552 SPECIAL PHYSIOLOGY. 



cient dilution with water, it is redissolved, and again becomes active. 

 The energy of pepsin, like that of salivin, in converting starch into 

 sugar, is catalytic. The action of contact or pressure, exhibited by 

 both these substances, differs from that of the yeast ferment in the 

 alcoholic fermentations, in not causing the evolution of any gas, and 

 in not being continually reproduced. It is said, however, by some, 

 that the pepsin does not itself undergo waste in the process of digestion ; 

 but the power of a given quantity is certainly limited. Salivin and 

 pepsin have been regarded as albuminoid bodies in a state of change, 

 and capable of inducing changes in other albuminoids with which they 

 are brought into contact. Putrescent albuminoid substances, as is 

 well known, can propagate putrescent changes to fresh albuminoid 

 substances, and can also convert starch into sugar, or one form of sugar 

 into another. But pepsin is not a putrescent body, nor is the peptone, 

 produced by its action on albumen, putrefied. On the contrary, it has 

 been shown by experiment, that fresh gastric juice, applied to putrid 

 meat, first arrests putrefaction, removing its signs, and then digests 

 the meat. Like fermentation and putrefaction, however, digestion is 

 retarded by low temperatures, altogether arrested at a temperature of 

 34, and is stopped by high temperatures, by the action of absolute 

 alcohol, strong acids, alkalies, and metallic salts. 



The action of the gastric juice varies, according to the character of 

 the food, its state of comminution or subdivision, and its condition of 

 dryness or moisture. In order to determine the time required for the 

 solution of different nutritive substances, these have been introduced, 

 inclosed in perforated tubes of metal or glass, into the stomachs of 

 animals, and then have been withdrawn ; or, animals have been fed 

 with such substances, and afterwards killed at certain intervals. The 

 most important observations, however, are those made by Dr. Beau- 

 mont in the human subject. In the stomach of Alexis St. Martin, a 

 mixed meal of animal and vegetable food was nearly all dissolved into 

 a pulp, within an hour; and the stomach was completely emptied in 2J 

 hours. A breakfast, consisting of three hard boiled eggs, some pan- 

 cakes with coffee, being taken at 8 o'clock, the stomach was empty at 

 10.15. Two roasted eggs and three apples, eaten at 11 o'clock on the 

 same day, had disappeared at 12.15. Roast pig and vegetables, after- 

 wards eaten at 2 P.M., were half dissolved at 3, and had disappeared 

 at 4.30. It was further observed, that a meal, consisting of boiled 

 dried cod-fish, potatoes, parsnips, bread and butter, eaten at 3 o'clock, 

 was about half digested at 3.30, the bread and parsnips having disap- 

 peared, the fish being separated into threads, and the potatoes being 

 least altered ; at 4 o'clock, very few pieces of the fibre of the fish were 

 found, but some of the potato was still perceptible; at 4.30 all was 

 completely pulpified ; and at 5 o'clock, the stomach was empty. Again 

 it was found that rice and tripe were digested in 1 hour ; that eggs, 

 salmon, trout, apples, and venison, took 1J hour; tapioca, barley, milk, 

 liver, and fish, 2 hours; turkey, lamb, potatoes, pork, 2J hours; beef, 

 mutton and poultry, from 3 to 3J hours; and veal a little longer. The 



