TIIJ-: I'KIt iriTIN KKA(TI<>\. 75 



and Blood Relationship," Nuttall published the results of 16,000 

 tests made with thirty different antisera on 900 species of animal 

 blood. Besides these qualitative tests there were included also 

 500 quantitative tests on various bloods. As a result of these 

 tests Nuttall was able to state that the degree of reaction between 

 an antiserum and various proteins was in proportion to the 

 degree of relationship of these proteins to each other. Here, 

 then, was a new method of measuring the "blood relationships" 

 of animals, and the results obtained by Nuttall confirmed in 

 general the existing classification of these animals based chiefly 

 on comparative anatomy and embryology. 



Since the outstanding works of Uhlenhuth and of Nuttall 

 there have been many other contributions to the study of animal 

 relationships based on precipitin tests. Hektoen, though inter- 

 ested primarily in the medico-legal aspects of the precipitin 

 reaction, has published numerous results which have a direct 

 bearing on problems of specificity and animal relationships. 

 Following up the discovery of Uhlenhuth that the lens proteins 

 of the Vertebrate eye are remarkably similar throughout, Hektoen 

 (1922) has made many tests confirming Uhlenhuth's statements. 

 Furthermore, Hektoen (Hektoen and Schulhof, 1924) has found 

 that there are two antigenically distinct proteins in the crystalline 

 lens and that apparently the lenses of all the chief groups of 

 Vertebrates have these two elements in common. Hektoen 

 (Hektoen and Welker, 1924) has also found that the blood serum 

 of animals can be divided into several specific protein fractions. 

 He has shown (Hektoen and Manly, 1923) that the semen of 

 animals gives specific and group reactions, and that the same 

 is true of their hemoglobins (Hektoen and Schulhof, 1923). 

 Throughout his work he has repeatedly succeeded in obtaining 

 specific precipitin reactions. The milk of mammals has been 

 shown to give much the same results in the study of relationships 

 as the blood serum. 



In all this work there has been a fair degree of uniformity in 

 results obtained. But there have been many other studies of 

 more uncertain value. Dervieux (1921) in working with an anti- 

 human semen serum claimed to have found an individual specific- 

 ness to the reaction. Geyer (1913) states that he could distinguish 



