REQUISITES FOR ELECTRO-MEDICAL INSTRUMENTS. 241 



§ IV. — Every apparatus for faradization should possess a means of 

 graduating the dose of electricity exactly, and proportionately to 

 the degree of excitability of the organs; a degree which ivill 

 vary with the state of health and tvith the nature of the disease. 



The considerations already set forth, in the second chapter, with 

 regard to the special excitability of different organs, of the muscles, 

 of the nerves, and of different regions of the skin, — an excitability 

 varying with the state of health, and with the nature of the disease, 

 — these considerations should suffice to show the importance and 

 the correctness of the proposition that is formulated above. 



How, indeed, would it be possible to limit the electric force 

 to any given organ, unless the apparatus were so constructed as to 

 allow us to apportion its proper dose to each ? I will make this 

 more clear by examples. In the normal condition, the cervix 

 uteri, the bladder, and the rectum, are but little sensitive, while, 

 on the other hand, the weakest currents act energetically upon 

 the sensibility of the muscles of the face. Between these extremes 

 there exist intermediate degrees proper to other organs. To be 

 convinced of this, we need only compare the differences of sensi- 

 bility and contractility which exist between the muscles of the 

 face themselves, although the least excitable of these muscles is 

 infinitely more sensitive than those of other regions. We shall 

 find that each facial muscle is endowed with a special degree of 

 excitability, which requires an electric dose that cannot be exceeded, 

 if we wish to obtain only partial contractions, without the pro- 

 duction of too acute pain. (I need not recur to this subject, after 

 what I have already said in the second chapter upon the degrees 

 of individual excitability of the muscles of the face.) We shall 

 understand the absolute necessity of giving to induction instru- 

 ments a means of exact graduation, upon a sufficiently extended 

 scale, if Ave bear in mind that the degree of excitability varies in 

 each of the regions, and even in eacli of the points, of the face. 

 Besides the differences in the excitability of organs, we must 

 consider also the differences which exist in the anatomical state of 

 the tissues on which we act (the greater or less thickness of the 

 skin, of the areolar adipose layer, and of the aponeuroses to be 

 traversed, and of the muscular layer in which it is desired to 

 localize the excitation), — an anatomical state that must be known 

 in order to produce, with any certainty, the electric recomposition 

 at any stated depth. 



But the graduation will not be exact, unless there be an 

 arithmetical proportion between the divisions of the graduator and 

 the progressive force of the apparatus. 



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