PRODUCTION OF ANTIPNEUMOCOCCIC SERUM 523 



individual animals. Not infrequently it has been observed that a 

 horse showing poor response to injections of diphtheria and scar- 

 let fever toxins or even of suspensions of Meningococcus may de- 

 velop a high titer of specific humoral antibodies following immu- 

 nization with pneumococcal vaccines. It is equally true that 

 animals of the same general type may produce serum exhibiting 

 considerable differences in potency. The trial-and-error method of 

 selection of horses for immunization, while expensive and time-con- 

 suming, appears to be the most reliable procedure available at the 

 present time. There is an impression in certain quarters at least, 

 that the age of the horse may be of some importance. Wadsworth 

 and Kirkbride 1470 used horses of over eleven years of age. Al- 

 though it has not been proved that older horses are more readily 

 immunized with pneumococcal vaccines, it can be said that the 

 more mature horses respond quite as well as do younger animals 

 and, furthermore, are likely to be more tractable. 



Prior to initiation of the immunization process, the horses se- 

 lected should be subjected to a rigid physical examination, with 

 particular attention to the existence of respiratory affections. 

 Animals exhibiting evidence of the "heaves" should not be used. A 

 quarantine period of three weeks should be the rule, during which 

 time a careful examination for glanders by physical means and by 

 the mallein and complement-fixation tests is made, and the absence 

 of other communicable diseases determined. When the animals have 

 satisfactorily passed the quarantine period they may be stabled in 

 permanent quarters and the immunization process begun. 



SELECTION AND STANDARDIZATION OF THE IMMUNIZING ANTIGEN 



The ideal pneumococcal antigen for the routine immunization of 

 horses is yet to be found. Such questions as the degree of virulence 

 of the cultures, whether the organism should be in a living or de- 

 vitalized state (or combinations of both), and which derivatives of 

 the pneumococcal cell possess the desired antigenic properties, 



