446 ABSORPTION 



proteolytic, amylolytic, fat-splitting, and inverting ferments which 

 have done their work in the small intestine are passed on into the 

 large, and may be demonstrated in its contents. Doubtless these 

 are able to act upon food substances which may have escaped com- 

 plete digestion and absorption in the higher parts of the alimentary 

 canal, as well as upon food substances injected into the rectum. 



Summary. With the proviso that in the case of the fats the 

 statement may in the present condition of our knowledge be some- 

 what ' diagrammatic/ we may sum up in a few words the chief 

 points in the absorption of the food materials. [All the fats must be 

 split in order to be absorbed in soluble form from the intestine, but 

 need not be split in the lumen of the gut in order to be utilized by the 

 cells. For this reason they are to a great extent resynthesized to 

 neutral fat after absorption, and find their way into the blood, mainly 

 by way of the lymph, in particulate form. Proteins could perhaps to 

 a small extent be absorbed as such, but must be thoroughly hydrolysed 

 in order to be utilized by the tissues, and also in order to be freely 

 taken up from the gut. Carbo-hydrates in certain forms (mono- 

 saccharides) are capable without change of being both freely absorbed 

 from the intestine and thoroughly utilized by the cells ; only the more 

 complex carbo-hydrates need to be hydrolysed in order to be absorbed, 

 but all above the monosaccharides must be hydrolysed to monosac- 

 charides in order to be utilized. The substances which eventually 

 circulate in the blood in solution reach it through the gastro-intestinal 

 capillaries ; the substances which eventually circulate in the blood in 

 particulate form reach it through the lymphatics^ 



PRACTICAL EXERCISES ON CHAPTERS VI. AND VII. 



i. Contraction of Isolated Intestines in Ringer's Solution. Arrange 

 a good-sized water-bath (a water-tight garbage-can holding 20 litres 

 will do) so that the temperature of the water is kept at 37 to 38 C. 

 For this a gas regulator is most convenient, and also a stirring arrange- 

 ment worked by a small motor. But if neither of these is available., 

 a student, by a little care, can easily keep the water at the required 

 temperature by raising and lowering the gas flame and stirring occasion- 

 ally by hand. In the bath, support (a) a stock bottle of Ringer's 

 solution (footnote, p. 66), (b) a wide-mouthed bottle containing Ringer 

 for the reception of the stock of intestine, (c) a small cylinder for 

 segments of intestine whose contractions are to be recorded, (c} is 

 conveniently made in different sizes by cutting down glass T-pieces. 

 One which holds 4 or 5 c.c. is convenient. The bottom is plugged with 

 a rubber cork in which is fastened a hook. In the side-piece is fixed 

 by a rubber cork a glass tube ending in the cylinder in a narrow 

 orifice. This is connected with the oxygen-supply, conveniently ob- 

 tained under constant pressure from a small gas-container which is 

 periodically replenished from an oxygen cylinder. A separate oxygen 

 cylinder is connected with a tube passing to the bottom of (b) . A lever 

 with two arms is arranged on the same stand as (c) , so that it can be 

 thrown on and off a slow-moving drum by a single movement of the stand. 



All being ready, a rabbit is killed by being struck on the back of the 



