Structure of Smooth Muscle. 505 



In the peristaltic type of contraction there passes simnltaneously 

 over neighboring fibers a very characteristic sort of contraction wave. 

 It has seemed important to determine whether the simultaneous 

 occurrence of contraction in contiguous fibers is due to nerve control 

 or to some morphological connection between the fibers themselves. 

 To determine this it was necessary to exclude stimulation of the 

 muscle fibers through the nerves. This was done by im- 

 mersing the tissue for some time in very weak solutions of 

 atropine sulphate. After such treatment the tissue could still be 

 mechanically stimulated to contraction. Atropine is supposed to 

 cause relaxation of smooth muscle cells hy paralyzing the motor 

 nerve endings in the fibers. This point has not been entirely proved, 

 but most recent work seems to confirm the statement. linger, 1907, 

 reviews the literature on this subject and gives additional data. In 

 testing the atropine effect the methods of Unger were used. 



The development of the power of contraction in smooth muscle was 

 studied in a series of pig and chick embryos, together with a few 

 observations on an eight months human foetus. In most instances the 

 fixative Avas relied upon to furnish the necessaiy stimulus. How- 

 ever, some experimental work wms done. The muscle from the small 

 intestine of pig embryos ranging in length from two centimeters to 

 thirty centimeters was stimulated in solutions of pilocarpine and 

 apomorphine, then fixed and sectioned. Tissue from the muscular 

 stomach and small intestine of the chick embryos from five days to 

 twenty days old, was studied both living and after fixation. The 

 fresh muscle was studied directly under the microscope. The fixed 

 muscle was stimulated mechanically before fixation. 



4. Methods of fixation, embedding and staining. 



The muscle was fixed in several different reagents, including 

 alcohol, alcohol-formalin, saturated aqueous solution of corrosive 

 sublimate, hot water, Gilson's, Flemming's and Zenker's fluids. 

 Zenker's fluid proved most satisfactory both for general structure as 

 well as for bringing out cytological details. The rapidity with which 

 it penetrates even large pieces of tissue makes it especially valuable 

 in this work. With it, the muscle fibers could be fixed in any stage 

 of contraction desired, the- reagent itself not acting as a stimulus. 



