BUREAU OF ANIMAL INDUSTRY. 143 



MKTHODS OF PKODUCING IMMUNITY AGAINST HOG CHOLERA. 



The cliemical studies of antiliog-cholera serum have been continued, 

 with the object of obtaining a better understanding of the effects of 

 the various processes, particuUirly heat, upon the various constitu- 

 ents of the serum and to develop new methods or to perfect old meth- 

 ods for the refinement or concentration of the serum. During the 

 year it has been found that heating clear serum or allowing the serum 

 to stand for lon^ periods of time in contact with phenol changes the 

 relative proportions of the globulin in the serum, the proportion of 

 the eu-globulins being increased by each of these factors. A similar 

 studv has been made on the defibrinated blood serum, but this work 

 has not been completed. 



Some years ago a method of removing blood cells from defibrinated 

 hog's blood was devised, and this has led to the commercial production 

 of clear virus. A very large volume of the defibrinated blood serum, 

 however, is still produced. During the year studies of the properties 

 and reactions of defibrinated blood, particularly old defibrinated blood 

 serum which has been kept for some time in storage and in which the 

 blood cells haA'e undergone more or less disintegration, have been car- 

 ried out. While no process for practical use can be recommended at this 

 time as a result of this work, the work has proceeded far enough to 

 show that hemoglobin in old hog-cholera serum combines with chlo- 

 roform so that the hemoglobin is rendered completely insoluble and 

 may be removed by centrifugalization. The clear serum thus ob- 

 tained amounts to approximately G4 per cent of the original volume, 

 and it may be heated without coagulation, which would be impossible 

 before the hemoglobin was removed. 



With the object of producing an effective and safe vaccine against 

 hog cholera an extensive series of experiments was carried out with 

 vaccine prepared by a new and original method. Work in previous 

 years having shown that ammonia (NH^OH) in quite low concentra- 

 tion (0.125 per cent) destroyed the virus of hog cholera within a 

 comparatively short time, the defibrinated blood from pigs sick of 

 cholera was mixed with ammonia in different concentrations and 

 allowed to stand for varying periods of time under different condi- 

 tions of temperature. Pigs were then injected with varying amounts 

 of this ammoniated virus at varying lengths of time after its 

 preparation, the injections being repeated at intervals of a week, and 

 the treated pigs were later exposed to hog cholera by virus injection 

 or by association with sick pigs. For the most part the injected pigs 

 remained well, but in isolated cases in the early experiments hog 

 cholera developed as a result of the vaccine. While the results of 

 these experiments were too irregular to permit the use of such a vac- 

 cine in practice, there was evidence of the production of considerable 

 resisting power in the pigs, and this line of work appears sufficiently 

 promising to warrant its continuance. 



The experiments mentioned, in last year's report, to determine the 

 duration of immunity against hog cholera following simultaneous 

 inoculation of young pigs, have been completed and the results pub- 

 lished in the Journal of the American Veterinary Medical Associa- 

 tion for May, 1920. volume 10 (n. s.), page ITO. These experiments, 

 although few in number, indicate that the simultaneous inoculation 

 of young pigs confers a lasting immunity. 



