RELATION OF SEROUS CANALS TO CAPILLARY LYMPHATICS. 319 



portion as the canal system is wider, and is consequently par- 

 ticularly well marked in the serous membranes and other 

 analogous structures (fig. 59). 



In preparations of this kind it is important to avoid everything that 

 may produce alterations in the structures under examination ; for if the 

 contours of the lymphatic vessels and serous canals are in the smallest 

 degree rendered indistinct and hazy, it is impossible to determine 

 accurately the nature of their connection. But such blurred images 

 are always obtained if the epithelium has not been carefully removed 

 previous to the impregnation of the preparation with the solution of 

 silver. His appears to have had only such indistinct specimens before 

 him, as he believed that an unskilled observer might remain in doubt 

 as to the continuity of the contours.* 



2. If the lymphatic vessels be injected towards their rootlets* 

 it is very easy, even with an insoluble injection, to produce 

 extravasation into the tissue, by which it becomes more or less 

 stained. Under the microscope we may then see in the softer 

 tissues only a dense mass of colouring matter, without any of the 

 ordinary canals being visible ; harder tissues must consequently 

 be selected, if we desire in this way to ascertain the path fol- 

 lowed by the injection. In the fascia of the thigh of the frog, 

 forming the wall of a lymph sac, I have succeeded in fill- 

 ing canals containing connective tissue cells with granular 

 colouring material, by injecting the sac ; and we may also force 

 very fine injections through the lymphatic vessels of the cutis 

 into the subcutaneous connective tissue, the fluid passing di- 

 rectly into channels that precisely agree in their form with the 

 plexuses containing healthy pigment, i.e., the ramifications of 

 the so-called pigment cells ; indeed, the injection may sometimes 

 be propelled into the plexus of pigment cells itself. We can- 

 not, therefore, entertain any doubt that the injection, if it 

 escape from the capillary lymphatics, enters into channel-like 

 spaces of the tissue, which are nothing else than the serous canals 

 themselves, since they here contain the pigmented connective 

 tissue cells. Moreover in all soft tissues, as, for instance, in the 

 villi of the small intestine, plexuses first make their appearance ; 

 and then, when the injection has been driven with great force, the 



* Zeitschrift fur wissenschaftliche Zoologie, Band xiii., Heft. 3, 1863. 



