230 Dynamic Theory. 



matter. They are usually made into precipitates from their aqueous solutions by aico- 

 hoi, corrosive sublimate, and neutral or basic lead acetate. They can be again made to 

 restore their specific properties by decomposition by sulphurretted hydrogen. They are 

 almost always accompanied by more or less albuminoid matter. " If the sublimate pre- 

 cipitates them from liquids extracted from the organism, it is rather by mechanical ac- 

 tion than by the fact of a chemical combination, " for " soluble ferments, when deprived 

 of albuminous principles, are not precipitated by the sublimate." 



Pure pepsin is extracted from natural or artificial gastric juice. It is 

 obtained from the mucous membrane of the stomach, which is cut up 

 and placed in water containing 5 per cent, of phosphoric acid, at a tem- 

 perature of 95 F. This is precipitated and further treated chemically. 



Pureptyalin, salivary diastase, is obtained from saliva. 



There are various methods employed by chemists for separating these 

 ferments from the vegetable or animal organs which contain them. 

 Von Wittich's method is to cut up the organ containing the ferment 

 into pieces, clear it from blood, if necessary, and leave it under alcohol 

 for twenty-four hours. It is then ' ' dried in the air, pulverized and 

 sifted. The powder is diffused in glycerine and this glycerine solution is 

 precipitated by alcohol. By repeating this operation several times, 

 solution in glycerine and precipitation by alcohol, an active powder, free 

 from albuminoid matter, is obtained. " 



The ferment of plants, which has the power to turn starch into dex- 

 trine and glucose, usually goes by the name of Diastase. An active ar- 

 tificial diastase, or, rather, a preparation of a natural diastase, is made 

 in the following manner : One part of germinated barley is powdered 

 and added to two parts of water. After steeping for an hour the water 

 is squeezed out and to it is added an equal quantity of alcohol at 176 F. 

 It is then filtered, and to the filtered liquid an equal volume of alcohol 

 is again added. Then it is filtered a second time, and the precipitate 

 remaining on the paper filter this time is dried slowly and the paper is 

 ready to be used as a ferment, and can be kept for any length of time. 



This diastase of germinated barley is practically identical with the 

 salivary ferment 'ptyalin. Either of these ferments, and several others, 

 are competent to cause the alteration of starch, sugar, the glycogen 

 matter of animal tissues, &c. , in a few minutes by hydration. The 

 process of the change in starch is shown thus: 



2 ( C 6 H M O.) + H, = C 6 H 10 5 + C 6 H 13 6 

 2 Starch -j- Water= Dextrine -f- Glucose. 



That is, the diastase causes two molecules of starch to take up a mole- 

 cule of water, and then fall apart into a dextrine molecule isomeric with 

 the original starch molecules, and a glucose molecule the same as a 

 starch molecule with the addition of the molecule of water. It is evi- 

 dent that the effect here of the diastase is to rearrange the atoms com- 

 posing these molecules so as to give them new shapes and new polar- 

 ities. In short, the action is purely magnetic, 



