THE ABSORPTION OF THE FOOD-STUFFS 833 



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 corre- 

 sponding 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 leaving the blood stream 

 in a manner which at present has not been determined. Not all the 



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