THE LAW OF THE MINIMUM IN THE SEA 197 



usually present in saturation amount ; while carbonic acid, if 

 it is not present in saturation proportion, is yet as abundant 

 in the sea as in the atmosphere. We have to consider, then, the 

 other substances. Compounds of nitrogen are, of course, 

 essential for all organisms ; silica is essential for the forma- 

 tion of the skeletons of the diatoms ; and phosphoric is 

 essential for both diatoms and the other organisms, but is 

 required in larger quantity by the peridinians. One of these 

 essential foodstuffs probably governs the production of living 

 matter in the sea. 



Naturally we think first of the compounds of nitrogen. It 

 is well known that the amount of living substance generated 

 in a water area depends on the amount of these salts (up to 

 a certain limit, of course) which enters the water mass. In the 

 German carp ponds, to be found in almost every village, sewage 

 matter is deliberately led into the water, and if the latter is not 

 absolutely poisoned, the more nitrogenous refuse which enters 

 the pond the more carp flesh is produced. So also with the 

 shellfish beds on our own shores. Nowhere do mussels, for 

 instance, flourish so luxuriantly as on a shore which is grossly 

 polluted with sewage. Both in the case of the carp ponds and 

 the mussels, the organic nitrogenous refuse is broken down by 

 bacteria, and the nitric and nitrous acids and ammonia so 

 formed are utilised as food by the diatoms. The latter are 

 eaten by the smaller invertebrates, which in their turn are 

 taken as food by the other animals. Considering the important 

 part played by the compounds of nitrogen in the metabolism of 

 the sea, Brandt came to the conclusion that it was these food- 

 stuffs that were present in minimum proportion. 



It was, therefore, necessary to ascertain the proportions in 

 which these inorganic nitrogenous compounds were present 

 in the sea. Now the amount is exceedingly small. Although 

 enormous quantities are brought down to the sea by rivers and 

 by electric discharges in the atmosphere, or may be formed 

 from free atmospheric nitrogen by the activity of certain marine 

 bacteria, yet the amount contained in sea-water never exceeds 

 a very small proportion. Because of the minuteness of this 

 proportion, it is exceedingly difficult to estimate exactly the 

 quantity of inorganic nitrogen in the sea. The older deter- 

 minations are inexact because methods of analysis had not been 

 fully developed, and also because no account had been taken 



