140 MICROSCOPIC AS ATOMY OF THE ORGANS. 



adenoid tissue of the pulp is distinguished from that of the 

 Malpighian bodies by the fact that the latter consists entirely 

 of lymphoid cells. 



Some authors claim that the spleen is a blood-forming 

 organ because erythroblasts are found there. Others regard 

 it as an organ in which destruction of blood takes place, for 

 the reason that fragments of blood corpuscles and blood pig- 

 ment are frequently found. 



The character of the blood-vessels in the spleen shows some 

 peculiarities. The arteries do not anastomose with one another; 

 their adventitia often shows a lymphoid character i. e., in 

 Malpighian corpuscles. The terminal arteries show a thicken- 

 ing of this lymphoid sheath to form the ellipsoids of the spleen. 

 In their final divisions the arteries branch like the hairs of 

 a brush (penicilli). The blood-vessels of the spleen are best 

 considered together with the so-called lobule. According to 

 Mall, the framework of the spleen, which can be demonstrated 

 by washing out the cellular elements of a spleen macerated in 

 water, is divided into sacs, each of which contains a spleen 

 lobule. These lobules have a distinct relation to the blood- 

 vessels. By injecting the vessels with celloidin or agar-agar 

 and macerating the tissue, this relation is demonstrated. The 

 arteries enter at the hilus, and divide into many branches, 

 one of which enters each lobule and passes along its centre. 

 The veins are always intimately related to the trabeculse, and 

 are always found at the periphery of the lobules. This is 

 shown in Fig. 99. The Malpighian corpuscle usually lies at 

 the hilus end of the lobule i. e., at the side away from the 

 capsule. The veins accompany the branches of the interlobu- 

 lar trabeculaB into the lobule, which is divided by these 

 branches into several compartments. The veins as well as the 

 trabeculse may be spoken of as interlobular and intralobular. 

 The central artery of the lobule branches to supply the various 

 compartments formed by the intralobular trabeculse, and the 

 blood is collected finally by the intralobular veins. A venous 

 injection of the lobule fills a plexus of veins (Fig. 99, P), in 

 whose meshes there are small areas of spleen pulp, the so- 



