246 PHYSIOLOGY CHAP. 



series of experiments which led to interesting although somewhat 

 schematic results. He studied the intestinal movements of an 

 isolated loop, after stripping off (from within outwards) one or 

 more of its coats. He found that when the mucous membrane 

 is removed, the movements persist unaltered, and concluded that 

 they are not reflex, excited by stimuli from the mucous coat, 

 but are automatic in character. The movements also continue 

 after the submucous coat has been removed, from which he con- 

 cluded that they are independent of Meissner's plexus. Lastly, 

 on separating the inner (circular) from the outer (longitudinal) 

 muscular coat by a circular incision, so as to sever the inner layer 

 of fibres completely from Auerbach's plexus, he saw that the inner 

 (circular) coat remained motionless, while the outer (longitudinal) 

 coat still contracted rhythmically. 



Magnus concluded that the intestinal movements are neuro- 

 genic not myogenic, automatic not reflex, and that the automatism 

 arises in the peripheral nerve centres of Auerbach's plexus. This 

 is a bold assumption. The violent removal of the mucous or 

 submucous coat cannot (as it seems to us) be equivalent to 

 sequestration from peripheral stimuli, but rather increases them, 

 in consequence of the trauma due to the laceration of so many 

 afferent nerve fibres. 



As regards the neurogenic character of the intestinal'movements, 

 another assertion of Magnus also appears to us to be strained, 

 viz. that the conduction of excitation from one point to another 

 of a loop takes place along the muscular coat, without the co- 

 operation of Auerbach's plexus, nor still less of Meissner's. 



Finally, the Eontgen rays, already applied by Guyon to the 

 study of gastric movements, have also been employed on the 

 intestine. Cannon, in particular, has carried out methodical 

 experiments by this method (see p. 194). He fed his experimental 

 animals (cats) on a diet mixed with bismuth sub-nitrate, which 

 intercepts the passage of the X-rays, and thus appears on the 

 photographic screen as a shadow. The animals were kept fasting 

 before the experiment, and the bowels cleared out with castor oil, 

 so that it became possible on living animals to follow the progress 

 of food down the alimentary canal. Cannon found that the food 

 was divided into many little segments in the small intestine, 

 owing to the rhythmic repetition of the pendular movements. 

 This segmentation of the food in a coil is repeated by the fusion 

 and redivision of adjacent segments, in a continuous process, so 

 that the churning-up of the chyme is actively promoted. In the 

 cat the rate of division into segments is about 30 divisions per 

 minute. From time to time a peristaltic wave drives the particles 

 forward, on which the process of segmentation recommences. When 

 the animals are made to react to painful stimuli, the intestinal 

 movements cease. During sleep, on the contrary, they continue. 



