762 PERCY FRIDENBERG 



ing as- and dissociation, or as a change in photo-electric conductivity re- 

 sulting in greater or less sensitization of the essential cells to light, as in 

 the case of selenium. It is significant that the completely pigmentless 

 eyes, as of lumbricoids, are structurally adapted for vision in the dark 

 only, while the eye in retinitis pigmentosa can see only in bright daylight. 



Pigment plays an important part in the histology of the ocular tissues, 

 notably that of the uveal tract (choroid, ciliary body, iris) as well as in 

 the functional reaction of the retina to light and color which is itself a 

 pigment dissociation in the terminal nervous elements of the perceptive 

 layer (rods and cones). The relation of pigment to visual processes is 

 indicated, clinically, by the incidence of marked irregularity of pigment 

 distribution and massing in the choroid and retina in various forms 

 of hereditary eye disease of which retinitis pigmentosa is the type and 

 hemeralopia a prominent symptom. The opposite condition of pigmentary 

 defect, or albinism, is characterized, similarly by defective vision associated 

 with ocular unrest due to nystagmus. 



The term, pigment atrophy, so frequently used seems to me in- 

 accurate. There is reason to believe that body pigment derived from the 

 blood as a constituent of tissues is never destroyed, however much in- 

 terned, transported, or rearranged under the influence of radiant energy, 

 heat, or inflammation, as in freckles, xanthelasma, or choroiditic deposits. 



The relation of biologic pigment to vital energy is suggested by the 

 difference in resistance to disease and exertion of blondes and brunettes. 

 The development of pigment seems to depend 011 and be related to hair 

 growth and secondary sexual characteristics, and like them to be under 

 the control of the adrenal, medulla or cortex. 



Ocular Pigment and Race. From the earliest times color was looked 

 upon as the determining factor in differentiating human species, and 

 we distinguished black, brown, red, yellow, and white races. Color re- 

 ferred pre-eminently to the skin, iris, and hair, and blonde meant generally 

 blue-eyed. The endocrin implications of ocular pigmentation have not 

 been worked out. My own experience is that the blue iris, which is es- 

 sentially an iris lacking in stroma pigment, is found more often in races 

 and individuals with a marked thyroidal dominance, that is, in Nordics 

 and in sympathetic-tonics. It is also more common in myopia which 

 may be considered as an overdeveloped eye with a tendency to excess 

 metabolism and chorioretinal affections involving pigment loss or re- 

 distribution. The dark iris of the Mediterranean and other brunette races 

 associates more often with a small pupil, round i. e. ? hypermetropic eye, 

 and relative vagotonia. It is generally accepted by most observers that 

 there is little or no stroma pigment in the iris at birth when it appears 

 gray, blue or slaty gray by translucence of the uveal pigment on the pos- 

 terior surface. Entrance of pigment granules into the stroma in the 

 course of early childhood produces various tones from hazel to brown 



