186 EXPEEIMENT STATION RECOKD. 



horse cholera serum and 2 cc. of virus and then several weeks before farrow- 

 ing fed or injected subcutaneously with hog cholera virus died from the disease. 

 In experiments with a number of litters from sows recovered from hog cholera 

 or previously vaccinated and infected 3 weeks before farrowing it was found 

 that after 5 months the litters were not immune to the disease. The details of 

 experiments conducted to test the length of immunity of hogs naturally infected 

 are reported in tabular form but no conclusions are drawn. 



Studies on hog cholera and preventive treatment, W. E. King and R. H. 

 Wilson (Kansas iita. Bui. Ill, pp. 139-195, figs. 8, dgms. 32). — This bulletin 

 reports the results obtained from investigations conducted since the report of 

 prelimiuai-y experiments, previously noted (E. S. R., 20, p. 881), was prepared. 



The results of field work conducted in 1908 with experimental horse serum- 

 hog cholera vaccine have been summarized in part as follows : " Twenty-four- 

 hour horse serum vaccine, as a rule, is lacking in infectious properties. It pos- 

 sesses some degree of protection, which, however, is not constant enough to 

 prove of practical use. Six-hour horse serum vaccine, under certain conditions 

 relative to character of diet and individual variation in susceptibility, produces 

 virulent hog cholera. It possesses greater protective properties than does 24- 

 hour horse serum vaccine, and under certain conditions in the field it may save 

 from 80 to 100 per cent of the treated animals. For practical field conditions, 

 however, 6-hour horse serum vaccine is not safe." 



In experiments conducted and reported in detail, it was found that "horse 

 serum virus (J-hour horse serum) does not represent a mere dilution of the 

 given hog cholera virus. A residence of hog cholera virus for a half hour in 

 the circulatory system of the horse appears to activate the virus. Half-hour 

 horse serum virus is capable of producing typical acute hog cholera when 

 injected subcutaneously. in relatively small doses (4 cc), into healthy hogs. 

 The minimal fatal dose of highly virulent hog cholera serum may perhaps be 

 found at some point between ^x' ^"d jis cc." 



The results of preliminary experiments relative to the attempted hyperim- 

 munization of horse serum virus here reported lead the author to conclude that 

 " horse serum and defibrinated horse blood may be injected into hogs in rela- 

 tively large quantities, subcutaneously, intraperitoneally, and perhaps intraven- 

 ously, without danger of loss from hypersusceptibility to the foreign blood. 

 Half-hour horse serum virus, when injected into immune hogs according to the 

 general technique employed in the original Dorset-Niles method, causes the 

 production of protective substances in the blood of the treated animals. The 

 degree of potency of the hyperimmune serum, prepared by the experimental, 

 modified method, may depend upon the amount of horse serum virus used and 

 the method of application." 



In observations relative to the influence exerted by hog cholera virus injected 

 intravenously upon the histological structure of normal horse blood, it was 

 found that the following changes took place after a period of 1^ hours : "A 

 decrease of approximately one and one-half million erythrocytes ; marked 

 leucocytosis. there being an increase of over 4,000 leucocytes ; a loss of approxi- 

 mately 4 per cent of the hemoglobin ; and a decrease in the specific gravity and 

 slight decrease in the time of coagulation." 



In a comparative study made of the blood of 43 normal swine and 22 suffering 

 from hog cholera, several changes in the case of hog cholera blood were found. 

 " The number of erythrocytes and the hemoglobin content were decreased, the 

 anemic condition increasing according to the progress of the disease. Fre- 

 quently poikilocytosis was observed in the blood from severe cases of the 

 disease. Leucopenia was shown in the blood of the diseased hogs, there being 

 an average decrease of nearly 5,000 leucocytes per cubic millimeter. This 



