TISSUES OF THE BODY. 



377 



and has been named by His the perivascular canal system. This observer 

 is inclined to regard it as belonging to the lymphatic system, in which 

 he is perhaps right. The merit of having first discovered this rests, 

 however, with Robin, who, several years previously, had maintained the 

 presence of lymph sheaths around the capillaries of the parts in question. 



208. 



Having discussed the disposal of the lymphatics, let us now turn to 

 the consideration of the nature of their peripheral portions, a point of 

 great importance. 



Are they, in the first place, vessels, that is, endowed with a special 

 wall like that of blood capillaries ? 



This has recently been declared to be the case by Teichmann (1), after 

 the most extensive researches, aided 

 by injections, and also by Koelliker, 

 who investigated the matter in the 

 tail of the tadpole ( 206). 



Another view, which has found 

 numerous defenders within the last 

 few years, is, however, directly op- 

 posed to this. According to it, the 

 peripheral circulation is only lacunal, 

 i.e., takes place within the interstices 

 of connective -tissue (2) (BriicJce, 

 Leydig, His, Ludwig). For my own 

 part, I have for many years looked 

 upon the lymphatics as bounded alone 

 by connective-tissue, which is, how- 

 ever, condensed and membranous, 

 and encloses the space completely, 

 playing the part of a sheath. Indeed, it was impossible, until very recently, 

 to make out anything but a homogeneous boundary layer around the 

 lymphatic passage (fig. 378, b). 



By means of the new reagent, however, dilute solution of nitrate of 

 silver, this apparently homogeneous limiting layer of connective-tissue has 

 been resolved into a series of united, smooth, 

 and nucleated cells or endothelia, allied to 

 those of the blood-vessels (fig. 379). 



But while in the blood capillaries this wall 

 maintains its independence in regard to the 

 adjacent tissue, it fuses here with the latter, 

 so that only as an exception, and where the 

 surrounding substance is of loose texture, can 

 it be isolated. 



The peripheral tymphatics, whose structure 

 is represented in fig. 380, are, according to 

 this, in contrast to the blood-vessels, by no 

 means regular vessels, but canals (p. 372). 

 In the last-mentioned woodcut, also, we see 

 that here, as in the blood-vessels, gaps or 

 sto'inata occur between the cells. 



A communication between the lymphatic system and the cavities of 

 serous sacs, namely, of the peritoneum and pleurae, by means of orifices 



Fig. 378. From the small intestine of the rab- 

 bit, a, reticular connective substance with 

 lymph cells ; 6. lymph cavity ; c. space for a 

 follicle of Lieberkulm ; d, one of the latter 

 with its cells: , /, capillary in transverse 

 section ; gr, thicker trunk. 



Fig. 379. Cells from a lymphatic 

 passage, a, elongated plates; 6, 

 broader specimens. 



