No. 637] 



UniUXE SERA 



101 



the other tissues of that species. Thus the blood-serum 

 of a rabbit which has been treated with sheep blood-serum 

 will form a precipitate not only with the sheep serum, but 

 with the extracts of sheep muscle, sheep liver, sheep 

 spleen, and other organs of the sheep. This clearly im- 

 plies that each species of animal possesses something in 

 common throughout all its tissue proteins, something 

 peculiar to that particular species which in last analysis 

 must be resolved into a problem of its general metabolism 

 and stereochemistry. This does not mean that organs 

 may not also have protein complexes peculiar to them- 

 selves. Indeed, it is an established fact that they do. 

 And what is more, some of these organal pecuUarities 

 may be common to various species. For example, the 

 fact of "organ specificity" has been established for the 

 crystalline lens. According to Uhlenhuth, immunization 

 with crystalline lens of a given species of animal yields a 

 precipitin which reacts with, the lens proteins of many 

 different species of animals. Von Dungem and others 

 have secured similar results with proteins derived from 

 the testis. Confirmatory evidence of this fact that a 

 type of specificity attaches to the nature of the organ 

 itself, irrespective of species, has also been established 

 by means of the reaction of anaphylaxis. 



The precipitin reactions, then, teach the biologist that 

 in the chemistry^ of the general proteins of a given ani- 

 mal, there are certain fundamental similarities, also that 

 there are constant species differences between the homol- 

 ogous proteins of different species of animals, and lastly, 

 that some proteins, in certain highly specialized organs 

 at least, though existing in different species, possess 

 similar chemical characteristics. 



These and related facts when considered in conjunction 

 with such as those of Reichert and Brown regarding the 

 stereochemical correspondences in the living matter of 

 allied species as demonstrated in the crystallography of 

 their hemoglobins, or the studies of Eeichert on the rela- 

 tions of the starches and tissues of parent-stocks to those 



