CLINICAL EVIDENCE OF VALUE OF SERUM 497 



pens, but not a single instance was reported in which anj^ of them 

 afterward became sick. 



This is one of the most interesting experiments reported, and 

 the lessons to be learned from it are many: 



In the first place, it shows again conclusively that 1 c.c. of 

 virulent blood can be injected into the body of a susceptible animal 

 without any danger, if accompanied by a proper dose of a potent 

 serum. There is absolutely no danger of producing cholera in this 

 manner if the serum used has been properly checked against the 

 virus and proved to have protective power sufficient to neutralize 

 the disease-producing bodies in the virus. 



Second, it is shown in this experiment that when the treated 

 animals were placed in the same feed lots and ranges with 15 un- 

 treated shoats there was no development of the disease in these 

 animals. The period of four weeks which passed between injection 

 of the treated animals and the development of the first signs of 

 sickness in the check shoat is entirely too long for the average case 

 of cholera. It can be said, with extreme positiveness, that this 

 outbreak in the check shoats did not appear as a result of associa- 

 tion with the treated animals. 



Very interesting, indeed, is the third point in this instructive 

 experiment: The young boar that had apparently entirely re- 

 covered from a mild attack of cholera proves capable of infecting 

 the new herd into which he is introduced. This again serves to 

 illustrate the fact that animals that have even apparently recovered 

 from cholera are unsafe to add to a susceptible herd, unless that 

 herd be first protected by serum or serum-simultaneous treatment. 

 It seems that the hog which passes through what appears to be a 

 mild attack of the disease is even more dangerous than the one 

 that has the disease in the more severe form. The incubation pe- 

 riod of eight days which passed between the purchase of this boar 

 and the first signs of sickness in the checks more closely corre- 

 sponds to the average incubation period of hog-cholera, and there 

 can be but little doubt that this is the source of the infection in this 

 herd. 



The results in the treated animals, in the face of an outbreak 

 of the disease, is a fourth point of extreme interest to be derived 

 from the experiment in this herd. With an unquestionable out- 



