AGGLUTININS 35 



normal rabbit serum agglutinates typhoid and 

 cholera bacilli. 



Of practical interest is the fact that normal serum 

 may agglutinate the red blood cells of another indi- 

 vidual of the same species. Following Ehrlich's nomen- 

 clature, we speak of this as is o agglutination. The 

 subject has been studied by a number of investigators, 

 and mostly in human blood. According to the extensive 

 investigations of Moss, isoagglutinins occur in the serum 

 of about 90% of adult human beings. Landsteiner 

 divided the individuals into three groups, namely : 



Group i. The corpuscles are not agglutinated by 

 sera of the other two groups, while the sera agglu- 

 tinate the corpuscles of both groups. 



Group 2. The corpuscles are agglutinated by the 

 sera of the other two groups, while the sera agglutinate 

 the corpuscles of Group 3, but not of Group i. 



Group 3. The corpuscles are agglutinated by the 

 other two sera, and the sera agglutinate the corpuscles 

 of Group 2, but not of Group i. 



An examination of this grouping shows that in no 

 case is there an agglutination of erythrocytes by their 

 own serum, in other words these are isoagglutinins but 

 not autoagglutinins. A somewhat different classification 

 was made by Jansky, and independently of him also by 

 Moss. Both these authors find it necessary to establish 

 four groups in order to embrace all the cases met with. 



Gay calls attention to the fact that the clumping of 

 erythrocytes by serum is not necessarily due to the pres- 

 ence of an agglutinin at all, but may be due to variations 

 in the molecular concentration of the serum constituents 

 or of the constituents of the blood cells. Whatever finally 

 proves to be the correct explanation, it is obvious that 

 the occurrence of isoagglutination in human blood might 



