164 



THE BIOLOGY OF AN ANIMAL. 



destructive action goes on ; for living matter is decomposed and 

 energy set free in every vital action, and vitality or lii'e is a con- 

 tinuous process. Like the syntheses, the decompositions are 

 probably not single actions, but form a long series. Foster has 

 illustrated the metabolic phenomena by a double flight of steps, 

 at the top of which are always free oxygen and living protoplasm 

 as it were aflame. Foods enter the body, pass up into the living 

 mass of protoplasm, are built into its substance and infected 

 with its properties ; sooner or later they are oxidized, and having 

 set free their energy are cast down by steps on the other side and 

 ultimately excreted. This, however, is only an attempt to picture 

 one of the most wonderful and complicated of all biological 

 phenomena. Of the real process we know absolutely nothing 

 save through its results. 



It is clear that no metabolic system can be recognized apart 

 from any other. Were any structures present especially devoted 

 to the temporary storage of reserve supplies (such as the fatty 

 tissue of many animals) they might be regarded as such a system. 

 Possibly the chloragogue-cells have such a function, but this is a 

 mere conjecture. 



OUTGO OF LUMBEICUS. 



Outgo. Both energy and waste matters leave the cells, and 

 finally leave the body the former as heat, mechanical work done, 



