2o8 A MANUAL OP VETERINARY PHYSIOLOGY 



the ruminant, introduced his arm into the organ through an 

 external opening. In the horse, carefully conducted feeding 

 experiments have helped to show what is occurring from hour to 

 hour, but it was not until the aid of X rays was taken advantage 

 of that the process could be seen occurring in the intact living 

 animal. 



If a cat be fed on a diet liberally mixed with bismuth, the 

 process of digestion can be watched by X rays, owing to bismuth 

 being opaque to these rays. Within a few minutes of the entry 

 of food into the stomach, contractions, which begin at the middle 

 of the organ and end of the pylorus, are started. As digestion 

 advances the contractions become stronger and regular, occurring 

 at intervals of about ten seconds, and travelling to the pylorus, 

 which is reached in twenty seconds. Periodically the pylorus is 

 relaxed, and chyme forcibly propelled into the duodenum ; after 

 every discharge it closes, and in course of time the process is 

 repeated. All idea of a churning motion occurring in simple 

 stomachs has now been abandoned ; it was difficult to disprove, 

 except in the case of the horse, until X rays were employed. In 

 the horse the arrangement of the food in the stomach in strata 

 as received never left any doubt that churning took no part in 

 the process of stomach digestion in this animal. It will be 

 observed that the cardiac end of the stomach of the cat takes 

 apparently no share in the movement, and it is probable that in 

 most animals the oesophageal end plays but a passive part. In 

 the horse, in fact, it may be regarded more in the light of an 

 oesophageal dilatation. 



If the abdominal cavity be rapidly opened in a recently 

 destroyed horse it may be possible to see the stomach at work. 

 Its peristalsis is slow, rather more deliberate and less energetic 

 than intestinal peristalsis, and not infrequently hour-glass con- 

 strictions may appear, though not to a marked degree. Many 

 observations may be made before gastric peristalsis is seen ; 

 unlike intestinal peristalsis, it is not always present after death. 



The mechanism controlling the opening and closing of the 

 pylorus is by no means clear ; solid bodies are denied a passage 

 for some time, and even for chyme the pylorus does not open 

 with every contraction wave which passes over the stomach. A 

 bullet administered as a bolus was found in the stomach thirty- 

 six hours later, though the animal had in the meantime been fed, 

 from which it seems certain that the pylorus is capable of 

 deciding what should and what should not pass. Yet in the case 

 of the horse some modification in this statement must be made, 

 for, as has been shown, owing to the small size of the stomach 

 and the bulky nature of the food in an organ already filled, an 

 amount passes out at one end equal to that being taken in at 



