THE STOMACH 



1159 



i,The circular layer of muscle is indicated at 16 mm.; the longitudinal much later, about 

 90 mm., and not completed before 240 mm. (F. T. Lewis). 



Variations. — The great variability of the stomach in form, position and relations has 

 already been repeatedly emphasized. These variations have been most carefully studied 

 recently by various observers in the living body by means of the Roentgen-rays. Some of the 

 results of study by this method are shown in figs. 918, 919. 



Peristalsis. — It would appear that most of the variations in the form of the stomach that 

 have been described are merely various phases in the series of changes undergone by the 

 stomach during the normal process of physiological digestion. The following account of these 

 changes is based largely upon the radiographic observations of Cole. Earlier observations by 

 various investigators upon the living stomach of man and lower animals (and especially the 

 radiographic study of the cat by Cannon) have shown that the cardiac portion of the stomach 

 is the first to become distended with food (and gas). Until a considerable degree of distention 

 is reached, the pyloric portion usually remains a somewhat narrow contracted canal, along 

 which distinct peristaltic contractions pass pylorus ward. 



Under favorable conditions, however, the peristaltic contractions may be observed to begin 

 in the cardiac portion, although they are usually most distinct in the pyloric portion. Each 

 individual contraction travels at the rate of about 2.5 cm. (1 inch) per second, so that it requires 

 several seconds for a contraction to travel from fundus to pylorus. The number of simultaneous 



Fig. 918. — Different Forms of the Stomach as Show^n by The Rcentgen Rays. 



not represented. (Cole.) 



Fundus 



C — "Drain-trap" 



D — "Fish-hook" 



contractions present in the stomach varies from 1 to 6 or 7, 3 or 4 being the most common. 

 In fig. 919, a series of 10 successive radiographs show the progression in a stomach with four 

 simultaneous individual peristaltic contractions. The peristaltic movements are further com- 

 plicated by the appearance (simultaneously in all) of successive periods of 'systole,' during 

 which the peristaltic contractions become stronger and deeper, and ' diastole,' in which the 

 contractions relax and become less distinct (Cole). In fig. 919, phases 1 to 6 represent the 

 'systole,' and 7 to 10 the 'diastole.' A 'systole' and a 'diastole' together make up a 

 ' gastric cycle.' During the entire progress of an individual peristaltic contraction from fundus 

 to pylorus, the number of ' cycles' appears to correspond to the number of peristaltic con- 

 tractions present. Thus the figure represents a stomach of the 4-cycle type. The time required 

 for a ' cycle ' varies widely, the average (in the 3- or 4-cycle type) being about 2 or 3 seconds. 



In the earlier stages of gastric digestion the pylorus usually remains closed, but after a 

 variable time it relaxes slightly (lumen about 3 mm. in diameter) at intervals, allowing the 

 chyme to be spurted into the duodenum. 



Thus the various constrictions often found in the formalin-hardened stomachs, and the 

 pyloric antrum, appear to be merely transient phases of the digestive process. The ' hour- 

 glass ' stomach is in many cases to be explained in this way; in others, however, the constriction 

 is pathological and permanent. Various forms of abnormal lobulations and dilations also 

 rarely occur. 



