THE LYMPHATIC SYSTEM. 309 



phibious reptiles there are irregularly-shaped spaces or lacunae, forming 

 part of the lymphatic system and interposed between adjacent organs 

 in various parts of the body. In the mammalia the peritoneal and 

 pleural cavities, and probably all the principal serous sacs, are also in 

 communication with the lymphatic vessels. This was first shown by 

 Recklinghausen * in the rabbit, by injecting the peritoneal cavity with 

 milk, or a watery fluid holding granules of coloring matter in suspen- 

 sion, after which the lymphatic vessels of the central tendon of the 

 diaphragm were found filled with the injection. Furthermore, the 

 central tendon of the diaphragm being removed from the recently- 

 killed animal, and a drop of milk placed upon its peritoneal surface, 

 the milk globules could be observed under the microscope, running 

 in converging currents to certain points on the surface of the tendon 

 and thence penetrating into its lymphatic vessels. The cavity of the 

 pleura has been found by similar means to communicate w^ith the lym- 

 phatic vessels in its neighborhood. The serous cavities accordingly 

 are either extensive lacuna?, forming in some regions the origin of 

 the lymphatics, or else they are wide and shallow expansions, situated 

 at various points in the course of these vessels. 



The Lymphatic Glands. During the passage of the lymphatic ves- 

 sels from the periphery toward the centre, they are repeatedly inter- 

 rupted by ovoidal gland-like bodies, of a pale reddish color, varying, in 

 man, from two to twenty millimetres in their long diameter. They do 

 not exist in fish and reptiles, but are always present in birds and mam- 

 malia. As a rule, each gland receives several lymphatic vessels, com- 

 ing from the periphery ; and several others leave it at the opposite sur- 

 face, continuing their course toward the centre of the circulation. The 

 former are called the " afferent," the latter the "efferent" lymphatic 

 vessels. The lymphatic glands have no excretory duct, and whatever 

 new materials they produce must be carried away either by the veins 

 or by the efferent lymphatic vessels. 



The lymphatic glands consist, first, of an external fibrous envelope, 

 with prolongations from its internal surface in the form of septa and 

 branching bands, dividing the interior into smaller spaces by their inos- 

 culation. The fibrous bands composing this framework are the "trabec- 

 ulae." Secondly, in the interstices between the trabeculae is contained 

 the pulpy substance of the gland. Thirdly, the blood-vessels in the 

 interior of the gland follow distinct routes in the spaces between the 

 trabeculae. They are surrounded and held in position by fine branch- 

 ing fibres attached to their external surface ; and in the meshes of 

 these fibres, as well as between the blood-vessels, are imbedded a great 

 number of rounded, granular, nucleated cells, about 9 mmm. in diam- 

 eter, similar to the white globules of the blood and lymph, and known 

 in this situation as " lymph globules." The presence of these cells, 

 between and immediately around the capillary blood-vessels, gives to 



Strieker's Manual of Histology, Buck's Edition. New York, 1872, p. 221. 



