144 NUTRITION AND METABOLISM. 



emulsin, amylase, inulase, raffinase, invertase, maltase and lactase. It 

 has been believed for a long time that certain enzymes are regular products 

 of the cell while others are formed only if the substance upon which they 

 act is present. According to Dox's investigations with Penicillium 

 camemberti, there is no evidence that enzymes not normally formed by 

 the organism in demonstrable quantities can be developed by special 

 methods of nutrition. The addition of a particular food compound does 

 not develop an entirely new enzyme, but stimulates the production of the 

 corresponding enzyme which is normally formed, although in small 

 amounts, under all conditions. 



THEORY OF KATABOLISM. 



Regarding katabolism as the sum of all destructive processes of the 

 living cell substance, i.e., of the protoplasm, and considering the cell 

 substance to be decomposed and renewed constantly as long as the cell 

 is performing the normal functions of life, then there must be a reno- 

 vating and a destructive process continuously going on in the proto- 

 plasmic molecules. If the food supply ceases, anabolism ceases with it, 

 but it has been demonstrated that katabolism may continue just the 

 same for some time. By this method, the products of katabolism can 

 be obtained free from the products of food digestion which would 

 obscure the results of experiment with katabolism in normally fed cells. 



It is difficult to determine to what extent katabolism is controlled by 

 endo-enzymes, the so-called autolytic enzymes, which have been mentioned 

 in the above paragraph. In the autolysis of yeast cells, the only well- 

 studied example of microbial autolysis, have been found guanin, adenin, 

 xanthin, hypoxanthin and ammonia. 



THEORY or ANABOLISM. 



INTERACTION OF ANABOLISM AND INTRA-CELLULAR FERMENTATION. 

 All changes discussed in the previous chapters are fermenting pro- 

 cesses in which organic or inorganic compounds are broken up to smaller 

 molecules. These processes are exothermic, i.e., liberating heat or 

 energy in other form. The opposite is true of the anabolic processes 

 which build up complex molecules from simple compounds. These 

 synthetic processes are endothermic, absorbing heat or energy in other 



