THE ABSORPTION OF THE FOOD-STUFFS 739 



where it is required for the metabolism of the body or where it may be stored 

 up as a reserve substance. 



The processes of digestion of fat result in the production of glycerin and 

 fatty acids, if the reaction be neutral or slightly acid. If the reaction of the 

 gut be alkaline the alkali will combine with the fatty acids to produce soaps. 

 Analyses of the contents of the gut after a fatty meal show that the greater 

 proportion of the fats are present as a mixture of fatty acids and soaps, the 

 amount of these substances as compared with unchanged fat increasing as we 

 descend the gut. 



In studying the absorption of fats the investigator is able to take 

 advantage of the fact that the micro-chemical detection of this substance is 

 usually very easy. Globules of fats or fatty acids containing any proportion 

 of the unsaturated fatty acids have the property of reducing osmic acid, 

 and therefore of being stained black by this reagent. Practically all the fats 

 which occur in the food or in the cells of the body contain oleic acid 

 or the glyceride of this acid in association with palmitic or stearic acid, and 

 therefore give the typical micro-chemical fat reactions. In many cases it is 

 useful to employ the specific stains for fats, such as Sudan red or alkanna 

 red. It is important to remember that the intensity of the fat reaction 

 given by a cell is only an expression of the fat or fatty acid contained in a 

 free state in the cell, and is no criterion of the total amount of fat which 

 may be present. Thus a normal heart muscle in section gives only a diffuse 

 light brown coloration with osmic acid. After poisoning by phosphorus or 

 by diphtheria toxin, every muscle- cell may be found studded with minute 

 black granules of fat. Chemical analysis shows, however, that the normal 

 heart muscle contains as much fat as the degenerated muscle. Our micro- 

 chemical methods will therefore throw no light on the amount of fat which 

 is actually in combination with the cell protoplasm. 



If an animal be examined a few hours after the administration of a 

 meal rich in fats, the lymphatics of the intestine are seen to be distended 

 with a milky fluid chyle and the same fluid is found filling the cisterna 

 lymphatica magna and the thoracic duct. The lymph from the thoracic 

 duct will also be milky, and chemical analysis shows that the opacity is due 

 to the presence of minute granules of neutral fat. The fat in such chyle 

 may amount to over 6 per cent., so that in a moderate- sized dog 12 grammes 

 of fat may be carried in the course of an hour from the intestine to the blood 

 by this means. This great access of fat to the blood during fat absorption 

 introduces corresponding changes in the blood. The plasma itself becomes 

 milky, and if the blood be allowed to clot, the serum expressed from the clot 

 is also milky. On standing, a layer of fat globules like cream may rise 

 to the surface of the serum. Fat is found in a free state in this finely divided 

 condition in the blood plasma so long as it is being absorbed in the intestine. 

 During starvation it disappears entirely, the serum becoming perfectly clear. 

 Thus part, at any rate, of the fat which is absorbed from the gut is carried 

 thence by the lymphatic channels in the form of neutral fat to the blood 

 stream, by which it is distributed to the various tissues of the body, gradually 



