THE CELL AND ITS ACTIVITIES 19 



be the leading one. During the period of growth 

 anabolic tendencies are uppermost ; females, on the 

 whole, are more anabolic than males, since they save 

 not only for themselves, but for a future generation. 

 Male insects, in particular, may be short-lived and 

 intensely active when they become adult rapidly 

 spending, as it were, the accumulations of their earlier 

 life. 



8. In accordance with these general principles, the Food 

 cell takes in and gives out substances solid, liquid, 



or gaseous. It is nourished by food. This food may 

 be of various kinds, but it is not identical with the 

 living protoplasm of the cell. Even when one animal 

 eats another alive, the victim is reduced to non-living 

 material of a relatively low grade before it can be 

 utilized as food. This food material is not put together 

 to form new cells ; it is built into the existing cells, 

 bit by bit, as infinitesimal particles. So only may the 

 cells grow, and the body grow by the increase of ma- 

 terial in cells which consequently divide to form new 

 cells. The process of thus taking in material and 

 making it part of the living stuff is called assimilation, 

 or "making like." Thus it is that the cells already 

 present at any time control the future growth ; with- 

 out their aid, nothing avails. 



9. Material is given out by the cells, as a result of Diverse 

 their metabolism. Carbon dioxid (CO 2 ), a stable or C gJJg 

 static compound of carbon and oxygen, is the result 



of a kind of combustion, in the course of which energy 

 is "liberated"; that is to say, appears in the form of 

 work or heat. This matter will be dealt with later in 

 connection with respiration. This carbon dioxid is a 

 gas, but there are also fluid and solid products of cells. 

 The bone cell entombs itself in a limy deposit. The 



