THE MESENTERIC GLANDS. 89 



development of cells in the villi of the intestinal tube, in countless 

 crowds, may therefore be within the bounds of possibility. 



If this be the case, the cells which thus come rapidly into existence 

 in the villi appropriate those articles of respiratory food which are of 

 imperfect solubility in water. To this class the oils belong. Each cell 

 then, as it dies, yields up its contents to the lacteal tube. In the white 

 fluid, the chyle, which flows along those tubes, are many pale or color- 

 less corpuscles continually coming into existence. These seem to im- 

 press a change upon the chyle, and, to give a full opportunity for such 

 action, that fluid is compelled to flow gradually through long and sinuous 

 channels, for the glands in the mesentery may be regarded as convoluted 

 windings, or rather plexuses of tubes, to which that particular form is 

 given for the sake of closeness of package. From the enveloping cap- 

 sule of fibrous tissue of the glands thin sheets are projected, Structure of 

 and so internetted as to divide the whole gland into many the mesenteric 

 alveoli. These are filled with a pulpy material supplied s ar 

 with delicate blood-vessels. The chyle either oozing through this ma- 

 terial eventually escapes from the gland by the efferent vessels, or makes 

 the passage in its own thin tube. In reptiles, in which there are no 

 such glands, the lacteals are extended to a very great length. 



The manner in which the chyle passes through the mesenteric glands 

 is therefore explained differently, according to the view Modeofaction 

 which is taken of the structure of those organs. If they ofthemesentc- 

 are considered as mere dilatations of the lacteal vessel, from nc s al 

 the sides of which partition processes are sent off, the interspaces being 

 filled with granular material, through which delicate blood-vessels pass, 

 the chyle is to be considered as oozing through this granular structure, 

 and crossing directly in contact with it. But if we accept the doctrine 

 that the chyle is conducted through the gland in a plexus arising from 

 the incoming lacteal, the granular material being outside, then the influ- 

 ence of that material, in whatever it may consist, takes effect through 

 the delicate walls of the plexus. The like remarks apply to the lym- 

 phatic glands. Physically, however, the condition in both cases is the 

 .same ; the incoming liquid is simultaneously exposed in the gland to 

 the influence of the granular pulp and to arterial blood. 



The chyle, delivered into the lacteal tube, is propelled by the conjoint 

 action of several different forces. The constant accumulation Causes of lhe 

 of liquid at the origin of the vessel produces a pressure which flow of the 

 can only be relieved by motion through the tube, and at the chyle ' 

 mouth, where the lacteal empties into a vein, as sooner or later all do, 

 either directly or through the intervention of the thoracic duct, a suction 

 force is exerted on the contents of the lacteal by the passing current of 

 the venous blood, upon the well-known hydraulic principle of Yenturi, 



