\ 



427 



portions may be removed and fixed in favorable fixing fluids with no 

 marked change in the condition of either the contracted or the un- 

 contracted areas, so far as can be judged from the macroscopic appear- 

 ance. In the intestine of Necturus, exposure to the air is not a 

 sufficient stimulus to produce strong contraction, so a mild electric 

 current was applied, giving fairly good results. However, here and in 

 the small intestine of mammals the muscle is very irritable toward 

 fixatives, which are apt to induce slight contraction. This contraction 

 may be entirely eliminated by immersing the fresh muscle for a short 

 time in narcotic solutions, such as cocaine, as has been shown by 

 other investigators. 



Several fixatives were employed, but for general purposes Zenker's 

 fluid gives by far the best results, not causing an appreciable amount 

 of contraction, even in entirely relaxed muscle. The material was 

 embedded in paraffin. The sections were cut from 3 to 10 micra in 

 thickness. 



For staining the nuclei. Van Gibson's method and the iron-hae- 

 matoxylin method of Heidenhain are the most satisfactory stains. 

 For bringing out the myofibrillse, the iron - haematoxylin method is 

 superior to all others used. With it, by washing out the stain to 

 varying degrees, the continuity of the myofibrillaj even through the 

 so-called homogeneous areas described by Heidenreich and others 

 may be demonstrated in many places. 



In all of the forms studied the intestinal muscle is a syncytium. 

 That is, there is protoplasmic continuity throughout, with apparently 

 no independent muscle cells or fibers. The author in a paper (to be 

 published shortly in Internat. Monatsschrift für Anatomie und Physiol.) 

 on the Histogenesis of Smooth Muscle in the Pig, has shown that in 

 this form the smooth muscle arises as a syncytium and persists as 

 such in the adult. In Necturus this syncytial structure is even more 

 apparent than in mammals. 



In the resting condition (Figs. 1 and 5 b) the smooth muscle is 

 made up of j^^ery slender, much elongated bundles of myofibriilae. 

 These bundles, together with a small amount of interstitial protoplasm, 

 form the so-called smooth muscle fibers, which are united together at 

 the ends and often at the sides by wide anastomoses. The myo- 

 fibrillse are very distinct in preparations stained with iron-haematoxylin. 

 They run in the main longitudinally, but in places cross from one bundle 

 to another through the anastomoses. Where there has been no passive 

 contraction (due to shrinkage or to contraction in adjacent muscle) 

 the myofibrillse run comparatively straight. Most of the myofibrillse 



