300 A MANUAL OF PHYSIOLOGY 



are still more favourable in the stomach for some time after 

 the beginning of a meal, while the reaction is yet weakly 

 acid. 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. 376). But this does not seem 

 to be 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 

 admixture with the secretions of the mouth. 



It is important to note here that hydrolytic changes of 

 very much the same nature as those produced by ptyalin 

 can be brought about in other ways. If starch is heated for 

 a time with dilute hydrochloric or sulphuric acid, it is 

 changed first into dextrin, and then into a form of reducing 

 sugar, which, however, is not maltose, but dextrose. If 

 maltose is treated with acid in the same way, it is also 

 changed into dextrose. When glycogen (p. 446) is boiled 

 with dilute oxalic acid at a pressure of three atmospheres, 

 isomaltose and dextrose are formed (Cremer). We shall see 

 later on that the action of other ferments can also be to a 

 certain extent imitated by purely artificial means. In fact, 

 some of 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 we may call more 

 violent methods. 



(2) Gastric Juice. The Abbe Spallanzani, although not, 

 perhaps, the first to recognise, was the first to study system- 

 atically, 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 composi- 

 tion 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 carried 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. 



