362 



THE PROPERTIES OF STRIPED MUSCLE. 



weight the muscle could just lift under the mechanical conditions 

 present. This having been ascertained, the stop was lowered so that 

 the weight began to act a little later. The weight, which was now 

 in excess, having been adjusted as before, the stop was then again 

 lowered and the observation was repeated with a similar result, and so 

 on. It was thus found that the longer after excitation the muscle 

 encountered the resistance of the weight (or, in other words, the more 

 it had already contracted), the less able was it to overcome that 

 resistance. 1 



The aim of Schwann's experiment was limited to the investigation 

 of the relation between the length to which an excited muscle is 

 extended, and the force which, when so extended, it is able to exert 

 in contraction. Helmholtz 2 subsequently applied the method of after- 

 loading in an investigation which differed from that of Schwann in this 

 respect, that instead of determining the tensions (" forces ") corresponding 

 to a series of lengths, he made the length constant, and observed the 



relation between 

 the tensions and 

 the times after 

 excitation at 

 which they 

 occurred. By 

 setting off the 

 times on a base 

 line, and drawing 

 ordinates which 

 represented the 

 tensions as meas- 

 uredbytheafter- 



FIG. 194. Isotonic (continuous line) and isometric (dotted line) curve loading method, 



of the same muscle, represented as springing from the same i, r^fainor] 

 base line. The two ascending lines designate the fourth and ^T 1 , 



eighth-hundredth of a second after excitation. On one of curve which he 



them the tension in grammes for the isometric curve are in- called the 

 dicated. The isotonic curve is drawn with the muscle loaded 



with 30 grras. After Fick (modified from Fig. 28, loc. tit., 



p. 132). the essential 



characters of 



which are identical with those of the isometric muscle curve (see 

 Fig. 194) as now obtained by a single observation. The most im- 

 portant outcome of the facts which have so far presented themselves, 

 in relation to the isometric curve, is that which was shadowed forth in 

 the preceding paragraph, namely, that the tension of a resisted muscle, 

 especially during the first part of its period of effort, is much greater in 

 proportion to its length than that of the same muscle when it attains 

 the same length in the course of an isotonic contraction; and con- 

 sequently that, although in muscle, whether in the relaxed or contracted 

 state, we have sufficient evidence that the relation between tension and 

 length is that which characterises elastic bodies, it cannot be asserted, 

 even with the proviso that the comparison is made at the same stage in 

 the excitatory process, that, the length being known, the tension can be 

 estimated from it. As Professor Tick expresses it, a muscle is always 



1 Schwann's experiment was first described in Miiller's "Physiologic," 1837, Bd. ii. 

 S. 59-61. 



2 Arch. f. Anat., Physiol. u. wissensch. Med., Leipzig, 1850, S. 303. 



