482 LECTURE XX. 



encountered them in tracing the course of the organic nutrient materials 

 in their passage from the alimentary canal to the tissues. It remains 

 only to classify them in a comprehensive manner. We may divide the 

 ferments into two main groups: (1) the hydrolytic, and (2) the oxidizing 

 ferments. The former may be further subdivided according to the material 

 to be attacked, e.g. (a) ferments which effect the decomposition of the 

 carbohydrates, (b) the proteolytic ferments which act upon the proteins, 

 and (c) the fat-splitting ferments. The diastatic ferments belong to class 

 (a). They hydrolyze starch into dextrins and maltose. The decompo- 

 sition of maltose into two molecules of dextrose is effected by maltase. 

 Invertase splits cane-sugar into one molecule of dextrose (d-glucose) and 

 one of laevulose (d-f ructose) . To this group belong a series of ferments 

 whose characteristics have been less carefully studied, such as cellulase, 

 which is supposed to decompose cellulose; inulinase, which acts on inu- 

 lin; seminase, which disintegrates mannans and galactans; and finally 

 pectinase, which is responsible for the hydrolysis of pectin. We might 

 also mention trehalase, melibiase, and Icwtase, which decompose the sugars 

 corresponding to their names. Special ferments are also known which 

 hydrolyze the glucosides, as well as a urease that changes urea into 

 ammonium carbonate. To class (6), the proteolytic ferments, belong 

 pepsin, trypsin, rennin, the fibrin-ferment, and pectase which hydrolyzes 

 pectin substances. The fat-splitting ferments form a class by them- 

 selves. Then there is lactic-acid ferment, which produces lactic acid 

 from sugar. It attacks all of the simple hexoses, and some pentoses, but 

 not cane-sugar or milk-sugar. It produces chiefly the a-hydroxypropionic 

 acid, CH 3 . CHOH . COOH. It is still a question whether the lactic 

 acid fermentation is to be looked upon as an independent process. 



The second main group comprises the oxidizing ferments which have 

 already been discussed. They obtain their oxygen either from the air or 

 from decomposed hydrogen peroxide. To the former class belong the 

 true oxidases, acting as oxygen carriers to the cells and tissues. Atmos- 

 pheric oxygen is also utilized during the acetic acid fermentation of 

 ethyl alcohol. 



Alcoholic fermentation is quite a special process. It is a complicated 

 affair, and the ferments producing it cannot, at present, be assigned to 

 any of the above groups. As we have already shown, 1 alcoholic fermenta- 

 tion plays a part of which we cannot at present estimate the extent in 

 plant and animal tissues, and inasmuch as an inspection of this process 

 will give us some idea of the progress of a fermentation reaction, we will 

 briefly discuss it. The reaction takes place according to the following 

 general equation: 



C 6 H 12 6 = 2 C 2 H 5 OH + 2 CO 2 . 



1 Cf. Lecture IV, p. 74. 



