GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 99 



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 doubt- 

 less 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^nd, 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 indi- 

 cated by the contraction wave passes in opposite directions for some 

 distance along the canal. As to whether this is accomplished by 

 protoplasmic processes extending from fiber to fiber, or whether the 

 uniting membrane differs in conducting power from the sarcqlerama, 

 is as yet a matter of doubt. >\ Frpm.the f act ^a^th^'tirjgferntwjpj thirds 

 of the ureter, though free of hefT^cfelfej 1 exhibits lateral 'conduction, 

 it is evident that it may take place 1 independent of s dje ney^cnis, sjy&tem. 



The Contraction of the TOcera1 ftJuselVV-THe general! character 

 of the contraction may be,w$thesse"c? ori 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 vig- 

 orous manner. The contraction wave beginning at various points 

 is propagated in both directions, running along the intestinal wall 

 for a variable distance. A succession of similar wa.ves may be ob- 

 served for some minutes. To the alternate contraction and relaxa- 

 tion of the muscle-fibers, which are circularly arranged, 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. Inasmuch as the cause is not apparent, these contrac- 

 tions are termed spontaneous or automatic. 



Graphic Record of the Contraction. For experimental pur- 

 poses 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 Dr. 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 pre- 

 pared, the muscle may exhibit for several hours a series of pulsa- 

 tions, rhythmic in character. With spontaneously acting mammalian 



