262 Dr. A. P. W. Philip on the 



but the influence of that system not only does not excite the 

 muscles of involuntary motion in their usual functions, but, as 

 I have already had occasion to observe, is communicated to 

 them in a way different from that in which it is communicated 

 to the muscles of voluntary motion. We shall here inquire in 

 what this difference consists. 



The following positions have been ascertained by repeated 

 experiments*. Chemical agents, applied to the brain and spinal 

 marrow, more powerfully influenced the heart than mechanical 

 agents, while the latter influence the muscles of voluntary mo- 

 tion more than chemical agents. Both, applied to the brain and 

 spinal marrow, excite the heart after they cease to produce any 

 effect on the muscles of voluntary motion. Applied to any part 

 of the brain and spinal marrow, they affect the action of the 

 heart, while the muscles of voluntary motion are only affected 

 when they are applied to the parts from which the nerves of 

 those muscles originate. Applied to the brain and spinal 

 marrow, they never excite irregular action in the heart, while 

 nothing can be more irregular than the action they excite in the 

 muscles of voluntary motion. Their effect on these muscles is 

 felt chiefly on their first application, but continues on the heart, 

 within certain limits, as long as they are applied. These dif- 

 ferences in the effects of agents applied to the brain and spinal 

 marrow must, it is evident, be explained, before we can under- 

 stand the relation which subsists between the nervous and mus- 

 cular systems. 



It appeared to me probable, from the result of several experi- 

 ments, that the cause of chemical agents, applied to the brain 

 and spinal marrow, producing a greater effect on the heart than 

 those which act mechanically is, that the former, from their 

 nature, act on a larger surface. If this opinion be correct, the 

 mechanical agent, it is evident, may be rendered the most 

 powerful, by confining the chemical to a smaller space than it 

 occupies, which was found from frequently-repeated experi- 

 ments to be the casef. 



Most of the experiments on this part of the subject, it may 

 be observed, as well as many to which I have already referred, 



* Ejpei. Inq., Part II., Cbap. 4. f lb. Exper. 41. 



