PROTEINS 503 



Kinship.— Few, if any, subjects in biophysics and biochemistry 

 are more fundamental than that of the chemical basis of kin- 

 ship. Plants or animals that are closely related are quite likely 

 to have a similar chemical constitution. If we attribute to 

 chromosomes all the responsibility for kinship between organ- 

 isms, we are but using a collective term for the substances of 

 which chromosomes are made. Chromatic material appears to 

 be primarily responsible for kinship, but other substances out- 

 side the chromosomes may be, if not responsible for, then at 

 least an indication of relationship. Among these latter sub- 

 stances are those in the body fluids, particularly the blood. 

 Blood specificity has become a large chapter in immunological 

 work. The older medical viewpoint, with its complex and 

 confusing nomenclature and somewhat vitalistic tone (for 

 specificity was thought to be too extraordinary to be due solely 

 to the laws of physics and chemistry), has now given way to a 

 strict physical and chemical interpretation. 



Among the first significant contributions to modern views on 

 specificity in organisms was that of Landsteiner on blood types. 

 Human beings have blood that belongs to one of four groups 

 (the fourth may be a mixture of more than one). The groups 

 are determined by agglutination tests. So definite is the type 

 that it is now used to establish parentage and relationships both 

 in theoretical biological studies on evolution and heredity and in 

 practical criminology and illegitimacy. 



In early work on immunity, it was noticed that species react 

 similarly in respect to their immunity from reinfection. Their 

 proteins should, therefore, show similar (precipitation) reactions 

 when combined with antibodies. This fact led a number of 

 workers to study the immunological reactions of species with 

 the hope of determining phylogenetic or family relationships. 

 Among those active in this field were Landsteiner and Nuttall 

 on animal relationship and Mez on plant relationship. When 

 a vegetable or animal protein (antigen) is injected into an animal 

 (of a different species), a precipitating antibody is formed. The 

 intensity of the precipitin reaction between these antibodies and 

 various plant or animal proteins gives an indication of the near- 

 ness of their relationship. On this basis, Nuttall obtained the 

 following results: 



