110 PHYSIOLOGY OF ALIMENTATION. 



trose or the removal of maltose from a reaction mixture con- 

 taining the two sugars in chemical equilibrium would there- 

 fore be followed by a synthesis of maltose, while the introduc- 

 tion of maltose or the removal of dextrose would be followed 

 by an analysis of the disaccharide if other external conditions 

 remained the same. 



3. Caseinase (rennin, rennet) is the name given to a ferment 

 found in many animal and vegetable cells and their secretions, 

 which has the power of changing caseinogen into casein 

 that is, the power of curdling milk. In the human being the 

 ferment is found in the secretions of the stomach from birth. 

 Milk-curdling ferment is found also in the pancreatic juice, 

 and though it differs somewhat from the caseinase found in 

 the stomach in its resistance to heat and chemical agents, it 

 is probably the same substance and may well be called by the 

 same name. 



A number of authors have pointed out the fact that case- 

 inase always coexists with a proteolytic ferment. In the case 

 of the human being (and certain other animals) caseinase 

 accompanies the acid-proteinase (pepsin) of the stomach and 

 the alkali-proteinase (trypsin) of the pancreas. Caseinase, 

 moreover, is found in largest amount in those portions of the 

 stomach where the most acid -pre teinase is found, namely, the 

 fundus. The constant association of the two enzymes has 

 given rise to the idea that they probably represent a giant 

 molecule, the different portions of which have different fer- 

 mentative functions and are differently affected by external 

 conditions. It has been shown by HERZOG, for example, that 

 antiproteinase (antipepsin) added to the combined ferments 

 inhibits only the proteolytic action, while the milk-curdling 

 action goes on undisturbedly. Digestion with weak acids will 

 at proper temperature quickly destroy the caseinase con- 

 stituent of the entire molecule, and by mechanical precipita- 

 tion HAMMARSTEN has succeeded in obtaining a caseinase solu- 

 tion free from any proteolytic activity. 



Preparations of caseinase are obtained by extracting, with 



