PROTEINS 505 



The statement is occasionally made that protein specificity 

 is not "biological" but chemical, by which is meant that the 

 reaction is not necessarily associated with life; i.e., living material 

 is not needed in order to establish a plant or animal relationship 

 on the basis of immunological reactions; old serum gives the 

 same result as fresh serum. 



The work of Moyer (page 386), in which plant relationship 

 between species of Euphorbia was established on the basis of 

 rate of cataphoretic migration (mobility curves) and isoelectric 

 points, appears to rest, in part at least, on the protein nature of 

 the covering of the latex particles, but Moyer is careful not to 

 assign all responsibility to the proteins. The constitution of the 

 covering of the latex particles is a chemical criterion of relation- 

 ship, but that this covering is completely or always protein is not 

 conclusively proved — in fact, there were observations against 

 it; often no test for protein could be obtained; the latex particles 

 of numerous species pass readily into oil, suggesting little or no 

 protein on the surface; isoelectric points were sometimes too low 

 for protein. These facts indicate that other substances may be 

 responsible. Likely ones are the sterols or the higher alcohols 

 (e.g., resin alcohol, C16H47OH; or cetyl alcohol, C16H33OH). 

 The sterols especially have come very much to the fore of late 

 as significant substances in biological systems (page 466). 



An interesting addition not only to protein specificity as the 

 determining factor in species relationship but also to methods 

 ascertaining these is the work of Svedberg on sedimentation 

 constants, molecular weights, and isoelectric points of respiratory 

 proteins. He found that sedimentation constants of proteins 

 determined by centrifuging are of the same value within a well- 

 defined animal group. Thus is biological kinship between species 

 related to the molecular weights of their proteins. 



Heredity. — Basing biological kinship on protein specificity is 

 a step, and a very definite one, toward a chemical interpretation 

 of heredity. A further step could be taken by enlarging on the 

 subject and raising it to the dignity of a chapter, but, attractive 

 as this would be, it would be premature. We might, however, 

 well look for a moment in this direction and realize that the day 

 may come when not only the laws of heredity but its basic 

 mechanism as well will be stated in terms of physics and chem- 

 'istry, just as the mechanism of muscular action and nerve con- 



