ELEMENTARY VITAL PHENOMENA 



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this transformation is, therefore, termed extracellular digestion, and 

 the ingestion of the dissolved food, resorption. 



The change of solid food, such as coagulated proteids, starches and 

 fats, into soluble compounds takes place through the action of 

 definite secretions which the cell-body gives off to the outside. 

 These characteristic secretions are called enzymes or unorganised 

 ferments. The result of their action can be demonstrated outside 



Fig. SQ.—licberhuImia, a. fresh-water rhizopod, from the egg-shaped shell of which branched 

 pseudopodial filaments protrude. 



the organism by allowing an enzyme, e.g., pepsin, which is produced 

 by the cells of the gastric glands, to act upon a bit of coagulated 

 proteid. If, e.g., there be placed in a beaker a solution of pepsin 

 in water to which has been added an equal volume of 0'4 percent, 

 hydrochloric acid, there is obtained an artificial gastric juice. If 

 there be put into this digestive solution a flake of fibrin, i.e., the 

 proteid the spontaneous coagulation of which causes the clotting of 



