THE ELASTICITY OF PASSIVE AND ACTIVE MUSCLE. 575 



is tetanized (M) by electrical stimulation; and the curve h i k is thus traced. 

 With the aid of the apparatus both the extension-curve with increasing weight 

 and the contraction-curve with diminishing weight can be recorded. Both curves 

 are necessarily analogous, except that their form is reversed. 



The elasticity of muscle may also be measured by its rate of oscillation when 

 twisted about its longitudinal axis. Kaiser found that the elasticity of active 

 muscle depends upon its length at the time. It is least when the muscle has 

 the same length in the active as in the passive state. If shortening occurs in 

 a muscle stretched by a weight, its elasticity is diminished, and this reaches its 

 minimum when the muscle becomes of the same length as the passive, unweighted 

 muscle. If the active muscle contracts still further, its elasticity increases. 



Under the influence of certain poisons the elasticity of the muscles is altered 

 as a result of changes in the condition of the contractile substance. Potassium 

 causes shortening of the muscle, with simultaneous increase in its elasticity. 

 Digitalin causes elongation of the muscle, together with increased elasticity. 

 Physostigmin also increases the elasticity, while veratrin diminishes it and inter- 

 feres with its completeness. Tannic acid renders the muscles less extensible, but 

 more elastic. 



Ligation of the vessels causes first a diminution, and later an increase in the 

 elasticity. Separation of the nerves from the muscle results in a diminution of the 

 elasticity. The influence of temperature on the extensibility is as follows: As the 

 temperature increases from o to 30 the muscle elongates, as its extensibility 

 increases. The increase in length is proportional to the load. At 34 contraction 

 occurs as a result of the thermal stimulation; above 47 the muscle-proteid 

 coagulates. 



Unstriated muscles possess an exceedingly small amount of elasticity; at the 

 same time the elastic after-effect lasts much longer, and immediately follows the 

 primary stretching. Fibrous connective tissue possesses the greatest elasticity, 

 elastic tissue less, and unstriated muscular tissue the least. The elasticity of a 

 complex organ, made up of these tissues, depends, accordingly, upon the relative 

 abundance of these elements. 



As a result of his experiments Edward Weber has reached the following con- 

 clusions as to the nature of the contractile energy of muscle. He assumes the 

 existence of two states in muscular tissue the passive and the active. Each of 

 these is characterized by a special natural form. The passive muscle possesses 

 the longer, thinner form; the active muscle the shorter, thicker form. Both the 

 active and the passive muscle tend to maintain their respective form. If, now, 

 the passive muscle be thrown into activity, the passive form suddenly changes 

 into the active form, by virtue of its elastic energy. It is this latter that is capable 

 of performing the work of the muscle. Schwann has already alluded to the simi- 

 larity between the energy of an active muscle and that of a long, elastic, tense spiral 

 spring. Both are able to lift the greatest weight only from the form in which 

 they are most stretched. The greater the shortening they have already undergone, 

 the smaller is the weight that they are further able to raise. 



Observations on elasticity can also be made on the muscles of living human 

 beings. Under such circumstances, however, not alone the simple physical law 

 of elongation is to be taken into consideration, for the elongation at the same 

 time causes in the muscle changes in its irritability and in the blood-supply, as 

 well as direct or reflex stimuli, all of which must necessarily modify its extensi- 

 bility. If the extremity of the foot in man be raised vertically by means of a 

 cord passing over a pulley and having weights attached to it, the muscles of 

 the calf will be stretched. Mosso and Benedicenti found that, as the weight 

 increased, the muscles became longer at the same or at an increasing rate, if 

 the weight were continuous and increasing. If, however, the muscle is completely 

 released, before the new, heavier weight is applied, then the length of the stretched 

 muscle diminishes as the weight is increased. Further, the curve of elongation 

 exhibits individual differences; it exhibits fluctuations in association with the 

 respiratory curves; it may exhibit after-extensions and after-contractions; it 

 changes with frequent repetition, with heat and cold. Strong, sudden stretching, 

 and previous voluntary contraction and fatigue likewise have an effect. Investi- 

 gations of this sort are designated myotonometry. 



