122 ANNUAL REPOKTS OF DEPARTMENT OF AGRICULTURE. 



sufficient serum being employed to prevent the appearance of any 

 clinical symptoms of hog cholera. All remained apparently well. 

 Three were studied over an extended period. When nonimmune pigs 

 were kept in the pen with some of them, and thus exposed merely by 

 association, the nonimmunes in all cases remained well. Notwith- 

 standing this fact, it was found that the virus of hog cholera was 

 present in the circulating blood of simultaneously treated pigs for 

 about two weeks following the inoculation. It is probable that the 

 precise time during which the virus so persists may vary in individual 

 cases. In order to determine the probability of this virus remaining 

 for an indefinite period, 15 healthy nonimmune pigs were given the 

 simultaneous inoculation in the ordinary way, and 28 days afterwards 

 enough blood was drawn from each to inoculate 2 nonimmune pigs. 

 All of the 30 pigs that were injected with this blood remained well. 

 They were later exposed to hog cholera and found to be susceptible. 



These experiments show why it is unnecessary, in applying the 

 simultaneous inoculation, to graduate the dose of serum and virus in 

 order to secure a permanent immunity. They show that although 

 an excess of serum be used so as to prevent entirely the appearance of 

 clinical symptoms of hog cholera, and so as to prevent the trans- 

 mission of disease from one animal to another by association, yet the 

 virus of hog cholera circulates in the blood of inoculated animals, 

 thereby producing an active immunity. With regard to the persist- 

 ence of the virus of hog cholera in simultaneously treated pigs, so 

 far as these few experiments will permit we may conclude that 

 (1) the virus of hog cholera persists in the blood of simultaneously 

 treated pigs for a period of approximately two weeks following in- 

 oculation; and (2) it is probable that where sufficient serum is given 

 to prevent the development of symptoms of disease following inocu- 

 lation the virus disappears from the blood before the twenty-eighth 

 day. 



In order to determine whether larger doses of serum than any 

 heretofore employed in experimental work would prove more ef- 

 fective, experiments were carried out by infecting pigs with the virus 

 of hog cholera, and, after the appearance of clinical symptoms of 

 hog cholera, treating them with doses of serum ranging in amount 

 from 100 to 300 c. c. In some cases doses of 300 c. c. were admin- 

 istered to pigs weighing 80 pounds on the fifth day following infec- 

 tion. The serum had been determined by test to be of sufficient 

 potency to protect certainly pigs of the same weight if injected 

 in doses of 20 c. c. either immediately before or simultaneously with 

 the virus. In none of the pigs treated with these doses of serum was 

 there any noticeable effect upon the course of the disease. The 

 treated pigs died as promptly as the untreated controls. 



The effect of heat upon hog cholera virus was tested. The virus 

 used consisted of defibrinated blood not phenolized. Nine experi- 

 ments were carried out, the different lots of virus being heated at 

 50°, 55°, and 60° C. for 12, 6, and 1^ hours, respectively. In no case 

 was the virus destroyed by the heat. 



Experiments were also conducted to test the effect of heat on the 

 potency of antihog-cholera serum. The serum used was defibrinated 

 blood from hyperimmunized hogs. In 14 separate experiments 

 serums were heated at 50° C. for 24 hours and 12 hours, at 55° C. 

 for 6 hours, and at 60° C. for li hours and % hour. It was found 



