500 Carolme McGill. 



Benda, 1902, described in smootli muscle two types of myofibrillse, 

 coarse and fine, corresponding somewhat closely to the "Grenzfibril- 

 len" and "Binnenfibrillen" of Heidenhain. He considered only the 

 fine myofibrilla3 contractile elements. The coarse myofibrillge he 

 believed to be elastic or supportive structures. 



Forster, 1904, studied contraction in amphibian and mammalian 

 muscle. According to his description, the muscle cell as a whole con- 

 tracts in such a way that it is rolled into a spiral. The nucleus follows 

 this spiral winding. From the amount of spiral winding of the 

 nucleus the amount of contraction of the muscle fiber may be deter- 

 mined. 



Schlater, 1905, like Forster, described the smooth muscle nucleus 

 as undergoing a spiral winding during contraction. He is of the opin- 

 ion, however, that the nucleus is entirely passive, but believes that, 

 at the same time, there may be an active decrease in length and 

 increase in diameter of the nucleus. 



Soli, 1906, 1907, in the smooth muscle of the stomach of birds, 

 found practically the same conditions described by Heiderich for 

 the peristaltic form of contraction. There is this difference, that in 

 al] of his material he found the contraction nodes of greater diameter 

 than the uncontraeted internodal segments. 



Verzar, 1907, in the smooth muscle cells of the amnion of the chick 

 found with ordinary hsematoxylin-eosin stains, very distinct bound- 

 aries to the cells. When stained with iron-hsematoxylin, no distinct 

 boundaries were present, and the myofibrillse, both coarse and fine, 

 apparently run from one cell to another. 



McGill, (3) 1907, in a preliminary paper described briefly the 

 fibrillar and nuclear changes which are given in more detail in this 

 present paper. 



III. Material and Methods. 



1. Material used. 



Smooth muscle from the following vertebrate sources was the mate- 

 rial used in this investigation : among Amphibia, from the alimentary 

 canal and urinary bladder of the frog and of N"ecturus ; among birds, 

 from the alimentary canal of the chicken; among mammals, from 



