466 DISEASES OF SWINE 



fall, the pigs that would be born the following spring would have a 

 protective power against cholera which would last for several 

 weeks. This immunity that is gained by pigs coming from a 

 mother that has received the double treatment or that possesses 

 an immunity as a result of an attack of the disease is a Httle in- 

 definite in the length of time that it will last. Some men, such, for 

 instance, as Dr. Dorset, of the United States Bureau of Animal 

 Industry, and Dr. Fitzgerald, of the Ohio State Experiment 

 Station, claim that this immunity lasts just about as long as the 

 pig sucks the mother. 



Other authorities claim that just as soon as the little pigs begin 

 to nibble about the yards, and take to eating infectious material, 

 they will become susceptible to the disease, and should, accordingly, 

 be injected with serum at about the age of three weeks. This is 

 one of the questions in regard to immunity produced from simul- 

 taneous treatment that needs a little more careful investigation. ■ 



In connection with the danger from injection of virus and 

 serum into pregnant animals as a cause for abortion some very in- 

 teresting facts have come to my notice in connection with the use 

 of pregnant sows in serum plants. In a number of serum plants 

 sows which have been purchased for use in the manufacture of 

 serum have proved to have been pregnant at the time of purchase. 

 These animals are given the double treatment at the serum plant, 

 and three to four weeks later are again injected with an enormous 

 dose of virulent blood, for the purpose of producing a hyperim- 

 munity. Yet, in these cases it is very seldom that the sows abort, 

 despite the fact that they are twice injected with virus blood, 

 once protected by a simultaneous injection of serum, and the next 

 time with only the protection afforded by the germ fighters formed 

 in their own body. 



These results would seem to indicate that the serum treatment 

 by either the single or double method is practically harmless as far 

 as any danger of producing abortion is concerned. 



In connection with these pigs born at serum plants it is of in- 

 terest to note that the immunity which they possess is very weak, 

 if in fact, they possess any at all. In a number of cases where these 

 little fellows are kept around the plant they will develop cholera 

 in about two or three weeks as soon as they begin to nibble food 



