RECENT WORK ON MARINE METABOLISM 17 



case is greater than in the case of the larger organisms. Bacteria 

 and protophyta absorb food solutions over their entire surface, 

 and while the mass decreases with the cube of the radius, the 

 surface decreases as the square of the radius. Thus if we take 

 the surface of a single bacterium to be approximately io/^ 2 , we 

 find 1 that 1 kilogramme of dry bacterial matter corresponds to 

 a total surface of about 62,500 square metres, while in man 

 1 kilogramme of dry organic matter corresponds to a surface 

 of only 0"i68 square metre. If we suppose that the general 

 proportions in which the various groups of organisms are present 

 in the plankton are represented by Lohmann's figures (which 

 I have quoted above), it is possible to calculate the aggregate 

 surface of the organisms belonging to each group. Putter gives 

 the following figures : 



Protozoa 291 



Metazoa 1,480 



Bacteria 4,000 



Protophyta 4>22q. 



the total surface being represented by 10,000. 



If then the intensity of the metabolism is proportional to the 

 absorptive surface, it follows from the above figures that about 

 82 per cent, of the total metabolic changes of the plankton is due 

 to those of the protophyta and bacteria. The latter groups of 

 organisms are therefore those which contribute in greatest 

 proportion to the formation of the carbon compounds present Li 

 solution in the sea, which we have reason to believe are utilised 

 by some at least of the lower invertebrata as a source of food. 



If a considerable proportion of the energy of some of these 

 animals is derived from the fermentation of carbon compounds 

 absorbed from solution in sea-water, we may ask what are the 

 precise functions of the organ systems usually termed digestive 

 and respiratory. It is evident that there cannot be a clear and 

 undoubted distinction in function between these two series of 

 structures. If Putter's results should prove to be accurate, it is 

 apparently the case that organs to which a respiratory function 

 is usually ascribed are rather to be regarded as, in general, 

 apparatus for the absorption of dissolved nutritive substances, 

 no less than organs by means of which oxygen is absorbed from 



1 Stojfhaashalt des Meeres, p. 343. 



