MINUTE ANATOMY OF THE CAPILLARY LYMPHATICS. 305 



plest view is, that no special limiting membrane exists (Briicke). 

 On the other hand, microscopic examination shows that there 

 is really a double, and not a mere single, outline to be seen in 

 the central lacteal and in the finest capillaries in the tail of the 

 Tadpole, from which the conclusion has been drawn that a 

 homogeneous investing membrane is present (Kolliker). It 

 was found also that in injected preparations the injection 

 tightly filled the capillaries of the chyle and lymphatic vessels, 

 without the escape of any of it into the surrounding tissues ; 

 and hence it was considered that the assumption was perfectly 

 justified, that these vessels were as completely enclosed by an 

 investing membrane as the bloodvessels themselves (Teichmann, 

 Frey). In point of fact, the presence of a special membrane in 

 the lacteals and lymphatics may be most easily proved by the 

 application of the silver method of staining the tissues adopted 

 by Recklinghausen. If a solution of silver be injected into 

 the lymphatics as far as the capillaries, or if the tissues be 

 generally impregnated with a solution of this salt, fine dark 

 lines appear in the lymphatic capillaries (fig. 57), which are 

 usually strongly looped or sinuous, including polygonal, or riot 

 unfrequently rhombic, areas, in all their peculiarities identical 

 with the silvered lines of the most various epithelial tissues. 

 The networks of silvered lines become visible as early as in the 

 rather larger vessels succeeding the capillaries, where the en- 

 closed areas are fusiform, and agree with those brought into 

 view by the agency of silver on the inner surface of the large 

 lymph and blood vessels. In the case of these last-named 

 vessels, it may easily be proved that the lines in question de- 

 pend on the presence of a single layer of flat epithelial cells lining 

 the tunica intima ; but, inasmuch as the same markings may 

 be traced continuously into the lymphatic capillaries, it follows 

 that these also possess a similar layer of tesselated epithelium. 



In fact, even in the capillary lymphatics, subsequent treat- 

 ment with carmine not unfrequently brings into view an oval 

 nucleus in each area. Moreover, if the intestinal villi be torn 

 off a few hours after death, we may sometimes meet with one 

 from the centre of which a wide tube projects, consisting of 

 flattened epithelial cells. 



It is no longer, therefore, a matter of doubt that the capil- 



