320 BIOLOGY: GENERAL AND MEDICAL 



1:10,000, 1:100,000, etc. and the mixtures of the test 

 antiserum and the serum to be tested allowed to stand 

 for, say, thirty minutes as a fixed period, it will be found 

 that the reaction of precipitation is specific in that the 

 homologous bloods precipitate in greater dilution and in 

 larger quantity than heterologous bloods. Thus, human 

 serum may be precipitated with anti-human serum in 

 dilutions even reaching 1:100,000; the blood of anthro- 

 poid apes in slightly less dilutions; those of other apes in 

 decidedly less dilutions; those of lower monkeys in less 

 and less dilution the further they are zoologically removed 

 from man; those of lower mammals only in the concen- 

 trated form, if at all; and the bloods of still lower verte- 

 brates and invertebrates not at all. 



If, instead of treating the rabbit with human blood, 

 injections of bovine blood be used and anti-bovine 

 serum secured, the precipitation measured by the same 

 method is found to occur in greatest intensity with ox- 

 blood, then with the bloods of other bovida?, then with 

 those of animals closely related to the bovidae, and not 

 at all with those of animals remote from the bovidse. 



We thus have a physiologico-chemical method of con- 

 firming the morphological classification of animals. 

 It is of interest to know that the one bears out the 

 other in practically all cases. 



The general principle may therefore be stated as 

 follows: If the blood or body juice Of one organism 

 is capable of acting as an antigen when introduced into 

 another organism, the two are not closely related. The 

 index of antigenic activity is to be found in the quanti- 

 tative reaction of precipitation resulting from the action 

 of the antibody upon the homologous serum. 



A most interesting and important recent addition to 

 our knowledge of blood relationships, thought by its 

 authors to be more accurate and discriminative than 

 the zooprecipitins, is the crystallographic character 

 of the hemoglobin of the blood. This is described in 

 ''The Differentiation and Specificity of Corresponding 

 Proteins and Other Vital Substances in Relation to 



