THE ORIGIN OF LIFE 23 



from view, is united with nitrogen, which has been taken into 

 the plant in the form of nitrites and nitrates, and is finally 

 built into the structure of living matter. The successive steps 

 are not known. Animals cannot live on inorganic salts, but 

 require their nitrogen in the form of proteins, and in this sense 

 are dependent upon plants for continued existence. In all 

 cells the presence of a nucleus or nuclear matter is indispensable 

 to metabolism, playing a predominant part in intracellular 

 oxidation. This has been proved in such cells as liver and 

 kidney cells and in frogs' red corpuscles. 



Cell Growth. The formation of new biogens or growth takes 

 place only when nuclear matter is normally present, and con- 

 tinues until the cell has reached its maximum size. At this 

 stage the extent of surface of the cell determining the quantity 

 of nutriment that can be absorbed is insufficient to supply 

 the mass of living matter. Such a point is always reached, 

 sooner or later, because, as the cell grows, the surface increases 

 only as the square while the volume increases as the cube of 

 their like dimensions. Reproduction now takes place, which 

 has appropriately been termed "discontinuous growth." It is 

 always essentially a separation from the body of an individual 

 of a portion of its own material, which under proper conditions 

 grows into an adult organism. In man growth continues from 

 the segmentation of the ovum to about the age of twenty- 

 five, and is increased by systematic exercise. It consists not 

 only of an enlargement and multiplication of cells, but of a 

 deposition also of intercellular material. It may be divided 

 into an embryonic period, & fetal period, infancy, childhood, youth, 

 maturity, and old age. As growth progresses, the capacity for 

 more growth lessens. 



The Origin of Life. It may be said that as long as the earth 

 was a molten mass of excessively high temperature life could 

 not have existed as we know it today. During the evolution 

 of the earth living matter must have arisen as the result of 

 physical and chemical factors, as all chemical compounds 

 whatsoever have arisen. The formation of living matter was 

 as necessarily the product of evolution as was the formation 

 of water. At first it was probably capable of manifesting 

 vital phenomena indefinitely, which, as a matter of fact, is 

 true of germ cells at the present time. Under proper circum- 



