202 



DIGESTION 



occur at all, is much slower, for in the dog the movement is said to occur 

 twenty times a minute only, while in the rat the segmentation takes place 

 every second, rhythmic movements being generally more rapid the smaller 

 the mammal. By this supposed rhythmic segmentation, occurring prob- 

 ably in many places in the gut at the same time, the food-mass may be 

 thoroughly mixed with the juices of the intestine and any lumps remain- 

 ing in it reduced. Moreover, by this means, if they obtain, the portion 

 of the chyle which is hydrolyzed and ready for absorption is squeezed 

 strongly against the absorbing organs, the villi thus furnishing a strong 

 pressure inward several times a minute. This pumping-action would 

 doubtless assist the capillary circulation of the villi and make them in 



FIG. 100 



The innervation of the gut (dog): png, vagus; pi. cae, celiac plexus; gg. m.s, superior mesenteric 

 ganglion; gg.m.i, inferior mesenteric ganglion; PI. hyp, hypogastric plexus; gsp, great splanchnic; 

 n. er, erector nerve; JD x ni, thirteenth dorsal pair; Z/ni, third lumbar pair; S 1 , first sacral pair. 



(Morat.) 



general much more active in all their functions than else they could be. 

 Further confirmation of this matter, however, is required before it is 

 generally accepted as above described as a normal and universal fact 

 in human digestion. 



The innervation of the small intestine is still a matter of discussion so 

 far as specific neural functions are concerned. Most observers deem the 

 vagus the motor or actuating nerve of the gut. In the dog, at least, there 

 is some evidence that the vagus contains also inhibitory fibers, perhaps, 

 however, coming indirectly from a special place (Jacobi). Pfliiger first 

 claimed that the sympathetic was the inhibitory nerve of the intestine, 

 and the opinion is being continually , supported by researches. Mayer 



