GENERAL PHYSIOLOGY OF MUSCLE-TISSUE 87 



from the ganglion pass directly into the muscle, where they frequently unite 

 to form a general plexus. From this plexus fine branches take their origin 

 and ultimately become physiologically associated with the muscle-fiber. 



Physiologic Properties. The visceral muscles which have been sub- 

 jected to experiment are mainly those of the stomach, intestine, bladder, 

 ureter, and iris. From the results of the experiments which have been 

 published, it is evident that all visceral muscles possess elasticity, tonicity, 

 irritability, and conductivity. 



The elasticity of the bladder muscle of the cat was strikingly shown 

 in the experiments published by Dr. Colin C. Stewart. When this muscle 

 was weighted with weights differing by a common increment, it was ex- 

 tended on the addition of each weight, though to a progressively less ex- 

 tent. On the removal of the weights the muscle eventually returned to its 

 former length. The records of the extension were similar to, if not iden- 

 tical with, those of the skeletal muscle. 



The tonicity of visceral muscles is as pronounced in many situations as 

 is the tonicity of skeletal muscles. Each muscle is continuously in a state 

 of contraction intermediate between that of complete contraction and that 

 of relaxation. In how far this is due to local and inherent causes or to 

 stimuli reflected from the nervous system as a result of peripherally acting 

 causes is not in individual instances readily determinable. From time to 

 time the tonicity varies, increasing and decreasing in response to these various 

 stimuli and in accordance with the functional activities of the organs in 

 which the muscle is found. 



The irritability manifests itself by a change of form, and doubtless by 

 the liberation of heat on the application of any form of stimulus mechanic, 

 chemic, thermic, electric. 



The conductivity is less marked in the visceral than in the skeletal 

 muscle, and, contrary to what is observed in the latter, the conduction extends 

 laterally as well as longitudinally from fiber to fiber. This is shown by 

 stimulation of the exposed intestine. Shortly after the stimulus is applied 

 the muscle contracts longitudinally i.e., in a direction at right angles to the 

 long axis of the intestine, partially obliterating its lumen. From this point 

 the conduction process indicated by the contraction wave passes in opposite 

 directions for some distance along the canal. As to whether this is accom- 

 plished by protoplasmic processes extending from fiber to fiber, or whether 

 the uniting membrane differs in conducting power from the sarcolemma, is 

 as yet a matter of doubt. From the fact that the upper two-thirds of the 

 ureter, though free of nerve-cells, exhibits lateral conduction, it is evident 

 that it may take place independent of the nervous system. 



The Contraction of the Visceral Muscle. The general character of 

 the contraction may be witnessed on opening the abdomen of a recently 

 killed animal, especially the rabbit. Shortly after exposure to the air the 

 walls of the intestine begin to contract in a most vigorous manner. The 

 contraction wave beginning at various points is propagated usually 

 downward, running along the intestinal wall for a variable distance. A 

 succession of similar waves may be observed for some minutes. To the 

 alternate contraction and relaxation of the muscle-fibers, which are cir- 

 cularly arranged, the term peristalsis is usually given. The excised 

 stomach of a dog kept under suitable conditions will exhibit similar move- 



