CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 525 



peptones. As we have said, the peptones in being absorbed appear 

 to undergo a change somewhere in the mucous membrane. We do 

 not know exactly where or how the change takes place. It seems 

 probable that so marked and difficult a change should require the 

 intervention of some active living tissue, and we may therefore 

 suppose that it is effected by the epithelium cells; but we have no 

 exact knowledge on this point. If the change be thus carried out 

 by means of the epithelium cells, then the latter stage of the 

 absorption of proteids, namely the passage from the epithelium 

 into the interior of the capillary is not a passage of diffusible 

 peptone, but of some other non-diffusible kind of proteid. It 

 may be however that the change takes place during the very 

 passage of the material through the capillary wall. 



The view that leucocytes are the agents of the absorption of 

 fat, by bodily taking up the fat into their cell-substance, has by some 

 been extended to proteids ; it has been urged that these take up 

 proteids either as peptones or in some other form and so carry 

 them into the lymphatic system. But the evidence for this view 

 is even less convincing than in the case of fat. 



