THE PROPERTIES OF PEPSIN. 551 



gested in the gastric fluid out of the body, at the expiration of two 

 hours, it was completely dissolved. 



From these and other experiments, it is evident, that, with the ex- 

 ception of the rapidity of the two processes, artificial and natural di- 

 gestion are identical in character. The rapidity of natural, as com- 

 pared with artificial digestion, may probably be explained, partly by 

 the more powerful action of a continuously fresh supply of gastric 

 juice, and partly by the constant removal of the outer pulpified layer 

 of the nutrient mass, by the incessant pressure and motion of this mass 

 bv means of the muscular coats of the stomach. Artificial digestion 

 is much accelerated by occasional agitation. 



The mere quantity of fluid employed in natural digestion must also 

 be very important. It has been shown, from experiments on the gastric 

 juice of the dog, that 20 oz. of fluid are needed for the digestion of 1 

 oz. of albumen. The daily quantity of gastric juice secreted by a 

 man, 140 Ibs. in weight, has been estimated at 14 Ibs. or 11 pints 

 imperial. A pint of saliva, which is a moderate estimate, and 2 pints 

 of water consumed as beverage, would make a total of 14 pints of fluid, 

 employed in the gastric digestion of the daily solid food; beyond the 

 stomach, 2J pints of bile, 1J pint of pancreatic juice, and 1 pint of 

 intestinal juice are added. The total quantity of fluid employed in 

 the digestive process in 24 hours, certainly exceeds the quantity of 

 blood in the body, which, taken at y^th part of the weight of the lat- 

 ter, would be, for a man weighing 140 Ibs., less than 11 Ibs. or 9 pints. 

 It is evident, therefore, that the large quantities of fluid daily secreted 

 for the purposes of digestion, can only be supplied by a circular move- 

 ment of the same aqueous particles, in successive acts of secretion, 

 absorption, re-secretion, and re-absorption. The water which leaves 

 the blood to form part of the digestive juices, re-enters the blood with 

 the absorbed food, once more leaves it in the newly formed digestive 

 juices, and is again re-absorbed, until digestion is complete. This 

 continued irrigation of the food, combined with the activity of the 

 freshly formed gastric juice, must greatly contribute to the rapidity of 

 natural digestion. 



That the pepsin of the gastric juice is the special agent in the gas- 

 tric digestion of albuminoid and gelatinoid substances, is easily shown. 

 By evaporating the natural gastric juice, or the artificial solution of 

 pepsin, to a viscid consistence, and adding strong alcohol to it, the 

 pepsin is precipitated in whitish flocculi, which may then be separated 

 by filtration, from ,the other constituents of the gastric juice, dried at 

 a low temperature, and preserved for months. The dried pepsin thus 

 obtained, forms a firm, grayish mass, or powder ; it is easily soluble 

 in, or miscible with, water, and 1 grain dissolved in so large a quantity 

 as 60,000 grains, i. e. 6J pints of ascidified water, still possesses diges- 

 tive properties. Pepsin, whether dry or dissolved, as in natural or 

 artificial gastric juice, loses its digestive power, if it be subjected to a 

 temperature a little above that of the body, for example, a heat even 

 of 120. It is likewise rendered inactive by strong chemical reagents. 

 It is remarkable that alcohol, which precipitates it, and temporarily 

 suspends its digestive properties, does not destroy them ; for on suffi- 



