THE SPLEEN 379 



stomach by the gastro-splenic omentum and is still further fixed by a 

 fold of peritoneum passing to the diaphragm. It is about five inches 

 (127 millimeters) in length, three to four inches (75 to 100 millimeters) 

 in breadth and a little more than an inch (25.4 millimeters) in thickness. 

 Its weight is six to seven ounces (170 to 198 grams). In the adult it 

 attains its maximum of development, and it diminishes slightly in size 

 and weight in old age. In early life it bears about the same relation to 

 the weight of the body as in the adult. 



The external coat of the spleen is the peritoneum, which is closely 

 adherent to the subjacent fibrous structure. The proper coat is dense 

 and resisting; but in the human subject it is quite thin and somewhat 

 translucent. It is composed of ordinary fibrous tissue mixed with 

 abundant small fibres of elastic tissue and a few non-striated muscular 

 fibres. 



At the hilum the fibrous coat penetrates the substance of the spleen 

 in the form of sheaths for the vessels and nerves. The number of the 

 sheaths in the spleen is equal to the number of arteries that penetrate 

 the organ. This membrane is sometimes called the capsule of Malpighi. 

 The fibrous sheaths are closely adherent to the surrounding substance, 

 but they are united to the vessels by a loose fibrous network. They 

 follow the vessels in their ramifications to the smallest branches and are 

 lost in the spleen-pulp. Between the sheath and the outer coat are bands, 

 or trabeculae, presenting the same structure as the fibrous coat. The 

 presence of elastic fibres in the trabeculae can easily be demonstrated ; 

 and this kind of tissue is very abundant in the herbivora. In the car- 

 nivora the muscular tissue is particularly abundant and can readily be 

 demonstrated ; but in man this is not so easy, and the fibres are less 

 abundant. These peculiarities in the fibrous structure are important in 

 their relations to certain physiological changes in the size of the spleen. 

 Its contractility may be demonstrated in the dog by the application of a 

 faradic current to the nerves as they enter at the hilum. This is followed 

 by a prompt and energetic contraction of the organ. Contractions may 

 be produced, though they are much more feeble, by applying the cur- 

 rent directly to the spleen. 



The substance of the spleen is soft and friable ; and a portion of it, 

 the spleen-pulp, may be pressed out with the fingers or even washed 

 away by a stream of water. Aside from the vessels and nerves, it 

 presents for study: i, an arrangement of fibrous bands, or trabeculae, 

 by which it is divided into communicating spaces ; 2, closed vesicles, 

 called Malpighian bodies, attached to the walls of the bloodvessels; 

 3, a soft, reddish substance, containing large numbers of cells and free 

 nuclei, called spleen-pulp. 



