MOVEMENTS OF THE ALIMENTARY CANAL. 729 



subjected to repeated divisions. From time to time the separated 

 pieces are caught by an advancing peristaltic wave, moved 

 forward a certain distance, and gathered again into a new mass. 

 In this new location the rhythmical contractions again segment 

 and churn the mass before a new peristaltic wave moves it on. 

 According to this description, the rhythmical movements are 

 local contractions (mainly of the circular muscles) which seem 

 to be due to the local distention caused by the food. They occur 

 rhythmically for a certain period and then cease until a new series 

 is started, and it is obvious that they must play a very important 

 part in promoting both the digestion and absorption of the food. 

 Mall* has suggested that these rhythmical contractions of the 

 circular coats may also act as a pumping mechanism upon the 

 venous plexuses in the walls and thus aid in driving the blood into 

 the portal system. Similar movements have been observed 

 in the human being, f The curious observation is reported} 

 that during the period of fasting (dog) the whole gastro-intestinal 

 canal, although empty, shows at intervals rhythmical con- 

 tractions of its musculature which may last for twenty to thirty 

 m mutes (see p. 790). 



Cannon suggests a new and convenient nomenclature for the movements 

 of the stomach and intestines as follows: 



(1) Rhythmic segmentations. The rhythmic localized contractions de- 

 cribed in the preceding paragraph. Exhibited throughout the small intestine. 



(2) Diastalsis. Downward moving wave of contraction with a preceding 

 wave of inhibition (myenteric reflex). Exhibited chiefly in the small intestine. 



(3) Anastalsis. Upward moving wave of contraction without a pre- 

 ceding phase of inhibition Exhibited chiefly in the proximal colon. 



(4) Katastalsis. Downward moving wave of contraction without a 

 preceding phase of inhibition. Exhibited chiefly in the stomach. 



Movements of the Intestinal Villi. Hambleton calls attention 

 to the fact that if the intestine of a living animal is opened and 

 spread out under suitable conditions so that the villi may be 

 examined under a binocular microscope, it can be shown that they 

 exhibit active movements of two kinds : First, lashing movements 

 from side to side in various directions; second, what might be 

 called pumping movements, in which the villi are alternately 

 extended and retracted. Doubtless these movements are due to 

 the contractions of the muscular slips, which run into the stroma of 

 the villi from the muscularis mucosae. If we can suppose that 

 they occur during normal digestion, it is evident that they add a 

 mechanical factor, not hitherto considered, which must help 

 materially in the absorption of the products of digestion, 



* Mall, "Johns Hopkins Hospital Reports," 1896, i., 37. 



t Hertz, loc. cit. 



j Boldireff, ''Archives des sciences biologiques," 11, 1, 1905. 



Hambleton, "American Journal of Physiology," 34, 446, 1914. 



