538 BIOLOGY OF PNEUMOCOCCUS 



such rest intervals is of sufficient value to counterbalance the loss 

 of serum which might have been obtained had the animals been 

 kept continuously on the routine schedule of immunization and 

 bleeding. 



Relation of materials injected to reactions in the horse. There 

 is usually a febrile reaction in horses following each injection of 

 pneumococcal vaccine. The rise in temperature varies with the in- 

 dividual animal and with the amount and kind of material injected. 

 More severe reactions follow the administration of living cultures, 

 dose for dose, than of killed suspensions. Thus, Avery, Chickering, 

 Cole, and Dochez 36 referred to a body temperature of 40.5° as 

 moderate, subsequent to the injection of living cultures. It is the 

 custom in some laboratories to omit injections if the temperature 

 of the horse under immunization remains above 38°. There ap- 

 pears to be no definite correlation between the temperature rise 

 and the degree of antibody production, although an increase in 

 body temperature may be related to immunological response to the 

 substance injected. 



There are reactions in horses undergoing immunization against 

 Pneumococcus that are of a more serious nature. In some instances 

 the animals exhibit symptoms of poor appetite and of gastro- 

 intestinal disturbances, or show abnormally high temperatures 

 lasting for several days. Not infrequently, when the animals come 

 to necropsy, extensive thrombus formation is observed, particu- 

 larly in the blood vessels of the portal circulation. Occasionally, 

 when respiratory disturbances are noted prior to death, thrombi 

 are found also in the lungs. While it cannot be considered as 

 proved, evidence has been accumulated to indicate that horses 

 given intravenous injections of formalinized suspensions of pneu- 

 mococci are more prone to develop thrombi than animals receiving 

 vaccines devitalized by heat. In comparing the antigenic effect of 

 heat-killed and formalinized cultures in rabbits, Barnes and White 

 noted a smaller loss of animals in the former than in the latter 

 group. 



