EPITHELIAL AND ENDOTHELIAL TISSUE. 343 



THE LYMPHATIC SYSTEM. 



During the last fifteen years many erroneous views con- 

 cerning the lymphatic system have arisen, due to the method 

 of studying viz.: by " parenchymatous injection" of colored 

 liquids. Perforations were made at random into the tissues of 

 the body, and liquids were then forced in from without. The re- 

 sults and views obtained by this means are only worthy of being 

 forgotten. On the other hand, careful injections of the lymphatics 

 themselves, by Teichmann, Langer, Sappey, and others, have 

 shown conclusively that the system of lymphatics is a closed one, 

 just as that of blood-vessels. Throughout the lymph-ganglia, 

 the spleen, and the lymph tissue in general, erroneously 

 termed " adenoid tissue," lymph-vessels probably do not exist. 

 The difficulties in rendering the lymphatics distinct by injection 

 are very great, on account of the delicacy and transparency of 

 their walls, their colorless contents, and the presence of valves 

 arranged in the same manner as in veins. 



The lymph-vessels form a reticulum, in the average wider than 

 that of the blood-vessels, exhibiting in its peripheral ramifica- 

 tions, besides loops, pointed or club-shaped terminations. Lymph- 

 vessels are characterized by irregular excavations and sinuses, 

 and run either parallel with the blood-capillaries or independ- 

 ently of them. They are, like the blood-vessels, found only in 

 connective-tissue formations. The walls of the lymph-capillaries 

 are composed of a single endothelial layer, whose elements, as a 

 rule, are larger than those of the blood-vessels. Often, there is 

 no other investment to be seen, and the lymph-capillaries in this 

 case have the appearance of being channeled in and supported 

 by the adjacent tissues. The lymph-capillaries are destitute of 

 valves 5 but the collecting ramules are always found to possess 

 valves which produce constrictions of the vessel, while close 

 above the valve, in the more central portion, there is a widening 

 of the caliber. The ramules accompany the arteries, often in the 

 shape of a reticulum, which is also found around the veins, 

 though less developed. The larger ramules exhibit a delicate 

 investing elastic layer immediately above the endothelia, and 

 with the increase of the caliber of the lymph- vessel this invest- 

 ment assumes a fibrous structure, and is supplied with smooth 

 muscle-fibers. A distinct stratification of the wall is apparent 

 only on those lymph- vessels which, in the extended condition, have 

 a diameter of 0.8 to 1 mm. (C.'Toldt). Here, three layers are 



