PHYSIOLOGICAL CHEMISTRY 375 



of pancreatic juice, of liver extract, of blood serum or of malt diastase may be 

 measured in the same way, but different amounts of the ferment solution must be 

 employed. 1 (Thus for blood serum and liver extract it is unnecessary to dilute 



40 

 the solution. ) The results may be expressed by the formula 2 D^rp , in which the 



temperature and the length of time of incubation are shown. In the above 



example D^ = l. 



To study the influence of weak acids, etc., on the action of ptyalin the above 

 method is very satisfactory, i.e. by adding some acid solution to one or more of 

 the tubes. In some cases it is desirable to prolong the incubation for twenty-four 

 hours, in which case some chloroform or toluol or thymol should be added to 

 retard the development of micro-organisms. If very close results are desired, the 

 observation should be performed with amounts of ferment solution which vary 

 from one another by smaller amounts, or a second observation should be made 

 taking amounts of ferment solution lying between the faintest blue and the next 

 tube. 



It is of interest to compare by the above method the comparative diastatic 

 powers of the various commercial preparations of diastase, taking human saliva 

 as the standard. 



CHAPTER XIII. 



* 



DIGESTION IN THE STOMACH. 



THE food, after being masticated in the mouth, is passed down the 

 oesophagus into the stomach, where it is acted on by the gastric juice, 

 and is gradually forced out through the pylorus. Normally the 

 stomach is again empty in about five hours after a meal. The food 

 collects at first in the fundus of the stomach, which becomes dilated to 

 receive it. By gradually contracting the fundus forces the food in 

 small quantities at a time into the pyloric region, in which there are 

 frequent peristaltic movements which cause the food to be moved 

 about, and thus more intimately mixed with the digestive juices. 

 When properly disseminated and distinctly acid in reaction this food 

 causes the pyloric sphincter to relax, so that it is passed into the 

 duodenum ; but only small quantities at a time are allowed to pass, the 

 sphincter closing between each portion. While lying in the fundus, 

 very considerable digestion of starch by swallowed ptyalin is taking 

 place. On entering the stomach the food is very little changed, except 



1 Care must be taken when using organ extracts, such as those of liver, that the 

 reaction of the incubation mixture is kept constant. This is best accomplished 

 by adding a few drops of a saturated solution of Na2HP0 4 to the solutions. 



2 D = diastatic power. 



