382 CONSENSUAL ACTIONS IN MAN. 



The insect will in fact appear to the fish a little above the 

 place which it really occupies ; and the difference is not con- 

 stant, but varies with every change in the relative positions 

 of the fish and the insect. Yet the wonderful instinct with 

 which the fish is endowed, leads it to make the due allowance 

 in every case ; doing that at once, for which a long course of 

 experience would be required by the most skilful Human 

 marksman, under similar circumstances. 



477. Though the Intelligence and Will of Man in a great 

 degree supersede his consensual impulses, in the same man- 

 ner as they hold in subordination his reflex movements 

 ( 471), yet we have many indications of the direct operation 

 of sensations in determining respondent movements. Of this 

 kind are the start produced by a loud sound, particularly if 

 unexpected ; the closure of the eyes to a dazzling light, or on 

 the sudden approach of a body that might injure them ; the 

 production of sneezing by a dazzling light ; the provocation 

 of laughter by tickling, or by some sight or sound to which 

 no distinct ludicrous idea or emotion attaches itself ; and the 

 excitement of vomiting by highly disagreeable sensations, as 

 the sight of a loathsome object, an offensive smell, a nauseous 

 taste, or by tickling the back of the mouth with a feather. 1 

 None of these " consensual " movements can be excited with- 

 out the consciousness of the subject of them; and this 

 circumstance marks them out as belonging to a different 

 category from the "reflex" movements performed through 

 the instrumentality of the Spinal Cord. In some convulsive 

 disorders, the attacks are excited by causes that act through 

 the organs of sense : thus, in Hydrophobia we observe the 

 immediate influence of the sight or sound of liquids ; and in 

 many Hysteric subjects, the sight of a paroxysm in another 

 individual is the most certain means of its induction in them- 

 selves. 



478. But we may trace the agency of the Sensory Ganglia 



1 This is the most ready way of exciting vomiting, when it is desired 

 to free the stomach from poisons or unwholesome articles of food ; 

 but care must be taken not to apply the feather so low down as to 

 cause it to be grasped by the muscles concerned in the act of swallow- 

 ing ; for its irritation, instead of producing vomiting, will then occasion 

 an act of deglutition ( 195), which may draw the feather from the 

 hand of the operator, and carry it down into the stomach of the 

 patient. 



