260 FOUNDERS OF OCEANOGRAPHY 



a minimum the nitrogen concentration in tropical waters, 

 may account for the relative scarcity of the phyto-plankton, 

 and consequently of the zoo-plankton, that has been 

 observed. It has been said that the colder seas, with more 

 plankton, contain more nitrogen (three parts in a million 

 parts of water) than the warmer waters, with less plankton, 

 which have only one part per million. But Gran, Nathan- 

 sohn, Murray, Hjort and others have shown that such 

 denitrifying bacteria are rare or absent in the open sea, that 

 their action must be negligible, and that Brandt's hypothesis 

 is untenable. It seems clear, moreover, that the plankton 

 does not vary directly with the temperature of the water. 

 Furthermore, Nathansohn has shown the influence of the 

 vertical circulation in the water upon the nourishment of 

 the phyto-plankton — by rising currents bringing up necessary 

 nutrient materials, and especially carbon dioxide from the 

 bottom layers ; and also possibly by conveying the products 

 of the drainage of tropical lands to more polar seas so as to 

 maintain the more abundant life in the colder water. 

 Putter's view is that the increased metabolism in the warmer 

 water causes all the available food materials to be rapidly 

 used up, and so puts a check to the reproduction of the 

 plankton. 



According to van t'Hoff's law in Chemistry, the rate at 

 which a reaction takes place is increased by raising the 

 temperature, and this probably holds good for all bio- 

 chemical phenomena, and therefore for the metabolism of 

 animals and plants in the sea. This has been verified 

 experimentally in some cases by Jacques Loeb. The con- 

 trast between the zoo-plankton of Arctic and Antarctic 

 zones, consisting mainly of large numbers of small Crus- 

 taceans belonging to comparatively few species, and that of 

 tropical waters, containing a great many more species, 

 generally of smaller size and fewer in number of individuals, 

 is to be accounted for, according to Sir John Murray and 

 others, by the rate of metabolism in the organisms. The 



