254 ANNUAL REPOK'rS OF DEPARTMENT OF AGRICULTURE. 



abort as a result of exposure to cattle strains of the abortion bacillus 

 may again abort as the result of exposure to strains virulent for 

 swine, a definite conclusion that this is the case must await stronger 

 evidence than has been so far obtained. 



Additional work on the differences between strains of abortion 

 bacilli isolated, respectively, from cattle and swine has been con- 

 tinued and has given results confirmatory of those previously re- 

 ported. 



TUBERCULOSIS. 



Investigations on tuberculosis have dealt with the mode of infec- 

 tion, the various ways in which animals may be sensitized for tuber- 

 culin, what may be done to modify and improve the available tests 

 for the purity and potency of tuberculin, and the occurrence of 

 virulent tubercle bacilli in butter and cheese. 



A study of the sensitization of animals for tuberculin was under- 

 taken because of its bearing on the occurrence of tuberculin reac- 

 tions in cattle in which no lesions of tuberculosis are found on 

 post-mortem examination. WTiile the great majority of such cases 

 are undoubtedly incipient and undeveloped cases of tuberculosis, a 

 small proportion requires some other explanation. As animals can 

 be sensitized to tuberculin through injections into their bodies of 

 either dead tubercle bacilli or tubercle bacilli which are not truly 

 pathogenic for them, it seems probable that the swallowing of tuber- 

 cle bacilli of the human type scattered by tuberculous attendants may 

 account for some cases. 



Tests of purity and potency of commercial tuberculins generally 

 have given satisfactory results. In a few instances in which either 

 the purity or the potency of a product was found to be lower than 

 the required standard measures were taken for its withdrawal from 

 the market. 



Tests of cheese revealed the presence of virulent tubercle bacilli in 

 the product of only one manufacturer, who, when he was informed, 

 adopted corrective measures which further tests proved to be effective. 



Tests of butter for tubercle bacilli revealed a very heavily con- 

 taminated condition of two samples. Correspondence with the 

 manufacturer led to the correction of the evil. 



MISCELLANEOUS WORK. 



A number of tests were made on the value of alleged cures for 

 infectious diseases of animals, and a number of minor investiga- 

 tions regarding animal diseases and their causes were conducted. 

 Tissues were examined to determine whether the animals from which 

 they were obtained had succumbed to infectious diseases requiring 

 special attention, and a number of cases of rabies in animals were 

 diagnosed. Rabies was unusually prevalent in the region in which 

 the experiment station is situated. 



A large number of small experiment animals were raised at a 

 cost hardly greater than half the current market prices. Biological 

 products of different kinds were supplied to other laboratories of the 

 bureau. Every available portion of the station's land was kept under 

 intense cultivation to raise forage for experiment animals. 



