228 STUDIES IN ELECTRO-PHYSIOLOGY: 



On being stimulated by light the granules of pigment in the 

 cells which overlie the outer part of the rod and cone layer 

 of the retina pass down into the processes of the cells, 

 which hang down between the rods " (see Fig. 119) ; 

 " these melanin orfuscin granules are generally rod-shaped, 

 and look almost like crystals. In addition to this, a 

 movement of the cones and possibly of the rods occurs ; in 

 the light the cones shorten, and in the dark they lengthen.*' 

 (Halliburton : Engelmann.) 



The property of transforming rays of light into nervous 

 impulses may reside in the " visual purple," but if the 

 pigment cells have no part in this and are designed merely 

 to provide the dark lining of the camera, why should they 

 be given movement, and why do they have processes 

 connecting, functionally if not structurally, with the rod 

 and cone layer ? 



THE EAR. 



The ear is divisible into three parts: i.e., the external 

 ear, the middle ear or tympanum, and the internal ear or 

 labyrinth. Physiologically described, " the filaments of 

 the auditory nerve end in peculiar structures buried 

 deeply in the hard portion of the temporal bone of the 

 skull, and special arrangements exist for conducting waves 

 of sound to this deeply seated sensitive part. The external 

 ear assists in collecting sonorous vibrations that pass along 

 a channel termed the external auditory meatus, and 

 impinge against a stretched membrane called the tympanic 

 membrane, or drum-skin. The vibrations thus set up in 

 the tympanic membrane are transmitted across the 

 tympanic cavity or middle ear by a chain of small bones 

 the malleus or hammer, the incus or anvil, and the 

 stapes or stirrup to the inner ear. The membranous 

 base of the stapes is placed in connection with the inner 



