480 GENERAL ANATOMY. 



also to the extent of surfaces. It remains sometimes after 

 death, in the nerves and muscles. 



This power seems to result from the action of a subtle fluid, 

 formed by the organic action of the nervous substance bathed 

 with the arterial blood. It appears that this fluid is formed 

 throughout, but especially where there are masses of the gray 

 and vascular substance. This subtle fluid seems to traverse 

 the interior and the surface of the nerves, form an atmosphere 

 about them, and, beyond their extremities, penetrate and im- 

 pregnate all the organs and the humours themselves. The 

 blood in particular seems to be penetrated with the same fluid, 

 and to owe to it the essential properties which distinguish it 

 during Hfe. 



In the mean time arterial blood furnishes the nervous sys- 

 tem with the material of its action; the arrival of arterial blood 

 is also a condition of this action. 



Asphleyxia, the cause of which has been sought for in the 

 interruption of the passage of the blood through the lungs, 

 (Haller,) in the arrival of the blood, which had remained ven- 

 ous, in the left ventricle (Godwin,) in this blood penetrating 

 into the muscular substance of the heart (Bichat,) is produced 

 rather by the dark blood penetrating into the nervous substance; 

 syncope in the same manner depends on the innervation be- 

 ing cut off from the heart: life being essentially connected with 

 the reciprocal action of the blood upon the nervous substance, 

 and of the nervous substance upon the blood. 



Does the nervous agent result directly and solely from the 

 reciprocal action of the blood and nervous substance? is it 

 drawn from without? can it pass from one individual to ano- 

 ther? does it result from the opposition of the white and 

 gray substances? of the action of the nervous fibre upon the 

 muscular fibre? Nervous action may then be compared to a 

 discharge of electricity. 



763. Nervous action is excited or put in play by external 

 or internal stimuli. 



764. The first moments of the formation and develop- 

 ment of the nervous system, can not be observed. Does this 

 system exist from the beginning, and does generation result 



