48 



HUMAN BIOLOGY 



on earth from fifty million to one hundred and fifty milHon 

 years had passed before the cell nucleus had evolved and 

 become fixed as an organ. 



There is not much uncertainty, if any, about the origin 

 of the inorganic composition of the blood plasma and 

 lymph of vertebrates. The first circulatory fluid of inverte- 

 brates was the sea water in which they lived, as it is today 

 in a number of forms. It passed through openings into the 

 channels of the primitive vascular system, and when in 

 higher forms, as they developed, this system became closed 

 off from the exterior, the fluid it contained was still sea 

 water of that early period, as still are, in the composition 

 and concentration of their salts, the blood plasma and lymph 

 of vertebrates of today. This is seen on comparison of the 

 ratios of the elements in it with those in the sea water of 

 today: 



The concentration of the salts in the plasma of mammals 

 is about 0.89 per cent (0.87 to 0.91 per cent), while in the 

 ocean they amount to 3.5 per cent, that is, really four times 

 as much as it must have been when the first vertebrate, 

 the eovertebrate, appeared. The Amphibia and Reptilia 

 began in the Carboniferous Period and the Mammalia 

 began in the Triassic. As these were chiefly land forms they 

 transmitted to their descendants the inorganic composition 

 of their blood plasma derived from their ancestors of the 

 Cambrian or Ordovician. 



The concentration of the salts in the ocean has ever 

 been increasing steadily, and with this increase there has 

 been an alteration in the ratios of the elements therein to 

 each other. The potassium and calcium have increased, but 

 not proportionately, for the former has been, and is, con- 

 stantly eliminated to form the mineral glauconite, scattered 

 over the floor of the ocean, and in the sedimentary deposits 

 of various periods, while of the calcium always added, a 



