GENERAL PHYSIOLOGY OF MUSCLE-TISSUE 87 



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 in both direc- 

 tions, 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 circularly ar- 

 ranged, the term peristalsis is usually given. The excised stomach of a dog 

 kept under suitable conditions will exhibit similar movements. The same 

 holds true of the bladder muscle of the cat, the muscle of the ureter, etc. 

 Careful observation shows a certain periodicity in the movements. Inas- 

 much as the cause is not apparent, these contractions are termed spontane- 

 ous or automatic. 



Graphic Record of the Contraction. For experimental purposes 

 narrow transverse sections of the stomach of the frog or the entire bladder 

 muscle of the cat, excised or in situ, according to the method of Prof. Colin 

 C. Stewart, may be employed. If kept moist, they will retain their irritability 

 for some hours. The changes of form may be recorded with the usual 

 muscle lever. When thus prepared, the muscle may exhibit for several 

 hours a series of pulsations, rhythmic in character. With spontaneously 

 acting mammalian muscle the contraction and relaxation periods are of 

 equal duration. With the amphibian muscle they are of unequal duration, 

 as a rule. In both classes of animals the character of the record, a suc- 

 cession of large and small contractions, would indicate that the general 

 rhythmic movement is compounded of two or three secondary rhythms 

 which differ in rate and character. A single pulsation may be recorded 

 by stimulating the bladder muscle with the induced or the make and break 

 of the constant current. A curve of such a contraction is shown in Fig. 42. 

 The contraction takes place more rapidly than the relaxation; the two 

 phases occupying five and thirty-five seconds respectively. The latent 



