CH. X] THE COXDITIONS OF LIFE IX THE SEA 239 



of some marine organisms. Probably most of the plants and 

 animals in the sea excrete this dissolved food-stuff (the mucus 

 of algae and of some fishes, like the hag, or skate, for instance) ; 

 and if we admit that the intensity of metabolism is proportional 

 to the surface of an organism, we may determine roughly what 

 part is played by the various groups of marine organisms. Putter 

 gives some figures for the construction of such estimates \ Assum- 

 ing a composition of the plankton, such as is represented by 

 Lohmann's tables, and regarding the total surface of all planktonic 

 organisms as equal to 1000, he finds that this surface is shared in 

 the following manner : 



Protozoa, 29, 



Metazoa, 148, 

 Bacteria, 400, 

 Protophyta, 423, 



and it would appear from these figures that the protophyta (the 

 diatoms and lower algae) play a more important part in the 

 production of dissolved carbon food -stuffs than any other group of 

 organisms in the sea. It is true that the total effect of the 

 bacteria would appear to be almost as great as that of the proto- 

 phyta, but we shall see that the general effect of the metabolism 

 of the bacteria is to convert all carbon compounds into COo, and 

 all nitrogen compounds into nitric acid, or even free nitrogen. It 

 is only the protophyta among the plankton which can utilise the 

 CO2 and nitric acid compounds, and so we see that upon these 

 rests the greater part of the task of elaborating the organised 

 food-stuff, as well as that of elaborating the dissolved food-stuff 

 of the sea. 



(3) Physical Conditions and the Metabolism of 

 Marine Organisms. 



Thus we are driven to consider that the variations in the 

 amount of food-stuffs — organic or inorganic — in the sea are 

 factors of the first importance in determining the variations in the 

 abundance of animal and vegetable life, from place to place, and 



1 Stoffhaushalt des Meeres, p. 366. 



