APP. l] THE CHEMISTRY OF THE PRIMITIVE OCEAN 301 



this process cannot take place on a very large scale. Salt is also 

 removed from the sea by the evaporation of water, but it comes back 

 again in the rainfall. During all the past history of the earth salt 

 has been dissolved out from the rocks and carried down to the sea in 

 the rivers and so it has gradually been increasing in amount. Thus 

 because of the mutual reactions of the salts themselves ; because of 

 the action of organisms ; and because of the solvent action of the 

 rivers on the rocks of the dry land, the composition of the salts 

 present in the sea has continually been changing : lime and potassium 

 have been decreasing ; sodium has been increasing ; and magnesium 

 has also been increasing. 



In many animals the liquid in the vascular system has much the 

 same composition as sea water ; in fact we may regard it as sea 

 water with some organic matter super-added. In the blood plasma of 

 vertebrate animals the relative proportions of the elements sodium, 

 potassium, and calcium are strikingly similar to the relative proportions 

 of these same elements in the sea water of the present day. But whereas 

 there are 11*99 parts of magnesium in the sea to every 100 parts of 

 sodium there is only 0*8 part of magnesium in the blood plasma to 

 every 100 parts of sodium. If again we analyse the substance of the 

 muscles, &c. of the vertebrate body we find that the relative proportions 

 of the elements sodium, potassium, magnesium and calcium are very 

 different from those present in the blood. 



Now there is probably a relation between the composition of the 

 salts of the blood and tissues of the body and that of the salts of the 

 watery medium in which this has lived. The first organisms probably 

 originated in the sea. They were unicellular organisms, neither plants 

 nor animals, but organisms from which both kingdoms of life have 

 originated. They lived bathed in water in which were dissolved salts 

 in certain proportions, and continually these salts in the sea reacted 

 on the living protoplasm of the organisms living there. Thus the 

 protoplasm acquired modes of metabolism which were due to the 

 reaction to its first environment. The relative proportions of the 

 elements sodium, potassium, magnesium and calcium present in this 

 original protoplasm became similar to the proportions in which those 

 same elements existed in the seas in which life appeared. 



By-and-by organisms became more complex. First of all they 

 became multicellular, and then among other structures they acquired 

 a circulatory system. At first the fluid in this circulatory system 

 was in open communication with the water of the sea : it was in fact 



