558 CHANGE OF SHAPE IN ACTIVE MUSCLE. 



which a constant current has an abnormally excessive effect, while induced cur- 

 rents are almost or completely without effect; irritability to direct, mechanical 

 stimuli is also increased. This increased irritability is observed at about the 

 seventh week. It then diminishes gradually, until it completely disappears at 

 about the sixth or seventh month. Beginning with the second week, the muscle 

 begins to undergo progressive fatty degeneration, to the point of complete atrophy. 

 In experiments on animals Schmulewitsch found, immediately after section of the 

 sciatic nerve, that irritability was increased in the muscles innervated by it. 



After death the muscles degenerate (excised muscles more rapidly), 

 and the earlier if they have been exhausted and exposed to stimuli of 

 considerable intensity. Thick muscles "survive longer (in their inte- 

 rior) than thin muscles. It would appear that there is a definite stage of 

 early or late death for each individual muscle; for example, the extensors 

 in man degenerate earlier than the flexors. 



The muscles of the frog degenerate in twenty-four hours at summer tem- 

 perature, in the course of two or three days at moderate temperature, and only 

 after about twelve days at o. The muscles of warm-blooded animals degenerate 

 on an average in the course of from one-sixth to twelve hours. The degeneration 

 of the heart is considered on p. 113. 



CHANGE OF SHAPE IN ACTIVE MUSCLE. 



Macroscopic Phenomena. i. Active muscle becomes shorter and at 

 the same time increases in thickness. 



The degree of shortening, which in exceedingly irritable frogs may amount 

 to as much as from 65 to 85 per cent, (on an average 72 per cent.) of the entire 

 length of the muscle, depends upon various factors: (a) To a certain degree an 

 increase in the strength of the stimulus gives rise to a greater amount of shortening. 

 (6) With increasing exhaustion after continuous, vigorous activity, the same 

 strength of stimulus causes less shortening, (c) Elevation of temperature up to 

 30 C. causes stronger contractions in the frog's muscles. If the temperature be 

 further elevated the degree of shortening is again diminished. 



2. The contracting muscle is somewhat diminished in volume. Con- 

 sequently, the specific gravity of contracting muscle is somewhat in- 

 creased, the ratio to that of non-contracting muscle (in the marmot) 

 being as 1062 : 1061. The diminution in volume amounts to only T ^ T - 



Method. Swammerdam placed a frog's muscle in a glass tube containing air 

 and drawn out into a thin tubule containing a small drop of fluid. The nerve was 

 conducted to the exterior through a small lateral opening. Mechanical stimulation 

 of the exposed nerve caused contraction of the muscle and descent of the small 

 drop. In an analogous manner Ermann placed irritable fragments of an eel 

 in a similar tube, filled with an indifferent fluid. The fluid rises to a certain 

 level in a thin tubule communicating with the glass container. When the muscu- 

 lature of the eel was made to contract, the fluid sank. Landois demonstrated 

 the diminution in volume of contracted muscle by means of the manometric 

 flame. The cylindrical glass vessel containing the muscle receives two electrodes 

 passing through its walls in an air-tight manner. It communicates at one point 

 with a gas-supply pipe, and at another point it gives off a thin tubule, at the 

 extremity of which a small flame is ignited at low gas-pressure. The muscular 

 contraction following each electrical stimulus causes a reduction in the size of the 

 flame. If a pulsating heart, naturally containing no air, be placed in the gas- 

 chamber, each pulsation will be attended with a reduction in the size of the flame. 



3. Under normal conditions, all stimuli applied to the muscle, as 

 well as to the motor nerve, will cause contraction in all of its fibers. The 

 muscle thus conducts to all of its fibers the impulses communicated 

 to it. Deviations from this rule are observed, however, in two direc- 

 tions: (a) When the muscle is greatly exhausted, or when it is about 



