STRAIN AND OVER-ACTION OF THE HEART. 11 



point of the functional disorder, should it pass into an 

 organic malady the physical signs are always the same — an 

 increase of the percussion dulness. and of the extent of the 

 impulse, which, as the vast majority'of instances lead to hyper- 

 trophy rather than to pure dilatation-,, is forcible, and becomes 

 associated with a prolonged, dull, first sounc?,* and a second 

 sound which gradually loses its exceeding distinctness. At 

 times a softish, inconstant murmur over the left ventricle re- 

 places the altered first sound, and these instances are very apt 

 to be regarded as mitral organic disease, which they are not. 

 But whether with or without murmur the action of the heart 

 becomes less rapid, and cardiac pain diminishes. 



I have now indicated to you how a functional disorder from 

 excitement or over-action of the heart, no matter how pro- 

 duced, may end in organic trouble. But you will ask me, in 

 what manner does the first derangement originate ? Is it- in the 

 muscular structure of the heart itself, or in its nervous appa- 

 ratus? In the latter, I believe, in the vast majority of cases; 

 and the perverted innervation is either primary, or more 

 usually the disturbance is reflected to the heart. But if you 

 tell me to show you what nerves are, in individual instances, 

 at fault, I shall have to say that I do not tliiuk that a 

 satisfactory and quite trustworthy answer can always be 

 given. Our knowledge of the nerve-supply of the heart, and 

 of the part each nerve plays, is not so positive that we can 

 unhesitatingly expound all clinical facts by it. Still it is, even 

 with our present knowledge, admissible to regard the constant 

 pain so common in irritable heart, as a hyperesthesia of the 

 sensory nerve-fibres ; and assuming the antagonism between the 

 pneumogastric and the sympathetic to be correct — that the 

 former slackens or suspends the action of the heart and the 

 latter quickens it — you will at once understand how anything 

 which exhausts the controlling action of the first, gives the 



power of the other full pla}' ; and how thus many instances 

 36 



