Structure of Smooth Muscle. 499 



lated fibers, the contracted filjers. In firmly contracted muscle, fibers 

 of type (b) predominate; in resting muscle, fibers of type (a). 



Heiderich, 1902, studied contraction of smooth muscle in the in- 

 testine, urino-genital tract and blood-vessels of a number of mammals. 

 He obtained contracted muscle by heating the tissue and by injecting 

 apomorphine. Heiderich's conclusions are almost diametrically 

 opposed to those of Henneberg. He found in contracted muscle, as 

 did Henneberg, two types of fibers: (a) fibers with homogeneous 

 protoplasm, showing marked affinity for eosin, (b) fibers with fibril- 

 lated protoplasm, showing little affinity for eosin. The former he 

 considered the contracted, the latter the expanded fibers. In fixed 

 and stained material after certain fixatives the homogeneous fibers 

 have smaller diameter than do the fibrillated fibers. In fresh material 

 this is not the case. Consequently Heiderich concludes that certain 

 reagents must cause more shrinkage in the contracted than in the 

 relaxed fibers. In the homogeneous fibers the nuclei are shorter and 

 thicker than in the fibrillated fibers. The elastic fibers in the neigh- 

 borhood of the homogeneous fibers run a wavy course, elsewhere they 

 are straight. These facts lend further evidence that the homogeneous 

 are the contracted and the fibrillated the resting fibers. Heiderich 

 describes quite fully the two types of contraction mentioned earlier 

 by Heidenhain, 1861. These types are (a) the peristaltic, occurring 

 in the smooth muscle of digestive and urino-genital tracts and (b) 

 the total, occurring in the blood-vessels. In type (a) the contraction 

 passes over the fiber in a series of waves so that several thickened, 

 lu mogeneous nodes may appear in each fiber. Between the nodes the 

 myofibrillae are distinctly seen. In type (b) there is general shorten- 

 ing and thickening of the entire fiber. In explaining the contraction 

 of smooth muscle Heiderich supports the inotagmen theory of 

 Apathy. He found nothing in the stracture of the myofibrillae, how- 

 ever, to indicate their relation to contraction. 



Schaper, 1902, in the muscle fibers in the mesenteiy of Urodela 

 found, at times, spindle-shaped enlargements of the fibers. The myo- 

 fibrillae in the mesenteric muscle are frequently segmented, made up 

 of alternate dark and light bands. Schaper mentions the possibility 

 that the segiuentation may be due to contraction set up by the fixative. 



