396 



p. 331): In the depressed parts of the Bay of Naples the bottom 

 consists of a soft mud containing carbonates and decaying 

 material, mostly from plants, and on this bottom the alkalinity 

 rises to 59.6, 58.3 and 58.8 mgrs., whereas in the corresponding 

 surface-waters it is only 52.4, 54.2 and 52.3. The Authors are 

 of opinion that the alkalinity is partly made up by ammonia 

 but they give no satisfactory proof of this contention. 



c. Deposition of silicic acid in the shells of the Diatoms 

 and other organisms must undoubtedly increase the alkalinity, 

 but in the ordinary method of alkalinity-determination all the 

 silicic acid is precipitate*d and variations in its quantity cannot, 

 therefore, show themselves. Besides, they are certainly very 

 small and probably altogether below the range of our analytical 

 powers. 



d. The deposition of lime in the shells of many organisms 

 is certainly the most important organic factor connected with 

 the alkalinity. 



We are accustomed in the case of the higher animals to 

 look upon the food as the sole source of the mineral as well 

 as of the organic components of the animal organism. If this 

 view were correct for marine animals we might discard the 

 accumulation of lime by animals as having no bearing upon 

 the problem of the alkalinity. The investigations of Irvine & 

 WooDHEAD (Proc. Roy. Soc. Edinburgh^ vol. 16, 1890, p. 324 

 — 354) proved however that crabs are able to utilize the calcium- 

 salts of the seawater directly and independently of tbe foodM- 

 Bischof had previously {op. cit. p. 585) expressed the same 

 opinion with regard to the mussels but without proof and appa- 



ll From a physiological point of view a more detailed study of this function 

 ■would be very interesting. Nothing is known about the ways and the 

 mechanism of the absorption. It is extremely Improbable that it takes 

 place through the intestinal tractus , as we have not the slightest 

 evidence that crabs drink the enormous quantities of seawater required 

 (1 gr. of CaCO^ is contained in 10 1. of water), nor, indeed, that the 

 drink at ail, Most probably the absorption takes place through the gills. 



