Metabolism; Digestion and Translocation 267 



for the food-stuffs must be made soluble prior to direct 

 absorption by the cells of the body. The parasitic fungus 

 or bacterium may be able to dissolve and to penetrate the 

 cell-wall. Then upon entering the cell the fungus may also 

 gradually " appropriate ' or digest the starch and other 

 foods, absorbing them in this case, as does the higher ani- 

 mal, after digestion. It matters not what the organism 

 may be which digests starch, the method is the same, 

 and it is dependent upon the ability of the organism under 

 the conditions to produce and often to secrete the starch- 

 digesting or the starch-splitting enzymes. The same 

 applies to other solid or indiffusible food substances, so that 

 in general it may be said the use of all such substances 

 as food is a factor of the specific digestive capacity of the 

 organism, however simple or elaborate the digestive 

 apparatus may be. 



After all, the whole phenomenon of nutrition of even the 

 green plant is not essentially different from that of the 

 animal. The green plant makes its carbohydrate foods 

 in certain cells, and it builds up nitrogenous substances out 

 of these and inorganic nitrogen ; but once sugar and nitrog- 

 enous bodies are formed, nutrition follows a course com- 

 parable in the two. 



155. Enzymes and enzyme action. - The enzymes 

 or soluble ferments are doubtless exceedingly numerous, 

 and possibly the digestive enzymes alone are almost as 

 many as the different kinds of reserve foods. So far as 

 the study of these substances has progressed, they seem 

 to be, for the most part, of protein character. At any 

 rate, they are precipitated with proteins, yet certain 

 analyses of the purified products disclose no nitrogen con- 



