476 



TOTAL AND PARTIAL MUSCULAR CONTRACTION. 



different bundles of muscular fibres. This is the case in the muscles of the tongue, 

 after section of the hypoglossal nerve ; and in the muscles of the face, after section 

 of the facial nerve. 



[In some phthisical patients there is marked muscular excitability, so that if the pectoral 

 muscle be percussed, a local contraction idio-muscular occurs, either confined to the spot, or 

 two waves may proceed outwards and return to the spot struck.] 



Cause of Fibrillar Contraction. According to Bleuler and Lehmann, section of the hypo- 

 glossal nerve in rabbits is followed by fibrillar contractions after sixty to eighty hours ; these 

 contractions may continue for months, even when the divided nerve has healed and is stimu- 

 lated above the cicatrix so as to produce movements in the corresponding half of the tongue. 

 Stimulation of the lingual nerve increases the fibrillar contractions or arrests them. This nerve 

 contains vaso-dilator fibres derived from the chorda tympani. Schiff is of opinion that the 

 increased blood-stream through the organ is the cause of the contractions. Sig. Mayer found 

 that, by compressing the carotids and subclavian, and again removing the pressure so as to per- 

 mit free circulation, the muscles of the face contracted. Section of the motor nerves of the 

 face did not abolish the phenomenon, but compression of the arteries did. The cause of the 

 phenomenon, therefore, seems to lie within the muscles themselves. This phenomenon may 

 be compared to the paralytic secretion of saliva and pancreatic juice which follows section of the 

 nerves going to these glands (pp. 214, 258). Similar fibrillar contractions occur in man under 

 pathological conditions, but they may also occur without any signs of pathological disturbance. 

 [Fibrillar contractions, due to a central cause, occur in monkeys after excision of the thyroid 

 gland ( 103, III.). Some drugs cause fibrillar muscular contractions, e.g., aconitin, guanidin, 

 nicotin, pilocarpin, but physostigmin produces them in warm-blooded animals (not in frogs). 

 According to Brunton these drugs probably act by irritating the motor nerve -endings, as the 

 contractions are gradually abolished by curara.] 



II. Microscopic Phenomena. 1. Single muscular fibrillse exhibit the same 

 phenomena as an entire muscle, in that they contract and become thicker. 2. 

 There is great difficulty in observing the changes that occur in the individual parts 

 of a muscular fibre during the act of contraction. This much is certain, that the 

 muscular elements become shorter and broader during contraction, and that the 

 transverse striae approach nearer to each other (Bowman, 1840). 3. There is great 

 difference of opinion as to the behaviour of the doubly refractive 

 (anisotropous) and the singly refractive media. j 



Engelmann's View. Fig. 319, 1, on the left represents a passive mus- 

 cular element from c to d is the doubly refractive contractile substance, 3 

 with the median disc, a, b, in it ; h and g are the lateral discs. Besides C 

 these, in each of the singly refractive discs there is a clear disc " secondary 5 

 disc " / and e, which is only slightly doubly refractive. This occurs only g 

 in the muscles of insects. Fig. 1, on the right, shows the same element in 

 polarised light, whereby the middle 



area of the element, as far as the con- 2 



tractile substance proper extends, 

 is, owing to its double refraction, 

 bright ; while the other part of the 

 muscular element, owing to its being 

 siugly refractive, is black. Fig. 

 319, 2, is the transition stage, and 

 3 the proper stage of contraction of 

 the muscular element. In both 

 cases, the figures on the left are 

 viewed in ordinary light, and on the 

 right, in polarised light. During -pig 319 



reSve "l^be^nS'a^l wh^e The ^copic appearances' during a muscular contraction 

 m^A &?bly ^^ ft th 7 e in^dnal^ments of the fibrillar. 1, 2, 3 (after 

 less so. Consequently, a fibre at a ^ngehrumn) ; 4, 5 (after Merkel). 



certain degree of contraction (2), when viewed in ordinary light, may appear homogeneous and 

 but slightly striped transversely = the homogeneous or transition stage. During a greater degree 

 of contraction (3), very dark transverse stripes reappear, corresponding to the singly refractive 

 discs. At every stage of the contraction, as well as in the transition stage, the singly and 

 doubly refractive discs are sharply defined, and are recognised by the polariscope as regular 

 alternating layers (in 1, 2, and 3 on the right). These do not change places during the con- 

 traction. The height of both discs is diminished during contraction, but the singly refractive 



d 



\ ''.' BBS 



