THE MECHANISTIC CONCEPTION 13 



a tube filled with finely divided porous bits of porce- 

 lain, the ammonia is decomposed into its constituent 

 nitrogen and hydrogen even at a much lower tem- 

 perature. 



The essential material basis of living things is 

 called protoplasm. The basis of protoplasm ap- 

 pears to be the material known as protein. Dead 

 protoplasm and protein are not identical, for the 

 cell contents embody many small particles of life- 

 less matter which have a different chemical consti- 

 tution from that of protein; for example, glycogen, 

 fats, fatty acids, and other substances of physiological 

 importance. The cell contents hold also the enzymes 

 which are so active in effecting chemical changes. 

 Although the enzymes probably share the chemical 

 nature of protein, they must be thought of as some- 

 thing quite distinct from the protein masses which 

 make up the greater part of the living or dead proto- 

 plasm. The chemical nature of these constituent 

 masses appears to determine in large degree the 

 character of the protoplasm. 



The proteins vary in chemical constitution within 

 rather wide limits. We know that the protein mole- 

 cule is always of great size as compared with the 

 sugar molecule or the fat molecule, and it is clear that 

 its colloid properties depend on this. It is quite 

 beside the present purpose to discuss the chemical 

 nature of the proteins. The exact grouping of the 

 various kinds of atoms in the most complex pro- 

 teins is still wrapped in darkness despite important 



