184 PHYSICAL CHEMISTRY 



near that of human blood since they all contain bicarbonates. 

 The PH of the blood of the conch (Strombus gigas) is about 

 7.5, that of the body fluid of the sea urchin (Cassiopea xamach- 

 ana) j.j. Although Mines supposes the PH of the blood of 

 Pecten to be about 6.5 this was determined with indicators and 

 does not seem to hold for the related genus, Pectenella. 



Sea Water 



It is maintained by A. B. Macallum (1904) that the salt com- 

 position of the blood of mammals is the same as that of the sea 

 during the Cambrian period. In passing from the marine in- 

 veretbrates (the osmotic pressure and proportions of whose blood 

 salts is the same as those of the sea) to the mammals, there is 

 a gradual lowering of the osmotic pressure and of the Mg con- 

 tent of the blood. Macallum supposes that the evolution of the 

 sea took the reverse direction and the osmotic pressure and Mg 

 content was low in the Cambrian period. The osmotic pressure 

 is constantly increased owing to the accumulation of salts carried 

 in by rivers, which now carry a greater proportion of Ca and 

 Mg. But the Ca is constantly being precipitated since the sea 

 is about saturated with calcite and the Mg alone is relatively in- 

 creasing. The osmotic pressure of the blood of various animals 

 is given above. The following table gives the relative composi- 

 tion of the ash, Na being taken as 100: 



To 100 parts Na : Ca K Mg 



Sea water 3.94 3.57 11.99 (F. W. Clarke, 1911) 



Medusa (Aurelia) 4.13 5-i8 n.43 (Macallum, 1904) 



Limulus blood 3.83 5-34 11.50 (Gotch and Laws, 1885) 



Sea urchin fluid 5.45 0.24 13.27 (Mourson and Schlagdenhauffen, 1882) 



Sea urchin fluid 12.00 2.20 ( Griffiths, 1892) 



Av'ge of Molluscs 5.43 12.20 3.07 " 



Lobster blood 8.03 7.12 2.88 (Macallum) 



Sipunculus (worm) 6.55 12.70 3.00 (Griffiths) 



Dog's serum 2.52 6.86 .81 



The discrepancies in the proportion of K ( in sea urchins, for 

 instance) may be due partly to the fact that cells containing a 

 larger proportion of K were sometimes included, and partly to 

 faulty analysis. 



Excised organs and cells of marine animals live for experi- 

 mental periods in sea water and M. L. Lewis (1916) has shown 

 that vertebrate tissues may proliferate in diluted sea water. 



