IN HYGIENIC PHYSIOLOGY. 203 



30. Why does a fall cause one to " see stars " ? * 



Whenever a nerve is excited in any way, it gives rise to the 

 sensation peculiar to the organ with which it communicates. 

 Thus, an electric shock sent through the eye gives rise to the 

 appearance of a flash of light ; and pressure on any part of 

 the retina produces a luminous image, which lasts as long as 

 the pressure, and is called a phosphene. If the point of the 

 finger be pressed upon the outer side of the ball of the eye, a 

 luminous image which, in my own case, is dark in the center, 

 with a bright ring at the circumference (or, as Newton de- 

 scribed it, like the " eye " in a peacock's tail) is seen ; and this 

 image lasts as long as the pressure is continued. HUXLEY. 



31. Why can we not see with the nose, or smell ivith the 



eyes ? 



Each set of nerves is adapted to transmit to the brain a 

 peculiar class of sensations alone. 



32. What causes the roughness of a cat's tongue ? 



The sharpness and strength of the papillae upon its tongue. 

 This is a peculiarity of the lion tribe. 



33. Is the cuticle essential to touch ? 



Yes. If the cuticle be removed, as in case of a blister, 

 contact with the exposed surface produces pain rather than a 

 sense of touch. 



34. Can one ticfcle himself? 



It is said not ; but the author has found persons who 

 averred that they could produce this sensation upon themselves. 

 The sense, it is noticeable, is present only in those parts where 

 that of touch is feeble. 



* On the occasion of a remarkable trial in Germany, it was claimed by 

 a person who had been severely assaulted on a very dark night, that the 

 flashes of light caused by repeated blows upon the head enabled him to 

 see with sufficient distinctness to recognize his assailant. But the evi- 

 dence of scientific men entirely refuted this claim, by pronouncing that 

 the eye, under the circumstances named, was incapacitated for vision. 

 HUTCHISON. 



