58 THE AMERICAN NATURALIST [Vol. LIV 



that several or all of the chromosomes of the father are 

 characterized by certain chemical groups which would be 

 the same in the cells of the same individual, but would 

 differ in the cells of different individuals. Each cell 

 of the child obtains a combination of chromosomes which 

 is the same in the same individual, but differs in the case 

 of different brothers or sisters. The chemical individ- 

 uality-character of the chromosomes should lead to 

 analogous chemical differences consisting perhaps in the 

 formation of chemical sidechains attached to proteins; 

 they should be present primarily in cell proteins and 

 secondarily in the proteins of the body fluids. While the 

 individuality-differentials in the tissues exist perhaps 

 even in the embryo, there are some indications that the 

 adapted substances in the body fluids originate after 

 birth. These side chains must be identical in all the pro- 

 teins of the same individual and differ in the case of 

 different individuals. We should then expect that the 

 individuality-differentials of the children, being a mix- 

 ture of those of the parents, however in proportions 

 which differ in the case of different children, should be 

 intermediate between those of the parents. Extremes in 

 the children may be almost identical with one or the other 

 parent. In transplanting tissue from one brother to 

 another the graft would in most cases find in the host the 

 same characteristic groups which its own cells possess, 

 but in a somewhat different quantitative relationship. 

 Therefore the life of the graft which finds all the char- 

 acteristic substances could be sustained; but the quanti- 

 tative differences which exist in most cases would grad- 

 ually lead to toxic effects which ultimately endanger the 

 life of the graft. In some cases, however, the host would 

 lack altogether some of the chromosomes or groups 

 present in the brother and then the result would be more 

 unfavorable, somewhat approaching that of homoio- 

 transplantation. 



In the case of transplantation from child to mother on 

 the other hand the graft would lack one half the chromo- 



