90 FORTY YEARS' EXPERIENCE OF A PRACTICAL HOG MAN 



It may have been noticed that no claim has been made that a cure 

 for this disease has been discovered. Our hope for its control lies in 

 its prevention rather than in its cure, and this brings us to the discussion 

 of the serum method of treatment, which is distinctly preventive rather 

 than curative in its nature. Success in fighting hog cholera lies in warding 

 it off rather than in overcoming it after the animals have become diseased. 



Method of Procedure. To understand this method of procedure it is 

 essential that one has in mind a clear idea of what is meant by immunity. 



It is common knowledge that when a person has once recovered from 

 an attack of certain contagious diseases he is thereafter less liable to 

 respond to a second attack of those same diseases, and this holds with other 

 animals as well as with human beings. Such individuals, whether persona 

 or other animals, are said to be immune to those particular infections. 



What this immunity consists in is still under debate, I believe, but 

 whatever its nature it is very clear that those animals possess a resisting 

 power they did not possess previous to the first attack of the disease. 



Scientists tell us that all disease-producing germs or bacteria develop 

 certain toxins or poisons which acting upon the body cells and nerve 

 centers tend to cause death. At the same time that this invasion is 

 going on nature, in her attempt to save life, begins the manufacture of 

 a counter-acting substance, called anti-toxin, the function of which is 

 the destruction of the living, death-producing microbes and thus stay or 

 limit the progress of the disease. There is, therefore, being carried on 

 within the system of the infected animal a life and death struggle between 

 these two opposing forces, the toxin and the anti-toxin, and the ultimate 

 success of the one or the other means either the death or the recovery 

 of the hog. In the large majority of cases, however, the body becomes 

 so thorough impregnated with the poisonous germs that the anti-toxin 

 cannot be developed rapidly enough and hence the animal dies. If, on 

 the other hand, the animal has at the beginning an unusual or sufficient 

 amount of native resisting power, or the infection be not of the more 

 virulent nature, recovery takes place and thereafter the animal is con- 

 sidered, and is in reality, immune. 



It is from the blood of these immune hogs that the serum is secured, 

 which, when injected into the systems of other hogs, renders them like- 

 wise immune to the attacks of hog cholera. 



Ordinarily, however, the blood of these merely immune hogs contains 

 only enough anti-toxin to protect the animals themselves against the 

 disease, and thus the serum from the blood of such animals, in small 

 doses, would not be effective in immunizing other animals. This necessi- 

 tates the production of what is known as a state of hyper-immunization 

 in the hogs from which the serum is to be taken. Hyper-immunization 

 is produced by giving to an already immune hog large doses of cholera 

 virus, thus causing the blood of the animal to become so saturated with 

 anti-toxin that small doses of serum from his blood may be successfully 

 used in immunizing other hogs. 



Preparing Serum. The method of preparing the serum may be briefly 

 stated as follows: 



Either a hog is procured that has recovered from an attack of hog 

 cholera, or more frequently, such an immune hog is artificially produced 

 by injecting him with a small dose of virus obtained from an acute case 

 of the disease, while at the same time -he is injected with a protective 

 dose of serum. Thus an immunity is established. Then one of two methods 

 may be employed. Either several successively increasing doses of virus 

 may be given at intervals of about a week apart, or one extraordinarily 

 large dose may be given at one time. Either of these methods is effective, 

 but that of giving the one large dose has the advantage in the point of 

 time saved. From a week to ten days after the last injection of virus the 

 animal is bled from the tail, about a pint of blood being drawn from a 

 hog weighing one hundred pounds. The blood so drawn is allowed to 

 clot and the clot is then strained under pressure, and the resulting serum 



