304 



LYMPH-FOLLICLES. 



nitrate reveals the presence of relatively large free openings or stomata lying between the 

 endothelium. Each stoma is bounded by several germinating cells, which have a granular 

 appearance, and undergo a change of shape, so that the size of the stoma depends upon the 

 degree of contraction of these cells ; thus the stoma may be open (a), half-open (b), or com- 

 pletely closed (c). These stomata are the origin of the lymphatics. The serous cavities 

 belong therefore to the lymphatic system, and fluids placed in the serous cavities readily pass 



Fig. 218. 

 Perivascular lymphatics. A, aorta of tortoise 

 B, artery from the brain. 



Fig. 219. 

 Stomata in the great lymph-sac (frog). 

 a, open ; b, half-closed ; c, closed. 



into the lymphatics. The cavities of the peritoneum, pleura, pericardium, tunica vaginalis, 

 testis, arachnoid space, aqueous chambers of the eye, and the labyrinth of the ear, are true lymph- 

 cavities, and the fluid they contain is to be regarded as lymph. [Hoffmann has found that a 

 nerve-fibre surrounds the stomata in the frog and sends branches between the germinal epi- 

 thelium.] 



(6) Free open pores have been observed on some mucous membranes, which are regarded as 

 the origin of lymphatics, e.g., in the bronchi, nasal mucous membrane, trachea, and larynx. 



Structure. The larger lymphatics resemble in structure the veins of corresponding size. The 

 valves are particularly numerous in the lymphatics, so that a distended lymphatic resembles a 

 chain of pearls. [Lymphatics have dilations here and there in their course (fig. 217).] 



197. THE LYMPH-GLANDS. The lymphatic glands belong to the lymph 

 apparatus. They are incorrectly termed glands, as they are merely much branched 



lacunar labyrinthine spaces 

 composed of adenoid tissue, 

 and intercalated in the course 

 of the lymphatic vessels. 

 There are simple and com- 

 pound lymph-glands. 



(1) The simple lymph-glands, 



d or, more correctly, lymph-follicles, 



are small rounded bodies, about 



the size of a pin-head. They 



consist of a mass of adenoid tissue 



(tig. 220, A), i.e., of a very delicate 



network of fine reticular fibres 



with nuclei at their points of 



Fig. 220. intersection, and in the spaces of 



Two lymph-follicles. A, a small follicle highly magnified, e , mesll f ork lie * he lv P h and 



showing the adenoid reticulum; B, a follicle less highly tne r lymph-corpuscles. Near the 



magnified, showing injected blood-vessels. surface, the tissue is somewhat 



.... denser, where it forms a capsule, 



which is not however a true capsule, as it is permeated with numerous small sponge-like spaces. 



bmall lymphatics come directly into contact with these lymph-follicles, and often cover their 



surface in the form of a close network. The surface of the lymph-follicles is not unfrequently 



placed in the wall of a lymph-vessel, so that it is directly bathed by the lymph-stream. 



Although no direct canal-like opening leads from the follicle into the lymphatic stream in 



