536 Caroline McGill. 



ferential. With it the myofibrillse of the uncontracted portions of 

 the fiber stain red in the fuchsin, the contraction nodes bright yellow 

 with orange G. Figs. 30-34. This stain cannot be entirely relied 

 upon as a chemical test, since orange G. is also known to be a physi- 

 cal stain. However, the exceedingly sharp differentiation of the 

 contraction nodes with all the above stains indicates marked chem- 

 ical changes in the smooth muscle fiber during contraction. 



An attempt was made by using neutral red and phenolphthalein 

 in physiological solution as indicators, to determine whether there 

 is a change in the alkalinity of smooth muscle during contraction. 

 If there be it should show at the contraction nodes. Small pieces 

 of the fresh tissue were mounted on a slide in solutions of the indi- 

 cator. When stimulated the tissue contracted, but there was no 

 apparent change in the color of the indicator. It should be remem- 

 bered that none of the indicators, neutral red, rosolic acid, etc., in 

 use at present are delicate enough for microscopic tests unless the 

 reactions be very marked. Schultz, 190Y, in studying this same 

 question in smooth muscle en masse determined that there was no 

 decrease in the alkalinity during contraction, such as has been 

 pointed out for striated nmscle. 



X. Development of Contractility. 

 The development of contractility in smooth muscle was studied 

 in the digestive tract in a series of chick embryos ranging in age 

 from three days to twenty-one days of incubation. First a series 

 of sections of embryos at different ages was made to determine when 

 smooth muscle arises. Smooth muscle begins to form between the 

 third and fourth day by an elongation of the cells in the mesenchy- 

 mal syncytium surrounding the epithelial tube. By the fifth day 

 the myofibrillar are rapidly forming as thick varicose structures. 

 They run for long distances through the cytoplasm without regard 

 for cell boundaries. By the seventh day the muscle nuclei are well 

 elongated. The tissue is still a distinct syncytium and remains 

 as such throughout development. The structure of the smooth mus- 

 cle in the chick after hatching was not studied, so later development 

 remains to be treated. 



