THIRTEENTH ANNUAL YEAR BOOK— PART VIII 481 



VACCINATING. 



DR. STANCE. AMES, IOWA. 



"To begin with I would like to explain something of the basis upon which 

 this vaccination works. You understand the diphtheria antitoxin used for 

 human beings and have heard more or less about the tetanus antitoxin 

 used for lock jaw. The idea in all of these methods is that an animal 

 that has recovered from any one of the contagious diseases is immune to 

 these diseases afterwards. We have some diseases in the human being 

 which after a person recovers will not attack that individual a second 

 time. Small pox is a good example of that. 



"Now we find that a hog that has recovered from hog cholera will not 

 ordinarily contract the disease a second time. This encouraged us to 

 think that sometime we would be able to produce a serum which would 

 protect hogs against this disease. 



"For a number of years there was some question. of doubt in regard 

 to the cause of hog cholera. It was supposed to be caused by a germ 

 similar to the typhoid baccillus which causes typhoid in man. However, 

 it was found that the actual cause of the disease was a virus, which we 

 think we know is a germ so small that it can not be seen and which will 

 pass through the pores of a porcelain filter. We can take the blood from 

 an affected animal, filter it, inject it into a healthy hog and produce the 

 disease in that hog. There is a disease in cattle which is called Rinder- 

 pest, a tropical disease, which is caused by a virus which acts in very much 

 the same manner and the noted Dr. Kock worked out a method of vac- 

 cinating animals which we applied to hog cholera and found to be suc- 

 cessful. We have, then, a cause which is fairly definitely known and a 

 method of vaccinating animals which has been quite successful, although 

 it is to some extent in the experimental stage and there are a great many 

 things which are not just as they should be. We have not mastered all 

 of the problems in connection with this disease. 



"Taking the method of vaccination, I will go over it briefiy. We have 

 two methods. One is called the serum alone and the other the serum 

 simultaneous method. One is a temporary protection and the other a 

 more permanent and lasting protection against the disease. In the one 

 case the animal body takes no active part in protecting itself against the 

 disease, while in the other case the animal body itself must produce sub- 

 stances which protect it against the germ. 



"To produce the serum we produce hog cholera in healthy animals, 

 preferably young pigs weighing thirty to forty pounds. When they be- 

 come sick we bleed them and inject that disease producing blood into 

 hogs which have recovered from the disease or that have been immunized 

 by the simultaneous method. This increases the resistance to a great 

 extent. I have myself injected sufficient disease producing blood into 

 one hog to kill about a hundred hogs at one dose, so that you see an ani- 

 mal that is immune to hog cholera will resist enormous doses of disease 

 producing blood. Then after about ten days we bleed this animal that 

 has received this large quantity of disease producing blood and that blood 



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