 1,375
{ 1,255

6
1,035

6
1,095

(')
1,125

/,2\5

(•)
1,215

4
695

4
675

4
685

Mar. 26

1,105

1,155

1,150

695

Mar.27

•{

:} r

6

5.5

6

6

4

4

Mar. 28

■ \ 1,.355

1,115

1,120

1,160

1,155

595

685

•{ 1,385

6

6

6

5

4

4

Mar. 29

1.150

1,155

1,165

955

695

675

Mar.30

•,{ 1,330

6
1,075

6
1.035

6
1,095

Dead.'

4

630

4
610

Mar.31

IV 1,325

6
1,170

6
1,110

6
1,140

4
690

4
605

Apr.l

-{ 1,335

6
1,050

6
1,050

6
1,120

4

625

4
620

Apr. 2

•;{ 1,390

6
1,125

6
1,090

6
1,155

4
695

4

625

Apr. 3

■{

200

1

Apr. 4

■ \ i.3(KJ

1,005

1,105

1,080

68.5

580

Apr. 5

■{ 1.3S5

i ^
\ 1.-260
r

;::.::::

0

1,090

7.5

1,010

6

1,130

7.5

1.050

6
1,090

8
1,110

4
655

4

630

Apr. 6

560

530

Apr.7

•{

(0

■\ 1,260

7.5
1,000

7.5
1,090

8
1,065

Apr. 8

Dead.

.\pr. 9

Dead

Sur-

Dead.

Dead.

vived.

1

vived.

1 On these davs 5 cc of salt solution was administered subcutaneously.

2 Dead Mar. 23.

' Found dead 9 a. m.

68

THE TOXICITY OF CAFFEIN".

Table 17. — Chronic intoxication of rabbits, series B, Group IV, on cumulation.

RABBIT, 370.

Date.

Weight.

Carrots.

Water.

Uriiie.

Caffeln

by
stomach.

Symptoms.

Aug 7

Grams.
2,155
2,030
2,105
2,095
2,105
2,125
2,120
2,170
2,175
2,170
2,175
2,095
2,120
2,120
2,120
2,040
2,030
1,950
1,885

Grams.
450
450
290
450
450
450
350
450
350
360
310
180
400
400
400
400
370
215
195

cc.
50
25
0
30
65
65
25
35

(?)
65
35
40

(?)

45
35
40
35

280
185
275
335
360
220
265
275
200
250
170
285
285
310
250
265
220
120
60

Mg per

kilo.

Aug. 8

Aug 9

Aug 10

Aug. 11

50
50
50
75
75
75
100
100
125
125
125
150
150
150
200

Aug. 12

Aug. 13

Aug. 14

Aug. 15

Aug. 16

Aug. 17

Aug. 18

Severe diarrhea.

Aug. 19

Do.

Aug. 20

Better.

Aug. 21

Do.

Aug. 22

Diarrhea bad.

Aug. 23

Diarrhea better.

Aug. 24

Do.

Aug. 25

Reflexes.

Aug. 26

Found dead at 9.

RABBIT, 373.

Aug. 7.
Aug. 8.
Aug. 9. ,
Aug. 10.
Aug. 11.
Aug. 12
Aug. 13
Aug. 14
Aug. 15.
Aug. 16
Aug. 17
Aug. 18
Aug. 19
Aug. 20
Aug. 21
Aug. 22
Aug. 23
Aug. 24
Aug. 25
Aug. 2G
Aug. 27
Aug. 28
Aug. 29

Aug. 30
Aug. 31

2,240
2,150
2,120

450
150
205

50

30

0

230
300
150

2,150
2,195

450
450

15
5

245
285

50

2,160

450

65

325

50

2,120

300

45

190

50

2,195

450

40

265

75

2,215

350

35

200

75

2,205

310

45

225

75

2,240

400

40

265

100

2,255

350

30

320

100

2,115

185

(?)

170

125

2,115

280

35

195

125

2,050

175

75

115

125

2,060

180

75

130

150

2,005

200

75

125

150

1,990

200

75

150

150

1,950

255

55

132

175

1,870

205

80

140

None

1,830

200

50

140

...do

1,950

400

25

265

...do

1,825

400

0

315

...do

1,850

10

140

...do

1,835

Severe diarrhea.
Diarrhea better.
Slight diarrhea.

Reflexes.
Slight diarrhea.
Severe diarrhea.

Do.

Do.
Slight diarrhea.

Very weak and in poor condi-
tion.

CHRONIC INTOXICATION — RABBITS.

69

Table 17. — Chronic intoxication of rabbits, series B, Group IV, on cumulation — Contd.

RABBIT, 371.

Date.

Weight.

Carrots.

Water.

Urine.

Cadcin.

Symptoms.

.\ug. 7

Orams.
2.240
2.2l«
2.310
2.295
2. 320
2. 280
2.300
2.205
2,200
2,295
2.180
2,150
2,075
2,075
2.105
2.105
2.080
2,105
2.055
2.040

Orams.
450
450
430
450
450
450
350
425
250
155
105
125
210
280
200
400
300
250
320
190

cc.
50
50

(?)
50
50
70
70
55
40
70
70
70

(?)
70
50
50
0
15
10
75

300
225
300
305
335
400
255
154
125

Lost

120
100
192
180
225
275
145
245
176
250

Mg per
Kilo.

Aug. 8

Aug. 9

Aug. 10

Aug. 11

50

60

50

75

75

75

100

100

100

100

None

...do

Aug. 12

Aug. 13

Aug. 14

Aug. 15

Aug. 10

Aug. 17

Aug. 18

Aug. 19

Diarrhea severe.

Aug. 20

Do.

Aug. 21

Aug. 22

Aug. 23

do Di.irrhea spverfi.

Aug. 24

...do

150
150

Do.

Aug. 25

RcQexes.

Aug. 20

Died at 1 p. m., without having
showed any symptoms other
than reflexes.

Series C.

The subjects used in these experiments were rabbits of medium size and were appar-
ently young or at any rate were not very old. The series was planned for the study
of the possible effect of diet on the toxicity of caffein when given for some time, and
therefore oats were substituted for carrots, which had been fed in the previous work, as
already stated. Caffein was given by mouth in the usual way, in 1 per cent solution,
100 mg. per kilo daily. Fourteen rabbits were used for these tests. Their weights were
recorded daily and observations made at frequent intervals during the day.

The only change noticed in all of the experiments of this series was progressive loss
of weight which set in from 3 to 8 days after the administration of the drug was begun.
The duration of life varied considerably. No. 382 died after the fiiJi"st dose. No. 389
lived 2 days. No. 386, 3 days, and No. 385, 5 days, No, 390 lived 7 days and No. 404
lived 20 days after the administration of caffein was begun. The duration of life in all
the others was from 11 to 16 days. The findings at autopsy are interesting and suggestive
as regards the possible explanation of the effects of repeated dosage of caffein . In eight
of the rabbits there was involvement of (he mucous membrane of the stomach or intes-
tines or of both. Since the same condition of the gastro-iutestinal canal was observed
in previous experiments with caffein when injected subcutaneously, the mere passing
of the tube into the stomach is obv-iously not the cause of this condition. The fatal
outcome due is therefore, as was suggested above, to inanition brought about by the
condition of the gastro-intestinal canal. Moreover parallel experiments carried out
on rabbits in the same way with alcohol 8ur\dved this treatment much longer.
Obviously then the passing of the soft rubber catheter is not the cause of this condition
of the gastro-intestinal canal nor the diet. Rabbits were fed oats exclusively for several
months in this laboratory' and thrived. The presence of pneumonia in the other
rabbits of this series may be regarded as accidental, as it is inconceivable that one or
two doses of caffein, as was the case in Nos. 382 and 389, could predispose the lungs to
infection. The results of these experiments therefore are in hai'mony with those of
the preceding two series, indicating that caffein does not accumulate in the body , and
that the toxicity of caffein, whether of the single dose or of repeated doses is the same,

70

THE TOXICITY OF CAFFEIN.

on a diet of carrots or of oats. These results also show that caffein is much more toxic
with repeated dosage. As stated in the historical part of this bulletin the same view
was held by Gourewitch.^^

Rabbit 386. Belgian female.

Given 1 cc of 1 per cent caffein for each 100 grams, through stomach tube.

Date.

Aug. 17.
Aug. 18.

Weight.

Grams.
1,300
1,215

Treat-
ment.

13.0
12.0

Date.

Aug. 19.

Weight.

Grams.
(?)

Treat-
ment.

(?)

August 20: Found dead 9 a. m. Autopsy: Lungs slightly congested; liver engorged
and friable; gall cyst well filled.
Rabbit 389. Black male.

Given 1 cc of 1 per cent caffein for each 100 grams, through stomach tube.

Date.

Weight.

Treat-
ment.

Date.

Weight.

Treat-
ment.

Aug. 17

Grams.
1,070

cc.
10.0

Aug. 18. . . .

Grams.
1,025

cc.
10.0

August 19: Found dead 9 a. m. Autopsy: Lungs severely congested and partially
hepatized; liver was engorged; other organs appeared normal.
Rabbit 382. Belgian female.

On August 17 weighed 1,035 grams; received 1 cc of 1 per cent caffein for each 100
grams; 10 cc of 1 per cent caffein given in all.

August 18: Found dead 9 a. m. Autopsy: Lungs congested and hepatized; liver
engorged; stomach showed numerous petechial hemorrhages on mucosa; kidneys
slightly congested; intestines appeared normal.
Rabbit 385. Belgian female.

Given 1 cc of 1 per cent caffein for each 100 grams, through stomach tube.

Date.

Aug. 17.
Aug. 18.
Aug. 19.

Weight.

Grams.
780
760
755

Treat-
ment.

8.0
7.5
7.5

Date.

Aug. 20.
Aug. 21.

Weight.

Grams.
715
700

Treat-
ment.

7.0
7.0

August 22: Found dead 9 a. m. Autopsy: Lungs exhibited pneumonic lesions,
with inflammation of adjacent pleura; a fibro-plastic exudate present around lung;
liver showed a coccidial infestation; stomach distended with ingesta; mucous mem-
brane characterized by a catarrhal inflammation; contents of small intestine liquid
in nature and bile stained; large intestine somewhat impacted; liver and kidneys
seemingly normal.

CHRONIC lis' TOXIC ATION iiABBITS.

71

Rabbit 404. While male.
Given 1 cc 1 per cent caffein for each 100 grama.

Date.

Aug. 20...
Aug. 21...
Aug. 22>.
Aug. 23...
Aug. 24..
Aug. 25 s
Aug. 2()...
Aug. 27. .
Aug. 28'.
Aug. 29..

Weight.

Grams.
l.-Uio
1,475

1,475
1,400
1,405
1,415
1,400

Treat-
ment.

14.5
14.5

14.5
14.0
14.0
14.0
14.0

1,310

13.0

Date.

Aug. 30
Aug. 31
Sept. 1 .
Sept. 2.
Sept. 3.
Sept. 4.
Sept. 5.
Sept. 6.
Sept. 7.
Sept. 8.

Weight.

Grams.
1,320
1,330
1,335
1,315
1,350
1,335
1,350
1,380
1,375
1.325

Treat-
ment.

13.0
13.5
13.5
13.0
13.5
13.5
13.5
14.0
14.0
13.0

1 Not fed.

2 Reflexes.

September 9: Found dead 9 a. m. Autopsy: Both lungs showed extensive pneu-
monia, with adhesions to pleura; pleuritis and pericarditis very marked; large amount
of fibrous exudate in pleural cavity; pyloric end of stomach slightly congested; liver
congested; other organs normal.

Rabbit 393. Belgian.
Given 1 cc of 1 per cent caffein to each 100 grams, through stomach tube.

Date.

Weight.

Aug. 17..
Aug. IS..
Aug. 19..
Aug. 20. .
Aug. 21..
Aug. 22 1.
Aug. 23..
Aug. 24..

Grams.
950
910
895
910
905

825
870

Treat-
ment.

9.5
9.0
9.0
9.0
9.0

8.0
8.5

Date.

Aug. 25. .
Aug. 26..
Aug. 27...
Aug. 281.
Aug. 29. .
Aug. 30 8.
Aug. 311.

Weight.

Grams.
835
780
765

710

Treat-
ment.

8.5
8.0
7.5

1 Not fed.

2 Condition very poor; not fed.

September 1: Found dead. Autopsy: Lungs congested and adhering to the pleura;
extensive inflammation of pleura; liver slightly enlarged and congested; mucosa of
stomach and small intestines slightly congested; other organs normal.

Rabbit 390. Belgian, male.
Given 1 cc of 1 per cent caffein to each 100 grams through stomach tube.

Date.

Weight.

Aug. 17
Aug. 18
Aug. 19
Aug. 20

Grams.
1,490
1,370
1,365
1,340

Treat-
ment.

15.0
14.0
13.5
13.5

Date.

Aug. 21.
Aug. 22 1
Aug. 23.

Weight.

Grams.
1,265

1,120

Treat-
ment.

12.5

11.0

I Not fed.

August 24: Found dead 9 a. m. Autopsy: Heart and lungs appeared normal;
abdominal viscera showed no apparent pathologic change other than coccidial infec-
tion of the liver and fullness of the blood vessels.

72

THE TOXICITY OF CATFEIN.

Rabbit 392. Maltese, female.
Given 1 cc of 1 per cent caffein to each 100 grams through stomach tube.

Aug. 17..
Aug. 18..
Aug. 19. .
Aug. 20. .
Aug. 21..
Aug. 22 1
Aug. 23..
Aug. 24..
Aug. 25..

Date.

■Weight.

Orams.
1,265
1,275
1,240
1,220
1.245

1.180
1.190
1.155

Treat-
ment.

12.5
12.5
12.5
12.0
12.5

12.0
12.0
11.5

Aug. 26.
Aug. 27.
Aug. 28 1
.Vug. 29.
Aug. 30.
Aug. 31.
Sept. 1 . .
Sept. 2..

Date.

Weight.

Grams.
1,140
1,140

1,115

1,080

1,020

995

930

Treat-
ment.

11.5
11.5

11.0
•11.0
10.0
10.0
9.0

1 Not fed.

Died at 3 p. m. September 2. Autopsy: The stomach and small intestines showed
numerous small hemorrhagic spots; a thick coating of mucus surrounded the con-
tents of the stomach; the other organs were apparently normal.
Rabbit 403. Black.

Given 1 cc of 1 per cent caffein for each 100 grams. i

Date.

Weight.

Treat-
ment.

.Vug. 20..
.Vug. 21..
.Vug. 221.
Aug. 23..
Aug. 24..
Aug. 25..

Grams.
1,640
1,640

1,490
1,515
1.475

16.5
16.5

15.0
1.5.0
15.0

Date.

Aug, 26..
Aug. 27..
Aug. 281.
Aug. 29..
Aug. 30..

Weight.

Grams.
1,390
1,330

1,130
1,055

Treat-
ment.

14.0
13.5

11.5
10.5

1 Not fed.

p. m. Autopsy: Extensive gastroenteritis; liver
slightly congested; peritoneum thickened and

August 31: Found dead at 3
enlarged and congested; spleen
congested; other organs normal.

Rabbit 384. Black, female.
Given 1 cc of 1 per cent caffein for each 100 grams through stomach tube

Aug. 16..
Aug. 17..
Aug. 18..
Aug. 19..
Aug. 20..
Aug. 21..
Aug. 221.
Aug. 23..
.Vug. 24..

Date.

Weight.

Grams.
1,195
1,205
1,140
1.180
1,145
1,145

1.005
1,035

Treat-
ment.

12.0
12.0
11.5
12.0
11.5
11.5

10.0
10.5

Aug. 25..
Aug. 26..
Aug. 27..
Aug. 281.
Aug. 29..
Aug. 30 2.
Aug. 31..
Sept. 1...

Date.

Weight.

Grams.
990
960
955

870
850
810
740

Treat-
ment.

10.0
9.5
9.5

9,0
8,5
8.0
7.5

.Vot fed.

i^oor condition, mucus from rectum.

September 2: Found dead at 9 a. m. Autopsy: The mucosa of stomach showed
numerous hemorrhagic spots; the first portion of the small intestines was slightly
congested; the other organs were apparently normal in appearance.

CHRONIC INTOXICATION RABBITS.

73

Rabbit SSS. Belgian , female .
Given 1 cc of 1 per cent caffein for each 100 grains through Btomach tube.

Date.

Aug. 16
Aug. 17
Aug. 18
Aug. 19
Aug. 20
Aug. 21

Weight.

Treat-
ment.

Orams.

cc.

995

10.0

1,005

10.0

990

10.0

895

9.0

945

9.5

965

9.5

Date.

Aug. 22 ' .
Aug. 2:}..
Aug. 24..
Aug. 25. .
Aug. 26..
Aug. 27..

Weight.

QramH.

875
855
850
785
710

Treat-
ment.

9.0
8.5
8.5
8.0
7.0

" Not fed.

August 28: Found dead at 9 a. m. Aulnpsif: Lung.s, heart, and epleen apparently
normal; liver infected with coccidia; stomach apparently normal; walls of small
intestines injected; colon marked congestion and hemorrhagic; kidneys hemorrhagic.

Rabbit S87. Belgian male.
Given 1 cc of 1 per cent caffein for each 100 grams through stomach tube.

Date.

Aug. 17..
Aug. IS..
Aug. 19..
Aug. 20. .
Aug. 21..
Aug. 221.
Aug. 23. .
Aug. 24. .
Aug. 25. .

Weight.

Grams.
1,200
1,340
1,335
1,300
1,325

1,205
1,200
1,285

Treat-
ment.

12.5
13.0
13.0
13.0
13.0

12.0
12.0
12.5

Date.

Aug. 2G.
Aug. 27.
Aug. 28 1
Aug. 29.
Aug. 30.
Aug. 31.
Sept. 1 .
Sept. 2.

Weight.

Grams.
1,185
1,255

1,115
1,135
1,175
1,050
900

Treat-
ment.

12.0
12.5

11.0
11.5
12.0
10.5
9.0

1 Not fed.

September 3, found dead. Autopsy: Stomach and small intestines showed num-
erous hemorrhagic spots; thick coating of mucus surrounded the contents of the stom-
ach; bladder was greatly distended with urine; the other organs were apparently
normal.
Rabbit 388. Belgian male.

Given 1 cc of 1 per cent caffein for each 100 grams, through stomach tube.

Aug. 17..
Aug. 18. .
Aug. 19. .
Aug. 20. .
Aug. 21. .
Aug. 22'.

Date.

Weight.

Grams.
1,080
1,115
1,150
1.130
1,120

Treat-
ment.

10.0
11.0
11.5
11.5
11.0

Date.

Aug. 23..
Aug. 24. .
Aug. 25. .
Aug. 20. .
Aug. 27..
Aug. 28 1.

Weight.

Grams.
1,020
985
960
900
875

Treat-
ment.

10.0
10.0
9.5
9.0
9.0

> Not fed.

August 29, found dead 9 a.m. Autopsy: Heart and lungs normal ; liver and kidneys
engorged; stomach normal; intestines showed a catarrhal inflammation, though not
severe; spleen normal; walls of colon somewhat injected.

74

THE TOXICITY OF CAFFEIlSr.

Rabbit 391. Belgian.

Given 1 cc of 1 per cent caffein to each 100 grams through stomach tube.

Date.

Aug. 17.
Aug. 18.
Aug. 19.
Aug. 20.
Aug. 21.
Aug. 221
Aug. 23.

Weight.

Grams.
940
950
955
935
945

835

Treat-
ment.

9.5
9.5
9.5
9.5
9.5

8.5

Date.

Aug. 24. . .
Aug. 25. . .
Aug. 26...
Aug. 27 2
Aug. 28 1
Aug. 29. .

Weight.

Grams.
805
800
765
690

565

Treat-
ment.

8.0
8.0
7.5
7.0

5.5

1 Not fed.

2 Poor condition.

August 30, found dead 9 a. m. Autopsy: Heart injected; lungs normal; liver affected
slightly with coccidiidea; stomach normal in appearance; small intestines normal,
but colon considerably inflamed; kidneys slightly engorged; other organs normal.

Rabbit 402. Black female.

Given 1 cc of 1 per cent caffein to each 100 grams.

Date.

Aug. 20. .
Aug. 21..
Aug. 22 1
Aug. 23..
Aug. 24. .
Aug. 25. .
Aug. 26. .

Weight.

Grams.
2,030
1,950

1,955
1,905
1,890
1,780

Treat-
ment.

20.0
19.5

19.5
19.0
19.0
18.0

Date.

Aug. 27.
Aug. 28 1
Aug. 29.
Aug. 30.
Aug. 31.
Sept. 1..

Weight.

Grams.

1,765

1,630
1,540
1,510
1,425

Treat-
ment.

17.5

16.5
15.5
15.0
14.0

1 Not fed.

September 2, found dead 9 a. m. Autopsy: The lungs were badly congested, the
posterior lobe of the right lung showing hepatization; the liver was considerably
enlarged and congested; the mucous membrane of the stomach and small intestines
was congested and showed numerous hemorrhagic spots; the kidneys showed slight
congestion; all other organs normal.

Series D. .

The evidence brought forth in the preceding pages regarding cumulation of caffein
naturally suggests the question whether or not the body acquires a tolerance for it.
This question has already been answered in the affirmative by Gourewitch,^^ but
owing to the method he used for the identification of caffein and the few experiments
made his results are not conclusive. The experiments of series A, B, and C might
be regarded as indicating that tolerance for caffein is not acquired by the rabbit. It
was noticed, however, that the rabbit apparently does tolerate increasingly larger
doses under certain conditions, as the following experiments show:

Rabbit 223. Belgian hare, male.

October 22: Weight, 1,520 grams; 15 cc 2 per cent caffein injected subcutaneously
at 2 p. m.

November 1: 10.30 a. m., weight, 1,510 grams; 17 cc 2 per cent caffein injected
subcutaneously (225 mg per kilo), reflexes observed, but no tetanus.

November 4: 10.30 a. m., weight ,1,535 grams; 19 cc 2 per cent caffein injected
subcutaneously at 2.40 p. m.; 4.40 p. m., no symptoms.

November 8: Weight, 1,425 grams; 20 cc 2 per cent caffein (285 mg per kilo) injected
at 11.45 p. m.; 5 p. m., no symptoms.

November 17: Weight, 1,325 grams; 22 cc 2 per cent caffein injected at 2.55 p. m.
(329 mg per kilo), no symptoms.

November 18: Rabbit in good condition.

CHRONIC INTOXICATION — DOGS. 75

Rabbit 224. Belgian hare, female. Diet, carrots.

October 18: Weight, 1,935 grams; 11.20 a. m., 15 cc 2 per cent caffein (155 mg per
kilo) injected.

November I : Weight, 1,780 grams; 20 cc 2 per cent caffein (224 mg per kilo) injected
subcutaneously, reflexes increa-sed, muscle tremors present, but no otner symptoms.

November 4: Weight, 1,710 grams; 21.5 cc 2 per cent calfein (252 mg per kilo)
injected.

November 8: Weight, 1,435 grams; 22.5 cc 2 per cent caffein or 314 mg per kilo
injected at 11.40 p. m.; 5 a. m., no symptoms.

November 17^ Weight, 1,340 grams; 24 cc 2 per cent caffein (358 mg per kilo)
injected subcutaneously.

November 18: 9 a. m., rabbit died.
Rabbit 226. Gray mule. Diet, carrots.

October 28: Weight, 1,045 grams; 10 cc 2 per cent caffein injected subcutaneously
at 1.50 p. m.; 4.30 p. m., tremors observed, but no other symptoms.

October 29: Rabbit in good condition.

November 1: Weight, 950 grams; 10.55 a. m., 11 cc 2 per cent caffein injected sub-
cutaneously (231 mg per kilo).

November 4: Weight, 930 grams; 2.50 p. m., 12 cc 2 per cent caffein injected sub-
cutaneously (258 mg caffein per kilo).

November 6: Weight, 945 grams; 11.45 a. m., 15 cc 2 per cent caffein (313 mg per
kilo) injected subcutaneously.

November 17: Rabbit still alive; weight, 890 grams.

The results of these experiments indicate that when sufficient time is allowed
between two successive injections, susceptibility to caffein is not increased. The
rabbit, on the contrary, seems to acquire a tolerance for the drug, for the fourth dose
was 15 per cent larger than the minimum fatal dose of caft'ein. This is in all proba-
bility due to the better elimination of caffein and its products of decomposition and
to recovery from the deleterious effects of each dose, made possible by long intervals
between injections.

The results of these experiments may be briefly summed up by stating that sub-
minimum doses of caffein given to the rabbit daily or at intervals (not too long) do
not produce any symptoms such as were observed in acute caffein intoxication,
namely, increased reflexes and convulsions, or increased rate of respiration, thus
showing that it is not cumulative. But evidence of undoubted summation of effect
wixs adduced to show that if the administration of subminimum doses of caffein
be continued daily for a period of 11 to 18 days the result is fatal. Tolerance,
however, may be acquired, although to a limited extent only, provided sufficiently
long intervals between injections are allowed to give time for repair of the injury
done by the drug and to develop a mechanism for its better decomposition and elimi-
nation. Furthermore, the evidence just given indicates that the elimination of sub-
minimum doses of caffein and its products of decomposition is probably accomplished
within 24 hours or thereabouts. That the elimination of larger doses is not accom-
plished in this interval is made probable by the following experiment:

Gray rabbit 455. Female. Diet, oats.

October 12: Weight, 1,185 grams; 3.30 p. m., 11.5 cc 2 of per cent caffein injected
into the lumbar muscles; 3 p. m., reflexes increased.

October 13: 10 a. m., rabbit weighed 1,070 grams; no symptoms of caffein poisoning,
reflexes normal; 10.30 a. m., 10 cc 2 per cent caffein injected into the lumbar muscles;
11.30 a. m., rabbit jumped off the table, had convulsions, and died.

EXPERIMENTS ON DOGS.

Having gained some information respecting the eft'ects of repeated doses of caffein
on rabbits, it was of interest to find out how carnivora reacted to the drug when simi-
larly administered. A number of dogs were used for the purpase. Considerable
variation in the mode of experimentation, as will appear later, was allowed.

Since the condition of the animal, its age, environment, or diet might be factors
influencing toxicity, tests were made on full-grown and on young growing dogs whose

76 THE TOXICITY OF CAFFEIN.

food was varied. The subjects of the experiment were kept under observation for
a few days to several weeks before the administration of caffein was begun, in order
to determine whether or not any morbid condition existed, as well as to ascertain
whether the new environment had any effect on these animals. Caffein was given
chiefly by mouth, but the subcutaneous method was also employed during a por-
tion of the experimental period in some dogs. The initial dose, which varied for
different individuals, was maintained for a variable length of time. It was then
progressively increased, in most cases until the death of the animal. With larger
doses the intervals between successive injections were also increased.

Series A.

■ Six dogs were used in this series. Caffein was administered by mouth for periods
of six days to five weeks. It was given daily or at intervals of two, and sometimes of
three, days. In a few instances the drug was withheld for four or even for seven
days, and its administration was resumed at the end of this time. The initial dose
in these experiments varied approximately between 40 and 140 mg per kilo. The
doses were then increased gradually, and thus the maximum resistance of the subject
to caffein was tested. The diet consisted either exclusively of meat or largely of
carbohydrates with a minimum amount of meat to give flavor to the food.

Dog 11. Female.

Diet consisted of rice, 250 grams; cane sugar, 250 grams; meat, 50 grams; cracker
meal, about 100 grams. Caffein was given by mouth daily or at intervals of one day,
when the dose did not exceed 1.5 grams. Before the dose was increased to 2 grams, or
approximately 0.213 gram caffein per kilo, an interval of two days was allowed. Symp-
toms were noticed the next day. An interval of two days was therefore allowed again
at the end of which the same dose was repeated. It will be remarked that there were
no symptoms this time, and the general condition of the dog seemed to be good. Two
grams of caffein were, therefore, given daily during the next two days without any
untoward effects; the dose was then increased to 2.5 grams. Even after this enormous
quantity no symptoms were observed except slight tremors. When this dose was
repeated 26 hours later, it proved fatal. No albumin or sugar was found in the urine,
although the dog was fed on a very liberal carbohydrate diet. The following is a
complete record of the experiment.

April 20: Urine acid, no albumin, no sugar.

April 21: Urine free from sugar.

April 22: Urine free from sugar. 1 gram caffein given in the afternoon.

April 23: 9 a. m., dog was very thirsty, drank a large quantity of water, urine did
not reduce Fehling's solution.

April 24: 2.30 p. m., 1 gram caffein, no sugar in urine.

April 25: 1 gram caffein administered.

April 26: Weight, 10.6 kilos, urine collected in the morning, no sugar; 4.10 p. m.,
1.5 grams caffein.

April 27: 1.5 gi-ams caffein; 1.30 p. m., diet as before, no sugar in urine.

April 28: Weight, 10.2 kilos, no caffein, no sugar in urine.

April 30: Weight, 10.4 kilos, no sugar in urine; 4.20 p. ra., 2 grams caffein.

May 1: Urine examined, sugar absent, weight 10 kilos, vomited, sick, tremors
observed, drank 500 cc water at one time, appetite poor.

May 2: No caffein, drank 150 cc water.

May 3: Urine, no sugar, moderate quantity of albumen present; 12 noon, 2 grams
caffein given by mouth, weight 10.3 kilos; 2 p. m., urine, sugar negative, condition
of dog good, no symptoms of caffein intoxication.

May 4: 10 a. m., about 10 cc thick, dark-colored mucilaginous urine found in col-
lecting bottle; albumin a little more than a trace, decidedly less than on May 3,
no sugar, condition of dog pretty good except for slight muscular tremors; 4 p. m.,
2 grams caffein by mouth (as usual).

May 5: Urine not examined, no symptoms; 4 p. m., 2 grams caffein.

May 6: Urine not examined; 2.30 p. m., 2.5 grams caffein given by mouth; 4 p. m.,
slight tremor, no other symptoms.

May 7: No examination of urine, no symptoms observed; 4 p. m., 2.5 grams
caffein.

May 8: 9 a. m., found dead, urine collected since last dose of caffein was given
did not contain any sugar or albumin, the amount of caffein fed to this dog was 18

CHRONIC INTOXICATION — DOGS. 77

grams in 18 days. Autopsy: Post-mortem examination showed marked enteritis
with hemorrhaj^c spots on the mucosa; liver and kidneys conj^ested and dark colored;
Lungs congested; thyroid gland was greatly enlarged and congested.
Dog 23:

April 30: Weight, (5.8 kilos; the diet consisted of 250 grams rice, 250 grams sugar,
100 grams cracker meal, and iOO grams of meat. (Jii May :5 his weight was 7 kilos.
He received 1 gram of caffoin by mouth at 12 noon. At 2 p. m. he vomited and
tremors were observed. Tlie next day, May 4, tremors were still present though less
pronounced. Examination of the urine for sugar and albumin was nei,'ative; on
May 4, 1 graqi caffein was given again and repeated on May 5. On this date his general
condition was not good — dog had no appetite and refu.sed to take caffein. As tiie dog
lost 10 per cent of his weight he was put on a meat diet exclusively and the do.se of
caffein was reduced to 0.5 gram. He became sick after the second dose, and the
administration of caffein was therefore discontinued. It was resumed after five days
and the caffein was administered in increasing amounts, i. e., on May 18, 0.5 gram;
May 19, 0.5; May 20, 1; !May 21, 1 gram in two doses of 0.5 each, given at intervals of
one hour; !May 22, 1 gram. Dog became irritable, but no other symptoms were
observed. The administration of caffein was omitted the next day. On the follow-
ing day when the same dose of caffein was given there was again marked irritability
and tremors. The experiment was therefore discontinued.

Dog 22. Male bulldog.

June 24: Dog weighed 13.7 kilos. Diet consisted of meat exclusively; 1 gram
caffein was given by mouth; diarrhea developed; no caffein was given for three
days.

June 28: Dog weighed 13.6 kilos, 1.5 grams caffein given at 10 a. m.

June 30: 1.75 grams caffein administered.

July 2: Dog weighed 13.5 kilos; 2 grams caffein or 0.15 gram per kilo, caused well-
marked thirst, but did not produce any other symptoms.
Dog 20. Female:

May 12: Weight, 7.7 kilos. Fed liberal carbohydrate diet, consisting of rice, 100
grams; sugar 100 grams; meat and cracker meal, a sufficient quantity to flavor the
food.

May 14: Weight, 7.7 kilos. Examination of urine for albumin and sugar gave
negative results. Urine was acid to litmus.

May 17: Weight, 7.4 kilos. Three hours after it was fed the dog received -0.5
gram caffein by mouth. The test of the urine the next day for sugar was negative,
but a trace of albumin was present. It will be noticed that the doses were increased
gradually and that symptoms were observed only after the fourth dose of 0.1 gram
per kilo. Later meat was substituted for the carbohydrate diet and the administra-
tion of caffein was stopped for four days. At the end of this period 100 mg caffein
per kilo was fed daily for five days, and the dose was then very gradually increased.
Diarrhea occurred twice, but no other symptoms, the second attack having lasted
a few days. The following is a complete record of the experiment:

May 19: 0.5 gram caffein 11.45 a. m.

May 20: 0.75 gram caffein 12.45 a. m.

Afay 21: 0.75 gram caffein 12 noon; no sugar, no albumin in urine.

May 22: 0.75 gram caffein; urine, same condition found; no symptoms.

May 23: Weight, 7.5 kilos; no caffein.

May 24: 0.75 gram caffein; tremors very marked.

May 25: No caffein.

May 26: 0.75 gram caffein.

May 27: 0.75 gram caffein.

May 28: 0.75 gram caffein.

May 29: 1 gram caffein in two doses of 0.75 and 0.25 gram.

May 30: No caffein.

May 31: No caffein; meat diet exclusively.

June 1: No caffein; meat diet exclusively.

June 2: No caffein; no sugar, no albumin in urine.

June 3: Weight, 7.6 kilos; 0.75 gram caffein; no sugar in urine.

June 4: Weight, 7.3 kilos; 0.75 gram caffein; no sugar in urine.

June 5: W'cight, 7.5 kilos; 0.8 gram caffein; drank 500 cc water; ate 200 grams meat.

June 6: Weight, 7.4 kilos; 0.8 gram caffein; 500 cc urine, drank 500 cc water; ate
200 grams meat; no symptoms.

June 7: Weight, 7.7 kilos; 0.8 gram caffein 10 a. m.; 400 cc urine, 500 cc water, 200
grams meat.

78

THE TOXICITY OF CAFFEIN.

June 8: Weight, 7.5 kilos; 0.9 gram caffein, 450 cc urine, 1 p. m.; 200 grams meat,
500 cc water.

June 9: Weight, 7.6 kilos; 0.9 gram caffein, 1 p. m.; 500 cc water, 200 grams meat
and bone dust; diarrhea and restlessness all afternoon.

June 10: Weight, 7.6 kilos; 1 gram caffein, 500 cc water, 200 grams meat, 480 cc
urine.

June 11: Weight, 8 kilos; 1 gram caffein, 470 cc urine, 500 cc water, 200 grams meat.

June 12: Weight, 7.8 kilos; 1 gram caffein, 710 cc urine, 500 cc water, 200 grams
meat.

June 13: 450 cc urine, 500 cc water, 300 grams meat.

June 14: Weight, 7.9 kilos; 1.2 grams caffein, 500 cc water, 300 grams meat, 490
cc urine.

June 15: Weight 7.8 kilos, 500 cc water, 300 grams meat, 550 cc urine.

June 16: Weight 8.0 kilos, 1.2 gram caffein, 500 cc water, 800 grams meat, bone dust
added to check diarrhea.

June 17: 500 cc water, 300 grams meat, 450 cc urine, diarrhea continues, bone dust
added.

June 18. Weight 7.8 kilos, 1.3 gram caffein, 300 grama meat, 500 cc water, 300 cc
urine.

June 19: Dog very thirsty, drank 1 liter of water and ate 350 grams of meat; 960
cc urine passed during the past 24 hour.

June 21: Weight 7.5 kilos, 1.5 grams caffein given at 10 a. m. At 2 p. m. convul-
sions and death. This dog received a total of 21.15 grams caffein in 25 doses during
a period of 35 days, which amounts to an average of 85 mg per kilo daily.
Dog 19. Female fox terrier.

May 13: Weight 6.4 kilos. Diet consisted of rice, 100 grams; sugar, 100 grams; and
a sufficient quantity of meat and cracker meal to give flavor to the food. Examina-
tion of the urine showed a trace of albumin but no sugar. The urine was acid to litmus.
Two days later the urine was alkaline to litmus. There was still a small amoimt of
albumin but no sugar.

May 17, 0.5 gram caffein was given by mouth. Examination of the urine collected
the next day still showed the presence of albumin and the absence of reducing sub-
stances. The dog had tremors. Caffein was, therefore, not administered.

May 19: 0.5 gram caffein was given by mouth.

May 20: 0.75 gram caffein was fed at 12.45 p. m. The dog vomited during the night
and tremors were observed the next morning. The urine collected was examined
for albumin and sugar, but neither was found.

May 21 : 12 noon, 0.75 gram caffein was fed. The dog weighed 6 kilos, which there-
fore repro.-ented a loss of 0.4 kilo. Grew abnormally thirsty and lost appetite, but
no other symptoms of caffein poisoning were observed.

May 22: The dog was again given 0.75 gram caffein at 12 noon. The examination
of the urine for albumin and sugar gave negative results. The dog died at 4.15 p. m.
The fatal dose for this dog was therefore 0.125 gram caffein yjer kilo, and the total
amount of caffein ingested in six days amounted to 3.25 grams, or 0.54 gram per day,
which makes 90 mg per kilo.
Dor)21. While fe ma k hull.

This dog was kept on a diet exclusively of meat, and was given water ab libitum.
From 0.5 to 0.6 gram of caffein was administered daily for seven days; the doses were
then increased and were given at longer intervals. No symptoms of the effects of
caffein were observed until a dose of 1.5 gram was fed, when diarrhea was noticed on
the next day. Jn the following record the details of the experiment are given:

Dale.

Weight.

Caffein.

Date.

Weight.

Caffein.

Kilos.
12.5
12.5
12.5
12.3
12.3
12.3
12.3
12.3

Grams.
0.5
.5
.5
.6
.6
.6
.6
.8

June 16

Kilos.
12.7
12.9
13.4
13.3
0)
13.5
13.5

Grams.
0.8

June 8 ...

June 18

1.0

June 21

1.2

June 24

1.5

June 25

.0

June 12

June 27

1.5

June 13

June 30

1.75

» Diarrhea.

CHRO>;iC INTOXICATION DOGS. 79

July 2: 11.30 a. m., 2.0 pram caffein fed by nioulh; 1.30.J). ni., tetanu.", dojr died.
The totiil amount of calfein fed to dog No. 21 out of the 25 days of the experiment was
14. -lo grams, or an average of 578 mg per day, \vhi<h amounts to about 42 to 4:i mg per
kilo of body weight.

Notwithstanding the diversity in the method of experimentation, there was a
striking uniformity in some of the results obtained. All the experiments of the series
showed absence of cumulative action of caffein. The experimental evidence pre-
sented indicate.^ that moderately large doses may be given at interval.-^ of ab<nit 24
hours without inducing any symptoms of nervous or any other disturbance. This is
illustrated in the tests on dog 11, which were preliminary in character. In this sub-
ject 100 to 150 mg of caffein per kilo were ingested daily for several day.s without
showing any changes. Later in the course of the experiment, after larger doses were
given, mild symptoms only, such as tremors, were observed. Additional evidence of
the absence of cumulative action of caffein was furnished by the results of the following
experiments:

Dog 23 received 142 mg of caffein per kilo on three successive days. His general
condition indicated that these amounts of caffein were toxic, but he survived. In
another series of tests, made after he was allowed to rest a few days, he again failed to
show any cumulation of the drug, as he survived this time a series of tests of longer
duration than the first.

A much better illustration of the absence of cumulative action of the drug is fur-
nished by the experiments on dog No. 20. In this case 100 to 125 mg of caffein per
kilo, given on 10 consecutive days, did not cause any marked effects. Diarrhea and
restlessness were the only symptoms observed. These experiments therefore show
that the elimination and decomposition of caffein are apparently effected by the body
within twenty-four hours or thereabouts.

Experiments on dog 19, however, form an exception — the third dose of 125 mg caf-
fein per kilo ha\'ing proved fatal. The very low protein content of the diet of this
dog suggests itself as a possible cause of the lower resistance to caffein of this subject.
But it may be observed that the same diet was furnished to dog 20, which stood such
amounts of caffein much longer. The presence of a trace of albumin in the urine of
dog 19 is likewise inadmissible as a cause of the difference in the toxicity of caffein
in this dog, for the urine of dog 20 likewise contained a trace of albumin. The alkaline
reaction of the urine, together with the fact that the first dose of only 60 mg of caffein
per kilo induced symptoms of toxicity, su^ests the presence of an abnormal condition
which in all probability was the cause of the death of this subject under the conditions
indicated.

In a lai^e number of experiments on caffein performed in this laboratory it has been
observed that symptoms due to caffein often disappeared when the administration of
the same dose of the drug was continued. Thus dog 19 vomited when the amount of
caffein was increased to 125 mg per kilo. WTien this amount was repeated the next
day there was no vomiting. Similar observations were made on dogs 11 and 23, also
on other dogs. No. 22 developed diarrhea at first; when the adminLstration of caffein
was resumed several days later, however, there was no diarrhea. In other experi-
ments performed in this laboratory, symptoms of nervous irritability induced by
caffein disappeared on continued treatment.

It was interesting, therefore, to inquire whether resistance to caffein would be
increased by the continued administration of progressively larger amounts of the drug.
When doses of 150 and over were fed, the intervals allowed were usually longer than
24 hours. Two and sometimes three days were permitted to elapse between two suc-
cessive doses. This was done in order to allow time for recovery from possible changes
induced by larger doses of caffein, and thus prevent the summation of effect. In the
experiment? considered, therefore, Nos. 11, 23, 20, and 19, the toxicity of caffein does
not seem to be greater than in the experiments on acute caffein intoxication in the

80 THE TOXICITY OF CAFFEIN.

dog. It was thought, however, that the large initial doses or the quick change to large

doses when the amounts used in the beginning were small, might have something to

do with failure to induce a marked degree of tolerance. The experiment on dog 21

was therefore carried out by giving from 40 to 60 mg per kilo for eight days, and then

increasing the dose, but tolerance could not be induced, as is shown in the protocol

to the experiment.

Series B.

According to the studies of Chittenden,''^ low protein diet improves the general
metabolism of the body, fatigue is diminished, and bodily vigor, therefore, corre-
spondingly increased. The expectation is, therefore, justified that the defense of the
organism against deleterious substances introduced into the body is much improved
by such a diet, thus increasing its resistance to poisons. Hunt's experiment on this
subject, also quoted by Chittenden, lends support to this view. He found that mice
fed on carbohydrates chiefly, or on foods containing only a small amount of protein,
were more resistant to acetonitril. It was interesting, therefore, to inquire whether
the toxicity of caffein differs under similar conditions of diet.

A fixed diet of the same calorific value was provided for all dogs of this series, but
the protein content for three of the animals was approximately one-third of the amount
visually fed to dogs. Caffein was at first administered subcutaneously, but all the dogs
on a low protein diet developed abscesses at the site of injection, while none of those
on high protein diet showed a local reaction. Feeding by mouth was then begun
and continued throughout the experiment in each case. The initial dose was 50 mg
per kilo, which was given daily for seven to nine days. It was then increased pro-
gressively by 25 mg per kilo; 75 mg per kilo were administered for one to two days,
100 mg for two to three days, 125 mg for one to two days, 150 mg for one to two days,
and a single dose of 175 mg. It will be remarked that sometimes an interval of one
day had to be allowed during which no caffein was fed.
Dog 30. Black and tan hound, male.

The dog was under observation for about eight weeks before the experiment was
begun and had received a high protein diet. He was then given 50 mg caffein for nine
consecutive days. On the tenth day the dose was increased to 75 mg per kilo. As no
symptoms developed, this dose was increased to 100 mg per kilo, and was fed one day
apart. It was then raised to 125 mg per kilo. For the first time since the drug was
fed, symptoms appeared; they were noticed a few hours after feeding and persisted
during the next day. Although the appetite was good, no caffein was given on this
day. On the following day this dose was repeated. As the symptoms were not serious,
150 mg per kilo were given daily for the next three days, until 175 mg per kilo was
reached. This dose proved fatal within six hours. Record of experiment follows:

October 9: Weight, 9 kilos, on full nitrogen diet, received daily 0.724 gram nitrogen
per kilo or 87 calories per kilo, received 18 grams meat per kilo, 4 grams lard per kilo,
3 grams carbohydrates per kilo, bone dust, ad libitum.

November 3: Weight, 9.10 kilos.

November 10: Weight, 9 kilos.

November 20: Weight, 9.55 kilos.

November 29: Weight, 8.70 kilos.

December 6, 7, 8, and 9: Received subcutaneously 22 cc 2 per cent caffein. Condi-
tion good, site of injection normal.

Deceml:)er 10, 11, 12, 13, and 14: Received 0.4375 gram caffein by mouth equal to
0.050 gram per kilo, no symptoms, appetite and general condition good.

December 15: 11.30 a. m., received 0.6563 gram caffein by mouth, or 0.75 gram per
kilo, no symptoms, appetite good, condition excellent.

December 16: 11 a. m., received 0.870 gram caffein l)y mouth, or 0.1 gram per kilo,
weight 8.70 kilos, no symptoms.

December 17: No caffein given.

December 18: Received 0.870 gram caffein, or 0.1 gi-am per kilo, no symptoms.

December 20: 2.45 p. m., received 1.0875 grams caffein, or 0.125 per kilo; 4 p. m.,-
ate food readily, seemed very uncomfortable and sick.

December 21: 9 a. m., stiffness in muscles, but no other symptoms, appetite good,
no caffein given.

CHRONIC INTOXICATION DUGS. 81

December 22: 11 a. m., received 1.0875 grams caffein, or 0.125 gram per kilo; 3 p. m.,
depressed in spirits and sick, but no other symptoms observed.

Decemi)er 23: 11.30 a. m., received 1.305 grams caffein, or 0.b50 gram caffein per
kilo; 1.30 p. m., apparently quite sick, l)ut no other symptoms, had good appetite.

December 24: 10 a. m., received 0.175 gram caffein per kilo; 4 p. m., wnen about
to be fed fell over and died; no autopsy.

The total amount of caffein given dog 30 was 11.3458 grams, administered for a period
of eighteen days. The average daily amount per kilo was therefore 72 mg. The feces
became offensive when the amounts of caffein were increased to 75 mg per kilo. It
will be observed that in this dog the appetite was uniformly good until trie day of his
death. Whether or not this is the cause of his resistance to caffein will be discussed
later.
Dog S2. White, male, young.

Although he was growing rapidly this dog's weight was constant, but he looked
anemic. He received a high protein diet until Deceml)er 3, when the rations were
increased by one-third. This dog was under observation from October 2lj to December
6 when the administration of caffein was begun. He then received 50 mg caffein

§er kilo daily for nine days consecutively without showing any effects, when the
ose was increased to 75 mg per kilo, then to 100 mg per kilo. This dose was further
increased to 150 mg per kilo without causing symptoms, which was repeated the
next day. No symptoms having been observed after such amounts of caffein, 175 mg
per kilo were fed. This dose, however, proved fatal within two hours. Record of
experiment follows:

October 26: Weight, 6.90 kilos.

November 3: Weight, 6.90 kilos.

November 10: Weight, 6.90 kilos.

November 20: Weight, 6.90 kilos.

November 29: Weight, 6.55 kilos.

December 3: Put into cage, diet increased one-third.

December 6, 7, 8, 9: Weight 6.30 kilos; 12.30 p. m., received 16 cc 2 per cent caffein
by subcutaneous injection in back, no symptoms of any kind noticed, site of injection
normal.

December 10, 14: 0.05 gram caffein per kilo.

December 15: Received 0.4725 gram caffein by mouth, no symptoms.

December 16: Received 0.655 gram caffein, 0.100 gram per kilo.

December 17: No caffein given.

December 18: Received 0.655 gram caffein daily, 0.100 gram per kilo, no symptoms.

December 20: Received 0.8188 gram caffein, 0.125 gram per kilo, no symptoms,
appetite good.

December 21: Received 0.9825 gram caffein, 0.150 gram per kilo, somewhat uncom-
fortable, no other symptoms.

December 22: Received 0.9825 gram caffein, 0.150 gram per kilo, no symptoms
except some uneasiness.

December 23: 9a. m., no symptoms, appetite good ; 11.30a. m., received 1.146 grams
caffein, 0.1759 gram per kilo; 1.30 p. m., died while making an effort to get out of cage,
tonic contraction of limbs observed before death.

The amount of caffein received during the entire experimental period was 9.2223
grams, or an average per day approximately of 80 mg per kilo, and therefore 10 per cent
more than dog No. 30 received. It will be observed that the appetite in dog No. 32
was likewise uniformly good, and that he received a very high protein diet which was
also of a very high calorific value.

Autopsy (dog 32). — Stomach presented a severe inflammation of the mucosa, espe-
cially in the fundus and pyloric portions. The gastritis was more marked in pyloric
portion, and the inflammatory condition extended along the whole course or email
intestines, which presented numerous hemorrhagic areas, and a thick catarrhal exudate
on the mucosa. The large intestine contained quite a large number of parasites,
probably round worms. The liver was enlarged and the gall cyst well filled. The
spleen was also considerably engorged, kidneys appeared normal, other organs all
appeared normal.
Dog 31. Black spaniel, male.

This dog had been under observation one month previous to the experiments with
caffein. The usual initial dose was then administered for nine days. There were no
signs of local irritation when the drug was given subcutaneously, but symptoms of
toxicity were present. These disappeared, however, when the drug was administered
by mouth. The dose was therefore increased to 75 mg per kilo. This, as will be seen,
proved fatal within six hours. High nitrogen diet, same as No. 30.

November 3: Weight 10.250 kilos.

18594°— Bull. 148—12 6

82 THE TOXICITY OF CAFFEIX.

November 10: Weight, 10.25 kilos.

November 20: Weight, 10.30 kilos.

December 1: Put in cage.

December 6, 7, 8, 9: Weight, 10.20 kilos; received 26 cc 2 per cent caffein Bubcu-
taneously, site of injection normal.

December 6: Very restless and excited, whined when handled as though muscles
were sore, appeared to be sick.

December 10-14: Condition good, received 0.51 gram caffein by mouth daily, no
noteworthy symptoms, apjietite continues good, somewhat restless at intervals.

December 15: 11.30 a. m., received 0.765 gram caffein per mouth (0.075 gram per '.
kilo); 2 p. m., depressed in spirit, seemed sick and uncomfortable; 4.15 p. m., when '
about to feed, animal jumped up, then fell back dead.

Autopsy (dog 31): Lungs congested; heart tilled with blood and contained small
amount of blood-stained fluid m pericardial sac. Liver deeply congested, soft and
friable; gall bladder distended with bile; kidneys showed inflammation of cortex;
spleen pale, normal in size and consistency; stomach practically empty, the mucosa of
the pyloric portion exhibited severe gastritis, with thick catarrhal exudate. This
catarrhal inflammation extended through the duodenum; remaining portion of small
intestine showed mild inflammation; large intestine appeared practically normal.
The total amount of caffein received by dog 31 during 10 days was 5.395 mg, or a daily
average of 53.9 mg per kilo. This unusually low resistance to caffein ^which was
practically the only case in all the experiments on dogs presented in this research)
suggests the presence of some abnormal condition. The bloody exudate in the peri-
cardial cavity indicating pericarditis, which is likely to induce secondary changes of
cardiac muscle, may be considered as a possible cause of the increased toxicity of
caffein in this case.
Dog 29. Male fox terrier, black.

This dog was kept on a low nitrogen diet for nearly five weeks before the feeding of
caffein was begun. The administration of 50 mg of caffein per kilo was then carried
on for eight days without showing any symptoms of toxicity. The usual increase of
dose was then given — 75 mg per kilo — which was followed by a manifestation of
symptoms. Further increase, however, to 100 mg per kilo had no visible effect.
Nevertheless it was considered advisable to suspend the feeding of caffein for one day.
The same amounts were then repeated on two consecutive days. No symptoms having
been observed, 125 mg per kilo were given. As symptoms of toxicity and especially
loss of appetite were observed, the dog was not given any caffein the next day. Since
his appetite had now improved, the experiment with larger doses was resumed. Death
followed after the second dose of 150 mg per kilo. Protocol follows:

Weight, 9.90 kilos. One-third nitrogen diet. Receives 0.269 gram nitrogen per
kilo (88.269 calories per kilo).

November 3: Weight, 9.85 kilos.

November 10: Weight, 9.55 kilos.

November 12: Weight, 9.40 kilos.

November 29: Weight, 9.85 kilos.

December 6: Weight, 9.90 kilos; 11.35 a. m., received 25 cc 2 per cent caffein solu-
tion by subcutaneous injection in back; 4 p. m., no sj'mptoms, appetite good.

December 7-9: Received 25 cc caffein 2 per cent solution — subcutaneous injection,
no symptoms, area of injection inflamed and swollen.

December 10, 13: Site of injection showed increased inflammation, received 0.495
gram caffein (50 mg per kilo) in 30 grams meat daily without showing any symptoms.

December 14: 12 noon, received 0.7425 gram caffein by mouth (0.075 per kilo); 2.30
p. m., restless and uneasy.

December 15: 11.30 a. m., received 0.7425 gram caffein by mouth; 2 p. m., depressed^
in spirits, although continues to have good appetite.

December 16: Weight, 9.50 kilos; 3.15 p. m., received 0.9509 gram caffein by
mouth; 4.50 p. m., no symptoms.

December 17: Animal rested.

December 18: Received 0.950 gram caffein by mouth, no symptoms.

December 19: Received 0.9509 gram caffein by mouth, no symptoms.

December 20: 2.45p.m., received 1.1875 grams caffein (0.125 gram per kilo); 4 p.m.,
restless and quite sick; ate only a little food.

December 21: 9 a. m., etill uncomfortable, allowed to rest, no caffein given, grad-
ually recovered appetite.

December 22: 11 a. m., received 1.875 grams caffein; 3 p. m., seemed sick, but
showed no other symptoms, appetite fair.

December 23: 9 a. m., showed no symptoms from the day before, ate food grad-
ually, seemed sick; 11.30 a. m., received 1.425 grams caffein (0.150 gram per kilo); 1.30

CHRONIC INTOXICATION — DOGS. 83

p.m., looked and behaved as if very sick, no other Kymptoms; 3.45 p. m., in attempting
to get out of box fell over on back, had convuIsionH, whined, dyspnoea, died within 30
seconds.

Autopsy: Stomach exhibited mild inflammation; small intestine inflamed and hem-
orrhagic area.s on mucosa; liver engorged and friable; spleen normal; kidneys slightly
congested; other organs appeared normal. The total amount of caffein fed to Dog 29
was 12.135 grams, which was given in 18 days. The average daily amount per kilo
was therefore 07. 08 mg.
Dog 28. Male fox terrier.

Low nitrogen diet was begun about four weeks before the feeding of caffein; 50 mg
of caffein was then fed for seven consecutive days. Partial loss of appetite was
observofl after the first dose. As the experiment progressed the desire for food steadily
diminished, and the feces became fetid. Symptoms of intoxication manifested them-
selves early in the experiment, and vomiting occurred after the fourth dose. The
dog was then put on a diet exclusively of meat. After an intermission of 10 days 109
mg caffein per kilo were given. Since there were no symptoms, the following day the
amount was increased to 125 mg per kilo. This dose proved fatal within IG to 20 hours.

This dog was stout and strong, weight 12.25 kilos, received daily 0.269 gram nitrogen
per kilo (88.269 calories per kilo).

November 3: Weight, 11.75 kilos.

November 10: Weight, 11.95 kilos.

November 20: Weight, 11.20 kilos. All through this period had been kept in a cold,
poorly ventilated room, put in a warm room, with bedding and good Aentdation.

November 29: Weight, 11.95 kilos.

December 1: Put in a cage; weight, 11.95 kilos.

December 6: Weight, 11.95 kilos; 11.45 a. m., received 0.050 gram caffein per kilo;
then received 30 cc 2 per cent caffein (0.6 gram) in practically one subcutaneous injec-
tion; 4.30 p. m., ate only part of food.

December 7: 10.25 a. m., received 30 cc 2 per cent caffein by subcutaneous injec-
tion (0.6 gram, or 50 mg, per kilo); 1.45 p. m., seemed sen.sitive to touch, no desire for
food, depressed in spirit.

December 8: 11.40 a. m., received 30 cc 2 per cent caffein by subcutaneous injec-
tion (50 mg per kilo); 1 p. m., depressed in spirit, hind legs seemed somewhat stiff,
no desire for regular food, site of injection inflamed.

December 9: 10.50 a. m., received 30 cc 2 per cent caffein by subcutaneous injec-
tion (50 mg per kilo); 2.30 p. m., had vomited, no desire for regular food.

December 10: Inflammation of site of injection, and swelling very pronounced;
2 p. m., received 0.5975 gram caffein, or 50 mg per kilo, with 30 grams of meat, refused
regular food.

December 11, 12: Received 0.5975 gram caffein by mouth, no symptoms except
refusal of regular food, feces fetid.

December 13-22: Put on meat diet exclusively, high temperature, no caffein,
weight 10 kilos, appetite good, feces fetid.

December 22: 12 m., weight 11 kilos, received 1.2 grams caffein by mouth (0.109
gram per kilo); 4 p. m., no symptoms.

December 23: 11.30 a. m., received 1.375 grams caffein (0.125 gram per kilo) had
vomited food of the day before, but could notice no caffein or capsules in vomit; 4.30
p. m., no symptoms, seemed in good .spirits, appetite good, had no meat to feed with, so
was given low nitrogen feed, of which be ate about one-fourth.

December 24: 9a. m., found dead, stiff, and cold. The mo.st striking effect of caffein
in this dog is the increased intestinal putrefaction. The feces were still fetid 10 days
after the administration of caffein was st(i])pod.

Autopsy, dog 28: Stomach partially filled witli an undigested food mass; mucosa
showed severe inflammation; small intestines presented a hemorrhagic enteritis along
whole extent; large intestine also exhibited mild inflammation; liver was engorged;
spleen appeared normal; kidneys slightly congested in cortical portion; other organs
appeared normal.

Dog 24. White and tan male: Was put on low protein diet six weeks before experi-
ments with caffein were begun. The initial dose of 50 mg per kilo was then admin-
istered on eight consecutive days. The only symptoms observed during this period
of caffein administration were those of intestinal putrefaction. Fetid feces were
noticed already after the first dose of caffein was injected. WTien the second dose
of 75 mg of caffein was repeated, mild symptoms appeared, but none have been
observed even with increased amounts of caffein.

One-third nitrogen diet. Received daily 0.269 gram nitrogen per kilo (88.269
calories per kilo).

84 THE TOXICITY OF CAFFEIN.

October 26: Weight 11.15 kilos. Food consisted of 5 grams cracker meal per kilo;
meat, 3 grams per kilo; lard, 2 grams per kilo; tapioca, 10.69 grams per kilo. Kept in
a cold, damp room with poor ventilation until November 20.

Novembers: Weight, 11 kilos.

November 10: Weight, 10.75 kilos.

November 20: Weight, 10.55 kilos; changed to a warm room, with bedding and good
ventilation.

November 29: Weight, 10.85 kilos.

December 1: Put into a cage.

December 6: Weight, 10.90 kilos; 11.25 a. m., received 28 cc 2 per cent caffein sub-
cutaneously in side, below the shoulders, area washed with alcohol and ether,
approximately 50 mg per kilo administered, no symptoms.

December 7: 10.15 a. m., received 28 cc 2 per cent caffein injected subcutaneously;
feces soft and very fetid; 1 p. m., depressed in spirit, eyes dull.

December 9: 10.45 a. m., received 25 cc 2 per cent caffein solution subcutaneously,
feces still fetid, site of injection inflamed and swollen, no other symptoms.

December 10: Inflammation of area of injection more pronounced; 2 p. m., given
0.5449 gram caffein and 30 grams of meat; 4 p. m., fed, no symptoms, feces fetid.

December 11: 12 m., given 0.5459 gram caffein and 30 grams of meat, no symptoms,
feces fetid.

December 12, 13: Given 0.5459 gram caffein daily, without noticing any symptoms.

December 14: 12 m., received 0.817 gram caffein (75 mg per kilo); 2.30 p. m., restless?
and uncomfortable, no other symptoms.

December 15: 11.30 a. m., received 0.8175 gram caffein by mouth; 2 p. m., depressed
in spirit, acted as though sick, no other symptoms.

December 16: Weight, 11 kilos; 11 a. m., received 0.100 gram caffein per kilo (1.100
grams) by mouth, no symptoms.

December 17: Rested.

December 18: 2.30 p. m., received 1.100 grama caffein by mouth; 4. p. m., no
symptoms.

December 19: 12 noon, received 1.100 grama caffein by mouth; 4.15 p. m., no
symptoms.

December 20: 2.45 p. m., given 1.375 grama caffein (0.125 gram per kilo); 3.45 p. m.,
vomited — one of the capsules being found intact, the other broken open; 4 p. m.,
given regular diet, containing 1.3757 grams caffein in capsules, ate most of this during
the night, whined at intervals, coordination disturbed, appeared very sick, but
exhibited no other symptoms.

December 21: 9 a. m., found dead, stiff, and cold.

The total amount of caffein received by dog 24 was between 10.109 and 11.484 grama.
As one of the capsules vomited was intact and the other broken open, the amount was
probably about 10.75 grams. The fatal dose in this case was tmdoubtedly less than
185 mg per kilo — somewhere between 125 and 185 mg. Autopsy showed heart in
diastole; posterior lobe of right lung deeply congested; liver engorged; gall cyst filled;
spleen appeared normal; stomach well filled with semifluid mass; pyloric portion of
stomach exhibited a severe inflammation of mucosa; mucosa of duodenum greatly
inflamed and showed hemorrhagic areas and catarrhal exudate; remainder of small
intestine also exhibited mild inflammation; kidneys deeply engorged, mesentery
injected.

A comparison of the fatal doses of caffein in the experiments on high and low protein
diet does not show much difference in the resistance to caffein, since 175 mg per kilo
proved fatal to Nos. 30 and 32, while No. 29 died after receiving 150 mg per kilo, and
No. 24 received 125 to 185 mg per kilo. Moreover, No. 28, which was changed from
low to high protein diet, succumbed when given 125 mg per kilo. Observations made
during the experimental period indicate, however, greater toxicity of caffein in the
subjects on low protein diet. Dog 30 showed the effects of the drug when the
dose was increased to 125 mg of caffein per kilo, while in No. 32, 150 mg per kilo were
received without any manifestation of symptoms. Dog 31, which was likewise on a
high protein diet, is evidently an exception, and its low resistance to caffein may be
accounted for by the condition found at autopsy. In other dogs on low protein diet
symptoms of intoxication appeared early in the experiment. In Noa. 29 and 24 it
was observed as soon as the amount of caffein was increased to 75 mg per kilo. In
dog 28 the first dose of caffein 50 mg per kilo was toxic. The symptoms of gastro-
intestinal disturbance were especially marked after caffein on low protein diet. This

CHRONIC INTOXICATION DOUS. 85

may seom to contradict the results of oxperinicnt.H on dotjH 11 and 20, in which larger
dosen of caffein failed to induce symptoms of intoxication. But it should be observed
that the diet, which consisted almost exclusively of carbohydrates, was given only
during the administration of caffein, while in the experiments of series B the sub-
jects received a low protein diet for several weeks before the administration of caffein
was begun, and it was continued through the entire caffein period. It will be re-
marked that the absence of cumulative action in the experiments of the preceding
series was also observed in dogs on high as well as on low protein diet. The appearance
of symptoms after smaller doses of caffein in the latter experiments might suggest
cumulative action, but since these symptoms disappeared on continued administration
of the substance cumulation is clearly not indicated. The gastrointestinal lesions
obeerved on post-mortem examination were, it will be recalled, also found in rabbits
similarly treated. The explanation suggested probably applies also in the case of
dogs.

Series C.

As already pointed out in the experiments on acute toxicity of caffein, young growing
dogs are probably more resistant to caffein than adults. That this may also hold true
in chronic caffein intoxication seemed indicated by the following experiments.
Dog SS. Black female puppy. Weight, 4 kilos. Had been continuously on a vuat

diet.

December 22: 2.30 p. m., received 0.69 gram of caffein (0.172 gram per kilo); 3.15
p. m., no symptoms except that feces were fetid.

December 23: 11.30 a. m., received 0.79 gram of caffein (0.197 gram per kilo); 1.30
p. m., no symptoms.

December 24: 11 a. m., received 0.87 gram of caffein (0.2009 gram per kilo); 4 p. m.,
no symptoms.

It will be observed that the only effect produced in dog 33 by feeding caffein was
increased intestinal putrefaction, although 2.37 grams of caffein were given in three
days. Additional data on the effects of the age of animals on the resistance to caffein
seemed desirable. The following experiments were therefore carried out. Six puppies
of the same litter were weaned when 7 to 8 weeks old and put on a milk diet. Three
of them received this diet throughout the experimental period. Meat was substituted
in the other three a few days before the administration of caffein was begun, and waa
continued until the end of the experiment. Caffein was given by mouth; the initial
dose, which was administered for several days and then gradually increased, being
IGO to 200 mg for each dog, except one, which received only 100 mg per kilo for several
days and then an increased amount.

86

THE TOXICITY OF CAFFEIN.

An intermission of a few days (during which no caffein was given) was allowed.
This was done on account of some studies carried on at the same time on the effect of
caffein on certain constituents of the urine.

PUP NO. 1.

Date.

Weight.

Food
(milk).

Treatment

(2 per cent

caffein).

Symptoms.

Apr.21

Grains.
1,450
1,520
1,450
1,375
1,420
1,390
1,400
1,405
1,420
1,430
1,450
1,515
1,475
1,495
1,515
1,535
1,525
1,530
1,500

1,490
1,535
1,460
1,475
1,545
1,550
1,555
1,500
1,450
1,500
1,565
1,545

1,595

1,495

cc.
300
300
250
250
250
250
250
250
250
250
250
250
250
250
250
250
250
250
250

250
250
300
350
250
250
250
250
250
250
250
250
250
250

250

cc.
10.0
10.0
10.0
10.0
10.0

None.

None.

None.

None.

None.
10.0
15.0
15.0
15.0
22.0
20.0
20.0
20.0
23.0

None.

25.0
None.
None.
None.
None.
None.

25.0
None.
None.
None.
None.
None.

27.0

27.0

No sjrmptoms.

Apr. 22

Do.

Apr. 23

Do.

Apr.24

Do.

Apr. 25 . .

Do.

Apr. 26 . . .

Apr. 27

Apr. 28

Apr.29

Passed worms.

Apr. 30

Do.

May 1

No symptoms.

May 2

Do.

May 3

Do.

May 4

Do.

May 5

Seems dull and whines.

May 6. .

Whines.

May 7

No symptoms.

May 8

Do.

May 9

Diarrhea; passed worms; tremor and rigidity of

May 10

legs; whines.
Completely recovered from the effects of 9th.

May 11

Can not balance itself; continually vomiting.

May 12

Recovered from eflects.

May 13

In good condition.

May 14

May 15

May 16

May 17

Salivated in cage; stiffness of muscles.

May 18.

Weak and stiff; diarrhea.

May 19.

No symptoms.

May 20

May 21

May 22

May 23

Tremors; gait clumsy; incoordination of move-

May 24

ments.
Diarrhea; vomited; weak and stiff; found dead

9 a. m. 25th.

> Sunday.

Autopsy: Marked pulmonary congestion; liver very pale; heart wall injected;
slight inflammation of stomach and intestines.

Date.

CHRONIC INTOXICATION — PUPPIES.
PUP NO. 2.

87

■Weight.

Oramx.
1.S50
1.240
1.250
1.205
1,220
1,210
1,210
1,205
1,200
1.210
1,220
1 . 220
1.2.35
1,235
1,2.35
1,250
1,235
1,250
1,1(15
1,2;«
1,300

1,200
1.215
1,280
1,300
1,310
1,310
1,250
1,245
1,310
1,325
1,325
1.325
1.315

Fo()<l
(milk).

300
300
200
2(J0
200
200
21K)
200
200
200
200
200
200
200
200
200
200
200
200
200
200

200
200
200
200
200
200
200
200
200
200
200
200
200

Troatmont

(2 per cent

callein).

cc.
5.0
5.0
7.5
7.0
7.0

None.

None.

None.

Nono.

None.
10.0
10.0
10.0
10.0
17.0
17.0
15.0
15.0
18.0

None.
20.0

None.

None.

None.

None.

None.
20.0

None.

None.

None.

None.

None.
22.0
22.0

8>-mptoms.

! To symptoms.
Do.
Do.
Do.
Do.

Pa-ssod worms.

No symptoms.

bo.

Do.

Do.
Whines.

Do.
Diarrhea and worms.
Diarrhea.

Little or no symptoms.
No svTnptoms.
Salivated in case; refused to eat; draws up hind

legs.
Recovered.
In good condition.

Salivated in cage; stiff; all symptoms.
Weak and stifl.
No symptoms.

Somewhat stifl.

Restless; scratches eyes; sick.

PUP NO. 3.

1,215

300

1,220

300

1,220

200

1,200

200

1,205

200

1,195

200

1,200

200

1,215

200

1,220

200

1,200

200

1,225

200

1,230

200

1.235

200

1,245

200

1,270

200

l,2(i0

200

1.240

2IX)

1,205

200

1,240

200

None.

None.

None.

None.

None.

None.

(')

None.

None.

None.
10.0
10.0
10.0
10.0
17.0

17.0

15.0
1.5.0
18.0

?'o symptoms.

Do.
Coughs and whines.
Passed worms.
Eyes appear dim and is continually scratching

"them.
Appears restless and draws up hind legs when

walking.
Eyes dim; passed worms; diarrhea.
Cou>,'hing continually; very rest less.
12 noon; salivatetl in cage; passed worms; diarrhea;

foaming at mouth; can not balance himself;

rigidity and tremor of hind legs. 2.15, found

dead.

' Urine squeezed from bladder.

Autopsy: Severe pulmonary congestion; catarrhal gastritis; mild enteritis with
small hemorrhagic areas on mucosa.

88

THE TOXICITY OF CAFFEIN".

PUP NO. 4.

Date.

Apr. 28 .
Apr. 29 .
Apr. 30 .
May 1 . .

May 2 . .
May 3 . .
May 4 . .
May 5 . .

May 6..
May 7. .
Mays..
May 9..
May 10.
May 11.
May 12.
May 13.
May 14.
May 15.
May 16.
May 17.
May 18.
May 19.
May 20.
May 21 .
May 22.
May 23.
May 24.
May 25.
May 26.
May 27.

Weight.

Grams.
1,670
1,670
1,070
1,690
1,690

1,720
1,735

1,760
1,745
1,710
1,750
1,750
1,755
1,730
1,785
1,835
1,820
1,835
1,860
1,855
1,770
1,755
1,780

1,785
1,795
1,630
1,600

Food.

Milh (.cc).
300
300
300
300
300
300
300
300

Meat
(grams).
60
80
180
180
180
180
180
180
115
115
115
115
115
115
115
115
115
115
115
115
115

Treatment

(2 per cent

cafleiii).

10.0
None.
None.
10.0
10.0
10.0
10.0
15.0
15.0
15.0
17.0
17.0
17.0

20.0
23.0

Symptoms.

No symptoms.

Do.

Do.
Passed worms.
Feces soft and black.
Stiff; loss of appetite.
Loss of appetite.

Do.
Restless.

Feces soft and black.
Loss of appetite.

Loss of appetite; threw up worms.
Loss of appetite; worms; cough; diarrhea.
Weak; no appetite; diarrhea; cough.
Found dead, 9 a. m.

Autopsy. — Lung uniformly congested; liver deeply congested; heart muscle pale
with hemorrhagic areas; kidneys pale with hemorrhagic spots on surface and in
cortex; slight catarrhal inflammation of stomach and the small intestines.

CHRONIC INTOXICATION — PUPPIES.
PUP NO. 5.

89

Date.

Weight.

Food.

Treatment
(2 percent
caffein).

Symptoms.

Apr. 28 .
Apr. 29.
Apr. 30.
May 1 . .
May 2..
May 3 . .
May 4..
Mays..

May 6. .
May 7..
Mays..
May 9..
May 10.
May 11.
May 12 .
May 13.
May 14.
May 15 .
May If).
May 17.
May 18.
May 19.
May 20.
May 21 .
May 22.
May 23.
May 24.
May 25.
May 26.
May 27.
May 28.
May 29.
May 30.
May 31 .
June 1 . .
June 2..
June 3..

GravM.
1,745
1,745
1,750
1,7()5
1,765

1,490
1,805

1,815
1,825
1,770
1,795
1,805
1,800
1,720
1,815
1,845
1,830
1,815
1,830
1,835
1,825
1,850
1,835

1,820
1,835
1,840
1,820
1,840
1,830

1,770
1,765
1,750
1,635

Milk (cc).
300
300
300
300
300
300
300
300

Meat
(grams).
60
80
180
180
180
180
180
180
115
115
115
115
115
115
115
115
115
115
115
115
115
115
115
115
115
115
115
115

10.0

None.

None.
10.0
10.0
10.0
15.0
15.0
15.0
15.0
17.0
17.0
17.0
20.0
20.0
23.0
25.0
25.0

None.

None.

None.
25.0
27.5
27.5

No symptoms.

Do.

Do.
Loss of weight; no other symptoms.
No symptoms.
Stiflness.
No symptoms.
A little stiff.
No symptoms.

Do.
Do.
Feces soft and black.

A little stiff.

Diarrhea; stiff in hind legs.

Diarrhea and worms.

Paralyzed; vomited; died at 3 p. m.

90

THE TOXICITY OF CAFFEIN.

PUP NO. 6.

Date.

Apr. 28 .
Apr. 29.
Apr. 30.
Mavl..
May 2..
May 3..
May 4..
Mays..

May 6. .
Mav7..
Mays..
May 9..
May 10.
May 11.
May 12.
May 13.
May 14.
May 15 .
May 16-
Mayl7.
May 18.
May 19.
May 20.
May 21 .
May 22.
May 23.
May 24.
May 25.
May 20.
May 27.
May 28.
May 29.

Weight. ! Food.

Grams.

1,280
1,290
1,315
1,330

1,360
1,365

1,395
1,365
1,340
1,380
1,400
1,425
1,470
1,485
1,510
1,500
1,485
1,480
1,485
1,495
1,500
1,500

1,470
1,465
1,450
1,450
1,355
1,270

Milk{cc)
300
300
300
300
300
300
300
300

Meat
(grams).
60
80
180
180
180
180
180
180
115
115
115
115
115
115
115
115
115
115
115
115
115
115
115

Treatment

(2 per cent

caffein).

14.5
None.
None.
14.5
14.5
14.5
14.5
19.5
19.5
19.5
17.0
17.0
17.0
20.0
20.0
23.0
2.3.0
23.0

Symptoms.

No symptoms.

Do.
Do.
Passed worms.

Feces soft and black; almost diarrhea.
Scratches her eyes and chases her tail.

Feces soft and black.

Diarrhea and worms.

Refused to eat all food.

Threw up worms, stiff, and has skin over both eyes.

Found dead.

Highest amount of caffein given, 362 mg per kilo. No autopsy.

Examination of the results obtained in the experiments of series C shows that
young and growing dogs tolerate large amounts of caffein. In four subjects of this
series, Nos. 1, 2, 3, and 6, no effect was observed when moderately large amounts
(160 to 200 mg per kilo of caffein) were fed. Symptoms were noticed only when
these amounts of caffein were increased from 50 to 60 per cent. The other two dogs,
Nos. 4 and 5, of this series were less resistant, however, to caffein, as 0.16 gram of the
drug per kilo induced well-marked symptoms. Since these were fed meat, while Nos.
1, 2, and 3 received milk, the difference in toxicity may be due to the diet employed,
but No. 6, which likewise received a meat diet, failed to show the effects of caffein
when 200 mg per kilo were fed. On the other hand, it should be noticed that No. 1
died after receiving 360 mg per kilo, No. 2 survived a dose of 334 mg, while No. 3 died
after a dose of 322 mg per kilo of caffein. The fatal doses for Nos. 4. 5, and 6 were 287,
335, and 300 mg per kilo, respectively. Although the differences are too small to
justify any definite conclusion regarding the effect of a milk diet or of a meat diet on
the toxicity of caffein, the results nevertheless suggest a reasonable possibility that
caffein is more toxic to young dogs when on an exclusively meat diet than when fed
milk. It is perfectly evident, however, that the resistance to caffein in either case is
very great, almost twice that of adult subjects. As shown in series A and B, 125 to
175 mg per kilo proved fatal to all but two animals in these experiments, while
symptoms of toxicity appeared after much smaller doses. In other respects the
behavior of young dogs toward caffein was the same as that of the adult. In neither
case was cumulation nor tolerance observed under the conditions of these experi-
ments. The findings at autopsy were likewise similar, as gastro-enteritis was the
chief lesion observed on macroscopic examination. It might be mentioned, however,

DI:3CUSS10>; (Jl- UKSL'LTS, <Jl

in this cnnnoctinn, that the symptoms of caff inn intoxication in yoiin.!^ dojiTS often
presented marked differences fnjin those observed in those of more advanced at^e.
The resemblance of the effects of caffein in youns? pnj)pies and in rabbits was very
atrikinij. In both, the tonic with clonic convulsions were observed after a sufficient
quantity of caffein was administered. In the dogs which were fully prown a large
dose of caffein was usually followed by tonic convulsions and almost instantaneous
death.

Moderately large amounts of caffein fed daily to pupj)ies f(jr several days — in some
cases as long as 10 days — induced mild symptoms only. No cumulative effect was
observed in any of the experiments of series C. There seems to be tcjlerance of certain
functions toward caffein, but no general tolerance of the body could be obtained in
these experiments. Caffein is apparently less toxic for adult dogs on high than on low
protein diet. lu young and growing dogs caffein is somewhat less toxic when milk,
rather than meat, forms the exclusive diet. Some pathological conditions apparently
increase the toxicity of caffein also in dogs. The symptoms of caffein intoxication
observed in young dogs are in some respects different from those in full grown and older
animals, and resemble those noticed in rabbits.

DISCUSSION OF RESULTS.

It was pointed out at some length in the introduction that the
toxicity of some drugs may not be the same for all forms of life.
This observation was also made by some investigators who experi-
mented with caffein on different species of animals. Thus Maurel ^^
stated that caffein is twice as toxic for the frog as for the rabbit when
administered by mouth. Froliner's -^ experiments, on the other hand,
made on domestic animals, failed to show great differences in the
toxicity of caffein. According to this observer, horses seem to be
more susceptible than cattle, goats, and swine, the minimum toxic
dose being the same for all of these, while the resistance of the dog to
caffein is about midway between that of the horse and the other
animals mentioned. It may be remarked, however, that Frolmer made
only 13 experiments. That these data are inadequate for the forma-
tion of any conclusions as to the toxicity of caffein is evident since
the most strikmg effect of cafTein observed in the work herein
reported was the comparatively wide range of variation in the re-
sistance of individuals of the same species to this drug. This was
found to be the case even when the conditions of experimentation
were approximately uniform, and was observed whatever the mode
of admmistration of the drug employed. The toxicity for different
individuals also varied in acute as well as in chronic intoxication.
It is for this reason that the number of tests employed were often
quite large, for no conclusions of any value could be drawn ^vithout
averaging the results of a sufficiently large number of experiments.
Furthermore, it is to be borne in mind that the action of a drug may
differ according to the mode of its introduction into the body and
that different species of animals may vary in this regard. This is
especially true of some substances when given by mouth, the range

92 THE TOXICITY OF CAFFEIlSr.

in toxicity for certain species of animals being much greater when
thus administered than when injected subcutaneously or intrave-
nously.

Maurel's ^^ investigations are of interest in this connection, as his
work embraces a systematic study of the toxicit}^ of a large number
of substances in the rabbit, pigeon, and frog when given by mouthy
subcutaneously, intravenously, or when injected into the muscles.
According to this investigator the range of variation of the toxicity
of a substance is "wadest when given by mouth. Potassium sulpho-
cyanid, for example, is about 2.5 times as toxic for the frog as for the
rabbit when given by mouth. Quinin hydrobromid is three times as.
toxic for the frog as for the pigeon, while for the rabbit it is twice as
toxic as for the pigeon. When given by hypodermic injection the
toxic dose per kilo weight is practicall}^ the same for all three species.
The difference of resistance according to the mode of administration
is even more marked for spartein sulphate. When given by mouth
the toxicity for the rabbit is six times as great as for the frog, but
when injected subcutaneously the toxic dose is about the same for
the rabbit and for the frog. The relation of the mode of adminis-
tration to toxicity is further shown in the following substances : For
the rabbit the minimum fatal dose per kilo of quinin hydrobromid is
1.5 grams administered by mouth, 0.5 gram when injected subcu-
taneously, and 0.07 gram by the intravenous path, while strychnui
sulphate is twice as toxic administered intravenously as subcuta-
neously, and six times as toxic as when administered by mouth.
The mode of introduction, however, does not always affect the
toxicity of a substance. This is made evident by the action of
strj^chnin on frogs in which, according to Maurel ^^, the toxic dose is
the same whether given by mouth or injected into the subcutaneous
tissues. This appears to hold true also for other animals as demon-
strated by the experiments of Hatcher ^^ on the cat, in which he
observed that strychnin is as readily absorbed from a full stomach
as from the subcutaneous tissues. These findings are extremely
interesting, especially in view of Maurel's " work on the subject,
according to which he finds that a substance is much less toxic when
given by mouth than when administered by hypodermic injection
or intravenousl3\ That tnis generahzation does not admit, however,
of universal apphcation is made evident by the work of various
experimenters. Claude Bernard ^° observed that curara is as poisonous
for the pigeon when given b}'' mouth as when injected subcutaneously,
while Zalesky ^ foimd that samandarin is more toxic for frogs when
introduced into the stomach than by injection into the Ij^mph sacs.
Our experiments with caffein likewise show that Maurel's generaliza-
tion does not always hold good, since it was found in experiments mth
gray rabbits that the minimum fatal dose is but moderately greater
by mouth than by the subcutaneous path.

DISCUSSION OF RESULTS. 93

Equally interestincjj is the observation of the writer, that in the
guinea ])i,i; the difToreuce in the toxicity between the subcutaneous
and intraperitoneal injections is very sli^jht, wliile in the cat tiie
toxicity of caffein is the same whether given by mouth or injected
into the subcutaneous tissues, and is markedly less when injected into
the j)eritoneal cavity. The experiments on dogs show considerable
variation of elTective dose when given by mouth, but the interest-
ing obsers'ation w^is made that the toxic dose by mouth may be
smaller in some cases than the average dose by subcutaneous injec-
tion. If the resistance to caffein by subcutaneous injection of the
diflferent species of animals experimented upon in the present research
be compared, it will be noticed that the gray rabbit or Belgian hare,
which is more resistant than the other varieties employed, stands
more caffein in proportion to the weight of the body than the other
animals.

Although the minimum fatal dose was found to be somewhat larger
for the guinea pig than for the gray rabbit when caffein was injected
intraperitoneally, it was on the contrary smaller by other patlis of
introduction, and approximated quite closely the minimum fatal
dose for rabbits of the other varieties. Cats as well as dogs were
found to be distinctly less resistant to caffein than the herbivora.

There are a number of factors far more important than zoological
differences which influence the toxicity of caffein. Some of these
are age, season, and pathologic conditions. As these factors have
already been dwelt upon in their appropriate places, further discus-
sion might seem unnecessary, but o\ving to their importance in deter-
mining the action of a drug, emphasis is desirable. Especially is this
the case with pathological conditions in relation to toxicity. Wli'Je
no positive proof of diminished resistance to caffein in pathological
conditions was obtained by subjecting the suggestion to experimental
test, it was observed in these experiments on rabbits that death
occurred in some individuals after small doses wliich are usually not
even toxic. The findings at autopsy indicate the presence of patho-
logical conditions. The same was observed in some experiments on
cats and dogs. It is extremely probable, therefore, that disease
modifies the reaction of the organism to caffein as well as to other
drugs.^^

That the resistance to drugs may var}' according to the age of the
subject has been maintained by a number of pharmacologists. Accord-
ing to Guinard, '" j'oung dogs, rabbits, and guinea pigs are very sus-
ceptible to morpliin, resembhng children in this regard." The mini-
mum fatal dose for these animals is about one-third less than for the

a A case of accidental poisoning reported recently by Wlchura (Munich, Med. VVoch., 1911, No. 30, p.
1618) throws some doubt on the accepted view that the sa^ceptibllity of young children to morphin is
greater than that of adults. Wlchura also found that the therapeutic doses of codein preparations ordi-
narily recommended lor children in pleuritic cough are not eSective In this condition.

94 THE TOXICITY OF CAFFEII^.

adult. This is not true, however, for the 3'oung of other species.
Cats under 15 days of age tolerate twice the toxic dose of morphin
for the adult cat. Young beeves and goats are likewise more resistant
to this alkaloid than adults. On the other hand, according to Livon,^*
young guinea pigs are more sensitive to alkaloids than adults. The
toxicity of caffein, as shown in the present investigation, was found
to be less in the 3'oung than in the adult. In dogs the 3^oung subjects
are in some instances almost twice as resistant as adults. The differ-
ence was found to be less in cats and rabbits than in dogs, but it was
quite marked.

The effect of season on the toxicit}^ of drugs has been discussed in
the section on the experiments on guinea pigs, which were more re-
sistant to caffein in the fall than in February and March, The effect
of season seems to vary with the animal, but it may also differ with the
substance employed. In Noe's ^^ studies on this subject cantharidin
was found to be more toxic for the hedgehog in November than in
July. The effect of season was different for morphin, as it was
observed that the resistance of the hedgehog was greater at the end
of the summer than earlier in the season.

The relation of diet to toxicity of drugs has been studied by Hunt.^®
His experiments indicate that this is an important factor in the resist-
ance to acetonitril. The studies here reported on the eft'ect of diet
on toxicity of caffein in rabbits were confined to experiments with
oats and carrots and do not show any mocUfication of the resistance
to caffein. The question of diet in chronic intoxication in dogs, how-
ever, suggests that in these animals diet may affect the toxicity of
caffein, although the data on this subject are far from satisfactory.
There is nevertheless sufficient evidence to suggest that a high protein
diet for the adult dog tends to greater resistance of the animal to
caffein and similarly the growing dog tolerates larger quantities of
caffein on a milk diet than on a diet of meat.

This brings us to a consideration of the behavior of caffein in
chronic intoxication. Although in both rabbits and dogs absence of
cumulation was evident, in other respects decided differences in the
resistance to caffein were observed. While the rabbit tolerates more
than tmce the single dose of caffein per kilo for the dog, the result is
quite different in repeated dosage of the drug, the rabbit succumbing
to continued administration of much smaller doses of the drug than
the dog. This is probably due to lesions of the gastro-intestinal canal
caused by caffein which occasions loss of appetite much more readily
in the rabbit than in the dog. The abundant energy reserve in the
dog makes it possible for this animal to stand inanition much longer
than the rabbit and other herbivora. The difference in the behavior
of the rabbit and dog toward caffein is interesting as sho^ving complete
reversal of resistance in acute and chronic intoxication. From the

CONCLUSIONS. 05

statement in the introduction it is evident that the size of the sin^jle
toxic or lethal dose of a substance is in no wise an index of the active
dcfijree of its toxicity. The experiments with caffein here reported
furnish additional evidence that this is trne, at least for the rabbit.

GENERAL SUMMARY AND CONCLUSIONS.

The toxicit}" of cafTeiu in the rabbit varies with the mode of its
administration, he'm<i: least when .iriven by raoutli and greatest by
intravenous administration. The toxicity is from 15 to 20 per cent
greater by subcutaneous injections than by mou<h, but is about half
of that when injected into the ])eritoneal cavity. \o dilference was
observed in the toxicity of calTein whether administered into gluteal
or into the lumbar muscles. "When introduced by this route the
toxicity was found to be less by one-third llian when it is injected
into the peritoneal cavity, but is about 30 per cent more toxic than
the subcutaneous injections. White or black rabl)its were found to
be less resistant to cafTein than gray rabbits.

The resistance of the guinea pig to cafTein, as of the ra))l)it, is
greatest when given by mouth. The minimum fatal dose is less by
intraperitoneal injections, but greater than by subcutaneous injec-
tions, thus differing from the rabbit in this regard. The adult cat
is less resistant than the guinea pig or rabbit to cafTein. The mini-
mum lethal dose by mouth is the same as by subcutaneous, and is
less than by intraperitoneal, injection. The minimum fatal dose
for dogs was found to be the same by mouth as by subcutaneous in-
jection and is almost the same as for the cat. The toxicity of cafTein
varies in the guinea pig according to season of the year.

Age is likewise a factor in the toxicity of cafl'ein, young animals
being more resistant than the full-grown and older animals; this was
shown in experiments on rabbits, cats, and dogs. The symptoms of
cafTein poisoning also were different in ])uppies and in full-grown dogs.
Different diets, such as carrots and oats, did not influence the resist-
ance of rabbits and guinea pigs to cafTein. Low protein diet tends
to decrease resistance to cafTein in dogs. Young growing dogs are
less resistant to cafTein on a meat than on a milk diet. CafTein is
not cumulative in the rabbit or dog, even if administered for a con-
siderable length of time. Some degree of tolerance may be induced
m the rabbit under certain conditions, but not in dogs under the
conditions of the experiments made in this investigation. The possi-
bility, however, that dogs may accjuire tolerance for cafTein is not
excluded. Although the rabbit tolerates a much larger single dose
of cafTein than the dog, it was found, in experiments on clironic
intoxication that the rabbit is less resistant to cafTein than the dog.
The toxicity of cafl'ein is probably increased under pathological con-

^6

THE TOXICITY OF CAFFEIN.

ditions, since comparatively smaller doses were fatal to rabbits, cats,
and dogs, when marked lesions not due to caffein were found at
autopsy. Glycosuria was observed in rabbits, guinea pigs, and cats ■
when caffein was given in sufficient amounts. ^

Table 18. — Acute caffein intoxication: Table showing average minimum toxic and
minimum fatal doses for adult animals.

Effect of
dose.

Dose per kilo (grams.)

Animal.

Subeuta-
neously.

By mouth.

Intraper-
itoneally.

Intra-
muscular.

Intra-
venous.

/Toxic...
\Fatal....

/Toxic . . .

0.15
.30

0.325
.350

0. 100-0. 125
.150

0. 13-0. 15
.20

0.05

0. 10- . 16

\Fatal....

/Toxic...
\.Fatal....

/Toxic...
\Fatal....

/Toxic . . .

.20

0. 15- . 16
.20- .24

.12- .14
.15

.290

.150
0.280- .300

.125
.150

. 100- . 120
, 140- . 150

.200
.240- .250

. 125- . 160
.180- .200

Cat

"

Dog.

\Fatal....

.15- .16

Note. — The doses given in this table are approximate.

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98 THE TOXICITY OF CAFFETX.

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expiration of a definite period after the date of borrowing,
as provided by the rules of the Library or by special ar-
rangement with the Librarian in charge.

DATE BORROWED

DATE DUE

DATE BORROWED

DATE DUE

AP

^^8Z003

lifAV 1 9^y«*^

)

1 2003

WM ^

t t.UWs*

C28'638)M80

QP921.C3
Salant

Sa33

m

COLUMBIA UNIVERSITY LIBRARIES

0041078314

'^^mm