FERMENTS AND MISCELLANEOUS PRODUCTS 87 



of hydrogen and of methane respectively. Upwards of 50 per 

 cent, of the total cellulose disappeared, and the composition of 

 the gases evolved was as follows : 



i. n. 



(Per cent, by volume.) 



Carbon dioxide and sul- 

 phuretted hydrogen . . 84-5 55-4 

 Hydrogen (free) .... 0*3 427 

 Nitrogen 27 1-9 



Methane . .... . . , , 12*5 



lOO'O lOO'O 



In both cases it is believed that the changes were due to 

 the action of micro-organisms, but these were not isolated. It 

 is now known that only a small proportion of the cellulose 

 which disappears in the process of digestion goes in this way 

 (p. 32), and that the larger part of the digestible cellulose is 

 converted into sugar and absorbed. 



Only a few of the ferments have been actually isolated. 

 Those which were first discovered were given various empirical 

 names, e.g. pepsin, trypsin, ptyalin, diastase. The great 

 majority are known only through their action. In recent "years 

 there has been an attempt to classify them accordingly. The 

 types to which they are referred are generally named with the 

 termination -ase, from diastase, but many of the older estab- 

 lished names still prevail. An enzyme which hydrolyses malt 

 sugar is called a maltase, one which acts on starch an amylase, 

 on urea a urease, on casein a casease, and so on. The fer- 

 ment diastase belongs to the amylase type, those which resolve 

 cellulose into sugars belong to the cytase type, and those 

 which saponify fats to the lipase type. 



Glucosides. Glucosides may be defined as vegetable pro- 

 ducts which are resolved into hexose sugars, chiefly glucose, 

 and other compounds acids, aldehydes, etc. by the action of 

 enzymes. A few yield pentoses instead of hexoses, and are 

 sometimes classified as a sub-group, under the name of pento- 

 sides. The enzymes which cause the hydrolysis are usually 

 associated with the glucosides in the plants in which they 



