518 Caroline McGill. 



when their origin from a common protoplasmic syncytium is remem- 

 bered. 



V. The Geoss Changes in Muscle Coats During Contraction. 



1. In the digestive tract. 



The gross changes of the muscle coats of the digestive tract were 

 studied in the small and large intestine of dog and IsTecturus. In the 

 large intestine of the dog during contraction there passes over the 

 organ from before backward a series of ringlike areas of contraction. 

 These areas include the entire circumference of the intestine. All of 

 the muscle in a cross section of a given segment is contracted about 

 the same amount. The gut may, however, be very firmly contracted 

 at one point and a neighboring segment may be completely relaxed. 



During contraction both layers of the muscularis thicken simul- 

 taneously. Along with this there is such a decrease in the lumen that 

 the whole diameter of the tract decreases. The two coats contract 

 in equal ratio so that if before contraction the ratio of the thickness of 

 the longitudinal coat to that of the circular coat is as one to two, 

 after contraction this same ratio is maintained. The following data 

 are from moasurenients taken on sections from closely lying seg- 

 ments of the large int(^stinc of dog: 



Intestine 1. 



a, contracted area l>, uncoutracted area 



circular coat, 1.1 mm. circular coat, 0.3 mm. 



longitudinal coat, 0.6 mm. longitudinal coat, 0.17 mm. 



0.6 : 1.1 = 1 : 1.8. 0.17 : 0.3 = 1 : 1.76. 



Intestine 2. 



a, contracted area b, uncoutracted area 



circular coat, 0.4 mm. circular coat, 0.2 mm. 



longitudinal coat, 0.12 mm. longitudinal coat, 0.065 mm. 



0.12 : 0.4 = 1 : 3.3. 0.065 : 0.2 rrz 1 : 3. 



Intestine 3. 



a, contracted area b, uncoutracted area 



circular coat, 0.61 mm. circular coat, 0.34 mm. 



longitudinal coat, 0.2 mm. longitudinal coat, 0.11 mm. 



0.2 : 0.61 ==1 : 3. 0.11 : 0.34 = 1 : 3. 



b. Smooth muscle with end to end anastomoses of fibers. 



