APPENDIX. 833 



power of exciting the ordinary change produced by the plant itself. 

 The action of micro-organisms in the alimentary canal and elsewhere is 

 also an example of the same nature. 



(2.) Unorganized or soluble ferments are those which are found in 

 secretions of glands, or are produced by chemical changes in animal or 

 vegetable cells in general; when isolated they are colorless, tasteless, 

 amorphous solids soluble in water and glycerin, and precipitated from 

 the aqueous solutions by alcohol and acetate of lead. Chemically many 

 of these are said to contain nitrogen. 



Mode of action. Without going into the theories of how these un- 

 organized ferments act, it will suffice to mention that: 



(1.) Their activity beyond a certain point does not depend upon the 

 actual amount of the ferment present. (2.) That the activity is de- 

 stroyed by high temperature, and various concentrated chemical re- 

 agents, but increased by moderate heat, about 40 0., and by weak solu- 

 tions of either an acid or alkaline fluid. (3.) The ferments themselves 

 appear to undergo no change in their own composition, and waste very 

 slightly during the process. 



The chief classes of unorganized ferments are : 



(1.) Amylolytic, which possess the property of converting starch 

 into glucose. They add a molecule of water, and may be called hydro- 

 lytic. The principal amylolytic ferments are Ptyalin, found in the 

 saliva, and a ferment, probably distinct, in the pancreatic juice, called 

 Amylopsin. These both act in an alkaline medium. Amylolytic fer- 

 ments have been found in the blood and elsewhere. 



(2.) Proteolytic convert proteids into peptones. The nature of their 

 action is probably hydrolytic. The proteolytic ferments of the body 

 are called Pepsin, from the gastric juice acting in an acid medium. 

 Trypsin, from the pancreatic juice acting in alkaline, neutral, or 

 acid media. The Succus entericus is said to contain a third such fer- 

 ment. 



(3.) Inversive, which convert cane sugar or saccharose into grape 

 sugar or glucose. Such a ferment was found by Claude Bernard in the 

 Succus entericus; and probably exists also in the stomach mucus. 



(4.) Ferments which act upon fats. Such a body, called Steapsin, 

 has been found in pancreatic juice. 



(5.) Milk-curdling ferments. It has been long known that rennet, a 

 decoction of the fourth stomach of a calf, in brine, possessed the power 

 of curdling milk. This power does not depend upon the acidity of the 

 gastric juice, since the curdling will take place in a neutral or alkaline 

 medium ; neither does it depend upon the pepsin, as pure pepsin scarcely 

 curdles milk at all, and the rennet which rapidly curdles milk has no 

 proteolytic action. From this and other evidence it is believed that a 

 53 



