THE ORGANS ANNEXED TO ABDOMINAL DIGESTIVE CANAL. 507 



former. The perivascular lymphatics appear to arise in a delicate adenoid tissue 

 enclosing the smaller arteries, partly from a plexus, and partly from lymph- 

 cavities, the walls of which are formed by endothelial cells alone. The trabecular 

 system arises in a plexus lying between the muscle-cell fasciculi. 



There is, according to Kyber, a distinct difference between the splenic pulp 

 and the adenoid tissue surrounding the artery, both histologically and patho- 

 logically. The latter he regards as performing the usual functions of the 

 lymphatic system ; while the former, he conceives, may exercise that digestive 

 action on the albuminoids of the spleen, which SchifF has demonstrated takes 

 place.) 



Nerves. — They are derived from the solar plexus, and, enveloping the splenic 

 artery, with it enter the spleen. (They appear to be very large, but this 

 appearance is due to the great proportion of ordinary fibrous tissue investing 

 them.) 



From what has been said above respecting the arrangement of the splenic 

 arteries and veins, it will be perceived that the areola formed by the trabecule 

 of the fibrous framework contain the pulp, and are not in direct communication 

 with the arterial capillaries. Such an organization belongs to erectile tissues. 

 The arteries communicate with the veins proper by venous canals channeled in 

 the splenic pulp, and are lined only by an endothelium of elliptical cells. These 

 venous canals are extremely dilatable, especially in the Horse. When the splenic 

 vein is inflated, their walls separate and press back the pulp, they become con- 

 siderably enlarged, and distend the cells of the fibrous structure ; but the air 

 does not reach the interior of these cells. 



Functions. — Nothing precise is known regarding the functions of the spleen ; 

 though they must be of very secondary importance, because animals in which the 

 organ has been extirpated, and which have recovered from the operation, have 

 continued to live in apparent good health. Numerous hypotheses have been 

 formed on this subject ; two of which, founded on the study of the anatomical 

 peculiarities of the spleen-tissue, and on exact physiological observations, are as 

 follows : 1. The spleen is a diverticulum for the portal vein. 2. The red corpuscles 

 of the blood are destroyed in the spleen. 



With regard to the first hypothesis, it is evident that, owing to the presence 

 of the venous sinuses already mentioned, and their great dilatability, as well as 

 to the elasticity and contractility of the spleen-tissue, the organ is favourably 

 constructed to act as a blood-reservoir. Goubaux, on the other hand, has 

 demonstrated that there is always an augmentation in the spleep's volume when 

 an animal has ingested large quantities of water, the consecutive absorption of 

 which determines a certain tension in the portal venous system. 



The second opinion, emitted by Kolliker, is founded on the existence in the 

 splenic pulp of blood- corpuscles in a state of decomposition, and in the analyses 

 made by J. Beclard of the blood in the splenic vein, which have proved that 

 there is a notable diminution in the proportion of these. These analyses 

 have, however, been much questioned, and, recently, !Malassez and Picard have 

 shown results which are in favour of the third hypothesis. They have found 

 that the red corpuscles increase in the blood of the splenic vein, while the 

 proportion of iron diminishes in the pulp ; and from this fact they conclude 

 that in the spleen there is a new formation of corpuscles, in which the iron 

 contained in the splenic pulp participates. 



It is to be remarked that, in the researches undertaken to discover the 



