429 



I 



traction area is meant the entire mass of muscle in a given segment 

 of the intestine, a whole or a part of the fibers of which have under- 

 gone active shortening and thickening. The term contraction wave 

 will be restricted to the deeply staining, so-called homogeneous bands 

 of firmly contracted muscle which pass irregularly across the con- 

 traction areas (Fig. 5 a). 



Contraction node refers to [, , -f 



the deeply staining, homo- 

 geneous area in the indi- 

 vidual muscle fiber, and 

 internodal segment to the 

 fibrillated, uncontracted or 

 weakly contracted portion 

 of the fiber between the 

 contraction nodes. 



The general changes 

 in the structure of smooth 

 muscle during contraction 

 are evident upon a com- 

 parison of Figs. 1, 2, 3, 

 4 and 5. Figs. 1 and 2, 

 from the intestinal muscle 

 of Necturus, are different 

 regions from the same cross 

 section, one side of the 

 intestine only being con- 

 tracted. Fig. 1 is from a 

 relaxed area and Fig. 2 

 from a contracted area. 

 From these two drawings 

 the great increase in the 

 thickness of the muscle 

 layers during contraction 

 is easily seen. As the t^- o t ^ .• * ^t . .• .i,- i 



*' Fig. 2. Intestine of Nectunis, entire thickness 



muscle contracts, the con- of serous and muscle coats, muscle contracted. 



traction waves appear in " longitudinal muscle; b circular muscle; c blood 

 '- '- vessel ; a mesothehum ; e loose connective tissue ; 



the contraction areas. These e' dense connective tissue in contraction wave ; 



contraction waves are irre- -^ intemodal segment showing myofibrillfe, longitudi- 

 nal ; /"' internodal segment showing myofibrillae, cross- 



gular in outline and branch section; g contraction node; h spiral muscle nucleus. 



and anastomose more or less ^^i^^tion. Zenker's fluid ; stain, iron-hiematoxylin. 



Leitz obj. 5, oc. 2, drawing reduced 75, magnification, 



(Fig. 5). They stain very i88 diameters. 



