The slow but gradual transformation of certain growths of tubercle bacilli should not be considered such an impossibility. Other forms of bacterial life yield to the peculiar influences of their environment, and why should not the tubercle bacillus be equally susceptible to change? In fact, experiments have been conducted which show conclusively that some tubercle bacilli may be transformed in form, pathogenicity, and cultural characteristics as well. More than this, cultures which seem incapable of attacking certain species of test animals with the degree of severity which one would expect, in view of their average virulence for animals of other species, may be brought to change their peculiar affinities until they will prove virulent for a species of animal formerly resistant.

An interesting experiment was recently made in the Pathological Division by cultivating a bovine bacillus upon sterilized human blood. After three months' growth upon this medium the bacilli became transformed into long, beaded organisms which grew more readily than upon dog or bovine serum, and closely simulated the human type of bacilli. They had evidently assumed a more saprophytic character and were capable of more rapid accommodation to cultural exigencies as a result of some constituent of the human blood.

RELATION TO PUBLIC HEALTH.

The latest researches into the question of intertransmissibility of tubercle bacilli from various sources have shown that Koch's doctrine, enunciated in 1901, is not warranted. Variations do occur among tubercle bacilli as among other forms of bacteria, but they are not constant. It is well known that Koch demanded as a criterion of the animal origin of tuberculosis observed in man the proof that cattle, when injected with human tubercle bacilli, will contract tuberculosis. Decisive proofs of such infection have now been obtained not only by the German Commission on Tuberculosis, which was appointed at Koch's request, but also by the Royal English Commission, besides numerous French, Dutch, English, Scandinavian, Austrian, and American investigators. In fact, there have been so many instances on record of bovine tubercle bacilli having been recovered from human tissues, and of instances of butchers and others receiving accidental infections of the skin directly from bovine lesions, that it appears entirely proven that man is susceptible to tuberculosis caused by bovine bacilli. This view was crystallized in a resolution adopted by the International Congress on Tuberculosis recently held in Washington, D. C., as follows:

Resolved, That preventive measures be continued against bovine tuberculosis, and that the possibility of the propagation of this infection to man be recognized.

While the presence of bovine tubercle bacilli in human beings is seen to be not infrequent, no definite conclusions can be drawn at present as to the extent of such infection, owing to the lack of data on the subject. But the fact that tubercle bacilli of one species may be transmitted to an animal of a different species or to man makes it apparent that any preventive methods for controlling tuberculosis, to be successful, must take into consideration all species of animals which are susceptible to tuberculosis.

DANGER FROM MILK AND MEAT.

The most frequent sources of danger from bovines to man, and the only ones to be considered, are the milk and the meat of tuberculous animals. The fact that most of the cases of bovine tuberculosis occurring in man are cases of infantile tuberculosis points with grave suspicion to the milk rather than to the meat supply. That milk coming from a tuberculous udder is capable of transmitting the infectious principle requires no further argument. It has been equally well established that in advanced generalized tuberculosis the udder may excrete tubercle bacilli without showing any indication of being affected. Other experiments have demonstrated that tubercle bacilli may be eliminated by cows affected with tuberculosis to a degree that can only be detected by the tuberculin test, so that in a herd of cows in the various stages of tuberculosis it is to be expected that some of them will excrete tuberculous milk, which, when mixed with other cows' milk, makes the entire product dangerous.

The ease with which tubercle bacilli may be eliminated by the udder was strikingly illustrated by an experiment conducted by the British Royal Commission, in which a cow, injected with human tubercle bacilli under the skin of the shoulder, began excreting tubercle bacilli from the mammary gland seven days later, and continued to do so until its death from generalized tuberculosis thirty days after inoculation. Furthermore, Titze, of the Kaiserliche Gesundheitsamte, proved that human tubercle bacilli when injected into the jugular vein of milch cows may be excreted with the milk. In his first experiment the excretion of the bacilli began in the third week and continued until the one hundred and forty-fourth day. In a subsequent test tubercle bacilli began to be excreted after twenty-four hours, but no tubercle bacilli could be found after ninety-nine days. In both these cows only the milk from the left hind quarter proved to be infectious. It has been shown by Gaffky and Eber in Germany, and Schroeder in this country, that even when the tubercle bacilli are not excreted by the udder the dust and manure of the stable where the diseased animals are kept are in many cases contaminated with tubercle bacilli. This contaminated material may readily

pollute the milk during the process of milking, even though the milk comes from a healthy cow. The importance of this method of infecting milk can not be too greatly emphasized when it is known that cattle with slight alterations in the lungs frequently raise tuberculous mucus into the pharynx while coughing, and by swallowing this material contaminate the feces.

Having ascertained the grave and positive danger to man of tuberculous milk it becomes necessary to determine if tuberculous meat contains the infectious agent, and if it can reproduce the disease in animals fed or injected with it. Through the extensive experiments of numerous investigators much evidence has been accumulated, to the effect that meat of animals affected with generalized tuberculosis may contain virulent tubercle bacilli. The experiments of Kastener, Hoefnagle, and Westenhoeffer are especially of interest, as well as of great importance, because they took into consideration the extent, character, and condition of the tuberculous lesions. In one series of tests Kastener fed to experiment animals meat from cattle which were affected with localized tuberculosis, the carcasses of which had been passed for food. In this series he could not obtain a single positive result, while with meat of condemned tuberculous carcasses his results in every instance were positive. It is therefore apparent that the condemnation of tuberculous meat is carried out not only from an esthetic standpoint, but because there is sufficient proof at hand which points to the danger that might arise from the ingestion of such meats. For this reason it appears desirable to have all products coming from animals affected with tuberculosis, as well as the slaughter and disposal of such animals, placed under the supervision of an experienced inspector. Since the flesh of all tuberculous animals is not equally dangerous, there must be rational discrimination between the meat of slightly or locally diseased carcasses and that of the more extensively diseased carcasses, the former having experimentally given negative results, the latter proving to be infectious.

PREVALENCE OF TUBERCULOSIS.

It is a well-known fact that tuberculosis is the most serious disease with which the American farmer has to contend. It is widely spread among cattle and is yearly appearing with increased frequency among our hogs. In addition, centers of poultry infection are recently being recorded in various parts of the country, which fact is naturally leading to great uneasiness among breeders of purebred fowls. There are other losers besides the farmer and poultry man, as the owners and keepers of menageries and zoological parks are forced to pay heavy animal toll to the ravages of tuberculosis. Monkeys and deer when kept in captivity rapidly succumb to tuberculous infection, while animals of the raccoon and beaver families, and occa

sionally some member of the bird tribes, will give evidence of their susceptibility to the disease.

Infection of cattle and hogs is most frequently seen in districts in which dairy interests are prominent, but the arid southwestern plains and even the Pacific mountain regions are not totally free. The losses from tuberculosis to the farmers of this country can hardly be appreciated or calculated. There were condemned during the fiscal year 1908 by the inspectors of the Bureau of Animal Industry 24,371 whole carcasses of beef and 77,584 whole carcasses of hogs, as well as a much greater number of parts of carcasses. State dairy inspectors condemn numerous dairy cows for tuberculosis, and large numbers are slaughtered at small private slaughterhouses where no record of numbers or values is kept. Breeders of purebred cattle are also forced to bear heavy burdens through losses of valuable breeding animals and through the disturbance of their trade with would-be purchasers. In this connection it may be stated that the breeder of purebred stock who is in position to warrant his stock as free from tuberculosis will find such guaranty to be a valuable recommendation for his herd, and satisfactory sales will no doubt result, which could not be made from a herd in which tuberculosis was suspected.

The recent awakening of interest in the matter of obtaining pure milk supplies for our various cities and towns, 41 of which have tuberculin-test ordinances, has led to the application of this test to many dairy herds. The extent of tuberculosis detected in these cases by the use of Bureau tuberculin has varied in the several States from 2.79 to 19.69 per cent.

It has been estimated in the Bureau of Animal Industry that the annual sum that may be charged to loss and depreciation through tuberculosis in cattle and hogs is in the neighborhood of $23,000,000.

The increasing frequency with which tuberculosis is being discovered among flocks of fowls and pigeons calls attention to another source of considerable loss through this disease. These centers of avian infection are widely separated, having been found on the Pacific coast, along the Hudson River, and at intermediate points. In all of the flocks attacked and examined it has been noted that the spread of the disease among the birds has been very rapid, and so virulent has the infection proved that only a few of the individuals in a flock escape after the infection has become established. The disease is spread readily from bird to bird by way of the digestive tract; and from the well-known habit of fowls picking their food out of dirt, and even from manure piles, it is evident that the infection will be quickly taken up by the healthy members of the flock.

FEDERAL WORK IN SUPPRESSING TUBERCULOSIS.

Inasmuch as there are already thirteen States enforcing laws regarding the entrance of tuberculous cattle, other States will naturally follow sooner or later in order to avoid becoming the dumping ground of tuberculous cattle not permitted entry into the first-mentioned States." While the laws in these States differ much in detail, the general plan is to require that cattle introduced for breeding or dairy purposes be tested with tuberculin and their healthfulness certified by the authorities of the State from which they originate, or, failing in this, by the authorities of the State in which they are destined to remain. With a large number of States demanding the tuberculin test for all breeding and dairying cattle entering therein, the establishment of tuberculin testing stations at appropriately situated stock yards for the inspection of cattle about to be shipped interstate will no doubt become a necessity, both from an economic as well as a sanitary standpoint, and such work will naturally come under the supervision of the Federal Government.

The Bureau of Animal Industry is already doing much toward reducing and preventing tuberculosis in the United States, which action is indicative of what may be expected in the future. About eight years ago the Bureau endeavored to assist the individual States in guarding against infection from foreign countries by requiring cattle imported from such countries to be accompanied by a certificate of healthfulness shown by a tuberculin test made by an official veterinarian, while those coming through the quarantine stations were tested by the superintendents during the period of detention.

Two objectionable features led to a change in these methods. The first was the frequently unsatisfactory certificates of tests made in the country of origin, and, second, the loss which was inevitable in case any of the imported cattle reacted after reaching the United States. To overcome these objections, the Bureau in 1900 detailed one inspector to Great Britain and another along the Canadian border for the purpose of testing all cattle intended for export to this country, in order that only healthy cattle would be brought in. This practice still continues in Great Britain, but reciprocity has been established with the Canadian authorities by which we accept tuberculin-test certificates from any of their official veterinarians. The benefit derived from this regulation is indicated from the fact that the inspector in Great Britain has rejected on account of tuberculosis as high as 33 per cent of all the cattle tested by him in one year for shipment to this country, and a large number of badly diseased herds have been located from which no importations are permitted.

a Since this was penned-in fact since January 1, 1909-nineteen additional States have enacted laws regarding the tuberculin testing of incoming cattle, making thirty-two States having such laws.

10765-10-11