DIFFERENTIALS AND EVOLUTION 593 



in the function of organisms and their constituent parts may be distinguished. 

 There is the specificity of the organismal differentials, and in particular of 

 the individuality differentials, on which depends the autogenous equilibrium 

 of a higher organism; the latter determines the controlled interaction between 

 adjoining cells and tissues and makes possible the integrity of the organism, 

 guarding it against invasion by strange organisms or their parts. The mutual 

 adaptation of tissues and also the specific adaptation between the bodyfluids 

 and the cells and tissues of an individual depend upon this specificity of the 

 individuality differentials. Upon such a specificity depend also primarily the 

 reactions to strange organismal differentials, which serve as antigens and cause 

 the production of the various kinds of antibodies as a means of defense against 

 the intrusion of foreign elements into the individual organization. This specific- 

 ity of the organismal, and especially of the individuality differentials, is the 

 basis of the "essential individuality." 



There is, secondly, the specificity of organs and tissues that interact within 

 the individual and this specificity depends upon the differences in the chemical 

 and structural constitution of the parts of which the organism is composed. 

 Various organs with interlocking functions form primary organ system, in 

 which the correlation between the functions of individual organs may be 

 controlled by nervous mechanisms or hormones, or both. These primary organ 

 systems are then combined into larger systems, until in the end the whole 

 organism acts as a unit. The interaction of the various organs within the same 

 individual is so perfect that it seems to express the underlying "wisdom of the 

 body," as Cannon has so aptly called it. The totality of these organs and organ 

 systems, together with other structural and functional peculiarities of the 

 organism, represent the "mosaic individuality." 



The organ specificities and various structural and functional characteristics 

 of an individual or species have developed in the course of evolution and they 

 exhibit a gradation corresponding in a general way to the phylogenetic rela- 

 tionships of individuals and species. It is possible to reconstruct, to a certain 

 extent, phylogenetic systems by means of these organ and other structural 

 characteristics. Certain constituents of organs or tissues may therefore exhibit, 

 in this respect, characteristics similar to those shown in the typical manner 

 by the organismal differentials, from which they differ, however, in their 

 chemical structure and in the fact that they are restricted to a single organ or 

 part of the body and are not inherent in all the constituent parts of an 

 organism, as are the typical organismal differentials. They may be designated 

 as secondary or accessory organismal differentials. It seems that various organ 

 differential substances may detach themselves from the stem of the organ- 

 ismal differentials at different stages during phylogenetic as well as during 

 ontogenetic development, and that these substances may undergo an evolution 

 more or less corresponding to the systematic relationships ; but still this differ- 

 entiation in other respects may develop independently of phylogenetic rela- 

 tionships. Indications of such a process may be noted in certain food reserves, 

 for instance those of the yolk of the egg and of the seeds of plants; here 

 there is a development of substances which more or less corresponds with the 



