86 PHYSIOLOGICAL CHEMISTRY. 



down with it the ptyaline, which may afterward be dissolved in water, 

 precipitated by alcohol from its watery solution, and again dissolved in 

 water. Evaporated to dryness, it is an amorphous nitrogenous sub- 

 stance, and when heated to decomposition, gives off the odor of burnt 

 horn. It appears to be constantly present in human saliva, within a 

 short time after birth, and in that of the gnawing animals, as rabbits 

 and guinea-pigs ; but is not found in that of the dog or horse. 



2. Pepsine. 



Pepsine is the digestive ferment of the gastric juice, by which the 

 albuminous matters of the food are transformed into peptone. It 

 operates only in an acidulated solution, since the influence of an acid is 

 necessary for the preliminary conversion of albuminous matter into 

 syntonine. It requires also a moderately elevated temperature, that 

 of the living body being most favorable. Pepsine is prepared from 

 gastric juice, according to the method of Schmidt, by neutralizing the 

 fresh juice with lime-water, evaporating the filtered liquid to a syrupy 

 consistency, and precipitating with absolute alcohol. The precipitate 

 is redissolved in water, again thrown down by chloride of mercury, 

 and the metallic precipitate decomposed by sulphuretted hydrogen. 

 The filtered fluid contains pepsine in solution. 



It is also obtained from the mucous membrane of the pig's stomach, 

 which is cut into small pieces and digested for several days with 

 glycerine. The glycerine extract is then treated by a large addition of 

 alcohol, and the pepsine, thus precipitated, after being washed with 

 alcohol, is dissolved in water. The solutions obtained by these processes 

 are not supposed to contain the ferment in a perfectly pure state ; but 

 if slightly acidulated, they will exhibit its digestive action on albumin- 

 ous matters at the temperature of the body with considerable energy. 

 Pepsine is a non-diffusible substance, soluble in water and in glycerine. 

 It is not precipitated by the mineral acids. It exists, with essentially 

 the same properties, in the gastric juice and gastric mucous membrane 

 of all animals hitherto examined, and is found in the stomach of the 

 human embryo as early as the beginning of the fourth month. 



3. Pancreatic Ferments. 



In the secretion of the pancreas there are, beside a certain quantity 

 of albuminous matter, no less than three ferments, differing in their 

 mode of action. The most important of these is "pancreatine," or 

 the sugar-producing ferment. It acts in a similar manner to ptyaline, 

 but with greater energy ; being, according to all observers, by far the 

 most prompt and effective of all known substances for the conversion 

 of starch into sugar. It is obtained by digesting the chopped pancreas 

 in lime-water, after which the solution is neutralized by phosphoric 

 acid, producing a precipitate of lime phosphate, by which the ferment 

 is thrown down, entangled with other organic matters. As these im- 

 purities are more firmly fixed by the calcareous salt than the ferment, 



