254 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



tify the wholesale mjection of cattle with living tul^crcle hacilli for 

 piirelx' economic purposes, even if the bacilli used are only wealdy 

 pathogenic in character. 



Some studios have been made on small exi)crinioiit animals relative 

 to the latency of tubercle bacilli hi the tissues of living anijuals. That 

 tubercle bacilli may enter and remain latent in the bodies of animals 

 for considerable periods of time, and afterwa -ds, for some reasons not 

 well understood, become active and cause tuberculosis, is a l)elicf held 

 by many com])ctent investigators. If this belief should prove true 

 it will have a very important bearing on all measures for the eradica- 

 tion of the (.lisease. The bureau's investigations have not progressed 

 far enough to warrant any conclusions. 



As there are man}^ tuberculous cows from which milk is used as food 

 for persons and lower animals, and as the use of properly pasteurized 

 milk from tuberculous cows is generally regarded as safe, an experi- 

 ment was made to throw more light on this subject. It seemed espe- 

 cially desirable to learn whether the ingestion of milk that contains 

 tubercle bacilli killed by pasteurization will cause either an increased 

 or reduced susceptibility to infection with living tubercle bacilli. 

 As far as this work has gone it indicates that dead tubercle bacilli 

 ingested with pasteurized milk have no harmful effects on guinea 

 pigs, but that living tubercle bacilli ingested with milk, even when 

 they cause no disease, increase the rapidity with which guinea pigs 

 die from subsequent inoculation with tubercle bacilli. 



The question of the relative value of raw, [.asteurized, and boiled 

 milk as food for young animals has received some attention, but it is 

 too early to report on this work, be3''ond stating that it clearly shows 

 that the artificial feeding of unweaned animals with milk of an alien 

 species is by no means conducive to their best development, and 

 when small, delicate animals, such as guinea pigs, are used the 

 mortality is very high. 



Further investigations relative to the sources from wdiich hogs 

 contract tuberculosis, as far as such investigations are possible at the 

 station, show that the exposure of hogs to the feces of tuberculous 

 cattle is a much more certain cause of their infection than their 

 exposure to milk from tuberculous cows or to hogs affected with 

 tuberculosis. It must not be concluded from this, however, that raw 

 milk from tuberculous cows is a safe food for hogs or that the presence 

 of tuberculous hogs in a hog yard is without serious danger. 



A number of samples of commercial tuberculin were tested to 

 determine whether they were of sulhcient potency to be reliable for 

 use as diagnostic agents for cattle tuberculosis. It is pleasing to be 

 able to report than all the samples tested were found to be satisfac- 

 tory. 



A number of tests of the difTerent ways in which dilTerent prepara- 

 tions of tuberculin can be aj)[)lied for diagnostic purposes have been 

 made. These tests prove that the subcutaneous injection of ordinary 

 old tuberculin is by far the most reliable manner in which tuberculin 

 can be used as a diagnostic? agent for cattle tuberculosis. Other 

 methods of application as yet hold out no real promise that they may 

 have value as a means for controlling those fraudulent practices which 

 are used by dishonest persons to defeat the power of a subcutaneous 

 injection of tuberculm to cause a reaction in the presence of tuber- 

 culosis. 



