300 ABSORPTION. 



decomposition. That this is the principal source of the intestinal gases, there can be no 

 doubt; and it is well known that certain articles of food, particularly vegetables, gen- 

 erate much more gas than others. The principal gases found in the intestinal canal may 

 all be obtained from the food. Some of them, as hydrogen and carburetted hydrogen, 

 do not exist in the blood ; and it is difficult to conceive how they can be generated in the 

 intestine except by decomposition of some of the articles of food. Hydrogen and its 

 compounds are always found in quantity in the small and the large intestine. 



It is said that gas is sometimes found in the intestines of the foetus, and that it may 

 be generated in a loop of intestine in a living animal, after a portion of the canal has been 

 drawn out, isolated by ligatures, freed from its liquid and gaseous contents, and returned 

 to the abdomeu. In some diseased conditions, also, it is very common for the abdomen 

 to become rapidly tympanitic, the gas being generated so quickly that its presence is not 

 easily explained by supposing it to be evolved by decomposition of the ingesta. It has, 

 indeed, been supposed that the intestinal mucous membrane is capable of secreting gases 

 as well as liquids ; but there do not appear to be any positive facts in support of this 

 view. No doubt some of the gases which may be formed in the intestine are capable 

 of absorption. It is impossible to say, however, that even the gases normally held in 

 solution in the blood, namely, oxygen, nitrogen, and carbonic acid, are exhaled from the 

 blood into the intestinal cavity. Oxygen is never given off in this way, for this gas has 

 been found only in the stomach and is there derived from air which has been swallowed. 

 With regard to the origin of the other gases found in the intestine under the peculiar 

 circumstances just mentioned, in which they are apparently generated with much rapidity, 

 there are not sufficient data to enable us to form an intelligent opinion. 



CHAPTER X. 



ABSORPTION LYMPH AND CHYLE. 



General considerations of absorption Absorption by blood-vessels Absorption by lacteal and lymphatic vessels- 

 Physiological anatomy of the lacteal and lymphatic system Absorption by the lacteals Absorption from parts 

 not connected with the digestive system Absorption of fats and insoluble substances Variations and modifica- 

 tions of absorption Imbibition and endosmosis Imbibition by animal tissues Mechanism of the passage of 

 liquids through membranes Capillary attraction Endosmosis through porous septa Endosmosis through ani- 

 mal membranes Endosmosis through liquid septa Diffusion of liquids Endosmotic equivalents Modifications 

 of endosmosis Application of physical laws to the function of absorption Transudation Lymph and chyle 

 Mode of obtaining lymph Quantity of lymph Properties and composition of lymph Alterations of the lymph 

 Corpuscular elements of the lymph Leucocytes Development of leucocytes in the lymph and chyle Glob- 

 ulinsOrigin and function of the lymph General properties of the chyle Composition of the chyle Compara- 

 tive analyses of the lymph and the chyle Microscopical characters of the chyle Movement of the lymph and 

 chyle. 



DIGESTION has two great objects : one is to liquefy the different alimentary princi- 

 ples ; and the other, to commence the series of transformations by which these principles 

 are rendered capable of nourishing the organism. The principles thus acted upon are 

 taken into the blood as fast as the requisite changes in their constitution are effected ; 

 and, once received into the circulation, they become part of the great nutritive fluid, sup- 

 plying the waste which the constant regeneration of the tissues from materials furnished 

 by the blood necessarily involves. The only group of principles which possibly does not 

 obey this general law is the fats. Although a small portion of the fat taken as food 

 passes directly into the blood-vessels of the intestinal canal, by far the greatest part finds 

 its way into the circulation by means of special absorbent vessels which empty into large 

 veins. In whatever way fat enters the blood, it is never dissolved, but is reduced to the 

 condition of a fine emulsion. 



