386 INTERNAL SECRETIONS OF PANCREAS AND SPLEEN. 



nerves alone transmit impulses to all the structures of the organ, 

 including the glands which, during this period, elaborate their 

 secretory products. 



When as a result of physical (reflex) or psychical stimuli the 

 pancreas becomes functionally active, the vagus impulses impose 

 their rhythm upon the general motor nerves, and the vagus system 

 assumes control of the secretory process. As a result, 



(a) The extrinsic arteries are constricted beyond their nor- 

 mal tonic caliber and the speed of the blood-flow through the organ 

 is increased. 



(b) The intrinsic arteries that do not supply capillaries to 

 the glands are also constricted, thus forcing the blood into these 

 capillaries and inducing glandular activity and the production of 

 pancreatic secretions. 



FUNCTIONAL MECHANISM OF THE SPLEEN. The innerva- 

 tion of the spleen includes, as a predominating feature, the 

 distribution of a fair proportion of the terminal fibers to the 

 muscular elements, which, in man, are mainly supplied to the 

 trabecula?. "We have evidence," says Professor Foster, "that 

 the muscular activity of the spleen, whether of the muscular 

 capsule and trabeculae and arteries combined, or of the latter 

 alone, is under the dominion of the nervous system. A rapid 

 contraction of the spleen may be brought about in a direct man- 

 ner by stimulation of the splanchnic or vagus nerves," . . . 

 "it may also be caused by stimulation of the medulla oblongata 

 with a galvanic current or by means of asphyxia. Though the 

 matter has not yet been fully worked out, we have already 

 sufficiently clear indications that the flow of blood through 

 the spleen is, through the agency of the nervous system, 

 varied to meet changing needs. At one time a small quantity 

 of blood is passing through or is being held by the organ and 

 the metabolic changes which it undergoes in the transit are 

 comparatively slight. At another time a larger quantity of 

 blood enters the organ and is let loose, so to speak, into the 

 splenic pulp, there to undergo more profound changes, and 

 afterward to be ejected by rhythmic contractions of the mus- 

 cular tra.beculaB." 



That rapid contraction of the spleen should occur under 

 stimulation of the splanchnic nerve is now easily accounted 



