BUREAU OF ANIMAL INDUSTRY. 247 



made in 1917 and five years old at the time of test was found to 

 retain its potency in like degree. 



The chemical studies of hog-cholera serum have progressed, and 

 some of the work has been reported in technical papers. 



HOG " FLU " AND NECROTIC ENTERITIS. 



The study of hog "flu" was continued, and a summary of the 

 information obtained was published. It has not been possible to 

 identify the causative agent in this disease. The opportunity was 

 presented to study a natural outbreak on a farm not far removed 

 from the bureau-station premises. Healthy pigs carried to the farm 

 and exposed to others sick at the time with "flu" contracted mild 

 cases of the disease. Efforts were made to infect healthy pigs by 

 artificial means, but in no instance was it possible to set up a disease 

 as severe as that which existed naturally on the farm under study. 



The peculiar, severe intestinal inflammation commonly known as 

 necrotic enteritis has been studied in the field as the opportunity 

 presented itself. The bureau's investigators have not been able to 

 reproduce this disease by injection of blood from affected animals 

 and have in only a few instances succeeded in reproducing it by the 

 feeding of diseased tissues. It has not been possible to reproduce the 

 disease by the use of the microorganisms isolated from sick pigs. 

 This work will be continued. 



TUBERCULIN AND MALLEIN. 



The production of both tuberculin and mallein was continued 

 throughout the year. The demand for mallein has been small, the 

 total amount supplied to bureau inspectors being only 24,775 doses. 

 The demand for tuberculin, however, has continued, although there 

 is evidence of the gradual substitution of the intradermic and oph- 

 thalmic tests for the subcutaneous test. The year's output, which was 

 supplied mostly to bureau inspectors, but also to State and local 

 officials, was as follows: Subcutaneous tuberculin, 1,819,080 cubic 

 centimeters, a decline of about 26 per cent from the preceding year; 

 intradermic tuberculin, 5,794,235 doses, an increase of more than 12 

 per cent; ophthalmic tuberculin, 1,577,880 disks, an increase of ap- 

 proximately 13 per cent. The solution of the mechanical difficulties 

 encountered in preparing ophthalmic tuberculin disks has enabled 

 the division to meet the extraordinary demand which has developed 

 during the past two years. 



An investigation of the factors which influence the growth of 

 tubercle bacilli on artificial media was begun. 



COOPERATION WITH INSECTICIDE AND FUNGICIDE BOARD. 



The routine examination of samples for the Insecticide and Fungi- 

 cide Board was continued and certain investigative work was under- 



ZOOLOGICAL DIVISION. 



The investigation of parasitio diseases of animals and the study, 

 ■collection, and determination of animal parasites have been con- 

 tinued in the Zoological Division under the direction of Dr. B. H. 

 Hansom, chief. 



78007— AGB 1923 17 



