RESORPTION BY THE LACTEALS. 301 



the Primum movens of the motions of the lymph. Since, more- 

 over, Lacauchie,* Gruby and Delafond,f and more recently 

 Briicke and Kolliker, have witnessed obvious contractions of the 

 villi, we can hardly doubt that it is these contractions which com- 

 municate the first impulse to the motion of the chyle in the 

 minutest ramifications of the lacteals. But although the discovery 

 of fibre-cells in the villi has revealed to us the mode in which the 

 commencing branches of the lymphatics are emptied, we have as 

 yet made no advance towards the explanation of the manner in 

 which these minutest lymphatic branches become filled. We have 

 already mentioned that the capillaries of the villi present a closer 

 resemblance than the lacteals to the root-fibrils of plants, in so far 

 as absorption is concerned. In the lacteals there is neither any 

 fluid which is so concentrated, nor any substance which is so 

 soluble, as to occasion an attraction of the fluids from the intestine ; 

 and indeed the apices of the lacteals do not even float in the in- 

 testinal fluids, which must pass through several series of cells, and 

 then come in contact with the minute capillaries, before they rea^h 

 the true lacteals. One might almost wonder that, considering how 

 great the absorbing power of the blood-vessels is, and that all the 

 fluids must pass over them, so much important nutrient matter 

 can find its way into the lacteals. It would appear, therefore, as 

 if only those matters were taken up by the lacteals which the 

 blood-vessels can only absorb with difficulty, or not at all. From 

 these considerations, based on anatomical structure, as well as 

 from certain experiments which showed that many membranes 

 are only permeable for certain substances (as, for instance, caout- 

 chouc for spirit, and not for water, the bladder of the pig for water, 

 and not for spirit, &c.), we have been led to believe, with Lotze,J 

 that the coats of the blood-vessels on the one hand, and those of 

 the lacteals on the other, have a specific action, and allow one 

 substance to pass through them, but not another. But even if we 

 assume that there is such a specific difference in the membranes in 

 question, we yet obtain no explanation as to the special agent 

 which forces the matters through the walls of the lymphatics. 

 The walls of the lacteals present opposition to the substances 

 which are heterogeneous to them, but they do not on that account 

 attract those by which they are permeable. The assumption of a 



* Compt. rend. T. 16, p. 1125. 



t Ibid., p. 1195. 



$ Allg. Physiologie. S. 2CO. 



