THE MECHANISMS OF DIGESTION 



459 



on account of the crossing and foreshortening of the loops, etc., but, as 

 their constancy testifies, there is no doubt that the results are sufficiently 

 close for the purpose of finding out how quickly food gains access to the 

 small intestine; and tne method has a great advantage over all others 

 in that digestion is allowed to proceed practically without interruption. 

 The points we have to determine are: (1) when the food first leaves the 

 stomach; (2) the rate at which different foods are discharged; (3) the 

 time required for the passage through the small intestine. 



Let us consider first of all the results obtained by feeding with prac- 

 tically pure fat or carbohydrate or protein. By plotting the length of 

 the shadows in centimeters along the ordinates, with hours along the 

 abscissae, curves such as those shown in Fig. 159 have been secured. 

 When fats were fed (dash line in chart), the discharge began rather 

 slowly, and continued at a slow rate. Even after seven hours some fat 

 still remained in the stomach, and at no time was any large quantity 



40 



30 



10 



> 2 1 



34 



Hours 



6 



Fig. 159. Curves to show the average aggregate length of the food masses in the small 

 intestine at the designated intervals after feeding. The curve for various fat foods is in the 

 dash line, for protein foods in the heavy line, and for carbohydrate foods in the light line. 

 (From Cannon.) 



present in the intestine, indicating that almost as quickly as it is dis- 

 charged into this part of the gastrointestinal tract fat becomes digested 

 and absorbed. The discharge of carbohydrates was quite different (light 

 line in chart) ; it began often in ten minutes, and soon became abundant, 

 reaching a maximum, as a rule, at the end of two hours, after which it 

 fell off, the stomach being empty in about three hours. Protein left at a 

 rate intermediate between that for fats and that for carbohydrates 

 (heavy line). Little left before the first half hour; the curve then 

 slowly rose, attaining a maximum in about four hours, and then gradu- 

 ally declining at about the same rate as it rose. It is interesting to note 

 that at the end of half an hour about eight times as much carbohydrate 

 had left the stomach as protein; at the end of an hour, five times as much. 

 These results are clearly dependent upon the rates at which the dif- 

 ferent foodstuffs assume an acid reaction in the stomach. Carbohydrate 



