USES OF ELASTICITY. 493 



of antagonistic muscles. The position of a passive limb depends upon the 

 resultant of the elastic tension of the different muscle groups. 



The elasticity of an active muscle is less than that of a passive muscle, i.e., it 

 is elongated by the same weight to a greater extent than a passive muscle. For 

 this reason, the active muscle, as can be shown in an excised contracted muscle, is 

 softer ; the apparently great hardness manifested by stretched contracted muscles 

 depends upon their tension. When the active muscle becomes fatigued, its 

 elasticity is diminished ( 304). 



Method. Ed. Weber took the hyoglossus muscle of a frog and suspended it vertically, 

 noticing its length when it was passive. It was then tetanised with induction shocks and its 

 height again noted. One after the other heavier weights were attached to it, and the length 

 of the passive and tetanised muscle observed for each weight. The extent to which the active 

 loaded muscle shortened from the position of the passive loaded muscle he called the "height 

 of the lift" (or " Hubhohe "). The latter becomes less as the weight increases, and lastly, 

 the tetanised muscle may be so loaded that it cannot contract, i.e., the height of the lift is = 0. 



Weber's Paradox. The case may occur where, when a muscle is so loaded that it cannot 

 contract when it is stimulated, it may even elongate. According to Wundt, even in this 

 condition the elasticity is not changed. [The usual explanation given is that, as the elasticity 

 of a muscle is diminished during contraction, it is more extended with the same weight in the 

 contracted as compared with the passive or uncontracted state, so that a heavily weighted 

 muscle, when stimulated, may elongate instead of shorten.] According to Wundt, however, 

 as stated, there is no change in the elasticity of the muscle. In these experiments, the length 

 of the active loaded muscle is equal to the length of the passive muscle when similiarly loaded, 

 minus the ' ' height of the lift. " 



Poisons. Potash causes shortening of a muscle with simultaneous increase of its elasticity. 

 Digitalin produces other changes with increased elasticity. Physostigmin increases it, while 

 veratrin diminishes it, and interferes with its completeness (Eossbach and v. Anrep), and. tannin 

 makes a muscle less extensible, but more elastic (Lewin). Ligature of the blood-vessels 

 produces at first a decrease, and then an increase, of the elasticity ; section of the motor nerve 

 diminishes the elasticity (v. Anrep) ; heat increases it. 



Eduard Weber concluded from his experiments that a muscle assumes two forms, the active 

 and the passive form. Each of these corresponds to a special natural form. The passive muscle 

 is longer and thinner the active is shorter and thicker in form. The passive as well as the 

 active muscle strives to retain its form. If the passive muscle be set into activity, the passive 

 rapidly changes into the active form, in virtue of its elastic force. The latter is the energy 

 which causes muscular work. Schwann compared the force of an active muscle to a long, 

 elastic, tense spiral spring. Both can lift the greatest weight, only from that form in which 

 they are most stretched. The more they shorten, the less the weight which they can lift. 



[Uses of Elasticity. As already pointed out, all muscles are slightly on the 

 stretch, so that no time is lost nor energy wasted, in " taking in slack," as it were; 

 but the elasticity also lessens the shock of the contraction, so that it is developed 

 gradually, and muscles are not liable to be torn from their attachments. The 

 muscular energy is transmitted to the mass to be moved through an elastic and 

 easily extensible body (muscle), whereby the shock due to the contraction is 

 lessened, but, as Marey has shown, the amount of work is thereby considerably 

 increased.] 



[Tonicity of Muscle ( 362) Sensibility of Muscle. That muscles contain sensory fibres is 

 certain ( 430). Section of inflamed muscles is painful, and during muscular cramp intense pain 

 is felt. Sachs discharged a reflex action by stimulating the central end of an intra-muscular 

 nerve-filament in a frog, while stimulation of the central end of the phrenic nerve raises the 

 blood-pressure {Muscular Sense, 430).] 



302. Formation of Heat in an Active Muscle. After Bunzen, in 1805 

 ( 209, 1, 6), showed that during muscular activity heat is evolved, v. Helmholtz 

 proved that an excised frog's muscle, when tetanised for two to three minutes, 

 exhibited an increase of its temperature of 0'14 to 0'18 C. R. Heidenhain 

 succeeded in showing an increase of 0*001 to 0*005 C. for each single contraction. 

 The heart is warmer during every systole (Marey). 



[Method. The rise in temperature of a frog's muscle may be estimated by placing the two 

 gastrocnemii of a frog's muscle on the two junctions of a thermo-electric pile, connected with a 



