234 THE HUMAN SPECIES 



varying extent in other Vertebrates, so that muscular contrac- 

 tions are set up not only by mechanical, thermal and electrical 

 stimuli but also by stimulation of the nerves which terminate 

 in the well-known "end-plates" upon the muscles. 



The medulla oblongata,in spite of its insignificant dimensions, 

 is the seat of the most important centres governing the physical 

 or purely animal life of the organism : in it are situated the 

 automatic centres for the respiratory and cardiac movements, 

 the vasomotor centre for the whole body, as well as the centres 

 for deglutition, mastication and vomiting, and for salivary and 

 lachrymal secretion. 



But the chief central organ is the brain. Here we find man's 

 superiority over animals most clearly expressed, for although 

 Thudichum's researches revealed no marked differences in 

 chemical composition, the weight of the brain as a whole is rela- 

 tively very much greater in man. Fremy (quoted by Thudi- 

 chum *) has shown clearly that the human brain is composed of 

 the same substances as are found in the brute brain, although 

 perhaps in different proportions. For instance, in a given 

 quantity of fatty substance the human brain contains more 

 cholesterin than the dog's. 



Succinic acid, C 4 H O 4 , is found in the brain substance of 

 man and animals, and there are a number of isomeres of the 

 cholesterin of the human brain which are met with in animals. 

 Thudichum 2 has demonstrated the presence of sarcolactic acid, 

 a constant constituent of the human brain, in the brain of 

 oxen ; he has also made the following exact analysis of the white 

 and grey matter : 



I. The white matter contains: 



Cephalin, lecithin and cholesterin 



(in ether extract) . . . 11*497 percent. 



Cerebroside and myelin . . .. 6*910 



Lactic acid ..... 0*0456 



Inosit 0-2171 



Alkalies (as carbonate) . . . O'i7i7 



Water 70*230 



Neuroplastin . . . . . 8*630 



1 Thudichum, Die chcmische Konstitution des Gehirns, Tubingen, 1901, p. 24. 



2 Thudichum, loc. cit., pp. 244, 276. 



