256 INFECTION AND IMMUNITY. 



It is necessary to know the virulence of a cul- 

 ture with which an antiserum is tested. It is pos- 

 sible to maintain some organisms at a rather con- 

 stant virulence by passage, i. e., infecting animals 

 with the microbe and recultivating it from the 

 tissues. With others, abundant controls must be 

 made at the time the serum is tested in order to 

 know at that moment the precise virulence of the 

 culture. In all probability it requires more serum 

 to protect against very virulent cultures than 

 against those of less virulence. 



B. HEMOLYSINS. 



Experimental The simplicity of hemolytic experiments and the 



Value of .,.. .., T . , ,, J , r i n 



rapidity with which they may be performed and 



terminated have rendered hemolytic serums par- 

 ticularly useful in the study of amboceptors and of 

 complements, for we are to understand that such 

 serums are toxic to erythrocytes only because of 

 the amboceptors and complements which they con- 

 tain. The most important facts which have been 

 learned concerning the action of hemolytic serums 

 have been found to hold true for bactericidal 

 serums as well; hence it is an indifferent matter 

 if principles which are common to both are illus- 

 trated by frequent references to serum-hemolysins. 

 of The corpuscles for hemolytic experiments arc 



Hemolytic ... , , ,, T /., . ,. - , i -, 



Experiment, obtained, by the denbrination of ireshly-drawn 

 blood and the removal of the fibrin. Usually they 

 are made into a 5 per cent, suspension by dilution 

 with isotonic (physiologic) salt solution. Inas- 

 much as the serum which is present may interfere 

 with the action of the complement or amboceptors 

 of the hemolysin, it is customary to remove it by a 

 washing process. The 5 per cent, emulsion, or the 



