DEMONSTRATION OF SPECIES DIFFERENTIALS 501 



growing parts of plants, in which storage of proteins, and possibly also of 

 other substances, is as yet less prominent than in fully developed parts, and 

 especially less prominent than in seeds. Before using material from growing 

 parts as antigen he freed it from its fatty constituents through extraction 

 with alcohol and ether, and this procedure greatly increased the specificity of 

 the reaction, which, as in the case of animal serum reactions, depends pri- 

 marily upon the proteins contained in the antigen solutions. Mez assumed 

 that the increase in specificity of the reaction, caused by previous absorption of 

 the lipids from the tissue furnishing the antigen, is due to the lack of species- 

 specificity of these lipid substances. By means of this method, Mez attempted 

 to trace the development of plants from bacteria to algae and mosses, and 

 from these to the higher organisms. More recently, Steinecke has extended 

 these investigations. According to Boyden, these phytoserological studies have 

 yielded data of crudely quantitative nature which support the concepts of 

 plant phylogeny advanced already on the basis of morphological studies. In 

 a similar way Wilhelmi found that the previous extraction of lipids from the 

 antigens increased the value of the precipitin reaction as a method for deter- 

 mining phylogenetic relationships of helminths. After the lipids had been 

 removed, the proteins acted as potent species-specific antigens, whereas the 

 presence of lipids interfered with this reaction, because these substances by 

 combining with a protein could function as haptens, which are less effectively 

 species-specific and may be organ-specific. 



In general, we may then conclude that substances of protein character, 

 which differ in their constitution in different, not too nearly related species, 

 may serve as antigens and lead to the production of precipitins which react 

 specifically with the antigen by the formation of precipitates. If we compare 

 the interactions of different antigens with the same immune serum, we notice 

 that the strength of these reactions indicates the graded relationship of these 

 antigens and of the animals from which they were obtained. By the introduc- 

 tion of certain refinements in the methods used, distinction may be made in 

 this way also between more nearly related species, although as a general 

 rule it is possible by the ordinary precipitin methods to distinguish only be- 

 tween species belonging to different orders, and it may be difficult to estab- 

 lish fine gradations even between different orders. In principle, then, these 

 antigens behave like the coarser types of organismal differentials. 



Soon after the precipitin test had been introduced as a serological test for 

 phylogenetic relationship, Marshall, in the laboratory of Ehrlich, used for the 

 same purpose, hemolysis, the solution of red corpuscles by means of pre- 

 formed or of immune sera. Thus he found a close relationship between the 

 antigens present in the erythrocytes of man and of Macacus monkeys. How- 

 ever, certain differences were observed in the hemolyzing power of active 

 monkey serum for human and monkey erythrocytes, respectively, and differ- 

 ences between these two kinds of blood were established also by absorption 

 tests, in which different antibodies present in the same immune serum could be 

 separated from each other by specific absorption with erythrocytes from 

 different species, to which these antibody fractions had specific affinities. 



