Structure of Suiootli Muscle. 501 



several regions of the alimentary canal and urino-genital tract and 

 from the blood-vessels of dog, cat, ox, pig and man. " 



2. Fixation of resting muscle. 



To obtain smooth muscle in the resting or relaxed condition several 

 methods were employed. When the tissue was found completely 

 extended, as it frequently is in the various organs of the alimentary 

 canal, pieces could be fixed in that condition. To do this, very small 

 pieces of the resting muscle were clipped out with shai-p scissors and 

 tlirown quickly into the fixative. The fixative should be one that acts 

 rapidly, such as hot water, hot sublimate solution or hot Zenker's 

 fluid. In using this method the work should be done rapidly or the 

 mere mechanical stimulus of handling the muscle will often cause it 

 to contract. When the fixative used penetrates rapidly, as does 

 hot Zenker's fluid, larger pieces may be fixed without undergoing 

 appreciable contraction. In the large intestine of mammals, where, 

 after stimulation, the contraction proceeds very slowly, whole seg- 

 ments of expanded muscle were removed and fixed in Zenker's fluid 

 without producing contraction. In the small intestine of mammals 

 the smooth muscle is so irritable that even the slightest stimuli set up 

 very rapid contractions. Hence it was found impossible to fix the 

 tissue rapidly enough to prevent some contraction. Even here, how- 

 ever, while small areas were contracted, there were many areas of 

 entirely resting muscle, unless the stimulus was strong and contin- 

 uous. In the alimentary canal of birds the tissue is so easily stimu- 

 lated that the pieces could seldom be fixed without showing some con- 

 traction. Here the only means of obtaining entirely relaxed muscle 

 was by employing narcotics. In Amphibia, especially during the win- 

 ter, the irritability of the smooth muscle of the alimentary canal is so 

 low that whole segments were removed and placed in any of the ordin- 

 ary fixatives without producing contraction. 



In the large arteries, upon section, the portion next to the heart con- 

 tracts firmly, that away from the heart, relaxes completely. Small 

 pieces, taken from the distal end of the cut carotid a few minutes after 

 the artery had been severed, were fixed in hot water or hot Zenker's 

 fluid. They show completely extended muscle. This, method was 

 successfully used by Henneberg, 1901, and by Heiderich, 1902. 



