330 THE TISSUES AND MECHANISMS OF DIGESTION. 



lum, it is simply emulsified fat consisting of globules small and large; within 

 the lacteal radicle it consists partly of the same easily recognized globules 

 but partly of the extremely divided " molecular basis " ( 252) ; it is now 

 no longer emulsified fat but chyle. How and by what means this extremely 

 minute division of the globular fat into the " molecular basis" takes place 

 we do not know ; nor do we know the exact manner in which the fat passes 

 from the spaces of the reticulum into the interior of the radicle. 



We may here, perhaps, remark that the contents of the lacteal radicle 

 consist not exclusively of fat, but of fat accompanied by the proteid and 

 other substances which go to make up the chyle. Proteid and other sub- 

 stances besides fat are also present in the lymph which occupies in part the 

 labyrinth of the body of the villus, and are derived, like the lymph else- 

 where, from the blood of adjacent capillaries ; at least, they are in part so 

 derived, though it may be not wholly, for, as we have just seen, the passage 

 of proteid material from the intestine into the substance of the villus past 

 the capillaries, though not proved, must still be considered as possible. 



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

 wandering cells of which we spoke under the general term of leucocytes. 

 These do not all present the same appearances and most probably are not 

 all of 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 eventually into the interior of the 

 intestine ; or following the reverse course may wander from between the 

 epithelial cells into the body of the villus ; some of them, moreover, un- 

 doubtedly contain fat. Hence the view has been suggested that these leuco- 

 cytes 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 case they carry 

 their burden of fat through the epithelium into the villus, or while wander- 

 ing 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 unusual 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 shows that leucocytes can have little to do in transferring 

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

 are no adequate reasons for attributing to them any real share in the trans- 

 ference of fat from the body of the villus into the lacteal chamber. 



264. 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 253. The pressure, 

 for instance, exerted by the peristaltic contractions of the intestine helps to 

 empty the lymphatic 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, 



