CHAP. L] TISSUES AND MECHANISMS OF DIGESTION. 553 



substances, part of the sugar for instance, arrived inside the 

 basement membrane should slip by the capillary blood vessel and 

 passing through the meshes of the capillary network make its 

 way into the lacteal. And indeed, as we have seen, 308, 

 under certain circumstances some amount of sugar appears to 

 take this course. But, as we have also seen, under ordinary 

 circumstances the current, whatever be its exact nature, from 

 the narrow lymph-spaces lying between the epithelium and the 

 capillary into the blood-stream is strong enough to carry all or 

 nearly all the sugar into the blood. In the establishment of this 

 current, in this second stage of absorption diffusion always plays 

 a part, and probably a still more conspicuous and decided part 

 than in the first stage, seeing that the epithelioid plate of the 

 capillary wall is a far less active structure than the columnar cell 

 of a villus. Indeed it might be open for us to contend that this 

 second stage was merely a matter of diffusion, whatever might be 

 the nature of the first stage. But remembering what was said 

 above, 302, in discussing the transudation of lymph, it seems 

 more in accordance with what we already know, to conclude that 

 in this second stage also diffusion is the servant and not the 

 master of the living capillary wall. 



A word may be added concerning the special case of the 

 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. At the same time, 

 bearing in mind that leucocytes, or cells resembling leucocytes, 

 many of them possessing, in the number and nature of then- 

 granules, or in other respects marked features, are found in the 

 reticulum of the villi, we may be prepared to admit, when fuller 

 knowledge comes to us, that these cells play some important part 

 in the process of absorption on which we have been dwelling. 



F. n. 36 



