ENZYMES 451 



A glance at each of the three equations given will show that 

 the resolution of the glucoside is due to the addition of the 

 elements of water. This is effected by the agency of the enzyme, 

 which in these cases acts as a hydrolysing agent, the chemical 

 compounds which result being the same as those which are 

 commonly produced by dilute acids or alkalis, though of course 

 the modus operandi must be different. A hydrolytic action is in 

 fact brought about by the majority of enzymes, but they differ 

 from inorganic hydrolytic agents in the fact that many of them 

 do not carry the process so far as acids do, and also that enzymic 

 action is very often specific. In this last respect, however, they 

 do not seem to differ essentially from some inorganic catalysts 

 and some of them, emulsin for example, act on a great variety of 

 substances. It would serve no useful purpose in this place to 

 attempt an enumeration of the enzymes mentioned in chemical 

 literature until more has been learnt concerning their composition 

 and the range of their activities. Some of the enzymes which are 

 known to hydrolyse the chief glucosides have already been 

 mentioned in connection with sugar. T\vo or three may be added 

 which are produced in the animal body and are concerned in the 

 processes of digestion. Ptyalin, secreted by the salivary glands, 

 changes cooked starch, as in food, into maltose and dextrin. Then 

 there is trypsin, which is secreted by the pancreas and causes the 

 degradation of proteins and their derivatives giving rise to ammo- 

 acids and the simpler polypeptides. 



Pepsin is contained in the gastric secretion, and papain from 

 the juice of the Carica Papaya or Papaw tree is said to have the 

 property of making meat tender. Pepsin acts best in an acid 

 medium such as the gastric juice which contains 0-2 per cent of 

 hydrochloric acid. Trypsin, on the other hand, works best in 

 an alkaline solution such as the pancreatic juice, which also 

 contains several other enzymes. 



Among the latter must be mentioned lipase, which splits 

 up fatty matters into glycerin and fatty acid. Other en- 

 zymes are secreted by the liver, the kidneys, and the 

 mucous lining of the intestines ; their action generally is 

 hydrolytic. 



But all enzymes are not hydrolytic in their action. A different 

 class is represented by rennet, which is prepared from the lining 

 of the stomach of the calf and is used for curdling milk in the 

 manufacture of cheese. The clotting of blood is brought about 



