144 PHYSIOLOGICAL CHEMISTRY. 



casional shaking for 24-72 hours. 1 Enzymes similar to erepsin 

 occur in various tissues of the organism. 



The three invertases sucrase, maltase' and lactase are also im- 

 portant enzymes of the intestinal mucosa. The sucrase acts upon 

 sucrose and inverts it with the formation of invert sugar (dextrose 

 and laevulose). Some investigators claim that sucrase is also 

 present in saliva and gastric juice. It probably does not exist nor- 

 mally in either of these digestive juices, however, and if found 

 owes its presence to the excretory processes of certain bacteria. 

 Sucrases may also be obtained from several vegetable sources. 

 For investigational purposes it is ordinarily obtained from yeast 

 (see p. n). In exhibits its greatest activity in the presence of a 

 slight acidity but if the acidity be increased to any extent the reac- 

 tion is inhibited. 



Lactase is an enzyme which inverts lactose with the consequent 

 formation of dextrose and galactose. Its action is entirely analo- 

 gous, in type, to that of sucrase. It has apparently been proven 

 that lactase occurs in the intestinal mucosa of the young of all 

 animals which suckle their offspring. 2 It may also occur in the 

 intestinal mucosa of certain adult animals if such animals be main- 

 tained upon a ration containing more or less lactose. Fischer and 

 Armstrong have demonstrated the reversible action 3 of lactase. 



For discussions of maltase and enter okinase see pages 55 and 

 141 respectively. 



PREPARATION OF AN ARTIFICIAL PANCREATIC 



JUICE. 4 



After removing the fat from the pancreas of a pig or sheep, 

 finely divide the organ by means of scissors and grind it in a mortar. 

 If convenient, the use of an ordinary meat chopper is a very satis- 

 factory means of preparing the pancreas. 



When finely divided as above the pancreas should be placed in a 

 500 c.c. flask, about 150 c.c. of 30 per cent alcohol added and the 

 flask and contents shaken frequently for twenty-four hours. 

 (What is the reaction of this alcoholic extract at the end of this 

 period, and why?) Strain the alcoholic extract through cheese 



1 See p. 13. 



2 Mendel and Mitchell: American Journal of Physiology, 1907, XX, p. 81. 



3 See p. 6. 



4 For other methods of preparation see Karl Mays : Zeitschrift filr phys- 

 iologische Chcmie, 1903, XXXVIII, p. 428. 



