90 CONTRACTILE ELEMENTS. 



takes and keeps the form naturally belonging to its structure, 

 which is that of a spiral spring, the coils of which, when iu 

 the state of repose, are as near as possible to each other. 



" The contraction of the muscular fibre of the style of the 

 vorticellus corresponds with the state of repose of the spring, 

 and is the direct consequence of its elasticity ; the lengthen- 

 ing of the fibre is the result of the forced extension of the 

 spring, by means of a movement connected with the act of 

 nutrition, and acting during the apparent repose of the con- 

 tractile organ. When the source of this antagonistic force 

 is dried up, the elasticity, by bringing the muscle back to its 

 original form, produces the said contraction. . . . The ten- 

 dency to a state of extreme contraction is thus an inherent 

 property of the living muscular fibre, a necessary result of 

 its structure and of its elasticity. During life this tendency 

 to shorten is combated by an extending cause which pre- 

 vails during the repose of the muscle, and is developed in the 

 change undergone by the elements of nutrition, increasing as 

 these are more abundant, diminishing or disappearing in their 

 absence ; and it may be momentarily suspended by any of the 

 excitants of muscular contractility, such as nervous action, 

 heat, a blow, etc." 



.In another series of investigations Professor Rouget, ex- 

 perimenting on the living animal, has shown that any thing 

 which is an obstacle to the nutrition of the fibre causes it to 

 contract. By tying the artery of a limb, and constantly in- 

 creasing the excitations by the application of increasing heat, 

 he found that he obtained always the same results. Accord- 

 ing to him, the effect of too frequent repetition of an excita- 

 tion, such as excessive heat, is to stop the progress of nutrition. 

 In both these cases the myograph (see p. 84) has shown that 

 the contractions of the fibrils, becoming more frequent, at 

 length follow one another so closely that there is no longer 

 any interval between them, and the muscle then enters into 

 the state of tetanic rigidity. Thus : " the tendency to shorten, 

 which is the result of the peculiar elasticity of the muscular 

 element, is permanent. During life and the repose of the 

 muscle it is combated by a tendency to lengthen, the energy 

 of which is in proportion to the activity of nutrition, and 

 expires with it. Contraction takes place at the moment 

 when the equilibrium between these two opposite tendencies 

 is broken by the withdrawal of the extending power. As 

 the coefficient of elasticity varies in the living muscle with 

 the different states of repose, contraction, and rigidity, so 



