340 EPITHELIAL AND ENDOTHELIAL TISSUE. 



matter of course, to a great extent imperceptible. Capillary blood- 

 vessels are by no means permanent formations, but, according 

 to the necessity of their vital activity, they are produced and 

 destroyed i. e., transformed into the connective tissue from 

 which they have originally sprung. That, with advancing age, a 

 number of capillaries are transformed into bone, I have demon- 

 strated (see page 236), and similar instances are found in all 

 varieties of connective tissue. 



All capillaries are surrounded by a delicate light rim, which 

 is traversed by minute spokes of bioplasson, interconnecting the 

 wall of the capillary with the adjacent tissue. This peri vascular 

 space, which certainly contains a liquid, was erroneously termed 

 a lymph-space, because colored liquids can be forced into it from 

 without by parenchymatous injection. Similar spaces, however, 

 exist around all bioplasson formations and around the territor- 

 ies of connective tissue (see page 132), but they bear no relation 

 to the lymphatic system. It will be seen that successful injec- 

 tions have demonstrated the presence, in the lymph capillaries, 

 of an endothelial wall, similar to that of the blood capillaries. As 

 both are permeable to the liquid and solid constituents of the 

 blood and lymph, the assumption of an ensheathing lymphatic sys- 

 tem around the blood-vessels is quite superfluous. Around the 

 capillary blood-vessels which lie close to the arteries and veins 

 there is often found a continuous layer of connective tissue, the 

 so-called capillary adventitial coat. A distinct coat of this kind 

 is found around all capillaries of the central nervous system 

 (His). According to Boll there is no reason for 'terming this 

 investing sheath, which is rendered very plain by parenchyma- 

 tous injection, a lyrnph-sheath. 



In the vicinity of capillaries, especially in the loose connective 

 tissue, large, coarsely granular plastids are often found, the 

 "plasma-cells" of Waldeyer, the significance of which is not yet 

 fully understood. Here, however, is the place of the most intense 

 nutrition, where the first and most prominent changes occur in 

 the process of inflammation. 



Upon being injected with a solution of nitrate of silver, the 

 capillaries exhibit in many localities an elongated frame of brown 

 cement-substance, with a varying number of stomata and stig- 

 mata. The flat endothelia, being broadest in their middle portion, 

 where the nucleus is located, exhibit a spindle-shape both in lon- 

 gitudinal and transverse sections of capillaries. In numerous 

 cases, however, no endothelium is rendered visible, even with the 



