532 LECTURE XXII. 



The latter are said to contain inhibitory fibers. The innervation relations 

 are, however, not perfectly understood. 



We must now turn our attention to the absorption of the digested pro- 

 ducts. We approach this part of the subject with considerable hesitancy t 

 for we must admit at the start that we are not yet able to give a full account 

 of the nature of the absorption process. We can indeed affirm that 

 undoubtedly physical forces come into play here, and that, for example, 

 osmosis plays a part, as is obvious from the already-mentioned observations 

 of Overton on the solubility of lipoids; and similarly we cannot doubt that 

 the surface-tension is to be regarded as important here, in the sense sug- 

 gested by Traube. 1 On the other hand, we are very well aware that none 

 of the attempted explanations of absorption have of themselves brought 

 the entire complicated process nearer to our comprehension. As soon as 

 a single phenomenon in a single process is applied to the entire absorption, 

 the explanation in all cases appears arbitrary. 



We are not able in explaining absorption, to circumvent the conception 

 of a specific action on the part of the cells. We can indeed believe that 

 probably a purely physical explanation will account for an inter-epithelial 

 absorption. The greater part of the products of digestion will, however, 

 be taken up by the cells themselves, and these are undoubtedly very active 

 in their work. We cannot imagine, for example, that the amino acids 

 and polypeptides, which represent decomposition products of the proteins, 

 penetrate into the cells purely on account of physical reasons without 

 active cooperation on the part of the cells themselves. We must not 

 forget that syntheses immediately follows the absorption; i.e., in other 

 words, the activity of the cells then begins, and, indeed, as the relatively 

 constant composition of the serum shows, in a quite definite direction. 

 We have no reason for assuming that in the epithelium of the intestine and 

 the cells of this organ, certain forces unknown to us are at work. If we 

 were to make any such assumption, it would be entirely without empirical 

 justification. Although, at present, we are denied an accurate insight 

 into the nature of absorption, still on trie other hand our knowledge of 

 the work performed by the cells is constantly increasing. The intestinal 



1 It would not be difficult with the aid of the H. J. Hamburger's " Osmotischer Druck 

 und lonenlehre in den medizinischen Wissenschaften " (1902) to cite the different 

 views held regarding intestinal absorption. On the other hand, it would be hard, 

 without going into a detailed explanation of the laws and investigations of physical 

 chemistry, to give a clear picture of the different hypotheses in this narrow field. We 

 would refer the reader, therefore, to the above book and to the following literature: 

 Rudolph Hoeber: Pfliiger's Arch. 70, 624 (1898); 74, 246 (1899); 86, 199 (1901); 94, 337 

 (1903); O. Cohnheim: Z. Biol. 36, 129 (1897); 38, 443 (1899), and 39, 167 (1900); also 

 Z. physiol. Chem. 33, 9 (1901); 35, 396 and 416 (1902). J. Traube: Pfluger's Arch. 

 105, 541 and 559 (1904). Cf. also Martin Heidenhain: Anatomische Hefte, 79-80, 

 26, 2-3 (1904). Published by Merkel and Bonnet. 



