43q_ 



readily with all the oniiuary stains. lu material stained with iroii- 

 haematoxyliii they are iu lougitudiual section very clearly diöerentiated as 

 black stripes within the contraction lU'ea. The portion of the muscle über 

 within the contraction wave is the contraction node. In places, the 

 waves are so close together that several nodes appear in a single 

 muscle über. While the iuternodal segments of the tiber are distinctly 

 tibrillated, the contraction nodes usually appear homogeneous. The 

 above changes have been described by numbers of investigators, and 

 by them have been variously interpreted, Koellikek C49), Roule 

 ('90, '91), ScHAFFER ('99) and Heidenkeich (02) considered the homo- 

 geneous nodes the contracted portions of the fiber. Henneberg ('01), 

 because he found that tliese nodes iu fixed and stained material were 

 usually of less caliber than the internodal segments, thought the latter 

 were the contracted areas. Heidexkeich ('02) from experimental 



Fig. 3. Intestine of Neeturus, from a contraction wave, a myofibrilla? thickening 

 as they enter a contraction node; b firmly contracted nucleus with the chromatin 

 massed at the ends; c connective tissue: J break in the smooth muscle fiber. Fixation, 

 Zexkek's fluid : stain, iron - ha^matoxylin. Zeiss apochrom. obj. 2 mm, comp. oc. 12, 

 drawing reiiueed '5. magnification 1200 diameters. 



evidence has shown quite conclusively that the deeply staining nodes 

 are the contracted portions of the fiber. That they usually appear 

 smaller iu cross section than the internodal segments he explained as 

 due to their being more subject to shrinkage in the ordinary reagents 

 than are the fibrillated internodal segments. 



While I have found the grosser changes in contraction somewhat 

 similar to those described by Heidenreich, there are some important 

 difieieiices. In the large intestine of the dog, in muscle very firmly 

 contracted before fixation, and then fixed in Zenker's fluid, the deeply 

 staining contracted nodes are always of greater diameter than the 

 internodal segments (Fig. 5). In Xecturus this is not the case, the 



