160 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



erinaxy uses and to throw light on the nature of the tuberculin 

 reaction. Likewise investigations are being conducted regarding 

 the time that elapses between the infection of cattle with tubercle 

 bacilli and the development of tuberculin sensitiveness and on the 

 causes on which variations in tuberculin sensitiveness depend. 



Tests regarding the purity and potency of commercial tuberculin 

 made it necessary in several instances to recommend the withdrawal 

 of some of this material from the market. The frequency with 

 which commercial tuberculin has been found to contain excessive 

 numbers of dead tubercle bacilli has greatly declined, which is a 

 desirable improvement, as it has been definitely proved that animals 

 may be sensitized to tuberculin through injections of dead tubercle 

 bacilli. 



Some studies have been made on the iype of the tubercle bacillus 

 in unusual and atypical tuberculous lesions in cattle. In all cases 

 the bacilli proved to be of the true bovine type. 



During the year a large number of samples of butter and of cream 

 cheese purchased on the open market were tested for tubercle bacilli. 

 The butter of only one company was found to be infected, and this 

 company has promised to take the necessary steps to insure the free- 

 dom of its product from contamination in the future. Likewise the 

 cream cheese of only one company was found to be contaminated, a 

 company from which samples had not previously been tested, and 

 this company also promised to correct the evil and to make its product 

 safe. On the whole the tests with samples of market butter and 

 cheese are gratifying, as may be judged from the following com- 

 parison : Less than 10 years ago it was found that something more 

 than 14 per cent of 122 samples of cream cheese purchased on the 

 open market were contaminated with living, virulent bovine tubercle 

 bacilli. Last year the examination of several hundred samples failed 

 to show a single contamination, and this year the examination of 

 several hundred samples revealed only a fraction of 1 per cent to 

 be contaminated. Tests regarding the possible occurrence of tubercle 

 bacilli in dairy products will be continued. 



MISCELLANEOUS WORK. 



Various studies are in progress concerning the influence of diet 

 on the rapidity with which tuberculous lesions develop in the bodies 

 of infected animals; the influence of diet on the permeability of the 

 mucous membranes for tubercle bacilli and other pathogenic micro- 

 organisms; the changes which occur in tuberculin when it is incu- 

 bated with various animal tissues and organs; the influence of the 

 vitamin content of the diet on susceptibility to diseases, etc. 



A large number of small experiment animals were raised at a cost 

 much lower than current market prices. Various tests were made 

 with pathological material suspected to contain the virus of infectious 

 diseases. Biological products of different kinds were supplied to the 

 other laboratories of the bureau. Every available portion of the sta- 

 tion's land was kept under intense cultivation to obtain forage for 

 experiment animals. 



