A HISTORY OF SCIENCE 



functions of the medulla oblongata and medulla spin alls, 

 and may therefore render it difficult or impossible to 

 determine those which are peculiar to each; if, in an 

 animal deprived of the brain, the spinal marrow or 

 the nerves supplying the muscles be stimulated, those 

 muscles, whether voluntary or respiratory, are equally 

 thrown into contraction, and, it may be added, equally 

 in the complete and in the mutilated animal; and, in 

 the case of the nerves, equally in limbs connected with 

 and detached from the spinal marrow. 



"The operation of all these various causes may be 

 designated centric, as taking place at, or at least in a 

 direction from, central parts of the nervous system. 

 But there is another function the phenomena of which 

 are of a totally different order and obey totally dif- 

 ferent laws, being excited by causes in a situation 

 which is excentric in the nervous system that is, dis- 

 tant from the nervous centres. This mode of action 

 has not, I think, been hitherto distinctly understood 

 by physiologists. 



" Many of the phenomena of this principle of action, 

 as they occur in the limbs, have certainly been ob- 

 served. But, in the first place, this function is by no 

 means confined to the limbs; for, while it imparts to 

 each muscle its appropriate tone, and to each system 

 of muscles its appropriate equilibrium or balance, it 

 performs the still more important office of presiding 

 over the orifices and terminations of each of the internal 

 canals in the animal economy, giving them their due 

 form and action; and, in the second place, in the in- 

 stances in which the phenomena of this function have 

 been noticed, they have been confounded, as I have 



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