THE MOVEMENTS OF THE STOMACH 73 



introduced into the contents of the alimentary canal, it 

 becomes possible to recognize the situation of this sub- 

 stance so long as it remains sufficiently concentrated. 

 More than this, if the cavity is well filled its outline is, of 

 course, identical with that of the included material. The 

 z-ray picture will then show the changing contour of the 

 organ in silhouette. The compounds most used to secure 

 opacity to the #-ray are the salts of bismuth, generally the 

 subnitrate or the subcarbonate. 



The most numerous experiments of this sort are those of 

 Cannon, and the cat has been the favorite subject. When 

 the animal has had a full meal of bread-crumbs and milk 

 with the bismuth salt evenly mixed in the mass the x-ray 

 shows the entire form of the stomach. The fundus has an 

 even outline and preserves it unchanged from hour to 

 hour, except that a very gradual contraction takes place. 

 The antrum is traversed by deep but slow-moving peris- 

 taltic waves, which originate near the transverse band and 

 pass to the pylorus. The tendency of such waves must be 

 to force successive portions of the food into the intestine, 

 but in the great majority of cases the waves bear down 

 upon a tightly closed pyloric sphincter. The only possible 

 result is then an eddying movement, the contents advanc- 

 ing only to rebound from what is, for the time, a blind 

 pouch. This favors the reduction of the larger morsels and 

 helps to secure at length the formation of the smooth, 

 creamy "chyme." But it is probable that most people 

 have an exaggerated notion of the mechanical powers of 

 the stomach. 



The waves which pass over the antrum arise in the cat 

 with strange regularity at intervals of ten seconds. Each 

 wave takes about half a minute to make its way to the 

 pylorus, so there are commonly three creases to be seen, 

 all shifting with a motion of clock-like slowness toward the 

 outlet. During the prolonged period required for the 

 emptying of the stomach of the cat eight hours or more 

 it is evident that the total number of the waves may be 

 over two thousand. When the pyloric sphincter momen- 



