484 DISEASES OF SWINE 



the cells of the animal body to take up the work of forming germ- 

 fighting bodies, and if the virus is not strong and active there 

 will be no results from its use. 



In many cases where the manufacturer of a serum is not cer- 

 tain as to the protective power of his product against real virulent 

 blood, "virus blood" has been supphed which was not virulent 

 blood at all. As a result, the effects produced were not what had 

 been expected or desired. It is in such cases as these that serum- 

 simultaneous treatment has been followed by an outbreak of 

 cholera several weeks later. In many cases this has been blamed 

 upon infection of the premises by virulent blood, when, as an actual 

 matter of fact, the trouble lies in the absence of any genuine virus 

 in the virulent blood used. To have success with the simultaneous 

 method of treatment it is equally necessary that we use a tested 

 virus blood as well as a tested protective serum. It is the combi- 

 nation of these two that produces the reaction on the part of the 

 tissues which gives to the animal the power of lifelong protection 

 against hog-cholera. 



It is worthy of note in this herd that the old sow put up a very 

 long fight against the disease. This is usually the case, and very 

 often these old sows are able to fight off the effects of the disease 

 and come through with a permanent immunity to further attacks. 

 As a rule, the older the animal, the better are its chances for re- 

 covery. 



Herd Number Thirty. — This herd was located within a quarter 

 of a mile of Herd Number 10, previously described, and was treated 

 on October 23, 1907, for the purpose of preventing spread of the 

 disease from the infected farm on which Number 10 Herd was 

 located. At the time of giving the treatment the animals were 

 all apparently in good health, and the entire herd was treated. 



Thirty-seven shoats, averaging in weight from 50 to 125 

 pounds, were given from 20 to 25 c.c. of serum with 2 c.c. of blood 

 taken from diseased animals. One old sow received 40 c.c, of the 

 serum alone. 



The blood used in this herd for virus purposes was afterward 

 tested at the station and did not prove very virulent. It was 

 perhaps sufficiently active to keep up stimulation of the cells of 

 the body long enough to cause development of antibodies. In 



