CH. III.] VIS NERVOSA OF INTERNAL IMPRESSIONS. 269 



tioiial internal impressions ; although it may be easily conceived 

 that these re-excited movements are simply direct nerve-actions 

 of external impressions on the heart, arising from inflation of 

 the lungs, and from the various stimuli applied to the throat, 

 stomach, intestinal canal, &c. But as these stimuli are applied 

 to the nerves adjacent to the heart, and which have a much 

 less degree of irritability than the cardiac nerves, they must be 

 applied strongly and for a lengthened period, before the external 

 impressions they receive are transmitted upwards to the points 

 of reflexion, and hence sent downwards ; and when the result 

 follows, the heart makes only a few strokes and then stops, so 

 that the stimuli must be renewed continually to keep up its 

 action. But if the heart be excited by stimuli applied directly 

 to its nerves, all this takes place more readily and actively. 



520. The changes in the pulse, resulting from the action of 

 the muscular fibres and nerves of the arteries, independently of 

 the heart, are direct nerve-actions from external impressions 

 derived from the blood, as in the case of the heart (460) . Why 

 should not these impressions on the muscular fibrils be pro- 

 pagated to the nerves, and, although not felt, nevertheless, at 

 least in some cases, be reflected so as to change the circulation 

 by means of indirect nerve-actions ? The possibility of this is 

 hardly doubtful, yet it is as difficult to demonstrate by experi- 

 ments, since the phenomena of direct nerve-actions from ex- 

 ternal impressions on the blood-vessels are scarcely perceptible 

 (460). As conceptional internal impressions, and particularly 

 those of external sensations (147, 151), excite changes in the 

 pulse and circulation, the same may result from primary in- 

 ternal impressions, or from external impressions reflected be- 

 fore they are felt (360, 503). 



521. Lastly, in so far as muscular action changes the pulse, 

 all those non-con ceptional internal impressions which excite 

 muscular action will influence the pulse. Every effort, or bodily 

 movement, whether convulsive or volitional, accelerates the 

 circulation, and often the causes of the movements are neither 

 felt nor perceived. 



522. The mouths of the capillaries are as subject to changes 

 from non-conceptional internal impressions, as from external 

 impressions, whether felt (207), or uufelt (462). The action of 

 certain remedies on the capillaries proves this : as Avhen certain 



