tuberculous cows in which the udder is apparently not invaded by the
disease should be considered dangerous or not. Some incline to the belief
that the milk secreted by healthy udders is never infectious, even when the
lungs or other organs are affected; that, in other words, the tubercle
bacilli are rarely, if ever, separated from the lesions which they produce,
and that the udder itself must be diseased before tubercle bacilli can
appear in the milk. Experiments made with the milk of tuberculous cows in
which there were no indications of udder disease do not bear out this
theory, since tubercle bacilli have been found in their milk. Some
authorities still believe that the udder is diseased when the milk is
infected, but that the disease escapes observation. However this may be,
the fact that the udder may be diseased and the disease not recognizable
simply casts suspicion upon all milk from tuberculous animals. We know that
the milk of tuberculous cattle may or may not contain tubercle bacilli when
the udder is apparently free from disease, but we have no rapid method of
determining whether in any given case the milk contains tubercle bacilli or
not. Moreover, the bacilli may be absent at one time and present at another
in milk from the same cow. When we consider, therefore, the extent of
tuberculosis and the hidden character of the disease, a certain degree of
suspicion rests upon all milk from untested cattle. Fortunately, tubercle
bacilli are readily destroyed by the temperature of boiling water, and
hence both meat and milk are made safe, the former by the various processes
of cooking, the latter by boiling for a few moments. It is incumbent upon
all communities to have dairy cows examined and tested with tuberculin. If
disease is detected, the affected animal should be killed at once or else
all opportunity for the sale of such milk removed by appropriate measures.
Where milk or cream is sold to the trade in large towns or cities
pasteurization should be required as an additional safeguard.
Recently there has been much discussion of the question as to whether human
and animal tuberculosis are identical diseases and as to the possibility of
the tuberculosis of animals being transmitted to man or that of man being
transmitted to animals.
The fact that tuberculous material from human subjects often failed to
produce serious disease in cattle was observed by a number of the earlier
investigators who experimented with such virus. It was the experiments and
comparative studies of Theobald Smith, however, which attracted special
attention to the difference in virulence shown by tubercle bacilli from
human and bovine sources when inoculated upon cattle. Smith mentioned also
certain morphological and cultural differences in bacilli from these two
sources, and in the location and histology of the lesions in cattle
produced by such bacilli. He did not conclude, however, that bovine bacilli
could not produce disease in the human subject, but said:
It seems to me that, accepting the clinical evidence on hand, bovine
tuberculosis may be transmitted to children when the body is overpowered by
large numbers of bacilli, as in udder tuberculosis, or when certain unknown
favorable conditions exist.
Koch, however, in his address at the British Congress on Tuberculosis, went
far beyond this and maintained that "human tuberculosis differs from bovine
and can not be transmitted to cattle." As to the susceptibility of man to
bovine tuberculosis, he said it was not yet absolutely decided, but one was
"nevertheless already at liberty to say that, if such a susceptibility
really exists, the infection of human beings is but a very rare
occurrence." He emphasizes this view in the following language:
I should estimate the extent of infection by the milk and flesh of
tubercular cattle and the butter made of their milk as hardly greater than
that of hereditary transmission, and I therefore do not deem it advisable
to take any measures against it.
This conclusion was so radically different from the views of most
experimenters and so out of harmony with facts which had apparently been
demonstrated by others that it at once aroused opposition in the congress,
followed by the adoption of dissenting resolutions, and led to numerous
investigations in various countries. Koch's conclusions were based upon his
failure to produce tuberculosis in cattle and other animals by inoculating
them with tuberculous material of human origin and his success in causing
progressive and fatal tuberculosis in the same kinds of animals when
inoculated with tuberculous material of bovine origin. With such
positiveness did he hold to the constant and specific difference between
the human and bovine bacillus that he promulgated an experimental method of
discriminating between them. Speaking of the etiology of intestinal
tuberculosis in man, he said:
Hitherto nobody could decide with certainty in such a case whether the
tuberculosis of the intestine was of human or of animal origin. Now we can
diagnose them. All that is necessary is to cultivate in pure culture the
tubercle bacilli found in the tubercular material, and to ascertain whether
they belong to bovine tuberculosis by inoculating cattle with them. For
this purpose I recommend subcutaneous injection, which yields quite
specially characteristic and convincing results.
These important and comprehensive conclusions followed from a comparatively
few experiments upon animals, and apparently no effort had been made to
learn to what extent human tubercle bacilli may differ in their virulence
for cattle or what grades of virulence there might be among bacilli of
bovine origin. Vagedes had already shown that bacilli were sometimes
present in human lesions which were as virulent as bovine bacilli, but his
work was wholly ignored by Koch.
A considerable number of investigators, including Chauveau, Vagedes,
Ravenel, De Schweinitz, Mohler, De Jong, DelÈpine, Orth, Stenstrˆm, Fibiger
and Jensen, Max Wolff, Nocard, Arloing, Behring, Dean and Todd, Hamilton
and Young, the German Tuberculosis Commission, and Theobald Smith, have
found tubercle bacilli in the bodies of human beings who died of
tuberculosis which proved to have about the same virulence for cattle as
had the bacilli from bovine animals affected by the disease.
Kossel, in a preliminary report, stated that the German commission had
tested 7 cultures of tuberculosis from cattle and hogs--4 from cattle and 3
from hogs. Two proved acutely fatal in cattle after eight to nine weeks; 4
likewise produced a generalized tuberculosis, but which certainly had a
more chronic course, while 1 of the cultures caused only an infiltration at
the point of inoculation, with some caseous foci in the adjoining
prescapular gland and in one of the mediastinal glands, and there was
lacking the spreading of the tuberculosis over the entire body which they
were accustomed to see after the injection of cultures of bovine
tuberculosis. "Hence," says Kossel, "among bovine tuberculosis bacilli
there can also occur differences with regard to the virulence."
The German commission also tested 39 different freshly made cultures from
tuberculous disease in man. Nineteen did not produce the slightest symptoms
in cattle; with 9 others the cattle exhibited after four months very minute
foci in the prescapular glands, which were mostly encapsuled and showed no
inclination to progress; with 7 other cases there was somewhat more marked
disease of the prescapular glands, but it did not go so far as a material
spreading of the process to the adjoining glands. There were 4 cultures,
however, which were more virulent and caused generalized tuberculosis in
the cattle inoculated with them.
It would appear, therefore, that hereafter everyone must admit that it is
impossible always to tell the source of a culture of the tubercle bacillus
by its effect when it is inoculated upon cattle. One of the bovine cultures
failed to produce generalized tuberculosis in cattle, and some of the human
cultures did produce it in such animals. Moreover, while some of the human
cultures caused no disease at all, others led to the development of minute
foci in the prescapular glands, and still others to somewhat more marked
disease of the glands. There were, consequently, four degrees of virulence
noted in these 39 cultures of bacilli from human sources and three degrees
of virulence in the 7 cultures from animal.
Now, if we accept the views of Koch as to the specific difference between
human and bovine tubercle bacilli, and that the human bacilli produce only
localized lesions in cattle, while bovine bacilli produce generalized
lesions in them, must we not conclude that the one non-virulent bovine
culture was in reality of human origin, and that the animal from which it
was obtained had been infected from man? This is a logical deduction, but
reverses the dictum laid down at London that human tuberculosis is not
transmissible to cattle. Again, how are we to explain the human cultures of
medium virulence? Are they human bacilli which, for some unknown reason,
are increasing in virulence and approaching the activity of the bovine
bacillus, or are they really bovine bacilli which have multiplied in the
human body until their virulence has become attenuated? In whatever manner
these questions are decided it would seem that the findings of the German
commission, instead of supporting Koch's views that we can decide with
certainty by the inoculation of cattle as to the source of any given
bacillus, really show that this method of diagnosis is extremely uncertain
in the present condition of our knowledge.
It is definitely admitted that 4 of the human cultures caused generalized
tuberculosis in cattle; Kossel suggest, however, that it may be possible
that the bacilli in cases of human tuberculosis under certain circumstances
can likewise attain a very high pathogenic activity for cattle without
being for that reason bovine bacilli. Undoubtedly the German commission is
confronting the two horns of a dilemma, either one of which is fatal to the
views of Koch as stated with such positiveness at London. If we accept this
suggestion thrown out by Kossel, we must conclude that Koch was wrong in
his claim that human tuberculosis can not be transmitted to cattle, and
thus with one blow we destroy the entire experimental support which he had
for his argument before the British Congress on Tuberculosis. If, on the
other hand, we accept the conclusion which follows from the principle laid
down by Koch for the discrimination between human and bovine bacilli, and
which appears to be favored by Kossel, we must admit that bovine
tuberculosis is an extremely important factor in the etiology of human
tuberculosis. Of the 39 cases of human tuberculosis tested, 4, or more than
10 per cent, were virulent for cattle and would be classified as of bovine
origin; however, these 4 cases, were all found among the 16 cases of
tuberculosis in children which the commission investigated; hence it is
plain that 25 per cent of the cases tested of tuberculosis in children
would by Koch's method be classified as of bovine origin.
In the Bureau of Animal Industry two distinct lines of experiments have
been carried on, in order that one might serve as a check against the
other. There has been, however, no discrepancy in the results. De
Schweinitz, in the Biochemic Division, Bureau of Animal Industry, isolated
9 cultures from human tuberculosis. Two were derived from human sputum, 3
from cases of generalized tuberculosis in adults, and 4 from cases of
generalized tuberculosis in children. By comparing these cultures with a
newly isolated virulent culture of bovine tuberculosis, there were found
among them 2 cultures from children which were identical in their cultural
and morphological characters with the bovine bacillus. These cultures also
killed rabbits and guinea pigs in as short a time as did the bovine
bacillus. Hogs which were inoculated subcutaneously with these 2 cultures
from children died of generalized tuberculosis. Two calves weighing more
than 300 pounds each were inoculated subcutaneously with these virulent
human cultures, and as a result developed generalized tuberculosis. A
yearling heifer inoculated with 1 of the cultures showed generalized
tuberculosis when killed three months after inoculation. Both the cattle
and the hogs had been tested with tuberculin and found to be free from
tuberculosis before the inoculations were made. It is important to observe
in this connection that 2 out of 4, or 50 per cent, of the cultures
obtained from cases of generalized tuberculosis in children proved virulent
for cattle.
Mohler, working in the Pathological Division, Bureau of Animal Industry,
obtained 3 very virulent cultures of tubercle bacilli from the human
subject. A goat inoculated subcutaneously with 1 of these cultures died in
37 days with miliary tuberculosis of the lungs involving the axillary and
prescapular glands. This bacillus was obtained from the mesenteric gland of
a boy. Of still greater interest is a bacillus isolated by Mohler from
human sputum. A goat inoculated subcutaneously with a culture of this germ
died in 95 days of pulmonary tuberculosis. A cat inoculated in the same
manner died in 23 days of generalized tuberculosis. A rabbit similarly
inoculated died in 59 days of pulmonary tuberculosis. Another rabbit
inoculated with a bovine culture for comparison lived 10 days longer than
the one inoculated with this sputum germ. Mohler also inoculated
subcutaneously a 1-year-old heifer with a culture derived from the
tuberculosis mesenteric gland of a boy 4 years of age. This culture was
always refractory in its growth under artificial conditions, and the
bacilli were short, stubby rods, corresponding in appearance to the bovine
type. At the autopsy, held 127 days after the inoculation, the general
condition was seen to be poor and unthrifty, and large, hard tumors were
found at the points of inoculation. On the right side the swelling measured
3-1/2 by 5 inches, and the corresponding lymph gland was 2-3/4 inches long
by 1-3/4 inches in diameter. This gland contained numerous calcareous foci;
one at the apex was an inch in diameter. The lesions on the left shoulder
of the animal were very similar to those found on the right side, but the
dimensions of the tumor were slightly less. The lungs presented an
irregular mass of tuberculous nodules, and 7 or 8 grapelike nodules were
seen on the parietal pleura. Bronchial and mediastinal lymph glands
contained numerous tuberculous foci, and the pericardium, peritoneum,
spleen, and liver also were affected.
In order to throw some light, if possible, upon the morphological constancy
of the different types of tubercle bacilli, Mohler made comparative studies
of bacilli from various sources, and which had been passed through various
species of animals, by making the cultures upon dog serum after the method
described by Theobald Smith. Some important results have been obtained. One
culture of human bacilli which had morphological and cultural peculiarities
similar to those of the bovine bacillus, and which produced only local
lesions in cattle, was passed through a series of five cats. It was then
found to be completely changed in its morphological characters, the rods
being elongated, slender, more or less beaded, and entirely of the human
type. Far from decreasing in virulence, however, as might be expected from
its morphological appearance, this bacillus had so increased in its
pathogenic activity that it produced generalized tuberculosis in a cow.
This cow was inoculated subcutaneously in front of each shoulder with 2
cubic centimeters of a salt-solution emulsion of the tuberculous omentum of
the last cat of the series. The cow rapidly lost flesh, had a temperature
of 104∞ F., with the point of inoculation and adjacent glands greatly
swollen. The autopsy revealed generalized tuberculosis, involving the
lungs, mediastinal glands, spleen, liver, and kidneys. Tubercle bacilli of
the bovine type obtained from the mesenteric glands of a sheep, hog, and
cow were similarly transformed in their morphological appearance after
being passed through a series of cats and recovered on dog serum. These
bacilli also increased in virulence, as the last cat in the series
invariably succumbed in a shorter time than the first of the series.
These experiments and observations indicate that the types of tubercle
bacilli are very inconstant, and that under suitable conditions they
readily change both in morphology and in virulence. A similar conclusion
was reached by other investigators in working with the avian and porcine
types of tubercle bacilli several years ago, and was reasonably to have
been expected with the human and bovine types.
Later investigations made by Park and Krumweide, of the Research Laboratory
of New York City, Novick, Richard M. Smith, Ravenel, Rosenau, Chung Yik
Wang, and others tend to show the incidence of bovine infection in the
human family. Chung Yik Wang stated in 1917 that studies of 281 cases of
various clinical forms of tuberculosis in Edinburgh, Scotland, resulted in
the isolation of the bovine tubercle bacilli in 78.4 per cent of cases
under the age of 5 years, in 70.3 per cent between the ages of 5 and 16,
and in 7.8 per cent over the age of 16. This investigator states that from
the prophylactic point of view any measure resorted to in combating the
disease should be directed not only against the human spread of infection,
but also, more particularly in children's cases, against the bovine source
of infection.
Ravenel, in summarizing the work of Drs. Park and Krumweide, as well as
others throughout the world, gives the following results:
Of 63 children dying of tuberculosis at the babies' hospital 59 cases
proved to be human infection and 4 bovine, a percentage of 6-1/3.
Of 9 children dying of tuberculosis at the foundling hospital 4 proved
to have derived their infection from human sources and 5 from bovine, a
percentage of 55.
Of a total of 88 children under 5 years of age who died of tuberculosis
77 proved to have derived their infection from human sources and 11
from bovine, a percentage of 12-1/2.
Combining the cases studied in New York with those of other observers in
different parts of this country and Europe, the following results are
obtained:
Adults, 787 cases--777 human and 10 bovine infection.
Children, 5 to 16 years, 153 cases--117 human and 36 bovine infection.
Children under 5 years, 280 cases--215 human and 65 bovine infection.
The figures of the foundling hospital show the real danger of unprotected
cows' milk.
The conclusion from these studies is inevitable, namely, that in children,
in addition to the large number of deaths which occur from bovine
infection, there are many cases of infection resulting in deformities,
necessitating operations more or less severe in character and which
frequently leave the patient disfigured permanently.
It must be plain to all, from these recent developments, that too much has
been made of the slight differences in cultural characteristics, in
morphology, and in virulence which have been observed in some cases in
comparing the human and the bovine bacilli. The observations were
interesting, and it was important that they be followed up until their
significance was made entirely clear, but it was an almost unpardonable
error, from a sanitary point of view, to promulgate sweeping
generalizations calculated to arrest and abolish important measures for
preventing human tuberculosis before the soundness of these generalizations
had been established by a thorough course of experimentation.
When Koch said in the British Congress on Tuberculosis that he should
estimate the extent of infection by the milk and flesh of tuberculous
cattle and the butter made of their milk as hardly greater than that of
hereditary transmission, and that he therefore did not deem it advisable to
take any measures against it, he went far beyond what was justified by any
experiments or observations which he reported, and he did a great deal of
harm, which will be manifested for years to come, to those who endeavor to
guard the human race from the dangers of animal tuberculosis. The
researches which have been alluded to make these dangers more definite and
certain than they have appeared before, and sanitarians should therefore
most earnestly endeavor to counteract the erroneous and harmful impression
which was made by Koch's address at London and his subsequent address at
the International Conference on Tuberculosis at Berlin.
VACCINIA OR COWPOX.
Variola of cattle, more correctly vaccinia, is a contagious disease of
cattle which manifests its presence through an elevation of temperature, a
shrinkage in milk production, and by the appearance of characteristic,
pustular eruptions, especially upon the teats and udders of dairy cows.
Although this is a contagious disease, strictly speaking, it is so
universally harmless and benign in its course that it is robbed of the
terrors which usually accompany all spreading diseases, and is allowed to
enter a herd of cattle, run its course, and disappear without exciting any
particular notice.
The contagion of cowpox does not travel through the air from animal to
animal, but is transfused only by actual contact of the contagious
principle with the skin of some susceptible animal. It may be carried in
this manner, not alone from cattle to cattle, but horses, sheep, goats, and
man may readily contract the disease whenever suitable conditions attend
their inoculation.
An identical disease frequently appears upon horses, attacking their heels,
and thence extending upward along the leg, producing, as it progresses,
inflammation and swelling of the skin, followed later by pustules, which
soon rupture, discharging a sticky, disagreeable secretion. Other parts of
the body are frequently affected in like manner, especially in the region
of the head, where the eruptions may appear upon lips and nostrils, or upon
the mucous surfaces of the nasal cavities, mouth, or eyes.
Variola of the horse is readily transmitted to cattle, if both are cared
for by the same attendant, and, conversely, variola of cattle may be
carried from the cow to the horse on the hands of a person who has been
milking a cow affected with the disease.
The method of vaccination with material derived from the eruptions of
cowpox as a safeguard against the ravages of smallpox in members of the
human family is well known. The immunity which such vaccination confers
upon the human subject has led many writers to assert that cowpox is simply
a modified form of smallpox, whose harmless attack upon the human system is
owing to a certain attenuation derived during its passages through the
system of the cow or horse. The results of numerous experiments which have
been carried out for the purpose of determining the relationship existing
between variola of the human and bovine families seem to show, however,
that although possessing many similar characteristics, they are
nevertheless distinct, and that in spite of repeated inoculations from
cattle to man, and vice versa, no transformation in the real character of
the disease ever takes place.