PRODUCTION OF ANTIPNEUMOCOCCIC SERUM 539 



Another serious disturbance sometimes encountered in horses un- 

 dergoing immunization is the occurrence of anaphylactoid reac- 

 tions. The symptoms usually occur within a short time following 

 an injection of vaccine and are characterized in typical cases by 

 their abruptness, by excessive perspiration, marked respiratory 

 embarrassment resulting in a blood-tinged, frothy exudate from 

 the nostrils, complete collapse, and death shortly after the onset 

 of symptoms. At necropsy, the gross pathological findings are 

 usually negative except for marked congestion and hemorrhages in 

 the lung tissue, and pulmonary edema. It is difficult to assign a 

 definite cause to the reactions. A study of records at the Massa- 

 chusetts laboratory showed that the majority of deaths of this na- 

 ture occurred after the first injection in a series following the rou- 

 tine bleeding subsequent to the rest interval, and that deaths 

 occurred most frequently in the period from two to eighteen 

 months after initiation of the immunization process. 



Because of these disturbances and the suggestion that the symp- 

 toms were indicative of a hypersensitive condition, the practice 

 was adopted of administering subcutaneously a small dose of the 

 vaccine on the day preceding the first of each series of three regu- 

 lar daily intravenous injections. These "desensitizing doses" were 

 given to horses that exhibited unusual reactivity to the routine in- 

 jections. Although the number of horses so treated has been too 

 small to justify definite conclusions, the impression has been 

 gained that the desensitizing treatment reduced the expected mor- 

 tality rate of horses undergoing immunization. In the experience 

 of the authors, the majority of sudden spontaneous deaths in 

 horses have occurred when formalinized suspensions were in use 

 and possibly may be referable, in part at least, to the more rapid 

 lysis of these preparations as compared with vaccines killed by 

 heating at 100°. Since the substitution of vaccines prepared in the 

 latter manner it has not been found necessary to employ desensitiz- 

 ing doses. Truche 1419 claimed that death due to hypersensitivity 

 could be avoided by diluting the organisms to be injected in a 



