136 Forty Years' Experience of a Practical Hog Man. 



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 likewise 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 ef- 

 fective in immunizing other animals. This necessitates the 

 production of what is known as a state of hyper-immuniz- 

 ation 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 its blood may be success- - 

 fully used in immunizing other hogs. 



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 hun- 

 dred pounds. The blood so drawn is allowed to clot and 

 the clot is then strained under pressure, and the resulting 

 serum is given sufficient of a five per cent solution of car- 

 bolic acid so that ultimately it contains one-half of one per 

 cent of carbolic acid, this being for the purpose of increas- 

 ing its keeping qualities. 



This bleeding process is repeated at least twice at in- 

 tervals a week apart, the whole being then mixed to give a 

 uniformity of product. It should then be tested by prac- 



