SPLEEN. CS5 



portion to the entire body, being as 1 to 700. The size of the spleen is increased 

 during and after digestion, and varies considerably, according to the state of 

 nutrition of the body, being large in highly fed, and small in starved animals. 

 In intermittent and other fevers, it becomes much enlarged, weighing occasionally 

 from 18 to 20 pounds. 



Structure. The spleen is invested by two coats; an external serous, and an 

 internal fibrous elastic coat. 



The external or serous coat is derived from the peritoneum ; it is thin, smooth, 

 and in the human subject intimately adherent to the fibrous elastic coat. It 

 invests almost the entire organ, being reflected from it at the hilus, on to the 

 great end of the stomach, and at the upper end of the organ on to the Dia- 

 phragm. 



The fibrous elastic coat forms the framework of the spleen. It invests the 

 exterior of the organ, and at the hilus is reflected inwards upon the vessels in the 

 form of vagina3 or sheaths. From these sheaths, as well as from the inner surface 

 of the fibro-elastic coat, numerous small fibrous trabeculse or bands (fig. 3-iT) are 

 given off in all directions ; these, uniting, constitute the areolar framework of the 

 spleen. The proper coat, the sheaths of the vessels, and the trabecula3, consist of 



Fig. 347. Transverse Section of the Spleen, showing the Trabecular Tissue 

 and the Splenic Vein and its Branches. 



a dense mesh of white and yellow elastic fibrous tissues, the latter considerably 

 predominating. It is owing to the presence of this tissue, that the spleen pos- 

 sesses a considerable amount of elasticity, admirably adapted for the very con- 

 siderable variations in size that it presents under certain circumstances. In some 

 of the mammalia, in addition to the usual constituents of this tunic, there are found 

 numerous pale, flattened, spindle-shaped, nucleated fibres, like unstriped muscular 

 fibres. It is probably owing to this structure, that the spleen possesses, when acted 

 upon by the galvanic current, faint traces of contractility. 



The proper substance of the spleen occupies the interspaces of the areolar frame- 

 work of the organ ; it is a soft, pulpy mass, of a dark reddish-brown color, consist- 

 ing of colorless and colored elements. 



The colorless elements consist of granular matter; nuclei, about the size of 

 the red blood-disks, homogeneous or granular in structure, and nucleated vesicles 

 in small numbers. These elements form, probably, one-half or two-thirds of the 



