EXISTING ORGANISMS— PHYSIOLOGY 97 



or solutions in salt solution wore prepared in test tubes, and a 

 drop or two of antiserum introduced. The result in the case of 

 related sera and antisera is the formation of a precipitate; un- 

 related sera do not react when the antiserum is added. Varia- 

 bility in the results is explained by Nuttall's statements that 

 "where a powerful antiserum is added to its homologous blood 

 dilution, the reaction is almost instantaneous, in other cases it 

 takes place more slowly. In the case of a strong antiserum, the 

 reaction takes place as a rule rapidly in related bloods, more 

 slowly in distantly related bloods. The rate at which the reaction 

 takes place may depend also upon the concentration of the blood 

 dilution, the more concentrated dilutions, within limits, reacting 

 earlier than higher dilutions. A weak antiserum will act more 

 slowly than a powerful one." Thus we might expect, all other 

 factors being equal, that the reaction would correspond to the 

 nearness of relationship as determined on the basis of classifica- 

 tion, and that in cases of doubtful relationship precipitin tests 

 might furnish a valuable corollary to the usual evidences. 



A few examples from Nuttall's extensive tables of results are 

 given in the table on page 98. In the horizontal line are listed the 

 antisera, in the vertical column, the blood tested. Only easily 

 interpreted examples are given, and the symbols have been 

 modified from the original to indicate great reaction, marked 

 reaction, moderate reaction, slight reaction, and no reaction, in 

 order as follows: 1,2,3,4,0. Blank spaces indicate the lack of a test. 



Even in the few cases here presented, it is obvious that the most 

 pronounced reaction is usually obtained with so-called homologous 

 sera, and that animals of different species react in a degree similar 

 to the degree of relationship determined in other ways. This is, 

 of course, subject to error, like all pioneer procedure in science, 

 but in the first three cases two show a maximum reaction of human 

 blood with human antisera, one a slightly greater reaction with 

 the antiserum of an anthropoid ape, all some reaction with anti- 

 sera of other primates and with some antisera of more distantly 

 related mammals, but none with antisera of the other classes. 

 In cases 5 and 6 the bloods of the orang and chimpanzee show a 

 maximum reaction with antisera of man and the anthropoids, but 

 none with other classes. However, in cases 12, 13, 14, and 15, the 

 bloods of various species of reptiles and birds show some reaction 

 with antisera of these two classes but with no others. 



