494 LIFE IN THE OCEAN. 



influence of external conditions, will not suffice; it is requisite besides 

 to extend the conquests of science to the things of the sea, and to 

 apply to the special beings that live therein the fundamental principles 

 and approved methods of animal and vegeta])le physiology which have 

 been deduced from the terrestrial world. We maj'^ sum up all these 

 researches as the science of the totality of exchanges of matter in the 

 ocean, and 1 will indicate here the most important of the investiga- 

 tions and the facts which must form the basis for the solution of the 

 problem. 1 shall dwell especially on those points which present a 

 general interest. 



Matter in nature follows a cycle which may be briefly described as 

 follow^s: The constituents of the air. the water, and the earth are trans- 

 formed by vegetiition into living substances; animals directlv or indi- 

 rectly absorbed the organic substances produced by plants, and finally 

 animals and plants after their death are decomposed by the influence 

 of certain bacteria into inorganic sulistances which, taken up again by 

 plants, are transformed anew into organic matter, and so on. 



It is the corpuscles of chloi'ophyll which (Miable plants in the pres- 

 ence of light to form organic substances from carbonic acid, water, and 

 certain salts. It is on the other hand from the vegetable kingdom 

 that all animals have to derive all the organic matter that is to form 

 their bodies and support their life. It follows that in any large terri- 

 tory the quantity of organisms is regulated by the condition that the 

 total mass of consuming animals has to remain inferior to the mass of 

 producing plants. Unless this condition is fulfilled, a part of the ani- 

 mals must sutter hunger or even perish. For the same reason among 

 terrestrial animals the mass of carnivores must be inferior to that of 

 the herbivores. 



But the plants can not perform the important function that devolves 

 upon them — the formation of organic substances — unless the}" find the 

 inorganic matter which is indispensable to them, and which presents 

 itself under the form of combinations of at least eleven or twelve known 

 chemical elements. If but a single one of these nutritive substances 

 is wanting the plant will not grow. In case of insufficiency the plant 

 just manages to exist; wdiile if there is superabundance it grows 

 rank. The growth of plants depends upon the quantity of nutritive 

 matter the}' get, and there is an indispensable minimum for each species. 

 The discovery of this fundamental law is due to Liebig, the founder 

 of agricultural chemistry. 



Generally speaking, the production of vegetable substances depends 

 upon the quantity of nitrogenous inorganic compounds in the soil. 

 We know that manures rich in nitrogen extraordinarily augment the 

 vegetable production, although this can not surpass a certain maxi- 

 mum characteristic of each kind of plant, beyond which all increase 

 of nitrogenous matter acts as a poison. 



