240 THE BLOOD 



we should have is the analysis of the ocean in prevertebrate days. 

 Not only has the concentration of the salts of the sea undergone 

 change, but alterations have taken place in the proportion of its 

 constituents. Sodium and magnesium have increased in concen- 

 tration and are still increasing. Material lixiviated from river 

 beds, etc., is rich in those salts. 



On the other hand, potassium and calcium have decreased. 

 The formation of soil leads to the abstraction of potassium from 

 the river water. Water evaporated from the ocean contains 

 potassium in not inconsiderable amounts. The rain falling in the 

 region of Caen is responsible for an annual increment to the land 

 of 1 -23 tons of potassium per square mile. Rivers discharge more 

 calcium into the ocean than they do of sodium, magnesium or 

 potassium and yet the concentration of this element appears to be 

 fairly steady. The cause for this lies in the formation of rock-beds 

 of gypsum (CaSO 4 ) and limestone (CaCO 8 ) and in the formation 

 of calcareous skeleta (CaHPO 4 ). From the study of fossil seas 

 and of lakes surrounded by pre-Cambrian formations as well as 

 from other geological considerations it has been decided that the 

 ocean of Cambrian days had a ratio of salts somewhat as follows. 



Na K Ca Mg 



Present day 100 3-6 3-9 11-9 



Cambrian - 100 6-0 3-0 2-0 



Serum - 100 6-6 2-5 0-8 



The following table (from Macallum) shows the evolution of 

 plasma through a series of animals. 



TABLE XXXIII. 

 A. MARINE INVERTEBRATES. 



Na K Ca Mg 



Ocean 100 3-61 3-84 11-99 



Limulus polyphemus 100 5-30 3-83 11-67 



Aurelia flairdula 100 5-18 4-13 11-43 



B. ELASMOBRANCHS, TELEOSTS, MAMMALS. 



Dog-fish - 100 4-61 2-71 2-46 



Pollock 100 4-33 3-10 1-46 



Dog- 100 6-86 2-52 0-81 



Man 100 9-22 3-37 0-76 



The salt content of the plasma is regulated by the kidneys. It 

 is interesting to note that while the blood is Cambrian the tissues 

 are decidedly pre-Cambrian in their salt content, e.g. Muscle. 

 Na=100, K=400, Ca=9-3, Mg=26-4. This may be in part 



