CHANGES IN A MUSCLE DURING CONTRACTION. 475 



injured animals even when given by the mouth. The nerves and muscles of poisoned animals 

 exhibit considerable electromotive force. [For the effect of curara on lymph-formation 

 ( 199, 6).] 



Atropin appears to be a specific poison for smooth muscular tissue, but different muscles are 

 differently affected {Szpilmann, Luchsinger). [This is doubtful. A small quantity of atropin 

 seems to affect the motor nerves of smooth muscle in the same way that curara does those of 

 striped muscle; we must remember, however, that there are no end-plates proper in the former, 

 so that the link between the nerve-fibrils and the contractile substance is probably different in 

 the two cases. It is well known that the amount of striped and smooth muscle varies in the 

 oesophagus in different animals. Szpilmann and Luchsinger found that, after the action of 

 atropin, stimulation of the peripheral end of the vagus will still cause contraction of the striped 

 muscular fibres in the oesophagus, but not of the smooth fibres, although both forms of muscular 

 tissue respond to direct stimulation.] 



After section of the motor nerve of a muscle, the excitability undergoes remarkable changes ; 

 after thi-ee to four days the excitability of the paralysed muscle is diminished, both for direct 

 and indirect stimuli (p. 473) ; this condition is followed by a stage, during which a constant 

 current is more active than normal, while induced currents are scarcely or not at all effective 

 ( 339, I.). The excitability to mechanical stimuli is also increased. The increased excitability 

 occurs until about the seventh week; it gradually diminishes until it is abolished towards the 

 sixth to the seventh month. Fatty degeneration begins in the second week after section of the 

 motor nerve, and goes on until there is complete muscular atrophy. Immediately after section 

 of the sciatic nerve, Schmulewitsch found that the excitability of the muscles supplied by it 

 was increased. 



297. CHANGES IN A MUSCLE DURING CONTRACTION. I. Macro- 

 scopic Phenomena. 1. When a muscle contracts, it becomes shorter and at the 

 same time correspondingly thicker. 



The degree of contraction, which in very excitable frogs may be 65 to 85 per cent. (72 per 

 cent, mean) of the total length of the muscle, depends upon various conditions : (a) Up to a 

 certain point, increasing the strength of the stimulus causes a greater degree of contraction ; 

 (b) as the muscular fatigue increases, i.e., after continued vigorous exertion, the stimulus 

 remaining the same, the extent of contraction is diminished ; (c) the temperature of the sur- 

 roundings has a certain effect. The extent of the contraction is increased in a frog's muscle 

 the strength of stimulus and degree of fatigue remaining the same when it is heated to 

 33 C. If the temperature be increased above this point, the degree of contraction is diminished 

 ( Schmulewitsch ) . 



2. The volume of a contracted muscle is slightly diminished (Swammerdam, f 

 1680). Hence, the specific gravity of a contracted muscle is slightly increased, 

 the ratio to the non-contracted muscle being 1062 : 1061 (Valentin) ; the diminu- 

 tion in volume is, however, only y^Vo"' although this has recently been denied by 

 J. Ewald. 



Methods. (a) Erman placed portions of the body of a live eel in a glass- vessel filled with an 

 indifferent fluid. A narrow tube communicated with the glass-vessel, and the fluid rose in the 

 tube to a certain level. As soon as the muscles of the eel were caused to contract, the fluid in 

 the index-tube sank, (b) Landois demonstrates the decrease in volume by means of a mano- 

 metric flame. The cylindrical vessel containing the muscle is provided with two electrodes 

 fixed into it in an air-tight manner. The interior of the vessel communicates with the gas 

 supply, while there is a small narrow exit-tube for the gas, which is lighted. Every time the 

 muscle contracts, the flame diminishes. The same experiment may be performed with a con- 

 tracting heart. 



3. Total and Partial Contraction. Normally, all stimuli applied to a muscle or 

 its motor nerve cause contraction in all its muscular fibres. Thus, the muscle con- 

 ducts the state of excitement to all its parts. Under certain circumstances, how- 

 ever, this is not the case, viz. : (a) when the muscle is greatly fatigued, or when 

 it is about to die, violent mechanical stimuli, as a vigorous tap with the finger or a 

 percussion hammer (and also chemical or electrical stimuli), cause a localised con- 

 traction of the muscular fibres. This is Schiff's " idio-muscular contraction." The 

 same phenomenon is exhibited by the muscles of a healthy man, when the blunt 

 edge of an instrument is drawn transversely over the direction of the muscular 

 fibres. (6) Under certain as yet but imperfectly known conditions, a muscle ex- 

 hibits so-called fibrillar contractions, i.e., short contractions occur alternately in 



