396 VARIOUS FORMS OF STIMULATION. 



II. Idio-Muscular Contractions. Obit. III. Place on 

 some flat surface a nerve-muscle preparation which has been 

 much exhausted by treatment or by long removal from the 

 body. 



Strike the muscle sharply with some thin but blunt instru- 

 ment (handle of scalpel), across the middle of the belly, at 

 right angles to its long axis. 



A contraction will probably follow a contraction which, as 

 usual, travels along the whole length of the fibres. 



When the contraction, however, has passed away, the line 

 where the blow fell will be marked by a wheal, i. e., by a local 

 shortening and thickening, which lasts for several seconds, but 

 finally disappears. This wheal, this local thickening and short- 

 ening, is the idio-muscular contraction. 



O6.s. IV. Wait till neither muscle nor nerve give any (ordi- 

 nary) contraction with an electric stimulus. Strike as before ; 

 the Ldio-m oscular contraction will still make its appearance. 

 The relaxation becomes slower the nearer the advent of rigor 

 morli*, with the onset of which the idio-muscular contraction 

 disappears. 



III. Chemical Stimulation of Muscle. Oba. V. Care- 

 fully dissect out the sartorius muscle in the front of the thigl 

 (liir. 27**). injuring it as little as possible, and taking away 

 with it a piece of the pelvis from which it has its origin. Clam 

 the piece of pelvis, avoiding any entanglement of the fibres <> 

 the sartorius itself, and attach the clamp to a stand so that the 

 muscle hangs vertical. If it be desired to record the contrac- 

 tions, thrust a fine needle through the middle of the muscle, 

 and either bring the muscle to bear directly on the recording 

 surface, steadying it with a shotted thread as in the kymo- 

 graphion (Chap. XVI., 33), or make the needle part of a 

 delicate lever. With a sharp pair of scissors, cut off the ten- 

 don of insertion so as to lay bare a transverse section of mus- 

 cular fibre. 



Place a drop of an}' or each of the below-mentioned fluids on 

 a rather greasy glass plate (so as to have a good convex sur- 

 face of lluid), and very gradually raise the plate until the fluid 

 c- tines in contact with the muscular surface. Immediate!}', or 

 very shortly after contact, spasmodic contractions of the 

 muscle will begin. 



The following substances applied directly to muscular fibres 

 produce contractions: 



Mineral acids, even when extremely diluted; solutions of 

 metallic salts ; strong solutions of neutral salts of the alkalies ; 

 lactic acid ; glycerin, even diluted to a considerable extent. 



O!,K. VI. The vapor of ammonia, even in mere traces, acts as 

 a powerful stimulus. Place a few drops of ammonia in a small, 

 flat, wide-mouthed bottle; cover the top with a greased glass 

 plate. Protect the muscle from all extraneous vapor of am- 



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