SEA-FISHERIES LABORATORY. 243 



The physiological interest of the figure so obtained lies 

 in its relationship to the protective power of the medium 

 against the invasion of the organism by alkaline or acidic 

 products of metabolism, or such arising from other causes. 

 Thus, sea-water is, while much more protective than fresh 

 water, much less efficient than the secreted fluids of marine 

 animals, and still less so than the blood-plasma or lymph of 

 terrestrial animals. For, while mammalian serum has a 

 reactivity (within the limits conventionally assigned above) of 

 about N/5, that of sea- water, as given by the above table, is 

 only about N/500. 



To reduce the figures to fractions of " molar " concentra- 

 tions, it is only necessary to remember that the titrations are 

 made with N/100 acid, and expressed in c.c. required for lOO 

 c.c. of sea-water. From this it follows that they must be 

 divided by 10~ 4 . The figure for sea- water in our determinations 

 as shown in the table accordingly varies around 21 N x 10~ 4 

 and 23 N x 10~ 4 . 



The fact that sea-water freshly collected, at least in the 

 region in which our samples have been taken, always gives a 

 pink colour with phenol-phthalein, and so is more alkaline than 

 the body-media of both marine and terrestrial animals, is of 

 some interest. The hydrogen-ion concentration of sea- water 

 is accordingly lower than that of these media, the exponential 

 value for the hydrogen-ion concentration lying between the 

 limits of P„, 10~ 81 and P„, 10~ 84 (see p. 254). 



It is of some interest to discuss the nature of the inorganic 

 salt, or ion, to which this higher alkalinity of the sea-water is 

 due. It is ascribed by Palitzsch 4 and by Bronsted and 

 Wesenberg-Lund 15 to the calcium-ion, but our observations 

 lead us to regard it as due to the accumulation of magnesium- 

 ions in the sea-water. This accumulation arises from the 

 higher relative solubility of the magnesium-ion in solutions 

 of chlorides containing also carbonic acid-ions in excess. The 



