504 PROTOPLASM 



Intensity of 

 Precipitin 

 Blood Serum from Reaction 



Human beings 100 



Anthropoid apes 100 



Common monkeys of the old world 92 



Capuchins and spider monkeys of the new world 78 



Marmosets 50 



Lemurs 



(The number 100 indicates a reaction identical in intensity 

 with that of the original serum used in immunizing — in this 

 case, human blood. The table, therefore, indicates the nearness 

 in relationship of the lower animals to man.) 



Landsteiner and Miller have shown a similar relationship 

 between man and the anthropoid apes. Manoiloff found that the 

 blood serums of cattle and horses can be distinguished by precipitin 

 reactions. He believes that the distinction lies in the albumins. 



The tame rat, Mus rattus, and the wild one, M. norvegicus, do 

 not cross. When artificially inseminated, the female gives sign 

 of pregnancy but later returns to normal; yet the two animals 

 are so closely related that they were formerly thought to be of 

 the same species. Such instances are probably due to protein 

 incompatibility, but the cause may also be purely genetical, 

 one or the other germ cell possessing what is known as a lethal 

 factor (or deadly gene) which prevents growth of the embryo. 

 However, as both adults may have progeny with other mates, 

 protein incompatibility is the likely factor. 



The serological studies of Mez on plant relationship permit the 

 construction of a plant family tree which corroborates almost 

 fully the older classification based on the usual taxonomic 

 (morphological) characters. Where differences in results by the 

 two methods exist, the correct relationship is just as likely to be 

 shown by the newer serological reaction as by the older ana- 

 tomical evidence. It is of great significance to the science of 

 evolution and phylogenetic relationship that a purely chemical 

 basis of classification should so well support a purely anatomical 

 one. Relationships between plants established by serological 

 methods hold well for families but not so well for genera and 

 not at all for species. This 'is due simply to a lack of delicacy 

 in the technique ; species differences in proteins must, of course, 

 also exist. 



