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should be what is known for all motor nerves and muscles, if the 

 cessation of the movements of the heart was the result of a per- 

 manent contraction. But the heart is not at all contracted, and, 

 on the contrary, it remains perfectly placid. 



This is entirely different from what we know to be the case 

 for other muscles. 



I have found that a violent mechanical excitation of the me- 

 dulla oblongata produces also the same stopping of the heart's 

 action. 



Is the heart in a state of rest in consequence of a loss of its 

 irritability or of an interruption of the excitation necessary to 

 its action ? The following fact proves that this second opinion 

 is the right one. When the heart is stopped, every direct exci- 

 tation upon it produces some beatings, and then, its irritability 

 appears to be entire. The stopping, consequently, depends on 

 the absence of excitation. 



The cause exciting the heart to beat is in the blood contained 

 in the capillaries of this organ, as I will try to prove in another 

 article. Now, if we suppose that the galvanization of the par 

 vagum produces a complete constriction of the capillaries of the 

 heart, it is easy to understand why the heart is stopped: it is 

 because the excitation cannot take place on account of the ex- 

 pulsion of the blood from the capillaries. 



It will be asked on what ground we base the supposition that 

 the capillaries are so contracted that they prevent entirely, or 

 nearly so, the passage of the blood. I will answer : 



1st. That it is known that a galvanization of certain nerves 

 (and I have discovered that it is so with the capillaries of the face 

 and ear when the sympathetic nerve is galvanized) may pro- 

 duce a considerable constriction of capillaries. 



2d. That it is known that the nerves of the heart are distri- 

 buted much more to its blood-vessels than to its muscular tissue. 



3d. That, by our supposition, we place the fact of the stopping of 

 the heart's movements among the well known facts, that an excita- 

 tion of a molar nerve produces a contraction of the muscles to 

 which it is distributed ; and, therefore, we are not obliged to admit 

 that an excitation of a nerve is able to produce directly either a 

 contraction of or the cessation of existing contractions. 



There is a practical consequence to be drawn from the fact that 



