522 Caroline McGill. 



In the small intestine of chicken, Figs. 2, 11, and of mammals the 

 contraction waves are narrower and closer together. There may be 

 several traversing each fiber. In fact they are often so numerous a3 

 to give the fiber a distinctly cross-striated appearance. It was prob- 

 ably this that led many earlier writers to describe a cross-striated 

 involuntary muscle in portions of the digestive tract. 



Here and there the peristaltic type of contraction does not produce 

 contraction waves. In such muscle there is apparently no relation 

 whatsoever between the contraction nodes of neighboring fibers. 

 This seems to be largely true for the smooth muscle of the urino- 

 genital tract. 



The conclusive way to study contraction phenomena is in fresh 

 muscle. Small pieces of living muscle from the small intestine of 

 Eecturus, from the small and large intestine of dog, and from the 

 muscular stomach of chicken were mounted as already described, in 

 Ringer's solution or blood serum, over small electrodes on a slide 

 and examined under the microscope. When the tissue was stimulated 

 it contracted and the contraction waves could be observed passing 

 over the muscle fibers, causing distinct enlargements of the fiber 

 as they passed. The contraction is initiated almost simultaneously 

 in neighboring fibers. Thus arise the contraction waves. 



To determine whether the form of the contraction wave is due to 

 nerve regulation or whether it is the result of some morphological 

 connection between the muscle fibers themselves, portions of the 

 intestine of cat were treated with atropine until the nerve endings in 

 the smooth muscle were completely paralyzed. They were then 

 stimulated mechanically. Marked contraction took place. Sections 

 of such contracted material, as well as the living muscle examined 

 directly showed identically the same form of contraction wave as 

 did sections from the normal material used for control. The methods 

 used are described under material and methods, so need not be de- 

 scribed here. The following data from a single experiment show 

 the effect of atropine : 



March 14, 1908. 



A large cat weighing 2700 gm. Avas decapitaled, the abdominal 

 cavity quickly opened and the intestines removed by clipping the 



