THE ELASTICITY OF MUSCLE. 



491 





succeed in doing work. The mean value of the daily work of a man working eight hours a 

 day is 10 (10 - 5 to 11 at most) kilogramme-metres per second, i.e., a daily amount of work = 

 288,000 (300,000) kilogramme-metres. 



[Ergostat. Sometimes it is desirable that patients especiauy those who suffer from excessive 

 corpulence should do a certain amount of work daily ; this can be carried out by Gaertner's 

 Ergostat, which resembles a winch, driven by a handle. The pressure upon the wheel can be 

 regulated by means of a strap, lever, and weights, and according to the weight and number of 

 revolutions of the wheel, can the amount of mechanical work be accurately regulated. This 

 instrument is recommended for therapeutical purposes.] 



Modifying Conditions. Many substances, after being introduced into the body, diminish, 

 and ultimately paralyse the production of work mercury, digitalin, helleborin, potash salts, &c. 

 Others increase the muscular activity veratrin (Hossbach), glycogen, [caffein, and allied alka- 

 loids], muscarin (Klug and Fr. Hogyes), kreatin and hypoxanthin ; extract of meat rapidly 

 restores the muscles after fatigue {Robert). [Those drugs which excite muscular tissue restore 

 it after fatigue. Kreatin is a waste product of muscle, and beef-tea and Liebig's extract of 

 meat perhaps owe their restorative qualities partly to these extractives.] 



301. THE ELASTICITY OF MUSCLE. Physical. Every elastic body has its "natural 

 shape," i.e., its shape when no external force (tension or pressure) acts upon it so as to distort 

 it. Thus, the passive muscle has a "natural form." If, however, a muscle be extended 

 in the course of its fibres, the parts of the muscle are evidently pulled asunder. If the 

 stretching be carried only to a certain degree, the muscle, in virtue of its elasticity, will regain 

 its natural form. Such a body is said to possess " complete elasticity," i.e., after being 

 stretched it regains exactly its original shape. By the term " amount of elasticity " (modulus) 

 is meant the weight (expressed in kilogrammes) necessary to extend an elastic body 1 milli- 

 metre in diameter, its own length, without the body breaking. Of course many bodies are 

 ruptured before this occurs. For a passive muscle it is ^=0*2734 ( Wundt) [that of bone = 2264 

 (Wertheim), tendon = 1 "6693, nerve = 1 '0905, the arterial walls = '0726 (Wundt)]. Thus, the 

 amount of elasticity of a passive muscle is small, as it requires only a slight stretching force to 

 extend it to its own length. It has, therefore, no great amount of elasticity. The term 

 " coefficient of elasticity " is applied to the fraction of the length of an elastic body, to which 

 it is elongated by the unit of weight applied to stretch it. It is large in a passive muscle. If 

 the tension be sufficiently great, the elastic body ruptures at last. The * 'carrying capacity" 

 of muscular tissue, until it ruptures, is in the following ratios for youth, middle, and old age, 

 nearly 7:3:2. [Instead of the word "elasticity," Bran ton suggests the use of extensibility 

 and retractibility, terms suggested by Marey, the one referable to the elongation on the appli- 

 cation of a weight, and the other to the shortening after its removal.] 



Curve of Elasticity. In inorganic elastic bodies, the line of elongation, or the 

 extension, is directly proportional to the extending weight ; in organic bodies, and 

 therefore in muscle, this is not the case, as the weight is continually increased by 

 equal increments the muscle is less extended than at the beginning, so that the 

 extension is not proportional to the weight. If equal weights be added to a scale- 



Fig. 341. 



Fig. 340. Curve of elasticity from an inorganic body (india-rubber). Fig. 341. Curve of 

 elasticity from the sartorius of a frog, obtained by adding equal increments of weight at 

 A, B, C, &c. Fig. 342. Curve of elasticity produced by continuous extension and recoil 

 of a frog's muscle ; x, abscissa before, x' after extension. 



pan attached to a piece of india-rubber, with a writing-lever connected with it, and 

 writing its movements on a plate of glass that can be moved with the hand, we 

 get such a curve as in fig. 340, while, if the same be done with the sartorius of a 

 frog, we get a result similar to fig. 341. A straight line joins the apices of the 

 former, while the curve of elasticity is a hyperbola, or something near it, in the 

 latter case. 



