504 Caroline McGill. 



In Amphibia, as previously mentioned, the muscle of the digestive 

 tract is very inactive. In order to obtain contracted muscle from 

 these forms the tissue was stimulated for some time with a rather 

 strong electric current. It was often possible on the side of the 

 intestine where the stimulus was applied, to obtain a very firmly con- 

 tracted area while the remainder of the muscle in the circumference 

 of the tube was entirely relaxed. 



For contracted arterial muscle, the proximal end of the previously 

 severed carotid was taken and rapidly fixed in hot Zenker's fluid. 

 Only mammalian blood-vessels were studied. 



In the urino-genital tract no special effort was made to get con- 

 tracted muscle, but usually in fixed material contraction waves were 

 seen. 



The mprphological changes in smooth muscle produced by a number 

 of drugs which cause contraction were studied. The tissue was 

 placed in a physiological solution of the drug until contracted, and 

 then examined, either living or after fixation in sections. The drugs 

 used were pilocarpine, apomorphine and strong solutions of atropine 

 (0.01 per cent, or stronger). The drug effects were tested on 

 intestinal muscle of ISTccturus, cat and dog. 



Contraction in smooth muscle was also examined directly in fresh 

 muscle. Small pieces of muscle from the intestine of ISTecturus, 

 chicken, dog and cat, and from the carotid artery of ox were clipped 

 out with sharp scissors and mounted in normal saline. Ringer's 

 solution, or blood serum, upon a warm slide. The slide was fitted 

 with foil electrodes for electrical stimulation. Thin longitudinal 

 strands of the muscle were placed between the electrodes, then a 

 cover-glass supported by thin strips of filter paper was adjusted. The 

 tissue was examined directly under the microscope. Low power 

 lenses were usually adequate, but for finer structures a water-immer- 

 sion (Zeiss H lens) was used. After mounting, the tissue was 

 allowed to stand for a few minutes, or until it relaxed completely, 

 then a weak electric current was passed through. As the stimulus 

 was applied the muscle, fibers contracted. The course of the con- 

 traction waves and some of the finer structnral changes accompanying 

 them could then be observed. 



