INVOLUNTARY MUSCLE 67 



of two or three Daniell cells one in contact with the lower, the other 

 with the upper electrode. This upper electrode need not touch the 

 tissue. Use a very slow drum. Stimulate by making and breaking the 

 circuit. If induced currents are employed there is usually no response 

 with a single make or break of the primary circuit 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 more readily obtained 

 by a rapid succession of induced currents, using the Neef's hammer, 

 but it is always a simple contraction, not a tetanus. This effect of 

 summation of stimuli can be well shown on involuntary muscle, which 

 does not, like voluntary muscle, show superposition or tetanus ; in this 

 respect resembling the heart. On the other hand, it exhibits great 

 variations in tone or postural shortening a condition of continued 

 contraction quite independent of the individual contractions caused 

 by excitations. 



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

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

 A longitudinal piece of rabbit intestine, or a short strip of either the 

 longitudinal or circular muscular coat, is attached below to the cork 

 and above to the lever. Rhythmic contractions occur and should be 

 recorded. For prolonged and exact experiments oxygen is allowed to 

 bubble through the Ringer so as to keep the solution saturated with 

 this gas. The piece is best taken from the duodenum. 



Action of drugs and animal extracts. Magnus' method is particu- 

 larly useful for investigating the action of drugs and extracts upon 

 plain muscular tissue. This may be illustrated (1) by adding a few 

 drops of adrenalin solution to the Ringer, (2) after washing through 

 with fresh Ringer, adding to it a few drops of 1 per cent, barium 

 chloride solution : the result in each case being recorded upon the 

 drum. It will be observed in the case of intestinal muscle that the 

 effect of adrenalin is inhibitory (chalonic), restraining the contractions 

 and tone : that of barium excitatory (hormonic), increasing the con- 

 tractions and tone. 



