272 Ofi the Agency of Nerves. 



the brain uniformly throws it into actioUj I shall most willingly 

 admit, that it is a fair example (and the only unequivocal one, 

 as fai as I know, on record) of the heart being directly stimulated 

 through the medium of the nervous system. But if his meaning 

 is, that the movements of the heart, continuing after it has been 

 emptied of blood, or renewed by other causes, are increased by 

 the application of spirits of wine to the brain, I think the correct 

 expression for the fact will be, that its contractile power is in- 

 creased, not Uiat it is directly stimulated*. 



But whether in these circumstances, so different from any that 

 ever occur in the natural state, a stimulus, strictly speaking, 

 may act upon the heart through the nervous system or not, I 

 think we have sufficient evidence, independently of the experi- 

 ments in question, that the contractile power of this and other 

 muscles is liable to increase, as well as to diminution, from 

 causes acting on the nervous system. For example, when the 

 mind is under the influence of any strong exciting passion, the 

 action of the heart becomes quicker and stronger. This appears 

 to me to be just the counterpart of the effect produced on its 

 action by depressing passions of the mind, which cause more or 



• Many physiologists, and Dr. Philip amongst the rest, use the 

 words stimulus and sedative, as if these were directly opposed to each 

 other. But 1 believe the word stimulus is most correctly applied to what 

 merely calls into action the power inherent in muscular fibres during life, 

 without necessarily either increasing or diminishing it ; the term sedative 

 to that which diminishes or destroys that power, and prevents its being called 

 into action in future in the same manner that it used to be. According to 

 this use of the term sedative, (which is, I think, the same as that to which 

 it is applied in Dr. Philip's writings,) the term which is strictly opposed 

 to it is stimulant, by which I understand, that which gives a temporary 

 increase to the contractile power of a living muscle, and so enables it to 

 perform its ordinary function in obedience to its ordinary stimuli mare vigor- 

 ously than it used to do. The effect of salt, sprinkled on a bare muscle, I 

 would express by the term stimulus ; that of wine taken into the stomach 

 on the action of the heart upon the blood, by the term stimulant. Whether 

 these terms are correctly applied or not, I think it must be allowed, that 

 there is a real and essential diiference between the modes, in which the 

 muscles are affected in these two cases ; and it appears from the passages 

 formerly quoted from Haller, that this distinction is juistificd by his authority. 



