210 THE SPLEEN. 



aided eye, though they always exist in the spleen in a healthy 

 condition. Their average diameter, according to Kolliker, is J. 2 of 

 an inch. They consist of a closed sac, or capsule, containing in 

 its interior a viscid, semi-solid mass of cells, cell-nuclei, and homo- 

 geneous substance. Each Malpighian body is cqyered, on its exte- 

 rior, by a network of fine capillary bloodvessels ; and it is now 

 perfectly well settled, by the observations of various anatomists 

 (Kolliker, Busk, Huxley, &c.), that bloodvessels also penetrate into 

 the substance of the Malpighian body, and there form an internal 

 capillary plexus. 



The spleen is accordingly a glandular organ, analogous in its 

 minute structure to the solitary and agrninated glands of the small 

 intestine, and to the lymphatic glands throughout the body. Like 

 them, it is a gland without an excretory duct ; and resembles, also, 

 in this respect, the thyroid and thymus glands and the supra-renal 

 capsules. All these organs have a structure which is evidently 

 glandular in its nature, and yet the name of glands has been some- 

 times refused to them because they have, as above mentioned, no 

 duct, and produce apparently no distinct secretion. We have 

 already seen, however, that a secretion may be produced in the 

 interior of a glandular organ, like the sugar in the substance of the 

 liver, and yet .not be discharged by its excretory duct. The j^eins 

 of the gland, in this instance, perform the part of excretory ducts. 

 They absorb the new materials, and convey them, through the 

 medium of the blood, to other parts of the body, where they suffer 

 subsequent alterations, and are finally decomposed in the circula- 

 tion. 



The action of such organs is consequently to modify the consti- 

 tution of the blood. As the blood passes through their tissue, it 

 absorbs from the glandular substance certain materials which it did 

 not previously contain, and which are necessary to the perfect con- 

 stitution of the circulating fluid. The blood, as it passes out from 

 the organ, has therefore a different composition from that which it 

 possessed before its entrance ; and on this account the name of vas- 

 cular glands has been applied to all the glandular organs above 

 mentioned, which are destitute of excretory ducts, and is eminently 

 applicable to the spleen. 



The precise alteration, however, which is effected in the blood 

 during its passage through the splenic tissue, has not yet been 

 discovered. Various hypotheses have been advanced from time to 

 time, as to the processes which go on in this organ ; many of them 



