i88 ANIMAL BIOLOGY. [Parti. 



through the agency of the cells themselves that the process is 

 effected; and it may be through the intervention of certain 

 amoeboid cells, which lie at the bases of the columnar epithelial 

 cells, and send up long processes between the cells. In any case 

 it is eminently probable that neither the absorption of emulsified 

 fats, nor the diffusion of soluble peptones and sugar is merely 

 a mechanical process. Both are probably processes effected 

 through the vitality of the tissues ; and there are good reasons 

 for believing that the epithelial cells themselves exercise a sort 

 of digestive property upon the ingested fat. 



The absorption of fatty matters is probably completed in the 

 small intestine where alone the villi are developed ; but the 

 absorption of diffusible matters may probably continue in the 

 large intestine where water is largely absorbed. And one may 

 well suppose that in the large csecum of the rabbit some further 

 process of digestion, not at present well understood, is effected. 

 As they pass onwards the contents of the large intestine become 

 more solid and acquire the character of faeces, and are finally 

 expelled from the body. Notwithstanding the very large quantity 

 of bile poured forth into the small intestine, the amount of bile 

 salts to be found in the faeces is quite insignificant. Whence it 

 has been inferred that the biliary salts are decomposed and the 

 taurine and glycine thus set free are reabsorbed. 



Before leaving the subject of absorption attention may be 

 drawn to the fact that, in the lower vertebrates, the epithelial 

 cells would seem to be capable of pushing forth amoeboid absorp- 

 tive processes, and that leucocytes have been shown in some 

 cases to migrate through the epithelium into the lumen of the 

 alimentary canal, and thus come in contact with the prepared 

 food. They have therefore been called phagocytes. Other pha- 

 gocytes may take up food particles which have passed through 

 the epithelium into the connective tissue. Phagocytes are also 

 said to absorb, and thus render innocuous, noxious substances, 

 or portions of tissues which have undergone retrogressive meta- 

 morphosis within the body. 



Preliminary Metabolism of Absorbed Products. We have thus 

 seen how the products of digestion are absorbed, partly into the 



