THE CHEMISTRY OF THE DIGESTIVE JUICES 343 



tents of the cardiac end are not freely intermixed with those of the 

 pyloric end, a greater proportion of sugar is found in the former, 

 and the difference is more marked with solid than with liquid food 

 (Cannon and Day). But during the greater part of gastric digestion 

 the degree of acidity is such that the ptyalin must be hindered. 

 Although the food stays but a short time in the mouth, there is no 

 doubt that, in man at least, some of the starch is there changed into 

 sugar (p. 350). But this is not the case in all animals. Something 

 depends on the amylolytic activity of the saliva, and something 

 upon the form in which the starchy food is taken, whether it is 

 cooked or raw, enclosed in vegetable fibres, or exposed to free ad- 

 mixture with the secretions of the mouth. 



The fact already mentioned that hydrolytic changes of the same 

 nature as those produced by enzymes cari be brought about in other 

 ways holds good for the salivary amylase. If starch is heated for 

 a time with dilute hydrochloric or sulphuric acid, it is changed 

 first into dextrin, and then into a sugar, which, however, is not 

 the disaccharide maltose, but the monosaccharide dextrose that 

 is to say, the hydrolysis with acid proceeds a step farther than the 

 hydrolysis in the presence of ptyalin. If maltose is treated with 

 acid in the same way, it is also changed into dextrose. When 

 glycogen (p. i) is boiled with dilute oxalic acid at a pressure of three 

 atmospheres, isomaltose and dextrose are formed (Cremer), Facts 

 already mentioned, and others to be cited later on, show that the 

 action of the other digestive ferments can also be imitated by 

 purely artificial means. Indeed, we may say that the ferments 

 accomplish at a comparatively low temperature what can be done 

 in the laboratory at a higher temperature, and by- the aid of what 

 may be called more violent methods. 



Gastric Juice. The Abbe Spallanzani, although not, perhaps, 

 the first to recognize, was the first to study systematically, the 

 chemical powers of the gastric juice, but it was by the careful 

 and convincing experiments of Beaumont that the foundation of 

 our exact knowledge of its composition and action was laid. 



It is difficult to speak without enthusiasm of the work of Beaumont, 

 if we consider the difficulties under which it was carr'ed on. An army 

 surgeon stationed in a lonely post in the wilderness that was then 

 called the territory of Michigan, a thousand miles from a University, 

 and four thousand from anything like a physiological laboratory, he 

 was accidentally called upon to treat a gun-shot wound of the stomach 

 in a Canadian voyageur, Alexis St. Martin. When the wound healed, 

 a permanent fistulous opening was left, by means of which food could 

 be introduced into the stomach and gastric juice obtained from it. 

 Beaumont at once perceived the possibilities of such a case for physio- 

 logical research, and began a series of experiments on dig stion. After 

 a while, St. Martin, with the wandering spirit of the voyag ur, returned 

 to Canada without Dr. Beaumont's consent and in his absence. 

 Beaumont traced him, with great difficulty, by the help of the agents 

 of a fur-trading company, induced him to come back, provided for his 



