100 



THE BIOLOGY OF AN ANIMAL. 



Thus it comes about that there is a more or less steady flow 

 of matter and of energy through the living organism, which is 

 itself a centre of activity, like a whirlpool (p. 2). The chemical 

 phenomena accompanying the flow of matter and energy through 

 the organism are those of nutrition in the widest sense. This 

 term is more often restricted especially to the phenomena accom- 

 panying the income, while those pertaining to the outgo are 

 regarded as belonging to excretion. The intermediate processes, 

 directly connected with the life of protoplasm are put together 

 under the head of metabolism; they include both the construc- 

 tive processes by which protoplasm is built up (anabolism) and 

 the destructive processes by which it is broken down (katabolism} 

 in the liberation of energy. 



Income. It is difficult to determine the exact income of 

 Lumbricus, but it may be set down approximately as follows : 



INCOME OF LUMBRICUS. 



The food-stuffs are converted by the animal into the sub- 

 stance of its own body (protoplasm and all its derivatives), and 

 they must therefore be the ultimate source of energy. It fol- 

 lows that the animal takes in energy only in the potential form 

 (i.e., in the chemical potential between the oxidizable proteids, 

 carbohydrates and fate, and free oxygen). It is true that the 



