506 THE DIGESTIVE APPARATUS IN MAMMALIA. 



seen included in a cell ; but more frequently the included blood-discs are altered 

 both in form and colour. Besides these, numerous deep-red, or reddish-yellow, 

 or black corpuscles and crystals, either single or aggregated in masses, are seen 

 diffused throughout the pulp substance ; these, in chemical composition, are 

 closely allied to the hasmatine of the blood. The colourless elements consist of 

 granular matter ; nuclei, about the size of the red blood-discs, homogeneous or 

 granular in structure ; and nucleated vesicles in small numbers. These elements 

 form a large proportion of the entire bulk of the spleen in well-nourished 

 animals ; whilst they diminish in number, and occasionally are not found at all, 

 in starved animals. The application of chemical tests shows that they are 

 essentially a proteine compound. The splenic or Malpighian corpuscles are round, 

 whitish, semi-opaque bodies, glutinous in consistence, and disseminated through- 

 out the substance of the organ. They are more distinct in early than in adult 

 life or old age, and vary considerably in size and number. From the manner in 

 which they are appended to the sheaths of the smaller arteries and their branches, 

 they resemble the buds of the moss-rose. Each consists of a membranous 

 capsule, composed of fine pale fibres interlacing in all directions. The blood- 

 vessels ramifying on the surface of the corpuscles, are the larger ramifications 

 of the arteries to which the sacculus is connected, and also of a delicate capillary 

 plexus, similar to that surrounding the vesicles of other glands. These vesicles 

 have also a close relation v.ith the veins, and the vessels begin on the surface of 

 each vesicle throughout the whole of its circumference, forming a dense venous 

 mesh in which each of these bodies is enclosed. It is probable that, from the 

 blood contained in the capillary network, the material is separated which is 

 occasionally stored up in their cavity ; the veins being so placed as to carry off, 

 under certain conditions, those contents that are again to be discharged into the 

 circulation. Each capsule contains a soft, white, semi-fluid substance, con- 

 sisting of granular matter, nuclei similar to those found in the pulp, and a few 

 nucleated cells, the composition of which is apparently albuminous. These 

 bodies are very large, after the early periods of digestion, in well-fed animals, and 

 especially those fed upon albuminous diet. In starved animals, they disappear 

 altogether.) 



Arteries. — These emanate from the splenic artery at different elevations, and 

 plunge into the tissue of the spleen, preserving theu' reciprocal independence. 

 Their terminal ramifications do not open, as has been said, into venous sinuses, 

 but into minute tufts of capillaries, which traverse the splenic pulp, to be con- 

 tinued by the venous network. 



Veins. — All the venous branches of the spleen open into the splenic vein, and 

 are lodged, with the corresponding artery, in the fissure of the organ. Traced 

 from their commencement, they are seen to gradually lose their constituent 

 membranes, and to open into sinuses which are only lined by the endothelium 

 of the vessels. It is in these sinuses that the network of venous capillaries 

 which succeed the arterial capillaries, originates. 



Lymphatic vessels. — These are found on the external surface of the organ, 

 and along the track of the blood-vessels. (There appear to be two systems of 

 lympjjatics in the spleen of the Horse — one belonging to the trabeculse, which 

 is in continuity with the lymphatics of the capsule ; and another accompanying 

 the branches of the splenic artery and its branches, investing these vessels like 

 a sheath. These two systems may be named, respectively, the trabecular and 

 the perivascular lymphatics. Occasionally, the latter can be injected from the 



