572 THE ELASTICITY OF PASSIVE AND ACTIVE MUSCLE. 



so that the amount of blood circulating through it is increased. Evidently the 

 vasodilator nerve-fibers contained in the same nerve-trunks as the motor nerves 

 are stimulated at the same time as the latter. 



In estimating the absolute muscular energy of single muscles or groups of 

 muscles in man, close attention should always be paid to the physical relations, 

 for example leverage, effects, direction of the traction, degree of shortening, and 

 the like. 



The absolute energy of certain groups of muscles may practically be measured 

 readily by means of the dynamometer. This is constructed in part on the principle 

 of the spring-scales, upon which the pressure or pull of the muscles in question 

 is allowed to act. Quetelet has determined statistically the strength of certain 

 groups of muscles. The pressure of both hands in man equals 70 kilos. The 

 pull amounts to double this weight. The strength of the hands of a woman is 

 about one-third less. Further, a man can carry more than twice his own weight, 

 a woman only half her weight ; boys are able to carry about one-third more than 

 girls. 



In estimating the work done by man, not only the amount of work he is 

 able to perform in any one moment should be taken into consideration, but also 

 the number of times in succession he can perform this work. In accordance with 

 practical experience, the mean value of the daily work performed by a man during 

 eight hours' activity has been estimated at from 6.3 to 10 (at most from 10.5 

 to n) kilogrammeters in a second, hence a daily usefulness of 288,000 (in round 

 numbers 300,000) kilogrammeters. The work performed by a horse in a second 

 is assumed to be 75 kilogrammeters horse-power or dynamic horse. 



This average performance of work may, it is true, be temporarily increased, 

 but, the organism then requires a prolonged rest after the work is done, so as not 

 to suffer in health as a result of the overexertion. The amount of work performed 

 in walking and in bicycling is discussed on p. 595. 



Some substances, when introduced into the body, impair and eventually 

 abolish muscular activity; for example mercury, digitalin, helleborin, potassium- 

 salts, apomorphin, and others. Others have been shown to increase the functional 

 activity of muscular tissue; for example caffein. theobromin, veratrin, muscarin 

 in small doses, glycogen, kreatin, and hypoxanthin; extract of meat likewise 

 causes rapid recovery of the muscles after fatigue. 



Unstriated muscles are capable of performing a great amount of 

 work, for example the uterus during labor, the craw of granivorous 

 animals. The longitudinal musculature of the earth-worm is capable 

 of raising more than 15 kilos, the frog's intestine of overcoming the pres- 

 sure of a column of water of i meters. 



THE ELASTICITY OF PASSIVE AND ACTIVE MUSCLE. 

 MYOTONOMETRY. 



Preliminary Physical Considerations. Every elastic body has its natural 

 form, that is the outer form that it possesses when no external force (traction or 

 pressure) operates upon it. Thus, the passive muscle also possesses a natural form, 

 when no traction or pressure is exerted upon it. If traction in a longitudinal 

 direction be made on a muscle its connected parts must be somewhat separated 

 from one another, and the natural form will be stretched under the influence of 

 the elastic energy. If the extending force be removed, the elastic body will 

 return to its natural form. A body is said to be completely elastic if it returns 

 entirely to its natural form after the tension ceases. By amount of elasticity 

 (modulus) is meant the weight, expressed in kilograms, by which an elastic body 

 having a cross-section of one square millimeter would be stretched the equivalent 

 of its own length, provided it did not previously rupture, as, naturally, often 

 it does. For passive muscle this equals 0.2734, for bone 2294, for tendon 1.6693, 

 for nerves 1.0905, for the coats of the arteries 0.0726. The amount of elasticity 

 of "passive muscle is, thus, small, as the latter yields readily to tractile force; 

 hence its elasticity is not great. The coefficient of elasticity is that fraction of 

 the length of an elastic body to which it is stretched by the unit of weight applied 

 to it. This is large for muscle at rest. When the traction reaches a certain 

 degree the elastic body finally ruptures. The carrying capacity of muscular tissue, 



