Chemical Basis of Genus and Species 67 



remarkable fact that the sera of certain individuals of 

 humans could hemolyze the corpuscles of certain other 

 individuals, but not those of all individuals. A system- 

 atic investigation of this variability led him to the 

 discovery of three distinct groups of individuals, the 

 sera of each group acting in a definite way towards 

 the corpuscles of the representatives of each other 

 group. Later observers, for example Jansky and Moss, 

 established four groups. These groups are, according 

 to Moss, * as follows : 



Group i. Sera agglutinate no corpuscles. 



Corpuscles agglutinated by sera of Groups 2, 3, 4. 



Group 2. Sera agglutinate corpuscles of Groups 1,3. 



Corpuscles agglutinated by sera of Groups 3, 4. 



Group 3. Sera agglutinate corpuscles of Groups i, 2. 



Corpuscles agglutinated by sera of Groups 2, 4. 



Group 4. Sera agglutinate corpuscles of Groups i, 2, 3. 

 Corpuscles agglutinated by no serum. 



The relative frequency of the four groups follows 

 from the following figures. Of one hundred bloods 

 tested by Moss in series of twenty there were found : 



10 belonging to Group I. 



40 belonging to Group 2. 



7 belonging to Group 3. 



43 belonging to Group 4. 



Groups 2 and 4 are in the majority and in over- 

 whelming numbers, which indicates that, as a rule, the 



1 Moss, W. L., Johns Hopkins Hospital Bulletin, 1910, xxi., 62. 



