Figs. 42-53. A series of nuclei from iiuisi-le cells in different stages of 

 contraction from the circular muscle of the contracted large intestine of dog. 

 Fig. 42 is a resting nucleus from an internodal segment. The chromatin is 

 in a fine reticulum. A few fine strands run longitudinally, giving the appear- 

 ance of longitudinal chromatic fibers — pi., plasmasome. Figs. 43, 44 show- 

 nuclei just beginning to contract. The chromatin strands have thickened. 

 Figs. 45-48 show further stages in the contraction of the nucleus. In Fig. 49 

 the chromatin has drawn into three masses with very thick strands. In 

 Fig. 50 one end of the nucleus was in a contraction node, so is enlarged and 

 deeply staining, the other end was in an internodal segment, so has the 

 structure of a resting nucleus. Figs. 51, 53 show the thickened chromatin 

 strands massed at each end of the completely contracted nucleus. Zenker's 

 fluid. Hansen's hiematoxylln. x 3000. 



Figs. 54-58. Nuclei in various stages of contraction from a contracted 

 mesenteric artei*j' of pig. During contraction the nuclei shorten and thicken. 

 Figs. 54, 57. Fig. 58 shows a folded nucleus occasionally met with. There 

 are few chromatic changes in these nuclei during contraction. Gilson's fluid. 

 Iron-hfematoxylin. X 3000. 



Figs. 59-64. Contraction stages of the nucleus from the internal iliac- 

 artery of man. During contraction the nucleus shortens and thickens. Ac- 

 companying this is some massing of chromatin at the poles. A certain 

 amount of folding or spiral winding may be normal for the contraction of 

 arterial muscle, Figs. G2. 03. Formalin. Hansen's hfematoxylin. x '^'iOO. 



