4 DISEASES OF THE BRAIN AND NERVES. 



Sir Charles Bell, in the course of his physiological investigations, 

 discovered that the nerves concerned in the functions of respira- 

 tion were not to be classed with the sentient and voluntary sys- 

 tems, or even with the ganglionic, but, on the contrary, formed by 

 themselves another, a distinct system ; and that their seat of pow er 

 and action was the medulla oblongata. 



Since this, Dr. Hall has developed what he calls his " true 

 spinal " or '* excito-motory" system, and insists that Sir Charles 

 Bell's " respiratory" must come included within it. And, further, 

 that the primiim niohile of the respiratory actions is not seated in 

 the brain, but in the nerves ; that the act is an *' excited " one, 

 arising from the presence and stimulus of carbonic acid ; and that 

 the medulla oblongata is but the centre or medium through which 

 the excitation or impression is conveyed to the motor nerves dis- 

 tributed to the respiratory muscles. 



This is not the place to enter into physiological inquiry. My 

 object in touching the subject thus lightly has been to impress 

 upon the mind of the scientific veterinarian the absolute necessity 

 of the study and comprehension of these new views, before he can 

 understand a pathology avowedly grounded upon them. 



Notwithstanding the brain is the source of all sensation, yet, 

 singular enough, in itself, is it a part entirely devoid of feeling : in 

 experiments on living animals its substance has been pricked, cut, 

 lacerated, burnt even, without the slightest manifestation of pain 

 or sensation. 



Very different, however, are the effects oi pressure. Impressed 

 in a vertical direction, even but slightly, the animal is prostrated, 

 deprived of sense and motion ; although the same degree of pres- 

 sure in a lateral direction produces no such effects. These are 

 facts which will prove of the greatest service to us when we come 

 to treat of injuries to the brain: they will enable us to compre- 

 hend why, as in Mr. King's case*, portions of brain may even be 

 removed without ill consequences ; while a portion of bone simply 

 depressed upon the organ might cost the animal his life. 



* This rare and curious case will be found related at page 9. 



