238 THE CONDITIONS OF LIFE IN THE SEA [PART III 



of water. After the spring months the amount of the silica again 

 begins to increase, and attains a secondary maximum in the 

 autumn, and immediately after this there is a secondary maximum 

 in the amount of the diatoms. 



So also with the peridinians, though the relation between the 

 abundance of these organisms and that of the various food-salts, 

 has not been studied in a very satisfactory manner. Still Raben's 

 estimations seem to shew that there may be a relation betAveen 

 the peridinians and the phosphoric acid in the sea, and that 

 the maximum period of reproduction of these protozoa in the 

 autumn may be connected with the maximum period of abund- 

 ance of phosphoric acid which also occurs in the autumn. But 

 much work remains to be done before this can satisfactorily be 

 established. 



Thus theie is a fair amount of evidence to shew that the 

 variations in the abundance of the organisms of the plankton are 

 to be attributed to variations in the abundance of the food-stuffs 

 which stand at their disposal ; and this is indeed what we should 

 expect. Even in a slowly multiplying human society we can trace 

 a connection between the fluctuations in the labour market (which 

 are indicative of changes in the general prosperity of the artisan 

 class), and minor fluctuations in the marriage and birth rates. 

 An increase in the demand for labour is followed by an increase 

 in the number of marriages^ But in the sea the lower organisms 

 multiply very rapidly, and so an increase in the amount of food 

 is soon followed by the multiplication of those creatures w^hich 

 utilise . this food. But the greater amount of mouths to be filled 

 soon reduces the available amount of food, and a drop in the rate 

 of multiplication very soon follows. 



It does not appear to me that the existence of saprozoic and 

 saprophytic modes of nutrition among marine organisms invalidates 

 the conclusion that the abundance of life in the sea depends on 

 the abundance of those food-stuffs which are present in minimal 

 quantity. If there is an immense store of food in the sea, in the 

 form of dissolved carbon compounds other than carbonic acid, it 

 is still the case that these substances (which may be compared 

 with the humus of the soils) are produced by the metabolism 



^ See Elements of Statistics, A. L. Bowley, Loudon, 1902. 



