CHAPTER VII. 



THE ACTION OF THE ENZYMES FOUND IN THE HUMAN 

 ALIMENTARY TRACT (Continued}. 



6. The Recognition and Quantitative Estimation of the 

 Proteinases. The methods which have been devised for the 

 qualitative recognition of the proteolytic ferments consist for 

 the most part in an exposure of a readily obtainable protein, 

 such as fibrin from blood or white of egg to an extract of the 

 animal or vegetable organ which is being tested, and'finding 

 that this is dissolved. Care must be taken in each case, of 

 course, to pro vide , through the addition of an acid or an alkali 

 to the mixture, an acid, neutral or alkaline reaction depending 

 upon whether acid-, ampho-, or alkali-proteinase (pepsin, 

 papain, or trypsin) is being tested for. Instead of utilizing 

 the disappearance of the protein as evidence of the presence 

 of a proteolytic ferment, the appearance in the reaction mix- 

 ture of certain well-established products of proteolytic activity 

 may also be used. Since acids, for example, can by them- 

 selves bring about the destruction of a protein (but only after 

 a long time at ordinary temperatures) , the time element also 

 plays a role in these qualitative tests, in that the destruction 

 of the protein and the appearance of digestion products must 

 occur within a relatively short time. The actual time con- 

 sumed in bringing about the total solution of a given amount 

 of protein may therefore be used as an index to the amount 

 of ferment present, a larger amount of ferment, under other- 

 wise similar conditions, bringing about a total digestion more 

 rapidly than a smaller one. 



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