DURATION OF STOMACH DIGESTION. 209 



this takes place at the most dependent portion, where the gastric 

 juice naturally gravitates, the explanation is simple. But if this 

 self-digestion can occur after death, why not during life? No 

 satisfactory answer to this question has yet been given, although 

 many theories have been advanced. One of these was, that there 

 was in living things the " principle of life," and that so long as 

 this principle existed it exercised a protecting influence ; but the 

 fallacy of this theory was made apparent when it was shown that 

 the leg of a living frog, passed through a fistula in a dog's stomach, 

 did undergo digestion. Still another theory was that the gastric 

 juice could act only when it contained the requisite amount of 

 hydrochloric acid, and that its acidity was neutralized by the 

 alkaline blood, so that the stomach, so long as life existed and 

 blood was flowing through its vessels, could not be digested. But 

 while this might explain the non-digestion of the stomach by the 

 gastric juice, it would not account for the non-digestion of the 

 intestine, which is also permeated by alkaline blood, but whose 

 digestive fluids are likewise alkaline. The presence of mucus has 

 been regarded by some as protecting the underlying mucous mem- 

 brane from the action of the gastric juice, while others have 

 attributed the same functions to the epithelium which covers it. 

 As a matter of fact, no explanation has as yet been given which 

 is perfectly satisfactory. 



Duration of Stomach Digestion. The duration of stom- 

 ach digestion is variable, and depends upon several circumstances, 

 among which is the composition of the stomach-contents. Some 

 kinds of food remain in the stomach longer than others. Stomach 

 digestion may in general be said to be from one and a half to five 

 and a half hours. The following table contains a list of some of 

 the substances with which Dr. Beaumont experimented, and the 

 length of time they remained in the stomach : 



Kind of food. Time. 



Pigs' feet and tripe 1 hour. 



Salmon 1 " 



Milk 2 hours. 



Potato, roasted 2 



Roast turkey , 2 



Soft-boiled eggs 2j 



Beefsteak, broiled 2j 



Hard-boiled eggs 3 - 



Potatoes, boiled 3 



Pork, boiled 41. 



" roasted 51. " 



The above table, and others of like nature, are to be very 

 cautiously made use of in determining the digestibility of the 

 different foods. The observations here recorded simply indicate 

 the length of time the respective articles remained in the stomach, 

 and nothing more. Substances are digested when they are in 

 condition to be absorbed, and not until then. Whenever any 

 u 



