PRESIDENT’S address. 
467 
1. Salinity. 
The following tables show 
the differences in 
chemical com- 
position of typical fresh and salt waters : — 
North Atlantic Water. 
Per thousand parts. 
Thames Water. 1. 
Per thousand parts. 
Calcium Carbonate 
'04 
768 
Magnesium Carbonate ... 
— 
’018 
Calcium Sulphate 
1'40 
’044 
Magnesium Sulphate 
2'2 1 
— 
Potassium Sulphate 
— 
’002 
Sodium Chloride 
2773 
•016 
Potassium Chloride 
'68 
'009 
Magnesium Chloride 
3"44 
— 
Silica 
'015 
‘009 
Organic Matter, etc. 
— 
•035 
35‘52 
’301 
Carbonate 
Sea. 
•3% 
River. 2. 
607% 
Sulphate ... 
10‘8°/o 
9'9% 
Chloride ... 
887% 
5 '2% 
Various 
‘2% 
24"8% 
These tables show how great is the contrast between the two 
kinds of water, not only quantitatively but also qualitatively, to 
which a migrant from the one to the other must accommodate 
itself. 
The external medium is not, however, free to act on the 
internal fluids of the body according to the ordinary laws of 
osmosis ; but it is quite clear that the external membranes of 
the body do exert a considerable selective action on the salts 
in solution, and do not act in the same way as simple dead 
membranes. 1 The different proportions of the salts in the 
serum of different invertebrates living under much the same 
conditions show that the membranes are not equally permeable 
to all salts, and it is remarkable that, even in the case of 
1. From Sollas. The Age of the Earth, 19U5. p. 171. 
2. From Schott, Phyo. Meereskunde, p. 43. 
1. See Dakiu. Int. Kev. Ges. Hydrob. Hydrog. V., 1912, p. 53, and Macallum. 
Proc. Roy. Soc. 82. 1910, p. 602. 
