102 PHYSICAL EXPRESSION. 



are blind. In some of the crabs the foot-stalk 

 for the eye remains, though the eye be gone ; the 

 stand for the telescope is there, though the tele- 

 scope with its glasses has gone. As it is difficult 

 to imagine that eyes, though useless, could be in 

 any way injurious to animals living in darkness, 

 their loss may be attributed to disuse. In one of 

 the blind animals, namely, the cave-rat (Wotama), 

 two of which were captured by Professor Sillman 

 at about half a mile from the mouth of the cave, 

 and therefore not in the profoundest depths, the 

 eyes were lustrous and of large size ; and these 

 animals, as I am informed by Professor Sillman, 

 after having been exposed for about a month to a 

 graduated light, acquired a dim perception of objects." 



This fact may, I suppose, be expressed by saying 

 that in successive generations, owing to the want of 

 the stimulation of light upon the parents' eyes, these 

 organs have ceased to be developed in the young. It 

 seems to me that this is equivalent to saying that 

 the stimulating effects of light are necessary, in all 

 probability, to prevent the organs specially suited 

 to receive light impressions and convey them to the 

 nerve-mechanism, from degenerating in successive 

 generations. This is a trophic action of light. 



The sight of a good dinner has been shown to 

 increase the quantity of gastric secretion. Like- 

 wise the sight of food stimulates the salivary 

 secretion. A woman in good health, after seeing 

 her husband killed (light effect only), took up her 

 infant and suckled it; the altered milk proved 

 poisonous to the child. 



