SENSE OF TOUCH. 21 



maritima), which keeps its flowers closely shut in the 

 night ; but he could produce no artificial effect with the 

 strongest light upon several species of wood sorrel 

 (Oxalis stricta and Oxalis incarnata), whose flowers 

 and leaves are both folded up at night. With the 

 sensitive plant (Mimosa pudica) again he succeeded 

 in so completely changing the hour of closure, that 

 on the third day from being placed in the lighted 

 cellar, it began to fold its leaves in the morning and 

 open them in the evening*. 



Insects are also peculiarly sensible to electric 

 changes in the atmosphere, though we do not find 

 facts sufficient to bear out all the speculations of 

 M. D'Isjonval upon this subject. Kirby and Spence 

 tell us, that "when the atmosphere is in a highly 

 electrified state, and a tempest is approaching, insects 

 are usually most abundant in the air, especially 

 towards the evening ; and many species may then be 

 taken which are not at other times to be met with : 

 but before the storm comes on, all disappear, and 

 you will scarcely see a single individual upon the 

 wing." They conjecture, that the organs destined for 

 perceiving these electric changes are the antennae, 

 particularly those furnished with a lateral bristle, and 

 the plumose and pectinated ones, from this form 

 seeming to be calculated to act on the electricity and 

 moisture of the atmosphere, " which, in certain states 

 and proportions, may certainly indicate the approach 

 of a tempest, or of showers, or a rainy season, and 

 may so affect these organs as to enable the insect to 

 make a sure prognostic of any approaching change ; 

 and we know no other organ that is so likely to have 

 this power f." 



This conjecture is, no doubt, ingenious, though 

 there is no plausible circumstance to support it besides 



* Medical Review, vol. vi 

 f Intr. iv. 246. 



