416 HANDBOOK OF PHYSIOLOGY. 



curve, after a few more contractions, becomes continuous with that be- 

 fore the rest. 



In the second diagram is represented the effect of a stream of oxy- 

 genated blood. Here we have a sudden restoration of energy: the 

 muscle in this case makes an entirely fresh start from A, and the new 

 fatigue curve is parallel to, and never coincides with the old one. 



A fatigued muscle has a much longer latent period than a fresh one. 

 The slowness with which muscles respond to the will when fatigued 

 must be familiar to every one. 



In a muscle which is exhausted, stimulation only causes a contraction 

 producing a local bulging near the point irritated. A similar effect may 

 be produced in a fresh muscle by a sharp blow, as in striking the biceps 

 smartly with the end of the hand, when a hard muscular swelling is in- 

 stantly formed. 



Accompaniments of Muscular Contraction. 



(1.) Heat is developed in the contraction of muscles. Becquerel 

 and Breschet found, with the thermo-multiplier, about 1 Fahr. of heat 

 produced by each forcible contraction of a man's biceps; and when the 

 actions were long continued, the temperature of the muscle increased 

 2. This estimate is probably high, as in the frog's muscle a consider- 

 able contraction has been found to produce an elevation of temperature 

 equal on an average to less than J C. It is not known whether this 

 development of heat is due to chemical changes ensuing in the muscle, 

 or to the friction of its fibres vigorously acting: in either case we may 

 refer to it a part of the heat developed in active exercise. 



(2.) Sound is said to be produced when muscles contract forcibly, 

 as mentioned above. Wollaston showed that this sign might be easily 

 heard by placing the tip of the little finger in the ear, and then making 

 some muscles contract, as those of the ball of the thumb, whose sound 

 may be conducted to the ear through the substance of the hand and 

 finger. A low shaking or rumbling sound is heard, the height and loud- 

 ness of the note being in direct proportion to the force and quickness of 

 the muscular action, and to the number of fibres that act together, or, 

 as it were, in time. 



(3.) Changes in Shape. The 'mode of contraction in the trans- 

 versely striated muscular tissue has been much disputed. The most 

 probable account is, that the contraction is effected by an approxima- 

 tion of the constituent parts of the fibrils, which, at the instant of con- 

 traction, without any alteration in their general direction, become closer, 

 flatter, and wider; a condition which is rendered evident by the approx- 

 imation of the transverse striae seen on the surface of the fasciculus, and 

 by its increased breadth and thickness. The appearance of the zigzag 

 lines into which it was supposed the fibres are thrown in contraction, 



