540 Caroline McGill. 



the miisciilaris contract simultaneously. As they contract they 

 thicken and in constant ratio. Aside from the thickening of the 

 muscularis the lumen as well as the whole diameter of the tube de- 

 creases, due to the shortening of the circular fibers, and the length 

 of the segment decreases, due to the shortening of the longitudinal 

 fibers. In the carotid of ox during contraction there is thickening 

 of the coats accompanied by a decrease in diameter, both of the 

 lumen and the whole tube. There is little change in length, for 

 there are few longitudinal muscle fibers. 



2. Two types of contraction have been described: peristaltic, 

 where a series of wave-like thickenings cross the fiber; total, where 

 the entire fiber shortens and thickens. In the material studied all 

 the muscle seems to belong to the first type, although in arterial 

 muscle there is in places a near approach to total contraction. 



3. In peristaltic contraction in the digestive tract contraction 

 waves pass over the muscularis. These are irregular anastomosing 

 areas of contracted tissue between which there are areas of resting 

 muscle. The contraction waves vary much, both in length and width 

 as well as in number. In length they may cross only a few muscle 

 fibers or they may include the entire muscularis. In width they may 

 be only narrow bands or they may be so wide as to include most of 

 the length of a muscle fiber. Where narrow and close together they 

 give the tissue a distinctly striated appearance. In the contraction 

 waves the muscle fibers are shorter, thicker and more deeply stain- 

 ing than in the uncontracted areas ; the nuclei are crowded closely 

 together, the connective tissue is much condensed. From the mate- 

 rial studied there is no evidence that the propagation of contraction 

 waves is due to nerve control. They are probably conducted from 

 fiber to fiber, by some protoplasmic connection between the cells 

 themselves. In syncytial muscle the protoplasmic anastomoses 

 probably serve this purpose. In arterial and urino-genital muscle 

 there are no distinct contraction waves. Here there are merely 

 scattered contracted fibers or groups of fibers among uncontracted 

 tissue. 



4. The portion of the muscle fiber in the contraction wave is the 

 contraction node, that in the uncontracted area is the internodal 



