404 ORIGIN OF THE LYMPHATICS. 



of the space within the capillary arch (B). The finest lymphatics are lined by a 

 layer of delicate, nucleated endothelial cells (e,e), with characteristic sinuous 

 margins, whose characters are easily revealed by the action of silver nitrate 

 (Fig. 158, L). This .substance blackens the cement substance which holds the 

 endothelial cells together. Between the endothelial cells are small holes, or 

 xtomata, by means of which the lymph-capillaries communicate (at x) with the 

 juice canals. 



It is assumed that the blood-vessels communicate with the juice 

 canals (J. Arnold, Thoma, Uskoff), and that fluid passes out of the 

 thin-walled capillaries through their stomata (p. 122) into these spaces. 

 This fluid nourishes the tissues, the tissues take up the substances 

 appropriate to each, while the effete materials pass back into the 

 spaces, and from these reach the lymphatics, which ultimately discharge 

 them into the venous blood. 



Whether the cells within these spaces are actively concerned in the pouring 

 out of the blood-plasma, or take part in. its movement, is matter for con- 

 jecture. We can imagine that by contracting their body, after it has been 

 impregnated with fluid, this fluid may be propelled from space to space towards 

 the lymphatics. The leucocytes wander through these spaces until they pass into 

 the lymphatics. Fine particles which are contained in these spaces e.g., after 

 tattooing the skin and even fatty particles after inunction are absorbed by the 

 leucocytes, and carried by them to other parts of the body. [The pigment 

 particles used to tattoo the finger are usually found within the first lymphatic 

 gland at the elbow.] 



After what has been said regarding the passage of colourless blood- 

 corpuscles through the stomata of the blood-capillaries, or through the 

 walls of the smaller blood-vessels ( 95), the passage of cellular 

 elements from the blood-vessels into the origin of the lymphatics is to 

 be considered as a normal process (E. Hering). Granular colouring 

 matter passes from the blood into the protoplasmic body of the cells 

 within the lymph-spaces ; and only when the granular pigment is in 

 large amount, does it appear as a granular injection in the branches of 

 the juice-spaces (Uskoff). 



(2.) The origin of lymphatics within villi i.e., of the chyle vessel or lacteal 

 lias been described at p. 389. The central lacteal communicates with the lacunar 

 interstitial spaces in the adenoid tissue of the villus, and this again with the 

 protoplasmic body of the epithelial cells. It is assumed that the lymph-corpuscles, 

 which lie in the meshes of the adenoid tissue, pass into the central lacteal (His), 

 while new cells are continually passing out of the blood-capillaries of the villi into 

 the tissue, where they perhaps undergo increase through division. 



(3.) Origin of lymphatics in perivascular spaces (Fig. 159). The smallest blood- 

 vessels of bone, the central nervous system, retina, and the liver, are completely 

 surrounded by wide lymphatic tubes, so that the blood-vessels are completely 

 bathed by a lymph-stream. In the brain, these lymphatics are partly composed of 

 delicate connective-tissue fibres, which traverse the lymph-space and become 

 attached to the wall of the included blood-vessel (Roth). Fig. 159, B, represents a 

 transverse section of a small blood-vessel, B, from the brain; p is the divided 

 perivascular space. This space is called the perivascular space of His, but in 



