CHAPTER XIV 



INVOLUNTARY MUSCLE 



Stomach or bladder of frog. Take either a transverse strip from the 

 stomach the frog should have been recently fed or preferably the 

 whole urinary bladder, fastening a thread to each end. Attach one 

 end to the metal disc used in the experiment on the effect of heat on 

 extensibility (fig. 38) ; let this lie in a small vessel of Ringer's solution, 

 and, as in that experiment, attach the other end to the short arm of a 

 light lever. Bring fine wires from the induction coil one in contact 

 with the bottom of the strip, the other with the top. This upper wire 

 must be spirally coiled or otherwise so arranged that the piece of tissue 

 can be stimulated and can contract without interference. Use a very 

 slow drum. Stimulate by making and breaking the primary circuit. 

 With a single make or break there is usually no response owing 

 to the short duration of the induction shock, but by repeating 

 the stimulus the tissue will contract and the lever will describe 

 a simple prolonged muscle curve on the drum. The contraction is 

 best obtained by a rapid succession of stimuli, using the Neef's 

 hammer, but in this case also it is a simple contraction, not a 

 tetanus ; it furnishes an example of the effect of summation of 

 stimuli (see p. 36). Involuntary muscle does not show superposition 

 nor tetanus, in this respect resembling the heart. On the other 

 hand, it exhibits great variations in tone i.e. a condition of greater 

 or less continuous contraction. 



Intestine of rabbit : Magnus' method. The same apparatus is 

 used, but the Ringer's solution must be kept warm (35 C. to 40 C.). 

 A longitudinal strip of rabbit intestine (descending colon), which 

 may be divested of its mucous membrane, is attached below to the 

 disc and above to the lever. Rhythmic contractions occur and 



should be recorded. Add to the Ringer solution of one preparation 



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