198 MICROBES AND TOXINS 



nothing to do with the white corpuscles. They have made 

 extracts of leucocytic exudates withdrawn from the body, and 

 shown that these extracts were either without bactericidal 

 power or that the bactericidal substance they contained 

 possessed properties quite different from those of complement. 



It is true that in extracts of white corpuscles prepared 

 by maceration or freezing no complement can be detected 

 capable of destroying bacteria, but such experiments do not 

 prove that the production of complement by these is 

 impossible. The complement may easily be lost in the course 

 of the maceration and freezing, rather brutal processes in any 

 case for living cells. It is also possible that the complement 

 may be neutralised by some antagonistic substance contained 

 in the leucocyte, some sort of anti-complement : we are 

 certainly far from knowing all the substances contained 

 by leucocytes. It is conceivable that they may respond to 

 a slight injury, received in the course of the manipulation 

 of the blood, by discharging into the surrounding fluid com- 

 plement alone, whereas when more seriously injured they may 

 discharge the neutralizing substance. Later it will be seen 

 that Pfeiffer's phenomenon when correctly interpreted supports 

 this view : in the body thoroughly immunized against the 

 cholera vibrio but with the white corpuscles uninjured, the 

 vibrios are not destroyed by the body-fluids and are altered 

 only in the interior of the cells. 



According to Metchnikoff the complement is secreted by the 

 phagocytes, never excreted, i.e., poured out into the serum or 

 the body-fluids, so long as the phagocytic process remains 

 normal ; it is only discharged when the phagocyte has been 

 injured ox phagolysed, as this semi-destruction has been called. 

 It resembles the zymase of the yeast cells of beer, which 

 are only liberated by processes which break up the cell. The 

 fact is one of great importance, as will be found again in 

 the discussion of Pfeiffer's phenomenon : the complement 

 action never takes place outside the bodies of the phagocytes 

 except when there has been phagolysis. 



In acquired immunity, i.e., in an animal which has 



