THE SCOPE OF BIOLOGY 5 



a type of growth spoken of as intussusception (Lat. intus 

 within + suscipere = to take up). With this understanding of 

 growth we can state that nothing grows except living things. 

 As the result of their activities, living things are constantly 

 wasting away; but by growth they repair and keep pace with 

 their own wastes and remain in a practically constant condi- 

 tion, in spite of their ceaseless activity. In time, however, 

 the disintegrating tendencies surpass the powers of repair, and 

 the organism dies of old age. 



4. Reproduction. The power of reproduction is found only 

 in the realm of the animate world, for only a living organism 

 can produce another like itself. Inanimate things cannot 

 reproduce their kind. 



As a result of this power of reproduction, held in common 

 by all things possessed of life, there is a constant replacement 

 of the individual, a constant wearing out and death, a constant 

 rebirth and growth, the new organism ever replacing the old as 

 it disintegrates and disappears. There is a constant tendency 

 to undergo cyclical changes present in all manifestations of life. 



5. Consciousness. Consciousness is characteristic of some 

 living bodies, but is probably not universal among them, for it 

 is practically certain that life occurs in many places without 

 consciousness, although some theorists have endeavored to 

 argue that all forms of life, even the plants, have a very dim 

 form of consciousness. This is very doubtful, and we cannot 

 regard consciousness as universally characteristic of life. 

 Wherever consciousness is found, however, it indicates the 

 presence of life, and thus may be deemed one of the most 

 important signs of life. 



CHEMICAL COMPOSITION OF LIVING TISSUES 



Chemical Elements in Living Tissues. Although there is a 

 large variety of chemical compounds found in living animals and 

 plants, nevertheless there is a certain uniformity among them. 

 All animals and plants are made up primarily of a small num- 



