STRIATED MUSCLE. 81 



inversion, of the normal current of the muscle under the 

 first form. 



C. Role of the Muscle in the System : its Function. 



Knowing the two forms of the muscle, and the properties 

 which it enjoys under each, we can now form some idea of 

 the manner in which the muscular element works in the 

 organism. The properties of the muscle which are of most 

 use in the system may be said to be : 



1. Its Elasticity. We shall see, farther on, that many 

 of the cavities with muscular coats profit more especially by 

 the perfect elasticity of the muscle, and the really wonderful 

 tendency to distension which it shows. With regard to the 

 stomach and the auricles of the heart, we shall see, in par- 

 ticular, that the muscle, placed in the coats of these mem- 

 branous bags, is especially useful, on account of the great 

 ease with which it enables these cavities to expand, and we 

 shall have no hesitation in admitting that the muscles (the 

 pulmonary alveoli, for instance, or at least the bronchi) act 

 much more by their elasticity than by their contractility. 



2. TJie property of passing from the first to the second 

 form constitutes the real vital activity, the essential physio- 

 logical property, of the muscular element : in this lies its 

 irritability. We must, therefore, study this irritability, in 

 order to see if it is really a property of the muscle, similar 

 to that which we have described in the globules ; what are 

 the agents which modify it ; the irritants which bring it into 

 play ; how the muscle responds to these irritants ; and, finally, 

 how we can undertake an explanation of the inward changes 

 which then take place in the muscle. 



Irritability of the Muscle. According to the course 

 which we have followed, showing that from the globule ; 

 which is the first form of all the tissues and the source of all 

 vital phenomena, the anatomical form and the physiological 

 properties of the muscular element are derived ; we can easily 

 conceive that the muscle preserves the same method of irri- 

 tability as the globule, and that the property of thus react- 

 ing, under the influence of excitants, is quite characteristic 

 of it. This has not been the method employed by all 

 physiologists, and, although Ilaller had already shown 

 irritability to be a property inherent in the muscle itself, 

 many authors have since maintained, and maintain still, that 

 the muscle is not directly irritable (Funke, Eckhard, Jac- 

 coud), and that all excitants applied to the muscle act upon 



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