302 ANIMAL FORCES. [ir. 



587. The answer must, as in the preceding paragraph, be 

 deduced from a consideration of the sensational conceptions, 

 and mutatis mutandis, the line of argument is the same. When 

 we imagine that we have swallowed an emetic, and the imagi- 

 nation excites retching and vomiting, as if an emetic had been 

 really taken, the conclusion is obvious, that the felt external 

 impression on the stomach of such an emetic, or its felt nerve- 

 actions (413), must have produced the same movement, namely, 

 vomiting, as a sentient action of the external sensation at the 

 irritated point, which the same external impression had excited 

 there at the same time, as a direct nerve-action. This occurs 

 also when purgation takes place, simply from dreaming that a 

 purgative has been taken; when we shiver from the imagination 

 of intense cold; when suffusion and blue marks take place, at the 

 spot where we dream that we have received a blow, pinch, &c. 



588. Although the direct nerve-actions of external impres- 

 sions, or in other words the results of irritability (432), do not 

 require the co-operation of the cerebral forces for their produc- 

 tion, still, in cases where the impression is felt, they may occur 

 also as sentient actions of the sensation. Consequently, it 

 would be erroneous to conclude, that a result of irritability 

 could not be at another time a sentient action of the sensation 

 caused by the irritant, or that it may not depend on sensibility. 

 This conclusion can only be made when the external impression 

 which causes the movement is not felt nor cannot be. 



589. We conclude therefore, that all nerve-actions of non- 

 conceptional internal impressions can be altogether replaced by 

 sentient actions, that is to say, induced by internal impressions 

 caused by conceptions (581). With reference particularly to 

 those excited directly by external impressions, it may be stated, 

 that they are developed as sentient actions by the external 

 sensation of the external impressions which excite them (584, 

 588). 



SECTION III. THE RECIPROCAL CONNECTION OF THE ANIMAL- 

 SENTIENT [cerebral] FORCES WITH THE VIS NERVOSA IN 

 THE NATURAL STATE. 



590. When an external impression is not felt, and a primary 

 internal impression is not excited by conceptions, the movements 



