444 Or ABSORPTION AND SANGUIFICATION. 



absorbent power which the bloodvessels of the Alimentary canal possess, is not 

 limited to alimentary substances; for it is through them, almost exclusively, 

 that soluble matters of every other description are received into the circulation. 

 This, which may now be considered a well-established fact, was first clearly 

 shown by the carefully-conducted experiments of MM. Tiedemann and Gmelin, 1 

 who mingled with the food of animals various substances, which, by their color, 

 odor, or chemical properties, might be easily detected in the fluids of the body : 

 after some time the animal was examined; and the result was, that unequivocal 

 traces of such substances were not unfrequently detected in the venous blood 

 and in the urine, whilst it was only in a very few instances that any indication 

 of them could be discovered in the chyle. The coloring matters employed were 

 various vegetable substances; suoh as gamboge, madder, and rhubarb; the 

 odorous substances were camphor, musk, assafetida, &c. ; while, in other cases, 

 various saline bodies, such as chloride of barium, acetate of lead and of mercury, 

 and some of the prussiates, which might easily be detected by chemical tests, 

 were mixed with the food. The coloring matters, for the most part, were carried 

 out of the system, without being received either into the veins or lacteals ; the 

 odorous substances were generally detected in the venous blood and in the urine, 

 but not in the chyle ; whilst of the saline substances, many were found in the 

 blood and in the urine, and a very few only in the chyle. A similar conclusion 

 might be drawn from the numerous instances in which various substances in- 

 troduced into the intestines have been detected in the blood, although the 

 thoracic duct had been tied; but these results are less satisfactory, because 

 even if there be no direct communication (as maintained by many) between the 

 lacteals and the veins in the mesenteric glands, the partitions which separate 

 their respective contents are evidently so thin, that transudation may readily 

 take place through them. 



464. This Absorption by the Bloodvessels is a simply physical operation, 

 depending upon the relative consistency and miscibility of the blood and of the 

 liquids to be absorbed, and upon the rapid movement of the blood through the 

 vessels. Where the contents of the alimentary canal are of less specific gravity 

 than the blood, and are capable of readily mingling with it, an endosmotic cur- 

 rent will be established, through the delicate parietes of the bloodvessels and 

 their thin investments, between the two liquids, the former passing towards the 

 other; and in this mode, albuminous, gelatinous, saccharine, saline, and other 

 soluble substances may be caused to enter the blood, if their solution be not too 

 concentrated. But if their density be equal to that of the blood, or nearly so, 

 little or no absorption is likely to take place; and one purpose which is answered 

 by the very copious discharge of aqueous fluid into the alimentary canal, during 

 the operation of digestion, is obviously the reduction of the density of the solu- 

 tion to a favorable point. If, again, the density of the contents of the aliment- 

 ary canal should exceed that of the blood, an endosmotic current might perhaps 

 be established in the opposite direction ; but their dilution would probably be 

 effected so speedily, that little of the contents of the bloodvessels would be thus 

 drawn forth, more especially as animal membranes appear to have a special 

 power of resisting the passage of Albumen, whilst they give free transmission 

 to Albuminose. 3 That the movement of blood in the vessels will vastly increase 



1 "Versuche iiber die Wcge auf welchen Substanzen aus dern Magen und Darmkanal 

 ins Blut gelangen," Heidelberg, 1820. 



2 It is considered by Liebig that the purgative effects of concentrated saline solutions 

 are to be accounted for on this principle the establishment of an endosmotic current 

 from instead of towards the circulating system. It is difficult, however, thus to account 

 for all the phenomena of saline purgation ; and the Author greatly doubts the validity of 

 the explanation. It may, however, be applied, with more probability, to the fact of which 

 the^ Author was assured by the late Dr. Prout; viz., that having fed a dog upon pure starch, 



