112 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



of contrast between them. Organized ferments are destroyed by com- 

 pressed oxygen ; soluble ferments are not. Solutions of borax prevent 

 the action of the unformed ferments, but are without influence on the 

 formed ferments. The organized ferments during their action reproduce 

 themselves ; the soluble ferments do not act. All the soluble ferments 

 have a high percentage of ash, sometimes as much as 8 per cent. Under 

 the action of ferments, fermentable bodies yield substances whose nature 

 is dependent on that of the ferment. So that any individual ferment- 

 able substance under the influence of different ferments will split up into 

 different substances. 



The following are the important ferments- found in animal organ- 

 isms: ptyalin, found in the saliva and converting starch into sugar; 

 pepsin, found in the gastric juice and in the presence of a dilute acid 

 converting albuminous bodies into peptones ; the milk-curdling ferment, 

 or rennet, found in the gastric juice and coagulating milk in neutral or 

 acid media; the amylolytic ferment of pancreatic juice, converting starch 

 into sugar ; the proteolytic ferment of pancreatic juice, converting proteids 

 into peptones in an alkaline medium; the fat-ferment of pancreatic juice, 

 splitting up neutral, fatty bodies into fatty acids ; the milk-curdling fer- 

 ment, also said to exist in pancreatic juice ; the inversive ferment, found 

 in intestinal juice*- and converting cane-sugar into inverted sugar; and 

 the liver-ferment, converting glycogen into sugar. The general subject 

 of the nature of the changes produced by these substances will be con- 

 sidered in the next section ; the mode of action of the digestive ferments 

 will be considered under the subject of Digestion. 



B. NON-NITROGENOUS ORGANIC CELL-CONSTITUENTS. 



I. Carbo-hydrates. — The carbo-hydrate tissue-constituents are 

 composed of carbon, hydrogen, and oxygen, the latter two in the propor- 

 tion to form water. Although occasionally present as constituents of 

 animal cells, they are almost exclusively produced by the vegetable king- 

 dom, and present many interesting examples of isomerism. They may 

 be divided into the three following groups : — . 



(a) Starches (C 6 H 10 O 5 ). 



(6) Grape-Sugar Group (C 6 H 12 O e ). 



(e) Cane-Sugar Group (C m H ss O m ). 



The members of the first group may, through the action of dilute 

 acids or the diastatie ferments, be transformed in great part into the 

 second group. The latter undergoes alcoholic fermentation when in 

 contact with malt. 



(a) The Amyloses, or Starch Group ?i(C 6 H 10 O 6 ).— This group 

 includes starch, dextrin, glycogen, cellulose, granulose, and imilin. 



