DIGESTION. 187 



Then a small piece of boiled-egg albumin, obtained by cutting thin slices 

 with a cork-cutter, is placed in each test, or a small flake of fibrin is added. 

 Of course care must be taken to add the same-sized slice of egg-albumin or 

 flake of fibrin. Now observe and note exactly the time when each test of the two 

 series begins to digest and when it ends, and it will be found that certain tests 

 of one series make about the same progress as certain tests of the other series. 

 It may be inferred from this that they contain about the same quantity of 

 pepsin. As example, it is found in one series of tests that the digestive 

 rapidity of the tests p , p ^ , p -fa is about the same as the tests p' 4, p |, p' \\ 

 therefore we conclude that the liquid A is about four times as rich in pepsin as 

 the liquid B. 



The rapidity of the pepsin digestion depends on several circum- 

 stances. Thus different acids are unequal in their action; hydro- 

 chloric acid shows a more powerful action than any other, whether 

 an organic or an inorganic acid. The degree of acidity is also of 

 the greatest importance. The most effective degree of acidity is 

 not the same with hydrochloric acid for different albuminous 

 bodies. For fibrin it is 0.8-1 p. m., for myosin, casein, and vege- 

 table albumin about 1 p. m., for hard-boiled-egg albumin, on the 

 contrary, about 2.5 p. m. The rapidity of the digestion increases, 

 at least to a certain point, with the quantity of pepsin present, un- 

 less the pepsin added is contaminated by a large quantity of pro- 

 ducts of digestion, which may prevent its action. The accumulation 

 of products of digestion disturb the digestion. At low temperatures 

 the pepsin acts slowly in warm-blooded animals, and it is nearly 

 without action at a temperature below -f 3 C. With increasing 

 temperature the rapidity of digestion increases, and at about 40 C. 

 it is greatest. The pepsin of cold-blooded animals also acts in the 

 neighborhood of C. If the swelling up of the proteid is pre- 

 vented, as by the addition of neutral salts, such as NaCl in sufficient 

 amounts, or by the addition of bile to the acid liquid, the digestion 

 can be prevented. Foreign bodies of different kinds can produce 

 different actions, in which naturally the variable quantities in which 

 they are added are of the greatest importance. Salicylic acid and 

 carbolic acid hinder the digestion, while arsenious acid promotes it 

 (CHITTENDEN), and hydrocyanic acid is relatively indifferent. 

 Alcohol in large quantities (10$ and above) disturbs the digestion, 

 while small quantities act indifferently. Metallic salts in very small 

 quantities may indeed sometimes accelerate digestion, but otherwise 

 they tend to retard it. The action of metallic salts in different cases 

 can be explained in different ways, but they often seem to form 



