BIOLOGICAL THERAPEUTICS 545 



Anti-hog cholera serum is prepared by hyperimmunizing immune 

 bogs with intravenous injections of blood from hogs sick with hog cholera. 

 Ten days following the injections the hyperimmunized hogs are bled and 

 either the defibrinated blood or the recovered serum is used for prophy- 

 laxis, and treatment of the disease. The defibrinated blood aside from 

 containing the inert corpuscular elements of the blood cannot be produced 

 in a sterile form, whereas the clear serum being free from corpuscles can 

 be readily sterilized by various methods, therefore possessing many ad- 

 vantages over the bloody serum. 



Anti-hog cholera serum is probably the most important biological 

 product produced in recent years. Its effectiveness in the prevention of 

 hog cholera caused by the filtrable virus is no longer questioned. How- 

 ever, it is essential to have a potent serum and to adhere to the strictest 

 precautions against contamination both in handling and administration of 

 the serum. In spite of the fact that the protective value of hog cholera 

 serum has been established beyond a doubt, numerous complaints are made 

 of its failure to immunize against hog cholera. Various factors are re- 

 sponsible for such failures. Among these, probably the most commonly 

 recurrent one is a mistake in diagnosis. Practitioners are very prone to 

 establish a diagnosis of hog cholera in case several animals die, without 

 determining the character of the post-mortem lesions. An insufficient 

 knowledge of other infectious diseases of swine may also be responsible 

 to some extent for the failure in hog cholera vaccinations. A serum 

 without the proper potency, used by the simultaneous method, with a 

 potent virus, may bring about bad results. It should be understood that 

 anti-hog cholera serum represents one of the crudest of biological prod- 

 ucts. We have no means of properly standardizing it, or of establishing 

 (With any degree of certainty the amount of protective substances con- 

 tained in the blood serum. 



It must be acknowledged that the study of diseases of swine has been 

 somewhat neglected. Veterinarians are apt to accept any outbreak of 

 infection as hog cholera, frequently relying for their diagnosis on lesions 

 which are far from pathognomonic. The lesions which are commonly ac- 

 cepted as those of hog cholera may also be associated with other diseases. 

 Thus, for instance, hemorrhages in the kidneys may appear in association 

 with any septicemia condition, as is likewise the case with the cutaneous 

 subpleural and subperitoneal hemorrhages. They may arise from exces- 

 sive acid or oily substances in the food, from injuries or from overheating. 

 It is therefore apparent that in order to establish an accurate diagnosis 

 of the "virus disease" it is essential to take into consideration everything 

 which is characteristic of the symptomatology and anatomical changes of 

 the disease. 



The preventive treatment of hog cholera consists either in the admin- 

 istration of serum alone or in the simultaneous treatment. 



The serum alone method of immunization is now used only in excep- 

 tional cases, principally due to the fact that the immunity produced by 

 this treatment is of only short duration, not over eight weeks. It is prin- 

 cipally used on suckling pigs in infected territories. The immunity con- 

 ferred upon such pigs is only temporary no matter what method is used 

 and revaccination with the double treatment should invariably follow at 

 the time of weaning. ES^i^tdaby HBm^SOif^d should also be used on 



