524 Caroline McGill. 



The behavior of the interstitial connective tissue during contrac- 

 tion is worthy of mention. All the changes noted are purely passive 

 ones, caused by the decrease in length and increase in thickness of the 

 nearby muscle fibers. During contraction the changes are similar to 

 those described by Heiderich, 1902. In uncontracted areas the col- 

 lagenous fibers form a loose reticulum, Figs. 2, 13, 15, 24, etc. ; 

 elastic fibers run straight, Fig. 12. In the contraction waves the 

 collagenous fibers become much condensed, Figs. 20-23, 28-30. This 

 explains why, by earlier workers on intercellular bridges, all of whom 

 considered the collagenous fibers protoplasmic connectives, the bridges 

 were described as being more numerous and larger in contracted 

 than in uncontracted muscle. If the pressure of the contracting 

 fibers in the contraction waves be great enough the collagenous fibers 

 become packed into distinct membranes. Fig. 31. The elastic fibers 

 where contraction waves pass over the muscle become distinctly wavy, 

 due to passive shortening, Fig. 12. 



Well defined contraction waves do not occur in arterial muscle. 

 Frequently a contracted fiber will be entirely surrounded by uncon- 

 tracted fibers. More often an irregiilar area, including anywhere 

 from a few fibers to the entire thickness of the muscle coat, is con- 

 tracted, while neighboring muscle is relaxed. In firm contraction 

 practically every fiber in the arterial wall may be contracted. 



b. The form of the contraction node. 



In peristaltic contraction the muscle fiber is traversed by one or 

 more thickened areas, the contraction nodes. They represent the 

 portion of the fiber included within the contraction wave, conse- 

 quently they are just as numerous in the fiber as are the contraction 

 waves passing over it. In the large intestine of dog and the small 

 intestine of INTecturus, when firmly contracted the single contraction 

 nodes may include as much as one-half of the entire length of the 

 fiber, Figs. 21, 23, 30. A^^ien less firmly contracted the contraction 

 nodes are not so wide, Figs. 35, 40. In the smooth muscle of the 

 small intestine of mammals and in the muscular stomach of chicken 

 the contraction nodes are shorter and more numerous. Fig. 11. In 

 the muscle of the oesophagus of the pig they are often so close together 

 as to make the fiber appear distinctly cross-striated. 



