No. 7. DEPARTMENT OF AGRICULTURE. 123 



series all tubercle bacilli from the tissues of tuberculous mammals 

 are not the same. In particular he discovered certain differences 

 between the forms found in the sputum of consumptives and those 

 found in tuberculous tissues of cattle; differences that are slight but 

 still definite and constant. The chief of these differences is that 

 what he termed the ^sputum bacilus' is of very low virulence or is 

 non virulent for cattle. In other words, cattle do not become tuber- 

 culous when inoculated with that form of tubercle bacillus that is 

 most in consumptive people.* 



''The bacillus that is most frequently the cause of tuberculosis 

 in man is now known as the tubercle bacilli of human type and that 

 of cattle as of bovine type. 



"Eepeated experiments by several investigators have shown that 

 it is possible to take advantage of this difference between the types 

 in accord with the principle of vaccination as discovered by Jenner 

 and deveoped by Pasteur. Such experiments have been made in Eu- 

 rope by McFadyean, von Behring, Koch and Neufeld and in this 

 country by your speaker in conjunction with Dr. Gilliland. The ear- 

 liest experiments directly on the immunization of cattle from tuber- 

 culosis were those of McFadyean. These experiments were very 

 suggestive and encouraging but they, like the earlier experiments 

 ,of von Behring, did not constitute a clear trial of the Jenner-Pasteur 

 principle. That is, the experimental animals were treated with 

 chemical substances, as tuberculin, and with tubercle bacilli of dif- 

 ferent degrees of virulence, some of bovine type, some of the avian 

 type, and not solely with cultures of tubercle bacilli of human type. 



"The first experimental work that wa^ published anywhere that 

 showed that it is possible to immunize animals from tuberculosis bv 

 treating them solely with tubercle bacilli of human type and that 

 furnished proof of the immunity of such animals by their resistance 

 to inoculation with quantities of virulent tubercle bacilli that pro- 

 duced extensive lesions in unvaccinated animals was recorded in the 

 paper of Pearson and Gilliland in 1902. (Philadelphia Med. Jour. 

 Nov. 2, 1902.) This work represented a development of work that 

 had been going on in the laboratory of the State Livestock Samtary 

 Board for several years. 



''Von Behring was the first to propose a definite method for the 

 practical application of vaccination against tuberculosis. But there 

 is no evidence that the method had been tested when it was pro- 

 posed and, after a year or so it was abandoned for another method 

 that differed from the first one in some important particulars. 



"Tlie State Livestock Sanitary Board recognized the importance of 

 this subject several years ago and authorized experiments on cattle 

 to test its practical applicability. It soon became evident that many 

 cattle would needs be used in such an experiment and that it would 

 be of greatest value if these cattle were kept under practical, farm 

 conditions. This matter was explained to the representative agri- 

 cultural breeders and veterinary organizations of Pennsylvania and 

 upon their recommendation to the legislature a suitable farm and 

 support have been provided for carrying on this work. The experi- 



•Whlle this important fact was firmly established by Smith, later Investigations have shown 

 that a considerable percentage of people are infected by precisely the same kind of germ that 

 causes tuberculosis in cattle. 



