Structure of Smooth Muscle. 637 



Next was detennined experimentally when contraction begins. 

 The interesting question to decide here is whether or not contrac- 

 tion is dependent upon the myofibrillse. If it be, one would expect 

 it not to appear until after the myofibrillse are formed. The intes- 

 tine and muscular stomach of the chick embryo were removed from 

 the living embryo, kept at a temperature of 37° C, and stimulated 

 mechanically, electrically or by heating. The tissue was stimulated 

 while in focus under the low power of the microscope. The first 

 contraction of the intestine observed occurred on the seventh day. 

 It was merely a very slow contraction arising after marked stimu- 

 lation. By the twelfth day, when the temperature is raised to 

 43° C, the intestine contracts rhythmically. By mounting small 

 living pieces on a warm slide and examining under the high power 

 of the microscope it was hoped that the finer details of contraction 

 could be made out. Until the late embryo there are so many yolk 

 granules present that this was not accomplished. 



Sections from the stimulated intestine were fixed and examined 

 microscopically. No contraction changes were observed in the fiber 

 until the twelfth day. Sections from contracted muscle at this time 

 show many of the nuclei slightly shorter and broader than in uncon- 

 tracted muscle. Figs. 73-76 show the degree of shortening observed 

 in the contracted intestine of a fourteen-day chick embryo. On the 

 twenty-first day, aside from shortening of the nuclei, the muscle 

 of the contracted intestine shows in many fibers irregular, areas 

 staining slightly deeper with eosin than does the rest of the fiber. 

 In these areas the nuclei are shorter than elsewhere. They probably 

 represent developing contraction nodes. At this time there are no 

 nodes which stain differently with iron-ha3matoxylin or Mallory's 

 anilin-blue connective-tissue stain. Everywhere the myofibrilla? can 

 be traced uninterruptedly through the muscle syncytium. The 

 author hopes soon to be able to trace the later development of con- 

 traction in the chick after hatching. 



Soli, 1907, traced the development of smooth muscle in the stom- 

 ach of the chick. He obtained the first elongation of mesenchyme 

 on the seventh day of incubation. He did not observe fibrillse until 

 the seventeenth day. Contraction nodes he found appearing on the 

 ninth day after hatching. 



