DIGESTION. 227 



etones. One is olive-green, faintly shining, formed of concentric 

 layers. On heating it melts with the development of an aromatic 

 odor. It contains as chief constituent LITHOFELLIC acid, C^H^Ot , 

 which is related to cholalb acids, and besides this a bile-acid, 

 LITHOBILIC ACID. The others are nearly blackish brown or dark 

 green, very glossy, consisting of concentric layers, and do not melt 

 on heating. They contain as chief constituent ELLAGIC ACID, a de- 

 rivative of tannic acid, of the formula C U H 6 8 , which gives a deep 

 blue color with an alcoholic solution of ferric chloride. This last- 

 mentioned bezoar-stone originates, to all appearances, from the 

 food of the animal. 



Ambergris is generally considered an intestinal concrement of the sperm- 

 whale. Its chief constituent is AMBBAIN, which is a non-nitrogenious sub- 

 stance perhaps related to cholesterin. Ambrain is insoluble in Vater and is 

 not changed by boiling alkalies. It dissolves in alcohol, ether, and oils. 



VI. Absorption. 



In discussing the absorption processes we must treat of the 

 form into which the different foods are transformed before absorp- 

 tion, of the manner in which this is accomplished, and, lastly, of the 

 force which acts in these processes. 



Starch and the other carbohydrates are chiefly absorbed as sugar, 

 in part also as organic acids (lactic acid), and perhaps in small 

 quantities as dextrin. Fats may indeed be partly absorbed as 

 soaps; still the quantity absorbed in this way is very small compared 

 with that absorbed as an emulsion. Emulsion is undoubtedly the 

 most important form under which fat is absorbed, and the neutral 

 fats, also the free fatty acids, are emulsified when they occur in 

 large quantities in the intestines. 



Peptone, as above stated, is the final product of the digestion of 

 albuminous bodies. Now as peptone is a very soluble and a rela- 

 tively easily diffusible modification of proteids, it is not difficult to 

 admit the deduction that proteids must be changed into peptone 

 in order that it may be readily absorbed. Certain observations of 

 FUNKES on animals confirm this view. He found in an untied 

 intestinal knot of a living animal that the peptone (in the old 

 sense of the word) was absorbed considerably faster than other 

 proteids. There is also no doubt that a part of the proteids is 



