150 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



cholera, studies of dips, disinfectants, and insecticides, laboratory 

 research relative to meat products, and the preparation of tuberculin 

 and mallein. 



HOG-CHOLERA INVESTIGATIONS. 



As indicated in previous reports, one of the important lines of 

 investigation regarding hog cholera has been the study of cases 

 where losses have occurred among hogs after immunization by the 

 simultaneous method. A State experiment station worker reported 

 that anti-hog-cholera serum and hog-cholera virus contained Bacillus 

 hotuUnus, from which it was inferred that many of the so-called 

 " breaks " in hog-cholera immunity were caused by the presence of 

 this organism or its toxin in commercial serum and virus. During 

 the year this division made a study of the subject. A large number 

 of samples of commercial anti-hog-cholera serum and of hog-cholera 

 virus, including a number reported to be contaminated, were care- 

 fully examined. In no case was it possible to demonstrate the pres- 

 ence of either Bacillus hotulinus or its toxin. Some experimental 

 work was also done to test the growth and effects of this organism 

 and its spores in this connection. The studies and experiments led 

 to the conclusion that Bacillus hotulinus is not an important factor 

 in causing " breaks " following the use of anti-hog-cholera serum. 



The relation of Bacillus suipestifer to breaks following simulta- 

 neous immunization has also been the subject of study and experi- 

 ment. Bacteriological examination of a large number of samples 

 of commercial hog-cholera virus failed to reveal the presence of this 

 organism in any case. It appears that there is no need to fear bad 

 results from its presence in properly prepared virus. The results 

 of experiments do not prove that Bacillus suipestifer is the cause 

 of any large proportion of breaks, but they do indicate that a severe 

 suipestifer infection occurring simultaneously with the administra- 

 tion of the simultaneous treatment may be a cause of trouble. It was 

 found also that ill effects resulting from the administration of this 

 organism at the time of simultaneous inoculation could be in a large 

 part overcome by the administration of increased doses of anti-hog- 

 cholera serum. 



In pursuing further the studies of the cause of breaks following 

 immunization, a number of samples of commercial serum and virus 

 have been studied. The serum in most cases was part of a batch 

 which was believed to be contaminated or lacking in potency as 

 shown by unsatisfactory field results. In no case was such serum 

 found to be contaminated in such a way as to make it injurious to 

 hogs, and only in exceptionally rare instances was it found to be of 

 low potency. Among six samples of commercial virus, purchased at 

 random on the market, one was found to be so entirely lacking in 

 potency that it did not produce disease when injected alone into 

 susceptible pigs, and it also failed to produce a lasting immunity 

 when injected simultaneously with serum. These tests of virus 

 suggest that when properly prepared and preserved there need be 

 little fear of injury due to infection other than hog cholera when 

 commercial virus is used. They also suggest that some of the so- 

 called late breaks in immunity that have occurred in herds treated 

 simultaneously several months earlier may occasionally be due to the 

 lack of potency in the virus at the time of use. 



