. A text-book of human physiology . t has been estimated by passing a littleballoon fastened to a string through a stomachfistula into the duodenum and measuring on thestring the rate at which the balloon was forcedalong. In the uppermost parts the rate wasgreater than in the lower parts, and in the formerreached the high value of 10-18 cm. in a view of the long time the food sojourns in theintestine this appears abnormally high. The intestine is of course constricted by thecontraction of its circular muscles; it is short-ened and at the same time dilated by contractionof its longitu
. A text-book of human physiology . t has been estimated by passing a littleballoon fastened to a string through a stomachfistula into the duodenum and measuring on thestring the rate at which the balloon was forcedalong. In the uppermost parts the rate wasgreater than in the lower parts, and in the formerreached the high value of 10-18 cm. in a view of the long time the food sojourns in theintestine this appears abnormally high. The intestine is of course constricted by thecontraction of its circular muscles; it is short-ened and at the same time dilated by contractionof its longitudinal muscles. Suppose, e. g., thatin Fig. 115 the small circles lying side by siderepresent cross sections of the longitudinal mus-cle fibers. When they contract, they becomethicker; each fiber therefore claims more space,and the fibers lying side by side becoming thicker all at once must have the effect of making the circumference larger—i. e., ofdilating the lumen. This conclusion has been confirmed also experimentally(Exner).. Fig. 115.—Schema to illustratethe relation of the lon^ fibers of the intestineto each other. With re<jard to the movements actually takinp; place in the intestine withinthe body. Cannon observed with the hel]) of tlie Rontgen rays, after feeding afood mixed with bismuth subnitrate, that the food in an intestinal loop isdivided all at once into small segments. From these segments new ones arecontinually being formed by rln/tlnniral confractlons [what Cannon callsrhythmical segmentation], at the rate of about thirty per minute. Bythis means the food is very intimately mixed with the intestinal fluids andis brought into close contact with the intestinal wall. The contents are thenpushed along and the process is repeated over and over (Fig. 116). The intestinal movements are to a certain extent independent of thecentral nervous system, for an exsected intestine may contract animals whose nerves to the intestine
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