156 CHEMISTRY OF IMMUNITY AGAINST BACTERIA 



precipitates in the blood of related animals ; e. </., immune 

 serum against human serum will cause precipitates in the serum 

 of the higher apes. The precipitin reaction is, therefore, only 

 quantitatively specific, not qualitatively. 



The precipitin reaction occurs only outside the body (Mich- 

 aelis). When serum precipitins are injected directly into the 

 blood, no precipitation occurs, but merely an active leucocytosis ; 

 if injected intraperitoneally, there is local leucocytosis. Probably 

 the leucocytes take up the precipitate as fast as formed, or else 

 the absence of precipitate depends upon the fact that a proper 

 proportion between the amount of precipitin and proteid must 

 exist, an excess of proteid causing a resolution of the precipi- 

 tate. 



The precipitation by precipitins is not an enzyme action, for 

 the precipitins are used up in the process. It apparently does 

 not differ from precipitations of colloids by other colloids of 

 opposite electrical charges, except in that the reaction is specific. 



