254 Wilson Philip on the 



pie founded on the simplicity usually apparent in the works of 

 nature, can afford, for believing the operation of the stimuli to 

 be similar in both cases. If, however, Dr. Alison has direct 

 evidence of his opinion, this analogy, however strong, must be 

 disregarded. Let us inquite into the evidence he adduces. 



The following paragraphs are the only passages in his paper 

 in which he attempts to support his opinion. After some obser- 

 vations on the opinion of Haller, he observes, (page 108), — "The 

 experiments of Dr. Philip have illustrated more fully than those 

 of any other physiologist, these two different modes in which 

 changes in the nervous system affect muscular action. The 

 general results of his observations, and of those of Haller, Bichat, 

 and others on this subject, may be stated to be, that the first 

 mode of action, that is, the direct excitation of muscular fibres 

 to contraction by impressions made on the nervous system, is 

 confined to the voluntary muscles ; and that the second mode 

 of action, that is the alteration of the vital power or tendency to 

 contraction of muscular fibres by impressions made on the ner- 

 vous system, is chiefly exerted on the involuntary muscles." 



In the foregoing observations, Dr. Alison refers to certain ex- 

 periments of mine as the chief proof of his opinion. These ex- 

 periments prove, that when any considerable part of the brain or 

 spinal marrow is exposed to the action of a stimulus or sedative^ 

 the heart and blood-vessels are affected by it, in a way similar to 

 that in which the muscles of voluntary motion are affected by the 

 same substances applied to certain parts of the same organs. 

 Now wliat relation these results have to the above opinion, I am 

 unable to perceive. In the following paragraph indeed, Dr. 

 Alison says, " although the term stimulus was very naturally 

 applied by him to the substances, which quickened the action 

 of the heart when applied to the brain or spinal marrow ; yet 

 various considerations might be stated to shew, that the effect 

 of these substances is more correctly expressed by saying, not 

 that they excited contractions of the muscular fibres of the 

 heart, but that they increased the tendency of the muscular fibres 

 of the heart to contract from the stimulus of the blood." Dr. 

 Alison, however, does not specify, nor can I at all conjecture 



