54 ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



writing lever. Allow it to register at intervals of two seconds. Allow 

 the drum to 'revolve very slowly and observe whether the muscle records 

 spontaneous contractions. 



Draw the abscissa, and adjust the writing lever properly in this line. 

 Start at the beginning of the paper and stimulate the muscle with a 

 single break shock. If the preparation does not react to this strength 

 of stimulus, put in two or more shocks in quick succession makes and 

 breaks, if you choose. Note the unusual length of the latent period. 

 Allow the muscle to relax fully, which, if the contraction possesses a 

 height of about 5 cm., may require the entire length of the paper. 



Produce a summation of contractions by stimulating the muscle first 

 by means of a make shock and again with a break shock very shortly 

 after it has entered upon its period of relaxation. Naturally, if single 

 stimuli do not prove effective, employ a number of them in quick suc- 

 cession. 



Employ a brief tetanic current, being careful not to contract the 

 muscle excessively, otherwise it might not be able to complete its period 



FIG. 33. CONTRACTION OF SMOOTH MUSCLE (CAT'S BLADDER). 

 L, Latent period; C, period of contraction; 7?, period of relaxation; time in seconds. 



of relaxation before the end of the paper has been reached. Does the 

 character of the " tetanic" curve of smooth muscle differ from that of 

 the curve obtained with single stimuli? 



Annotation. Preparations of smooth muscle may be obtained most conveni- 

 ently from the stomach of the frog and the stomach, intestine, and bladder of the 

 cat. No doubt, the bladder is best adapted for this purpose. Having opened the 

 abdomen in deep narcosis, the bladder is partially emptied and lifted out of the 

 wound. A long silk thread is then tied around the urethra at a distance of 1 to 2 

 cm. from the cervix of the bladder. The upper pole of the fundus is securely fastened 

 to a pair of needle electrodes and quickly placed in the moist chamber prepared 

 as described above. The silk thread is attached to the writing lever placed at a 

 convenient distance below the floor of the chamber. Do not injure the organ 

 mechanically, and moisten it from time to time with slightly warmed saline solution. 



If the stomach is employed, cut a ring about 1 cm. in width from its pyloric 

 portion and fasten it in this position to the rod of the moist chamber. To its upper 

 pole attach one of the wires from the secondary coil of the inductorium. To its 

 lower pole attach the writing lever by means of a thread and also the other wire 

 from the secondary coil. The same procedure is to be followed in the case of seg- 

 ments of intestine. Be sure not to arrange them horizontally, because only the 

 circular muscle-fibers will give a marked movement of the lever. Under proper 

 conditions of experimentation the frog's stomach will yield contractions 2 to 3 cm. 

 in height. 



