ALIMENTARY TRACT AS AN ABSORPTIVE SYSTEM. 287 



coming from the intestines was secreted externally, that 

 less than 1 / 2 gram of sugar was excreted through this channel 

 after a feeding of 100 grams of starch and sugar, in other 

 words, not even 1 percent of the absorbed carbohydrates. 1 



9. The Absorption of Fat. The means by which the 

 often enormous quantities of fat 100 to 200 grams daily 

 which the human being consumes are absorbed has for more 

 than half a century been the subject of most active research 

 and discussion. It is clear that in the fat of our food we have 

 a substance which is, practically speaking, insoluble in water 

 and but little more soluble in protoplasm. In discussing 

 the problem of fat absorption we must, therefore, ask first 

 of all, Can fat be absorbed as such or is it first changed into a 

 soluble form? 



Those authors who have held to the idea that fat is ab- 

 sorbed as fat have called attention to the fact that even 

 though it is insoluble, fat can be very finely divided and kept 

 suspended in water in a so-called emulsion. Not only do 

 many^fats enter the alimentary tract in the form of such an 

 emulsion for example, milk and raw yolk of eggs bulfa 

 number of "agents exist>in the body which have the power of 

 emulsifying fats to a very high degree. As of first impor- 

 tance in this direction we must mention the bile, under the 

 influence of which any of the ordinary fats of the diet, such as 

 butter, the fat of meat, and olive-oil, may be speedily emulsi- 

 fied. 



While these agents exist which can alter so markedly the 

 physical state of the fats, there are others which are equally 

 potent in bringing about a chemical change in them. Of 

 first importance in this direction is lipase, a widely distributed 

 ferment which has the power of splitting fats into fatty acid 

 and alcohol. This chemical change which fats may suffer 

 in the body affects markedly the question of fat absorption, 

 for these products of fat digestion are many of them soluble 



1 SeeMuNK: Ergebnisse d. Physiol., 1902,1, Ite Abth.,p. 309, where 

 references to the literature will be found. 



