288 A MANUAL OF PHYSIOLOGY 



stomach, and worked up thoroughly with the gastric juice. 

 Kept in constant circulation, it gradually becomes reduced 

 to a semi-liquid mass, the chyme, which is at intervals driven 

 against the pylorus by strong and regular peristaltic con- 

 tractions of the lower end of the stomach, the sphincter 

 relaxing from time to time by a sort of reflex inhibition to 

 admit the better-digested portions into the duodenum, but 

 tightening more stubbornly at the impact of a hard and 

 undigested morsel. The cardiac end, with the exception of 

 the portion that borders the transverse band, appears to 

 take no share in these peristaltic movements. And, indeed, 

 it is far more difficult to cause such contractions by artificial 

 stimulation in the fundus than in the pylorus. The two 

 portions of the stomach seem to be partially, or in certain 

 animals from time to time completely, cut off from each 

 other by the contraction of the sphincter of the antrum. 

 The fundus, so far as its mechanical functions are concerned, 

 appears to act chiefly as a reservoir for the food, which it 

 gradually passes into the antrum as digestion goes on, by a 

 tonic contraction of its walls. These facts have been mainly 

 ascertained by observations on animals, such as the dog and 

 the cat, either by direct inspection after opening the abdomen 

 (Rossbach), or in the intact body by means of the Rontgen 

 rays (Cannon). In the latter method the food is mixed with 

 subnitrate of bismuth, which is opaque to these rays, so that 

 when the animal is looked at through a fluorescent screen 

 the stomach appears as a dark shadow in the field. 



In the intestine two kinds of movements are to be seen : 

 (i) Gentle, swaying, ' pendulum ' movements, sometimes 

 irregular, but often recurring rhythmically at the rate (in the 

 dog) of 10 or 12 in the minute. Both the longitudinal and 

 the circular muscular coats contract, causing slight waves of 

 constriction, which may originate at any part of the gut, but 

 nearly always travel from above downwards, with a velocity 

 of 2 to 5 centimetres per second. (2) True peristaltic move- 

 ments, in which a ring of constriction, obliterating the 

 lumen, moves slowly down the tube, with a speed, it may 

 be, no greater than I mm. per second. The portion of the 

 intestine immediately below the advancing constriction is 



