PHYSIOLOGICAL CHEMISTRY 387 



to a fine point at both ends, is filled with egg white, the ends closed in the 

 flame, and the tubes then heated so that a column of coagulated albumin is 

 obtained. It is then cut into segments of equal length, and two of these are 

 placed in a test tube which contains the pepsin solution acidified with 0'2% 

 hydrochloric acid. Two similar tubes are placed in another test tube with the 

 other pepsin solution. Both are placed in the incubator for several (10) hours. 

 The length of dissolved protein column is then measured in both cases, and the 

 desired result is obtained by squaring this distance. 



Thus if in one test tube the length were 2, and in the other 3, the strength of 

 the two pepsin solutions has the ratio of 4 to 9. 



This method is only accurate when weak pepsin solutions are used. If more 

 than 4 mm. of protein are digested, the estimation must be repeated with diluted 

 solutions. 



CHAPTER XIV. 

 DIGESTION IN THE INTESTINE. 



IN about half an hour after the food enters the stomach, small portions 

 of it begin to pass through the pyloric sphincter into the duodenum. 

 These have undergone gastric digestion and constitute chyme. This 

 leakage goes on until the stomach has completely emptied itself, the 

 length of time necessary for this (3-10 hours) varying with the quantity 

 and quality of the food, and with the activity of the gastric juice. 



The chyme, as it leaves the stomach, is strongly acid in reaction to 

 all indicators. In the duodenum, it becomes mixed with the secretions 

 of Brunner's glands and with those of the pancreas and liver, which 

 latter are poured into that portion of the intestine by one common duct, 

 and, as it travels on to the jejunum, it also becomes gradually mixed 

 with the intestinal juice, secreted from Lieberkiihn's follicles. These 

 various secretions are alkaline in reaction, in consequence of which the 

 acid of the chyme becomes neutralised, so that the contents of the 

 lower portion of the duodenum and of the upper portion of the jejunum 

 become alkaline in reaction to litmus. Although the acidity of the 

 gastric juice prevents the growths of organisms in it, it does not kill 

 their spores, and these are carried into the intestine along with the 

 chyme. When this latter becomes alkaline, however, the conditions 

 are very favourable for organismal growth, and the spores become 

 transformed into the active organisms which multiply quickly, mean- 

 while receiving their nourishment from the half-digested foodstuffs. In 

 this way the organisms assist the digestive juices in decomposing the 

 foodstuffs. Among the products of this organismal growth are several 

 organic acids, so that the food, before it has gone far along the intestine, 



