APP. l] THE CHEMISTRY OF THE PRIMITIVE OCEAN 303 



the necessity of this element is indicated in some queer facts of 

 mammalian physiology : in the necessity for the presence of a calcium 

 salt in the coagulation of the blood, for instance. The ancestral 

 vertebrate organisms became adjusted to an environment in which lime 

 was a prominent factor, and heredity has stamped this adjustment on 

 the metabolism of the living vertebrates, which secrete their skeletons 

 in the manner that their ancestors in Silurian times did. Usually 

 one thinks only of morphological and psychical characters as being- 

 hereditary, but after all these are only transitory features of the 

 relatively unalterable "protoplasmic basis of life." 



So just because the primitive unicellular organisms lived in a sea 

 in which the salts in solution were present in certain proportions their 

 living substance came to contain these salts in the same relative 

 proportions as did the sea water. Heredity fixed this proportion 

 of the elements sodium, potassium, calcium and magnesium in the 

 protoplasm of the primitive organisms, and we see it to-day in the 

 composition of the protoplasm of living animals. Then multicellular 

 animals possessing a circulatory system containing a liquid which had 

 the same relative composition as that of the surrounding medium were 

 developed. By-and by the circulatory system, originally in connection 

 with the sea, became closed off from the latter, and when this happened 

 the inorganic constituents of the blood were similar, in respect of 

 their relative proportions, to those of the sea of the time. But even 

 after the circulation had been shut off from the sea, and long after the 

 composition of the latter had changed, heredity maintained the 

 composition of the blood. The proportions of the salts of sodium, 

 potassium, calcium and magnesium in the blood of living vertebrate 

 animals are therefore those in which these salts were contained in the 

 sea in very remote geological times. 



