194 THE DUCTLESS GLANDS. INTERNAL SECRETIONS. 



sule and the surface of the vascular sheaths there pass off numerous intersecting 

 and branching trabeculae (the trabeculae of the spleen) , which form a rich mesh- 

 work in the interior of the viscus, comparable to the cavities of a sponge. Fibril- 

 lated connective tissue, mixed with elastic and unstriped muscle-fibers, forms the 

 foundation of this portion of the viscus. The interior of the meshes contains a 

 delicate reticulum of adenoid tissue (Fig. 131), which, together with the cellular 

 elements contained in the meshes, is designated the splenic pulp. 



The smaller arterial branches, which gradually lose their fibrous sheath, ulti- 

 mately break up into brush-shaped terminal twigs without anastomoses (peni- 

 cils) . The points of division of the small arterial branches serve for the lodgment 

 of the whitish Malpighian vesicles, which may attain the size of a pinhead and 

 the structure of which in every respect resembles that of solitary lymph-follicles. 

 The Malpighian bodies are found on examination to be spherical, lymphatic masses 

 that have partially separated from the vascular sheath. In some animals, instead 

 of exhibiting a spherical form, they appear as loose arterial sheaths, in a measure 

 as perivascular lymphatic sheaths, so to speak, which may extend to the smallest 

 arterial twigs. According to Tomsa, lymphatic vessels coming from the Malpigh- 

 ian vesicles are found in the subsequent course of the arterial sheath as far as 

 the hilus of the spleen. Other lymphatics form a network in the capsule. 



With regard to the connection between the ends of the arteries and the veins, 

 it is supposed that there is no continuous channel between the smallest capillary ar- 

 terial twigs and the smallest venous branches and that the meshwork of the pulp- 

 reticulum represents an intermediate vascular area devoid of walls. The blood, 

 accordingly, passes through the meshwork of the spleen traversed by the reticu- 

 lum, just as the lymph-stream passes through the spaces of the lymphatic glands. 

 According to another view, there is really a closed vascular channel connecting the 

 ultimate arterial and the corresponding venous capillaries, which, however, con- 

 sists of dilated spaces (like the cavernous spaces in erectile tissues) . These inter- 

 mediary spaces are, however, completely surrounded by spindle-shaped endothe- 

 lium. 



Within the meshes of the reticulum are found cellular elements of various 

 kinds: (i) White blood-corpuscles of various sizes, some swollen and filled with a 

 granular material; (2) leukoblasts or embryonal forms of leukocytes, which multi- 

 ply by division; (3) erythrocytes ; (4) embryonal forms of the latter, also desig- 

 nated erythroblasts, which multiply by mitosis; (5) so-called blood-corpuscle-con- 

 taining cells. 



The numerous nerves of the spleen consist of so-called Remak's fibers; they 

 are sensory, motor, and vasomotor. 



Of the chemical constituents there should be mentioned globulin and nucleo- 

 albumin, nucleinic acid, leucin, tyrosin, xanthin, hypoxanthin, taurin; further 

 lactic, butyric, acetic, formic, succinic, uric, and glycero-phosphoric (?) acids; 

 as well as fats, cholesterin, a gluten-like body, glycogen, inosite, iron-containing 

 pigments, and even free iron oxid. The pulp becomes black on addition of ammo- 

 nium sulphid. The ash is rich in phosphoric acid and iron, but poor in chlorin- 

 combinations. 



With respect to the function of the spleen, the following points are note- 

 worthy : 



1. The spleen may be removed without injury to the individual, as has been 

 proved both in animals and in man (more than QO cases, with about 40 recoveries). 

 After removal of the spleen the hematopoietic activity of the bone-marrow appears 

 to be increased. In frogs, extirpation of the spleen has been observed to be fol- 

 lowed by the appearance of brownish-red nodules in the intestine, which have 

 been regarded as vicarious spleens. Tizzoni speaks of splenic neoplasms in the 

 omentum (horse, dog) after obliteration of the parenchyma and blood-vessels of 

 the spleen. In extremely rare cases total absence of the spleen has been observed 

 in man. 



2. By virtue of its unstriped muscle-fibers the spleen is capable of undergoing 

 change in volume. Irritation of the spleen or of its nerves (by heat or electricity, 

 by quinin, eucalyptus, ergot, and other agents) causes diminution in the size of 

 the viscus, with anemia and granular change. As the spleen is found to be en- 

 larged a few hours after digestion, at a time when the digestive organs have per- 

 formed their work and contain less blood, the spleen has been regarded as an 

 apparatus for the regulation of the vascularity of the digestive organs. 



According to Roy the circulation in the spleen is dependent not alone upon 

 the blood-pressure in the splenic artery, but in marked degree on the contraction 



