46 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



Such vaccination involves the use of living tubercle bacilli of a mild 

 strain, and it is found that these mild germs sometimes remain in 

 the vaccinated cattle for some years and are discharged in the milk. 

 It appears, therefore, that the result of such vaccination would be 

 to harbor the infection in a mild form in some cases. 



The bureau has continued its Avork for the suppression of bovine 

 tuberculosis by applying the tuberculin test in certain sections of 

 the country where cooperative arrangements have been made with 

 State and city authorities, and also by testing breeding and dairy 

 cattle for interstate shipment. The testing in Virginia and Mary- 

 land shows over 18 per cent of tuberculous cattle among those tested 

 for the first time, and only 3 per cent in herds to which the test had 

 been previously applied and from which the reacting animals had 

 been removed. In the District of Columbia the proportion of tuber 

 culous cattle on first test in previous years was nearly 19 per cent, 

 but on retests made during the past year it Avas only a little over 1 

 per cent. As a result of this work a large number of previously in- 

 fected herds are now being maintained free from tuberculosis. 



HOG CHOLERA. 



Officials in various States and farmers and stock raisers generally 

 have shown increased interest in the work of combating hog cholera 

 through the use of the serum developed by the Bureau of Animal 

 Industry. At the present time 30 States are distributing serum. 

 In most of these States the serum is prepared in official laboratories, 

 but a few of the States purchase their supply from private manu- 

 facturers and distribute it to the farmers at cost. In some of the 

 States preparing their own serum no charge is made to the farmers 

 for the serum, while in other States the cost price of manufacture is 

 charged. Up to this time considerably more than 1,000,000 doses of 

 hog cholera serum have been manufactured and applied in all of 

 the various States combined, and the results are reported by State 

 officials generally as being very satisfactory. 



The demand for hog-cholera serum has been greater than could be 

 met by the State laboratories and has led to its preparation by com- 

 mercial firms. In order to insure that only a reliable quality of 

 serum is sold in interstate commerce it is desirable that the depart- 

 ment should be given legal authority to supervise the preparation of 

 the serum. 



The scientific investigations of the past year with regard to hog 

 cholera have been devoted to determining the best methods of pre- 

 serving by means of chemicals the hog-cholera virus that is necessary 

 in the production of the serum. Experiments have also been made 

 to learn whether or not the offspring of immune sows are likewise 



