THE MANIFESTATIONS OF LIFE 91 



be met. It is not enough, for example, that an animal 

 build up great quantities of muscular tissue to meet the 

 requirements of locomotion; it is quite as necessary that 

 it provide for neutralizing the loss of energy resulting 

 from these muscles in action. If this were not done the 

 muscles would waste through self-combustion as they were 

 called into action, and would soon disappear. The com- 

 pensation is afforded by the food. An equivalent of the 

 expenditure in the form of assimilable material is sup- 

 plied to the muscle-cells as their food, and the katabolic 

 destruction of the muscle-tissue itself thus prevented. 

 So the energy stored in the food is utilized by the living 

 organism and its own structure saved from destruction. 



So "food" furnishes the means of growth through 

 anabolism or further synthesis, and the source of heat and 

 energy through katabolism or analysis. 



REPRODUCTION. 



As living beings are subject to such wear and tear as 

 results from their activities and to accidents of various 

 kinds, the persistence of life is dependent upon the 

 ability of living substance to reproduce its own kind, 

 Reproduction is, therefore, a fundamental manifestation 

 of life. 



The new individual, no matter how produced, is 

 endowed with potentialities and possibilities the sum of 

 which constitute youth and, therefore, constitutes a new 

 generation qualified to repeat not only the structure, but 

 also the functions of its parent. 



As will be shown in a future chapter, the particular 

 form of reproduction varies with the simplicity or com- 

 plexity of structure, yet all forms of reproduction are 

 ultimately referable to simple phenomena, such as are 

 seen in the most simple forms of life i.e., the cells and 

 consist of cell-division. This is a manifestation the 

 cause of which has long been sought by biologists with 

 little success. It was at one time supposed to depend 



