Chap, i.] TISSUES AND MECHANISMS OF DIGESTION 419 



The spaces of the reticulum of the villus are more or less 

 occupied by wandering cells of which we spoke under the gen- 

 eral term of leucocytes. These do not all present the same 

 appearances and most probably are not of all the same kind. 

 Some of these leucocytes wander not only through the labyrinth 

 of the reticulum but pass into the epithelium between the cells, 

 and may project processes into, or even make their way even- 

 tually into the interior of the intestine ; or following the re- 

 verse course may wander from the inside of the canal between 

 the epithelium cells into the body of the villus ; some of them 

 moreover undoubtedly contain fat. Hence the view has been 

 suggested that these leucocytes are important agents, indeed 

 the chief agents in the absorption of fat. It has been supposed 

 that they, receiving the globules of fat into their cell substance, 

 in fact eating the fat exactly after the manner of an amoeba, 

 either while projecting between the columnar cells, in which 

 they carry their burden of fat through the epithelium into the 

 villus, or while wandering in the labyrinth of the villus, bear it 

 away bodily into the lymphatic system. But the number of 

 leucocytes really containing any appreciable quantity of fat is 

 too small to account for the amount of fat absorbed. Nor is 

 the abundance of leucocytes in the mucous membrane during 

 the period of digestion a sure proof that they are concerned in 

 absorption, but rather an indication only that active changes 

 of some kind are going on, since after the administration of a 

 saline such as magnesium sulphate, which produces effects the 

 very reverse of absorption, these leucocytes are present in unu- 

 sual numbers. Moreover under some circumstances, as in the 

 villi of a new-born puppy after a meal of milk, they are absent 

 even when digestion of fat is rapidly going on and the lacteals 

 are filling with fat. In fact, what we stated above concerning 

 the presence of fat in the bodies of the columnar cells shews 

 that leucocytes can have little to do in transferring fat from 

 the interior of the intestine into the body of villus ; and there 

 are no adequate reasons for attributing to them any real share 

 in the transference of fat from the body of the villus into the 

 lacteal chamber. 



§ 252. The lacteal chamber opens at the base of the villus 

 into the valved lymphatic vessels lying below, and in these the 

 flow of lymph (chyle) is being promoted by the various causes 

 detailed in § 242. The pressure, for instance, exerted by the 

 peristaltic contractions of the intestine helps to ern^ty the lym- 

 phatic vessel into which a lacteal chamber opens and so pro- 

 motes the emptying of the latter. In addition to this the plain 

 muscular fibres of the villus supply a special muscular pump 

 for the emptying and filling of the lacteal chamber. These 

 fibres and small bundles of fibres running through in vari- 

 ous directions and varying in number and arrangement in 



