236 



INFECTION AND IMMUNITY. 



Formation of 

 Precipitin. 



Concerning 

 Antoprecipi- 

 tins and Iso- 



precipitins. 



is true, of course, that little has been learned con- 

 cerning the nature of the end-product ; its chemis- 

 try is as dark as that of the proteids in general. 



As stated in the chapter on "Natural Immun- 

 ity/' normal serums occasionally have the power 

 to cause precipitates in other serums. Precipitins 

 for egg albumin and goat serum have been found 

 in extracts of organs, although at the same time 

 they were absent from the serum of the animal. 

 In this case the active bodies exist in the cells as 

 "sessile receptors/' and by the process of extraction 

 they are brought into solution. During immuniza- 

 tion these same receptors are stimulated to over- 

 production and are thrown into the circulation as 

 free precipitin receptors. 



The power of forming precipitins may be widely 

 distributed among the organs. This function has 

 been assigned to the leucocytes (Kraus and Leva- 

 diti, Moll), and in one case they were formed 

 locally in the anterior chamber of the eye (v. 

 Dungern, Komer). 



For the artificial production of precipitins the 

 precipitinogenous fluid may be injected into the 

 veins, peritoneal cavity or the subcutaneous tissue. 

 Within from four and a half to five days the pre- 

 cipitin has been formed to such an extent that it 

 may be demonstrated in the serum of the im- 

 munized animal. 



As in the case of agglutinin formation, not all 

 animals have equally the power of forming a pre- 

 cipitin for a given albumin. This point, as re- 

 lated to serum precipitins, is of particular impor- 

 tance, and involves a factor which is of no conse- 

 quence in bacterial agglutinins. In the first 

 place, an animal will not form a precipitin which 



