397 



rently without perceiving the physiological difficulty. He calculated 

 that the amount of carbonate of lime present in the shells of a single 

 oyster corresponds to 172 — 293 kgrs. of seawater or 28000 to 

 76000 times the weight of the animal. There can now be no doubt 

 that Bischof was right in supposing that such large quantities 

 of lime must be absorbed directly from the water circulating 

 within the mantle, and if луе venture to extend the results 

 obtained by Irvine & Woodhead to all the marine lime-producing 

 organisms M we must conclude that their combined action will 

 have some diminishing influence upon the alkalinity of the ocean. 

 According to Murray [Challenger narrative^ vol. 1, p. 980) 

 as much as 16 tons of CaCO.^ may be present in the shells 

 of organisms in a mass of ocean-water possessing an area of 

 1 sq. mile and 100 fathoms deep from the surface. This 

 seemingly large figure corresponds however to only 0.025 mgrs, 

 of lime per 1. or to the alkalinity of O.oi mgrs. About twenty 

 times must the formation of this quantity be reiterated in the 

 same mass of water and the shells removed by sinking, before 

 the result is detectable by the alkalinity-method. 



3. Evaporation concentrates the surface-waters and aug- 

 ments the alkalinity which remains, however, during this process 

 strictly proportional to the salinity. 



4. Dilution with freshwater is easily detected and quantita- 

 tively determined by its influence on the saHnity or the percentage 

 of chlorine, but its influence on the alkalinity is more com- 

 plicated. 



a. Freshwater produced by melting ice. It is probable, 

 though I do not know that it has been experimentally verified, 

 that ice formed in the sea is much less alkaline than the 



') It must be admitted of course tliat some lime is in all probability 

 derived from the food, and some organisms are perhaps reduced, more 

 or less, to this source of lime. Wesenberg-Lund maintains [Medd. 

 Dansk Geol. Foren. Nr. 7, 1901) — on rather inadequate grounds — 

 that this is the case with all Gasteropods. 



