FOOD FROM THE SEA. 397 
only artificial fertilizers, since without a supply of the necessary accessory 
organic substances, which act as growth stimulants, the crops are unable 
to make use of the food supply which these artificial fertilizers provide. 
The accessory substances are, however, produced in the minute quantities 
required when a certain proportion of organic manure is also employed. 
But it is time for me to return to the conditions which prevail in the 
sea, although I hope that these digressions into animal nutrition, into the 
causes and cure of certain diseases, and into the treatment of agricultural 
crops have been of some service in throwing light upon the subject in 
hand. What is the source from which the sea obtains the food substances 
necessary for the growth of its plant life—the phosphates, nitrates and 
other inorganic salts and the organic substances of the nature of growth 
stimulants ? There is clearly within the sea itself a continuous cycle 
of these plant foods, and we may to that extent regard the sea as a self- 
contained whole. The plant makes use of the food substances dissolved 
in the water and is then itself eaten by some animal. The animal, either 
directly as the product of its own vital activity or indirectly through 
the action of putrefying bacteria when it dies, returns the plant foods 
to the sea. 
In addition, however, to this food cycle within the sea itself, there 
is another source of supply, the importance of which is probably very 
great, though up to the present it has not been studied with all the 
attention it deserves. This source of supply is the material carried into 
the sea by drainage from the land, the great bulk of it being, of course, 
brought down by the rivers. The subject has recently been discussed 
in an important memoir by Prof. Gran of Christiania. It has long been 
known that life in the sea is specially abundant in the neighbourhood 
of the coasts and in regions which are under the influence of currents 
containing a great admixture of river water. The study of the distribu- 
tion of the plankton, or floating life of the sea, has helped greatly in 
throwing light upon this question. The quantity of plankton in coastal 
waters is very much greater than that found in the open ocean far from 
land. The proportion has been estimated at 50: 1. 
Prof. Gran maintains that this can only be explained by supposing 
that the coastal waters are richer in nutritive or food substances, and 
these nutritive substances must have been supplied by drainage from the 
land. It has been found that the development of the plankton, especially 
of the plant plankton, commences in the inshore or coastal waters and 
from thence spreads out gradually into the ocean. All the ereat fishing 
areas are found in regions where coastal water predominates and where 
the admixture of river water is large. The North Sea, the most productive 
