THE LYMPH-GLANDS. 363 



the adventitia (Virchow- Robin spaces). In part these possess a well-developed 

 endothelmm. In their further course, where the vessels increase in caliber, the 

 blood-vessel penetrates the wall of the lymph-vessel at one spot, and both continue 

 separately side by side. Wherever the lymph-vessels serve as peri vascular 

 sheaths, the passage of blood-plasma and lymph-cells into the lymph-stream is 

 greatly facilitated. It should be especially mentioned that, in tortoises, even 

 the larger vessels are often covered by the lymph- vessels as a sheath. In Fig. 

 130, II, A, the bifurcation of the aorta, with the peri vascular lymph- vessels, is 

 shown according to Gegenbaur. The animals referred to exhibit macroscopically 

 the same relations that warm-blooded animals present microscopically; ancl 

 thus the illustration may serve also as the microscopical picture of small peri- 

 vascular lymph- vessels in warm-blooded animals. 



Commencement in the Form of Interstitial Spaces Within the Viscera. In 

 the testicles the lymphatics commence simply in the form of numerous spaces, 

 which occur between the multifarious coils and convolutions of the seminiferous 

 tubules. They will, therefore, here present the form of spaces bounded by the 

 arched, cylindrical surfaces of the tubules. The limiting surfaces are, however, 

 lined with endothelmm. The lymphatics acquire independent tubular walls 

 only beyond the parenchyma of the testicle. Similar conditions are found in 

 the kidneys. In many other glands the glandular substance is likewise sur- 

 rounded by lymph-spaces. Into these the blood-vessels first pour lymph, from 

 which the secreting cells remove the material for the formation of the glandular 

 secretion, as, for example, the salivary glands. 



Commencement by Means of Free Stomata upon the Walls of the Larger 

 Serous Cavities (Fig. 130, III). From the investigations of v. Recklinghausen , 

 C. Ludwig, Dybkowsky, Schweigger-Seydel, Dogiel and others, it has been found 

 that the old view of Mascagni, that the serous cavities communicate freely with 

 the lymphatics, is correct. Upon examining serous membranes (most readily 

 the peritoneal lining of the large lymph-cavity in the frog) , best after moistening 

 them with argentic nitrate, followed by exposure to the action of light, disseminated, 

 relatively large, free openings of the stomata are found lying between the endo- 

 thelial cells. Groups of the latter include a stoma among them. A portion 

 of motile protoplasm lies in the cells surrounding the stoma, close to the edge 

 of the opening. Upon the state of contraction of this protoplasm appears to 

 depend the fact whether the stomata are widely open (a) , half closed (b) , or com- 

 pletely closed (c). These stomata are thus the beginnings of the lymph-capil- 

 laries. Fluids, introduced into the serous cavities, therefore readily reach the 

 path of the lymphatics. The cavities of the peritoneum, the pleurae, the peri- 

 cardium, and the serous covering of the testicle, further the arachnoid space, the 

 chambers of the eye, and the -labyrinth of the ear have shown themselves to be 

 true lymphatic cavities; the fluid in them is thus to be designated lymph. Fluids 

 in the peritoneal cavity are absorbed, in part, also by the veins. The endothelial 

 cells of the serous membranes are capable of movement and communicate with 

 one another by means of connecting bridges of protoplasm. In the animal king- 

 dom the free surfaces of the cells are frequently provided with cilia. 



Even upon the free surface of a number of mucous membranes, it is stated, 

 open pores have been observed as the commencement of the lymphatics: in the 

 bronchi, in the nasal mucous membrane and in the larynx. 



The larger lymphatics arising from the lymph-capillaries closely resemble 

 veins of equal size in the structure of their walls. Especial stress is to be laid 

 upon the presence of a large number of valves, which are placed so closely behind 

 one another that the distended lymphatic is not unlike a string of pearls. 



THE LYMPH-GLANDS. 



The so-called lymph-glands are peculiar to the lymphatic apparatus. They 

 are inappropriately designated glands, because they really represent only many- 

 branched, lacunar, labyrinthine spaces, constituted of adenoid tissue, interposed 

 in the course of the lymphatics. Simple and compound lymph-glands can be 

 distinguished. 



The simple lymph-glands, more correctly designated simple lymph-follicles 

 or cutaneous follicles, are present either isolated (solitary follicle) , as in the intes- 

 tine, the bronchi, the spleen; or collected in masses (conglobate follicle), as in 

 the tonsil, Peyer's patches, the follicles of the tongue. They are small, spherical 

 vesicles, attaining approximately the size of a pin's head, and they consist through- 



