2O2 BLOOD AND BLOOD-FORMING ORGANS. 



(at the hilum). On leaving the trabeculae their walls are formed of 

 endothelium and adenoid reticulum, which separates them from the 

 blood-sinuses. They end (or begin) in lacunae with thin walls 

 which are perforated and communicate with the blood-sinuses 

 (Weidenreich). Nerves have been traced to the hemolymph glands 

 by Lewis (dog, rat). They probably end in the involuntary muscle 

 of the capsule and trabeculae. Typical hemolymph glands have no 

 lymph-vessels. In certain glands both blood- and lymph-sinuses 

 are found. In such glands there is apparently an intermingling of 

 blood and lymph, so that red blood-cells may pass into the 

 lymphatics. 



The marrow lymph-glands are not so numerous. They have a 

 thin capsule consisting of fibrous tissue but containing little elastic 

 and muscular tissue. The blood-sinuses are not so well developed. 

 In the lymphoid tissue the basophile and eosinophile cells are more 

 numerous than in the splenolymph glands, and large cells similar to 

 the large bone-marrow cells are now and then met with. 



As appears from the accounts of the majority of observers who 

 have studied hemolymph glands, they have a hemolytic function, 

 in that the red blood-cells are destroyed in them. Robertson and 

 Clarkson ascribe to them a blood-forming function. This has also 

 been observed by Warthin in the case of marrow lymph-glands, 

 under certain conditions. The hemolymph glands are seats of 

 origin for the white blood-cells which appear also to be destroyed 

 here (eosinophile cells, Weidenreich). 



C THE SPLEEN. 



The spleen is a blood-forming organ, in which white blood-cells 

 and, in embryonic life and under certain conditions in adult life also, 

 red blood-cells are formed the former in the adenoid tissue (Mal- 

 pighian corpuscles) and spleen pulp, the latter only in the spleen 

 pulp. 



The spleen is covered by peritoneum, and possesses a capsule 

 consisting of connective tissue, elastic fibers, and nonstriated muscle- 

 cells. This capsule sends numerous processes or trabeculae into 

 the interior of the organ, which branch and form a framework in 

 which the vessels, especially the veins, are imbedded. This con- 

 nective-tissue framework breaks up to form the reticular tissue 

 which constitutes the ground substance of the spleen. 



On examining a section of the spleen with the low-power mag- 

 nifying glass, sections of the trabeculae, and round or oval masses 

 of cells, having a diameter of about 0.5 mm., and in structure and 

 appearance similar to the lymph-nodules (Malpighian corpuscles), 

 are clearly defined ; between and around these structures is a tissue 

 rich in cells, blood-vessels and blood-corpuscles, known as the 

 spleen pulp. 



