338 DUCTLESS GLANDS. 



been supposed to indicate that the spleen serves as a reservoir for 

 the blood which is needed during the time of digestion, and 

 especially for that taking place in the stomach. The enlargement 

 is caused by relaxation of its muscular tissue and a dilatation of 

 the blood-vessels. 



A peculiar movement of contraction and expansion has been 

 found by Roy to occur in this organ at intervals of about a 

 minute. This he demonstrated by the use of an oneometer (Fig. 

 182). The principle on which this is constructed is the same as 

 that of the plethysmograph (p. 329). It is a metal box made up 

 of two halves, fitted together in such manner that they can be 

 tightly closed, openings being left for the vessels of the organ 

 which is enclosed, be it spleen or kidney. To each half is attached 

 a membrane between which and the metal is a space filled with 

 oil. Any increase in the size of the contained organ is accom- 

 panied by an expulsion of the oil, which returns when the organ 

 becomes smaller. These changes are recorded by the oncograph. 



While the functions of the spleen have not as yet been satis- 

 factorily determined, still they are doubtless comprehended in the 

 various theories which have from time to time been formulated. 



FIG. 182. Roy's oncometer for spleen : A, open ; B, closed. 



(1) It is a producer of white blood-corpuscles. As to this func- 

 tion there is great unanimity of opinion. The blood emerging by 

 the splenic vein contains more of these cells than that which 

 enters the gland, and this number is greatly increased in leuko- 

 cythemia or leukemia, in which the spleen and the Malpighian cor- 

 puscles especially are hypertrophied. This disease may also be 

 due to affections of other organs, as the bone-marrow and 

 lymphatics. 



(2) It destroys red blood-corpuscles. This theory is based upon 

 the fact that red blood-cells are found in the pulp in different 



