208 PHYSIOLOGY CHAP. 



acid actual reaction), suggested that the acidity of the intestinal 

 contents might be due to the fact that the pancreatic juice and 

 the succus entericus were unable to neutralise the acidity of the 

 gastric juice. U. Lombroso, however, contemporaneously with 

 G. Rossi (1907), objected that in this case it would be, not the 

 actual, but the potential, reaction that must be considered, and 

 that the alkaline potential reaction of pancreatic juice is very 

 strong. 



Foa (1908) accepted this criticism, but maintained that the 

 acid reaction of the intestinal contents was due solely to the 

 hydrochloric acid of the gastric juice. He observed that no free 

 hydrochloric acid was to be found in the filtrate of the gastric 

 and intestinal contents in the dog after a meal of flesh or milk, 

 but only hydrochloric acid combined with proteins. Examination 

 of the filtrate, however, does not exactly account for the various 

 acid constituents of the intestinal contents, since we know that 

 the higher fatty acids to a large extent remain on the filter. We 

 cannot therefore attribute the acidity of the intestinal contents 

 solely to the combined hydrochloric acid, but must admit (par- 

 ticularly in view of the known data as to digestion and absorption 

 of fats which we are about to discuss) that all the other factors 

 above enumerated contribute to it. 



In the preceding chapters we have already referred to the specific 

 enzymic activity of the various digestive secretions. It is now 

 time to determine more exactly the mode in which these various 

 factors in the complex problem of alimentary digestion come into 

 play what favours and what thwarts their function and how 

 that functional correlation is effected between the different secre- 

 tions which is necessary to the conversion of the food-stuffs into 

 the form that precedes their absorption. 



In virtue of its enzymes, pancreatic juice acts, as we have seen, 

 on the three different groups of alimentary substances, viz. carbo- 

 hydrates, fats, and proteins. Its action in vitro can be studied 

 either with natural juice or with the extract of the gland. 



The saccharifying action of pancreatic juice on starch (due to 

 amylopsin) is similar to that of saliva, but much more energetic, 

 since at body- temperature (37-40 C.) it acts rapidly on boiled as 

 well as on raw starch. The rapidity of this conversion, and the 

 intensity of the effect, are astounding. Thus if pancreatic juice be 

 dropped into a test-tube containing starch paste stained with a 

 drop of tincture of iodine, the deep-blue colour disappears, and is 

 replaced by a violet -red (erythrodextrin), then by pink, until 

 finally it becomes colourless (achroodextrin). Minkowski suggested 

 a method for the rapid estimation of amylolytic activity, based 

 upon this sequence of readily observed phenomena. 



According to Roberts, one part of amylopsin is able to convert 

 40,000 parts by weight of starch in less than a minute. 



