STRUCTURE OF THE SPLEEN, 399 



with -whatever amount of muscularity they may possess, renders the 

 spleen capable of the great and sudden alterations in size to -which it is 

 subject. 



The pulp of the spleen is of a dark reddish-brown colour : when 

 pressed out from between the trabecule it resembles grumous blood, 

 and, like that, acquires a brighter hue on exposure to the air. 



When a thin section is examined under the microscope the pulp is seen 

 to consist of a reticulum of branched connective-tissue. corpuscles, which 

 are of various forms and sizes ; in some parts little but the intercom- 

 municating branches remaining, forming a fine retiform tissue, in other 

 parts the cells being larger and in closer connection (fig. 285, p). 

 These corpuscles, which may be termed the supporting cells of tlie pulp, 

 contain each a clear oval nucleus, like connective tissue cells generally ; 

 moreover, in teazed-out preparations of the fresh spleen substance it' is 

 not uncommon to find within them yellowish pigment granules of 

 various sizes, presumed to be derived from blood corpuscles ; indeed, 

 every stage of retrogressive metamorphosis of blood corpuscles may be 

 noticed to occur within them. The interstices between these "^sus- 

 tentacular cells are, in sections, always found to be occupied by blood 

 (fig. 285, hi), the white corpuscles being, however, in rather larger pro- 

 portion than in ordinary blood, especially in the neighbourhood of the 

 Malpighian corpuscles to be immediately described. 



Blood-vessels. — The splenic artery and vein, alike remarkable for 

 their great proportionate size, having entered the spleen by six or more 

 branches, ramify in its interior, enclosed within the trabecular sheaths 

 already described. The smaller branches of the arteries leave the tra- 

 beculiB, and, passing into the proper substance of the spleen, terminate 

 in small tiifts of capillary vessels arranged in pencils (fig. 283). 



The external or connective tissue coat of these smaller arteries 

 becomes transformed into lymphoid tissue, which forms a comparativelv 

 thick sheath along each. This lymphoid sheath becomes suddenly 

 dilated here and there into small s})heroidal bodies, measuring on an 

 average y^ of an inch in diameter, but varying in size from much smaller 

 than this up to -jtth of an inch, and closely resembling the lymphoid 

 follicles met with in the intestine and elsewhere. These lymphoid 

 expansions may be seen on the surface of a fresh section of the organ 

 as light-coloured spots scatcei-ed in the dark substance composing the 

 pulp, and have been long noticed and described as the Malpighian 

 corpuscles of the spleen (fig. 283 ; fig. 284, c c). In some cases they are 

 developed upon one side only of the arterial wall, upon which they then 

 appear to be sessile; whilst in other instances — and this is the most 

 ft-equent in the human subject — the expansion takes place all round 

 the circumference of the vessel, by which they appear to be pierced, 

 and which is generally smaller in these cases and sends off radiating 

 branches which are distributed in the Malpighian corpuscle. This latter 

 then appears attached by a short peduncle to the vessel of which its 

 artery is a branch. 



The Malpighian corpuscles are, as just stated, localized expan- 

 sions of the lymphoid tissue of which the external coat of the smaller 

 arteries of the spleen is formed. The reticulum of the tissue is com- 

 paratively open, being almost absent towards the centre of the cor- 

 puscle : at the confines it becomes closer ; there is, however, no 

 distinct boundary separating it from the retiform tissue of the pulp 



