i GENEEAL PHYSIOLOGY OF MUSCLE 87 



hold with Tick that the two curves tend to converge asymptotic- 

 ally without meeting. 



These studies of Weber on the elasticity curve of resting and 

 active muscle were subsequently confirmed and extended with 

 better methods by Marey (1868) and Blix (1874) on excised frog 

 muscles ; by Bonders and Van Mansvelt (1863) and by Chauveau 

 and Laulanie (1899) on human muscles. 



Other work on muscular elasticity has shown that it varies 

 under the influence of different toxic and medicinal substances. 

 In this connection Eossbach's and Anrep's observations (1880) on 

 the frog are striking. These showed that the changes which the 

 elasticity of muscles loaded with low weights (2 grms.) undergoes 

 by the action of certain poisons may be utilised as a good method 

 of toxicological analysis. They found that curare and cocaine, 

 which paralyse the motor or sensory nerve -endings, produce 

 elongation of the muscle (lowering of tone) without perceptibly 

 affecting elasticity ; pliysostigmine, in addition, causes an increase 

 of elasticity by acting on the contractile substance ; digitaline 

 causes elongation of the muscle and increase of its elasticity, 

 independent of the action of the nerves, i.e. by direct action on 

 the contractile substance ; veratrin (injected in doses of 1-5 mgrms.) 

 produces first elongation, then contracture of the muscle, inde- 

 pendently of the nerve, and in both stages depresses the elasticity 

 and makes it imperfect ; lastly, potassium salts shorten the muscle 

 and simultaneously increase its excitability, while sodium salts in 

 the same dose and same concentration produce no visible change 

 either in the length or the elasticity of the muscle. 



Progressive muscular fatigue, too, alters elasticity in the same 

 way as poisons, raising it in the first stage, and subsequently 

 decreasing it in proportion as contracture sets in. After death, 

 when rigor mortis begins, muscle is highly elastic, that is, but little 

 extensible, and its elasticity simultaneously diminishes, for when 

 the traction is removed it no longer returns to its initial length. 



All these and other experimental observations confirm Weber's 

 theory, and show that elasticity is not a constant physical property 

 of the muscle, but is perhaps the most variable and least stable of 

 all its properties. 



But Weber's assertion that the contraction of the muscle 

 is only the result of a sudden change in its elasticity, due to 

 the chemical changes produced by excitation, is no more than 

 a schematic restatement, whatever its theoretical value. Its 

 simplicity, however, signalises a considerable advance in mechanical 

 notions of muscular activity ; for, by excluding Fontana's theory, 

 which assumes contractility and elasticity to be two opposite or 

 antagonistic properties, it leads on logically to the formulation of 

 a more exact idea, harmonising better with the facts, of the process 

 by which relaxation follows on the contraction of the muscle. 



