EXHA USTION AND DEATH OF MUSCLE. 385 



is approaching, and after the quick contractions have already ceased. Rollett 

 also observed them in strips of excised beetle muscle, and estimated the rate 

 of propagation of the wave to be about 0*116 mm. per second. He found it 

 impossible to measure the rate of propagation of the twitch in insects, on 

 account of its extreme quickness, which must considerably exceed that of the 

 quickest muscles of vertebrates. The length of the slow wave he found to 

 be very inconsiderable, being only about 0"097 mm. i.e., involving from 

 twelve to twenty-nine transverse striations of the fibre. 



In those vertebrates in which they have been observed, 1 slowly progressing 

 waves are only called into existence by mechanical stimuli applied directly to 

 the muscle when it is in some peculiar, but as yet undefined, condition, which 

 is not that of diminished excitability. The local muscular swellings first 

 described by Schiff, 2 which may be produced in much the same way, also 

 under abnormal but equally indefinable conditions, may represent arrested slow 

 waves which are prevented by loss of excitability and conductivity of the muscle 

 from being propagated. They will be again referred to in the next section. 



Exhaustion and Death of Muscle. 



Exhaustion (fatigue).— By the word exhaustion, as applied to 

 muscle, is meant a state consequent on previous exertion, in which the 

 maximal effect of stimulation, whether instantaneous or tetanic, as 

 measured either by increase of tension or diminution of length, is less than 

 normal. The notion suggested by the word, namely, that the chemical 

 material which is the source of mechanical energy set free in contraction 

 has been during the antecedent period of exertion used up more rapidly 

 than it has been replaced, is substantially true. Exhaustion may also be 

 defined as a condition in which the normal relation of tension to length 

 is altered. An excited muscle requires, when exhausted, a less weight to 



extend it to any given length than it did before ; the quotient -=- 



is therefore diminished at the same time that the value of A — i.e. the 

 equilibrium length of the muscle in the excited state — is increased. This 

 may be also expressed by saying that the extensibility of excited muscle 

 is increased by exhaustion. As is implied by the lengthening of A, the 

 same stimulus which before was adequate to raise a weight to a certain 

 height becomes inadequate in muscular exhaustion. To obtain the same 

 result as before — that is, to shorten A to its original length, and to 

 restore the relation of tension to length to its previous value — the 

 strength of the stimulus must be increased. 



In the muscles of the frog two changes relating to its power of 

 contracting, present themselves for examination, namely — (1) The gradual 

 lengthening of a tetanised muscle, which immediately follows the attain- 

 ment of its maximum degree of shortening ; and (2) the much slower 

 diminution of the height to which a weight is lifted, when a muscle is 

 successively excited at time-intervals of such length that the effect of 

 each excitation passes off before that of the succeeding one begins. The 

 first of these effects was described by Ed. Weber fifty years ago, and was 

 afterwards recorded graphically by Wundt, who found that the descending 

 limb of the curve of a prolonged tetanus is concave upwards, indicating 

 that the muscle lengthens quickly at first, less and less so afterwards. 

 The first investigation of the fatigue produced by subjecting a loaded 



1 See Biedermann, " Elektrophysiologie," S. 129 ff. 



2 "Lehrbuch d. Physiologic, " S. 26. 

 VOL. II. — 25 



