CHANGE OF SHAPE IN ACTIVE MUSCLE. 559 



to degenerate, a violent mechanical, and also a chemical or electrical 

 stimulus, applied to a circumscribed portion of the muscle will cause 

 contraction in this portion alone; so that an elevated thickening of 

 the fibers (Scruff's idiomuscular contraction] is observed at this point. 

 The same phenomenon may be induced in the muscles of a healthy 

 person, and especially in weakened and poorly nourished individuals, 

 if the fibers be struck with a blunt edge at right angles to their course, 

 (b) Under certain conditions, as yet not fully known, the muscles will 

 be seen to exhibit so-called fibrillary contractions, that is the various 

 bundles of fibers in the muscle are from time to time traversed by short 

 contractions. Such a condition is observed in the tongue -muscles of 

 the dog after section of the hypoglossal nerve, and in the face-muscles 

 after section of the facial nerve. 



According to Bleuler and Lehmann, section of the hypoglossal nerve in the 

 rabbit is followed in the course of from sixty to eighty hours by fibrillar con- 

 tractions that persist for months, even when stimulation of the healed nerve 

 above the point of union again excites movements 

 in the corresponding half of the tongue. Stimu- 

 lation of the lingual nerve increases the fibrillar 

 contractions. This nerve contains vasodilator 

 fibers from the chorda tympani. Schiff believes 

 that the cause of the contractions resides in the 

 increased blood-supply to the tongue. Sigm. 

 Mayer also observed contractions in the facial 

 muscles in rabbits, after restoration of the cir- 

 culation in the carotids and subclavians, pre- 

 viously compressed. Section of the motor nerves 

 in the face does not abolish the phenomenon, 

 while repeated compression of the arteries does FIG. 191. The Microscopic Phenomena 



SO. The Cause Of the contractions resides, ac- of Muscular Contraction in the Indi- 



cordingly, in the musculature itself. This motor EnSSLS?* 8 f the Fibrils (after 



phenomenon is designated pseudomotor. It may 



be compared to the paralytic secretion of the 



salivary glands. Similar phenomena have been observed also in man under 



pathological conditions, but at times fibrillar contractions may be observed even 



in the absence of other evidence of pathological disturbances. 



Microscopic Phenomena. i. The separate fibrils of the muscle 

 exhibit the same phenomena as does the entire muscle, in that they be- 

 come shorter and thicker. 2 . The observation of the individual muscle- 

 elements is attended with especial difficulties. In the first place, it is 

 certain that during contraction they become collectively shorter and 

 thicker, so that the transverse striations appear to be pushed more closely 

 together. 3. Opinions are not fully in accord as to the behavior of the 

 constituent parts of each muscle-element during contraction. 



Fig. 191,1 represents, according to Engelmann, on the left a muscular element 

 at rest; from c to d extends the doubly refractive, contractile substance, in the 

 middle of which the median disc a b is situated; h and g are the terminal discs. 

 In addition, there is in each singly refractive light layer an accessory disc, f and 

 e, which is doubly refractive in but slight degree, and occurs only in the muscles 

 of insects. Fig. i shows on the right the same element in polarized light, the 

 middle portion of the element, so far as the actual contractile substance extends, 

 appearing light on account of the double refraction; while the remainder of the 

 muscle-element appears black on account of the single refraction. Fig. 191, 2 

 represents the transition-stage, and 3, the actual contractile stage of the muscle- 

 element, both on the left as viewed in ordinary light, and on the right in polarized 

 light. 



According to Engelmann, during contraction (3) the singly refractive 

 layer becomes on the whole more highly refractive, and the doubly re- 



