760 PHYSIOLOGY OF DIGESTION AND SECRETION. 



most definite facts known about the spleen are in connection with its 

 movements. It has been shown that there is a slow expansion and 

 contraction of the organ synchronous with the digestion periods. 

 After a meal the spleen begins to increase in size, reaching a maximum 

 at about the fifth hour, and then slowly returns to its previous size. 

 This movement, the meaning of which is not known, is probably due 

 to a slow vasodilatation, together, perhaps, with a relaxation of the 

 tonic contraction of the musculature of the trabeculae. In addition 

 to this slow movement, Roy* has shown that there is a rhythmical 

 contraction and relaxation of the organ, occurring in cats and dogs 

 at intervals of about one minute. Roy supposes that these con- 

 tractions are effected through the intrinsic musculature of the organ, 

 that is, the plain muscle tissue present in the capsule and trabeculse, 

 and he believes that the contractions serve to keep up a circulation 

 through the spleen and to make its vascular supply more or less 

 independent of variations in general arterial pressure. The fact 

 that there is a special local arrangement for maintaining its cir- 

 culation makes the spleen unique among the organs of the body, but 

 no light is thrown upon the nature of the function fulfilled. The 

 spleen is supplied richly with motor nerve fibers which when stimu- 

 lated either directly or reflexly cause the organ to diminish in 

 volume. According to Schaefer,f these fibers are contained in the 

 splanchnic nerves, which carry also inhibitory fibers whose stimu- 

 lation produces a dilatation of the spleen. 



The chemical composition of the spleen is complicated, but sug- 

 gestive. Its mineral constituents are characterized by a large 

 percentage of iron, which seems to be present as an organic compound 

 of some kind. Analysis shows also the presence of a number of fatty 

 acids, fats, cholesterin, and, what is perhaps more noteworthy, a 

 number of nitrogenous extractives belonging to the group of purin 

 bases, such as xanthin, hypoxanthin, adenin, guanin, and uric acid. 

 The presence of these bodies seems to indicate that active metabolic 

 changes of some kind occur in the spleen. As to the theories of the 

 splenic functions, the following may be mentioned: (1) The spleen 

 has been supposed to give rise to new red corpuscles. This it un- 

 doubtedly does during fetal life and shortly after birth, and in some 

 animals throughout life, but there is no reliable evidence that the 

 function is retained in adult life in man or in most of the mammals. 

 (2) It has been supposed to be an organ for the destruction of red 

 corpuscles. This view is founded chiefly on microscopical evidence 

 according to which certain large ameboid cells in the spleen ingest 

 and destroy the old red corpuscles, and partly upon the fact that the 

 spleen tissue seems to be rich in an iron-containing compound. This 



* "Journal of Physiology/' 3, 203, 1881. 

 t/6id., 20, 1, 1896. 



