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TUBERCULOSIS AND THE FOOD SUPPLY.'

BY D. E. SALMON, D. V. M., CHIEF OF THE BUREAU OF ANIMAL INDUSTRY, WASHINGTON, D. C.

from it, make it important time the possible means of

The frequency of tuberculosis in mankind, and the great number of deaths which result for us to consider from time to prevention, and to inquire as to whether we are doing all in our power to this end. It is not my intention to treat the subject at great length, or to enter into the details of scientific work which must be already quite familiar to the members of this congress. I desire rather to bring out clearly a few salient points, and to make some practical suggestions.

I shall assume without argument as already established by scientific investigations that tuberculosis is a parasitic disease; that it is caused by the multiplication of a specific micro-organism in the tissues of the animal body, and by no other means; that this micro-organism has no habitat in nature outside of the animal body, that it may be distributed in various ways from this habitat and generally gains entrance to the bodies of its victims, either by being inhaled with the air in which it is floating or by being ingested with infected food or drink; and, finally, that hereditary transmission of this disease has been greatly exaggerated as a factor in its production, and may, from a practical point of view, be left out of consideration.

Of the two methods by which the disease is contracted,

1Read before the American Public Health Association, 1893.

with men as well as with animals, it may be admitted that the most frequent, and, therefore, the most important, is the inhalation of the micro-organisms suspended in the inspired air. My paper, consequently, deals with the less important of the two principal modes of infection; but while it is the less important etiologically, it is the more important from the point of view of preventive medicine, because it is more easily controlled by the efforts of sanitarians.

I have no means of estimating the proportion of the cases of tuberculosis which arises from infected food, but am prepared to admit that tuberculosis of the abdominal organs and tubercular meningitis, particularly of children, are generally caused in this way. For convenience in treating the subject, we must consider separately infection. through the milk supply and infection through the meat supply.

Tuberculosis is one of the most common diseases of milch cows. It exists in many dairies, and may effect 50, 75, or 100 per cent. of the animals in large herds. We do not know the average proportion of affected cows in this country, but in the dairies around our large cities from three to five per cent. have been found affected when the diagnosis was made by the ordinary methods of examination. By the use of tuberculin, a much larger number of infected animals is found. In Europe, by the use of tuberculin, from 50 to 80 per cent. of cows have been found to give the reaction when a considerable number was tested. In the United States, we have no statistics of the results of the tuberculin test except with herds known to be tuberculous. As many cases of the disease are revealed by tuberculin, however, which would not be discovered otherwise, it is certain that the proportion of affected cows in the United States, if not as large as in Europe, must nevertheless be very considerable. If no more than fifteen or 20 per cent. of our cows should prove to be infected, it would still be a very serious

matter and one well worthy the consideration of this congress.

Fortunately the milk from all tuberculous cows does not contain the bacilli. When there are tubercules in the udder, however, the milk may contain immense numbers of these germs, and this is particularly the case if the tubercular mass softens and its contents escape into the milk ducts. The milk from cows so affected must be considered an extremely dangerous article of food.

In case there are no tubercles in the udder the milk of affected cows may or may not contain the bacilli,—generally it does not. As the disease progresses and the vital forces are diminished, the number of bacilli in the milk and the frequency of their occurrence increases. In other words, the nearer we approach the death of the animal the more certain we are to find bacilli in the milk. At this period the milk secretion is, of course, greatly diminished, and may entirely cease.

The danger from using infected milk increases with the number of bacilli which such milk contains, and decreases with the degree in which it is mixed with the milk of healthy cows. If there is but one tuberculous cow in a large herd, and the milk of the herd is all mixed together before it is consumed, the danger to the public health would largely disappear, but if the milk is not so mixed, or if a large proportion of the herd is tuberculous, then the danger would be correspondingly greater.

With these facts before us, we are prepared to consider the great practical question, How can the prevalence of tuberculosis in dairy cows be lessened, and the danger from infected milk be diminished? Evidently the accomplishment of this object requires a careful and periodical inspection of the herds from which the milk supply is obtained. This inspection must consist not only of a physical examination, but must also include the tuberculin test. There must in addition be some means provided for securing the

destruction of animals found to be tuberculous. The great obstacle to the introduction of such measures will no doubt be found in the expense which must necessarily be incurred. The test with tuberculin requires time, and the animals must be kept under constant observation for at least two days. This makes it necessary to have a larger number of inspectors than would otherwise be the case.

Tuberculin has been very expensive and difficult to obtain in large quantities. Recently the bureau of animal industry has been preparing it, and furnishing it to state and municipal boards which have the subject of tuberculosis in animals under their jurisdiction. It has seemed to me that this was one of the most practical methods of cooperation between the national and local authorities for controlling this disease, and I hope the bureau may be able to continue it, and increase its facilities to keep pace with the demand. This, however, depends somewhat upon the appreciation with which our effort meets, and the support which is received from those interested. With an unlimited supply of tuberculin furnished without expense by the government, or even for the actual cost of its preparation, the problem of control is considerably easier.

Nevertheless, the difficulties at best are enormous. Eighty per cent. of a herd may react to the tuberculin test. Of these some will be advanced cases of generalized tuberculosis, with the mammary glands affected. The disposition of such cases would be an easy matter. A large number, however, would be but slightly affected, and would require a most careful post-mortem examination to discover the lesions. In some, it would be impossible to find any lesions. Many cattle would, therefore, be condemned by the tuberculin test, the milk of which would be perfectly wholesome; and, on the other hand, some cows in an advanced stage of tuberculosis, with very prominent lesions, show no reaction to the tuberculin test.

It must be evident from these statements that while

tuberculin is a great aid to the diagnosis of tuberculosis, it is not infallible, and may lead to some errors. It is also evident that the disease cannot be eradicated with certainty by our present means of diagnosis, unless every animal in an infected herd is slaughtered. On account of the extent and distribution of this plague, the slaughter of all herds in which tuberculous animals are found does not appear to be practical.

If by the tuberculin test we could infallibly detect every infected animal, it would be possible to establish herds free from the disease, and to maintain this freedom by testing all additions to the herd. This was the hope inspired by the first experiments made with this remarkable agent. Later, when it was found that some tuberculous animals did not respond to the test, those interested in the subject became more or less discouraged, and have settled down to the conclusion that tuberculosis is still an unconquerable disease, as it has always been in the past. Theoretically this conclusion is correct, but there is often a wide difference between theory and practice, and the conclusions from laboratory experiments, and from a few tests in the field, should not be allowed to arrest our efforts in this direction.

Whatever may prove to be the proportion of tuberculous animals in the dairies of the country as a whole, I know from experience that many herds of cows are entirely free from the disease. This may be proved, both by the history of the herds, and by the tuberculin test. Now, taking such herds as a starting-point, with proper precautions to prevent their infection, I believe it quite possible to breed a race of cattle practically free from the disease. And while this is being done, the known infected herds should be destroyed.

A great work like this cannot be accomplished by an individual, nor by a single board of health. There must be co-operation, a unity of effort, and the combined influence and power of the nation, the state, the local authority, the

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