in DIGESTION IN THE MOUTH AND STOMACH 171 



whether dissolved, or coagulated and insoluble, are transformed 

 into soluble and readily diffusible substances, called by Lehmann 

 peptones. 



We cannot enter upon the exposition and critical analysis of 

 the various opinions successively put forward as to the nature of 

 peptonisation, and must confine ourselves to enumerating the 

 more positive of the experimental data : 



(a) No protein is (caeteris paribus) more readily digested by 

 the gastric juice than fresh fibrin extracted from the blood, and it 

 was therefore chosen by Briicke as the common measure of com- 

 parison between the digestive power of artificial and of natural 

 gastric juice. Next to fresh fibrin, casein is the most rapidly 

 digested ; next, boiled fibrin ; next again, coagulated egg-white. 

 As a rule it may be said that proteins of animal origin are digested 

 more easily than those of vegetable origin. 



(&) Apart from the disparate nature of the proteins, the rapidity 

 of their digestion and solution depends on the degree of tem- 

 perature, the amount of pepsin, and the amount of acid which 

 the digestive juice contains. The optimum degree of temperature 

 is approximately that which is normal to the body. Below 35 C. 

 digestion is retarded, at C. it is entirely suspended. The 

 amount of pepsin required to obtain a marked digestive action is 

 very small, certainly less than 0'067 per cent. According, how- 

 ever, to Schiitz (infra), when the amount of the enzyme is 

 increased, the quantity of acid and protein to be digested remain- 

 ing constant, then on estimating at regular intervals the amount 



o o o 



of protein dissolved, it is found that the rapidity of digestion 

 increases in proportion with the square root of the concentration of 

 the pepsin. If the amount of acid is varied, while the amount of 

 pepsin and of protein remains constant, it is found that excess 

 or deficit of acid retards or suspends digestion, while the 

 optimum amount of acid varies with the nature of the protein to 

 be digested (e.g. for fibrin the optimum is 0'9 per cent of hydro- 

 chloric acid, for coagulated egg-white on the contrary it is l - 2-l - 6 

 per cent). 



An admirable method for the quantitative determination of the proteo- 

 lytic power of the gastric juice and therefore of its pepsin content is ha>ed 

 upon the Schiitz law. This method, as first described by Mett (1894), can 

 also lie used fur testing the digestive power of trypsin, and is as follows : 



Fresh, liquid egg-white is aspirated into a glass tubr with a lumen of 

 1-2 nun., which is plunged for one minute into water heated to 95 C. The 

 tube of coagulated albumin is then slowly cooked, and cut with a tile into 

 small pieces, taking care that the cylinders of egg-white fit exactly the 

 end of each tube, so that no empty space isleft in the latter. The glass tubes 

 are then plunged into 1-2 c.c. of the digestive fluid and left for 10 hours at a 

 temperature of 37-40 J C. The albumin is evenly dissolved during this time 

 lii'Ui the outer end of the tube inwards. At the end of the time the length 

 of the. little tube and of the column of egg-white left undissolved are 

 measured. The difference gives the length of the cylinder of digested egg- 



