BUREAU OF ANIMAL INDUSTRY. 275 



cooperation with other divisions of the Bureau, and the provision of 

 facilities for the other divisions to make investigations of a kind that 

 require farm and field conditions not obtainable within the limits of 

 the city. As indicated elsewhere, the new Beltsville farm will pro- 

 vide facilities for experimental work in animal husbandry and 

 dairying, and the work at Bethesda will probably be confined here- 

 after to veterinary investigations. 



TUBERCULOSIS INVESTIGATIONS. 



The most important investigations made during the past year 

 related to tuberculosis. An experiment to determine the value of 

 various methods of inmiunizing cattle against tuberculosis, begun 

 several years ago, was continued and is now about complete. It was 

 found that the methods of so-called bovo-vaccination, devised by 

 Pearson in America and Von Behring in Europe, actually confer a 

 considerable degree of immunity on the treated animals; not an 

 absolute immunity, but an undeniable increased resistance to infec- 

 tion with tuberculosis, which holds out great hope for the results 

 that may be obtained with investigations in the future. At present, 

 however, the extensive use of these methods for conferring immunity 

 can not be recommended, as our knowledge about the latency of 

 tubercle bacilli in the animal body, the channels through which the 

 elimination of tubercle bacilli from the bodies of animals into which 

 they are injected for protective purposes occurs, etc., is insufficient 

 to enable us to draw the conclusion that the practice of bovo-vaccina- 

 tion is free from danger to the herds to which it is applied, and, what 

 is of greater importance, free from danger for the persons who use 

 the products derived from the vaccinated cattle. As living tubercle 

 bacilli are employed in all the systems of bovo-vaccination which 

 have, as far as they have been tested at the Experiment Station, given 

 any proof that they are capable of protecting against tuberculosis in- 

 fection, and as the use of such bacilli can not be regarded as free 

 from danger, it seems that an ideal system of immunization would 

 require the use of some other agent. Some preliminary experiments 

 on a small scale relative to the protective treatment of animals against 

 tuberculosis Avitliout the use of living tubercle bacilli have been made 

 at the station, and this subject has been given considerable careful 

 thought and study, but so far nothing of an encouraging nature can 

 be reported. 



The method of bovo-vaccination devised by Prof. J. F. Heymans, 

 of Belgium, has been carefully tested with both cattle and hogs, and 

 has been found to be wholly without value. This method, to judge 

 from the claims made by Professor Ileymans, has given excellent re- 

 sults in his own country, where it has been extensively used. These 

 results may possibly be due to a careful supervision of the herds to 

 which the treatment was applied by trained veterinarians. Such 

 supervision would certainly, in the first place, lead to improved 

 hygienic conditions and the removal of all advanced or clinical cases 

 of tuberculosis from the treated herds, and clinical cases of tubercu- 

 losis are the most important source for the spread of tuberculosis 

 among cattle, even though apparently healthy tuberculous cattle 

 scatter tubercle bacilli quite freely. 



