76 PERSONAL APPEARANCES IN HEALTH AND DISEASE. 



ture set, as it were, in front of a white or bluish-white 

 surface, " the white of the eye," but little of which is 

 visible between the lids when the eye is directed straight 

 forwards. This white part is well furnished with small 

 blood-vessels, which when the eye is rubbed or irritated 

 by particles of dust, &c., become visible and give it a 

 reddened or " blood-shot " aspect. The round aperture 

 seen behind the centre of the glassy structure and called 

 the pupil appears black to the observer ; it is bounded by 

 a circular membranous or rather muscular curtain called 

 the iris, and the pupil can increase in size or diminish 

 by reason of the muscular fibres which compose the chief 

 thickness of the iris ; fibres going round it, being for the 

 purpose of diminishing the size of the pupil, and others 

 radiating on all sides, for the purpose of increasing its 

 size. It is this membranous curtain that is coloured, 

 and gives the colour to the eye, that colour depending 

 upon collections of pigment 'granules in a layer of cells 

 which covers its hinder surface. In dark brown eyes 

 this pigment is very abundant ; in " blue " and " grey " 

 eyes it is very scanty. There is also a large amount of 

 pigment in the cells composing the middle membrane of 

 the globe of the eye, the choroid coat as it is called. 

 The choroid is really an extension of the membrane 

 forming the iris. In dark-haired and dark-complexioned 

 people this choroidal pigment is very abundant, in fair 



