COMPARATIVE PHYSIOLOGY AND BIOCHEMISTRY 



of proteins from various plants related to the original test plant. Those 

 which give a precipitate when added in very dilute solution are regarded 

 as being closely related to the test plant, while those which give a precipi- 

 tate only when added in concentrated solution are regarded as being only 

 distantly related. The results lead to a classification which compares very 

 favorably with that which has been worked out by plant morphologists. 

 Thus the method of comparative serology has unexpectedly wide appli- 

 cations, and it seems probable that the method of Mez could profitably 

 be applied to any group of organisms. 



Blood Groups. The well-known A-B-O blood groups of man are based 

 upon antigenic proteins of the red blood cells. Red cells may carry antigen 

 A, or B, or both (AB), or neither (O), and a person's blood group is 

 named accordingly. Any person's serum contains antibodies capable of 

 agglutinating and destroying cells carrying those antigens not present in 

 his own blood. This immune system is inherited upon a simple basis 

 (multiple alleles: Chapter 13). Comparable series of blood groups have 

 been found in many other animals, but only with other Primates, which 

 are morphologically closest to man, does man share the A-B-O groups. 

 Chimpanzees are predominantly group A, but group O also occurs among 

 them. Gorillas and orang-utans are known to possess groups A, B, and AB. 

 Among various species of Macaca (the rhesus group) all four blood 

 groups are known. In lower Primates, the same antigenic proteins can be 

 demonstrated in the saliva (as also in man), but not on the blood cells. 

 The inference of relationship is unavoidable. 



BIOCHEMISTRY AND RECAPITULATION 



Phosphagens. Few chapters in physiology have been so thoroughly 

 investigated as muscle contraction. Energy-rich phosphate compounds 

 play a key role. Very briefly, adenosine triphosphate ( ATP ) breaks down 

 to yield energy for the contraction. Then a second energy-rich compound, 

 called a phosphagen, breaks down and releases energy for the resynthesis 

 of ATP. These reactions are anaerobic, but the cycle is completed by the 

 oxidation of glucose to provide energy for resynthesis of the phos- 

 phagen. 



In the muscle of vertebrates, the phosphagen is always a specific com- 

 pound, creatine phosphate, while in most invertebrates it is arginine phos- 

 phate. It is important to determine which characterizes the most primitive 

 chordates, and which characterizes those groups from which the chor- 

 dates may have arisen. Actually, the Hemichordata, the most primitive 

 group allied to the chordates, has both phosphagens, a condition found 

 elsewhere only in certain echinoderms, allies of the sea stars. On embryo- 

 logical grounds, echinoderms were already considered as probably close 

 to the ancestry of the chordates. 



This picture is not uncomplicated, for, although most invertebrates have 

 only arginine phosphate, annelids lack this and have instead a substance 

 which is similar to creatine phosphate and may be identical with it. How- 

 ever, serological evidence affirms the relationship of echinoderms and 



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