Villi in Man and certain of the Mammalia, 169 



Not only are these bodies the germs of all the tissues, as de- 

 termined by the labours of Schleiden and Schwann, but as 1 

 have observed, they are the immediate agents of secretion. 

 (Trans. Roy. Soc. Edin. 1842.) A primitive cell absorbs from 

 the liquor sanguinis which surrounds it, and which is supplied 

 by the capillaries, the matters necessary to enable it to form, 

 in one set of instances, nerve, muscle, bone, if nutrition be 

 its function ; milk, bile, urine, in another set of instances, 

 if secretion be the duty assigned to it. The only difference 

 between the two functions being, that in the first, the cell dis- 

 solves nd disappears among the tissues, after having per- 

 formed its part ; in the other, it dissolves, disappears, and throws 

 out its contents on a free sm*face. Now, it will be perceived 

 that before a cell can perform its function as a nutritive cell, 

 or as a secreting cell, it must have acted as an absorbing cell.* 

 This absor[.tion, too, must necessarily be of a peculiar and 

 specific nature. It is in virtue of it, that the nutritive cell 



* " Absorption/' says Professor Miiller, Baly 's Translation, p. 301, " seems 

 to depend on an attraction, the nature of which is at present unknown, but 

 of which tlie very counterpart, as it were, takes pUice in secretion ; the flu'ds 

 altered by the secreting action being impelled towards the free surface only 

 of the secreting membranes, and then pressed onwards by the successive 

 portions of fluid secreted. In many organs, for instance in those invested 

 with mucous membranes — absorption by the lymphatics and secretion by 

 the secreting organs, are going on at the same time on the same surface." 

 It appears, however, from what I have stated in the present paper, and in 

 Trans. Roy. Soc. Edin. 1042, that Prof. MUller, and indeed all the physiolo- 

 gists hitherto have been in error in supposing the forces of secretion and ab- 

 sorption as of different and opposite tendencies, — the one attractive, the other 

 repulsive. They are both attractive, absorption being but the first sti\ge in 

 the process of secretion. Secretion, in fact, differs from absorption, not phy- 

 siologically, but morphologically. 



What has been statetl in the present paper explains also how, in the mu- 

 cous membranes, " absorption by lymphatics and secretion by secreting or- 

 gans are going on at the same time on the same surface." (Miiller, loc. dt.) 

 There is no physiological mystery in this. It depends on a moi-phological 

 circumstance. The absorbing chyle cells are on the attached surface of the 

 primary membrane — the secreting epithelia ai'e on its free surface; the for- 

 mer are interstitial cells, the latter peripheral ; the former cast their con- 

 tents into the substance of the organism, — the latter into the surrounding 

 medium. It may bo here observed that absorption, as it occurs in the chyle 

 vessels, takes place as in the absorption which occurs in all the secreting 

 cells, through two structureless membranes, probably molecular in their ecu- 

 stitution— the primary membrane and the membrane oi the cell. 



