and the Cure of QUaract. 25 



expectation is founded, are more of a physiological than of a 

 physical nature, I am desirous of submitting an account of 

 them to the Medical Section, that they may undergo that 

 strict examination which they could receive only from the 

 experience and science of that distinguished body. 



On the Cause, the Prevention, and the Cure of Cataract, 



Having submitted to the Physical Section an account of a 

 singular change of structure produced by the action of distilled 

 water upon the crystalline lens after death. Sir D. Brewster 

 was desirous of communicating to the Medical Section some 

 views which this, and previous observations, have led him to 

 entertain respecting the cause and the prevention and cure of 

 cataract. 



" The change of structure to which I have referred consists 

 in the development of a negative polarizing band or ring be- 

 tween the two positive rings nearest the centre of the lens ; 

 the gradual encroachment of this new structure upon the 

 original polarizing structure of the lens ; and the final burst- 

 ing of the lens after it had swelled to almost a globular form 

 by the absorption of distilled water. 



" As the crystalline lens floats in its capsule there can be 

 no doubt that it is nourished by the absorption of the water 

 and albumen of the aqueous humour, and that its healthy 

 condition must depend on the relative proportion of these in- 

 gredients. When the water is in excess the lens will grow 

 soft, and may even burst by its over absorption ; and when 

 the supply of water is too scanty, the lens will, as it were, 

 dry and indurate, the fibres and laminae formerly in optical 

 contact will separate, and the light being reflected at their 

 surfaces, the lens will necessarily exhibit that white opacity 

 which constitutes the common cataract. o 



" This defect in the healthy secretion of the aqueous hu- 

 mour, as well as the disposition of the lens to soften or to in- 

 durate by the excess or defect of water, may occur at any 

 period of life, and may arise from the general state of health 

 of the patient; but it is most likely to occur between the ages 

 of 40 and 60, when the lens is known to experience that 

 change in its condition which requires the use of spectacles. 

 At this period the eye requires to be carefully watched, and 

 to be used with great caution ; and if any symptoms appear 

 of a separation of the fibres or laminae, those means should be 

 adopted which, by improving the general health, are most 

 likely to restore the aqueous humour to its usual state. 

 Nothing is more easy than to determine at any time the sound 

 state of the crystalline lens ; and by the examination of a small 



Phil Mag, S. 3. Vol. 12. No. 71. Jan. 1838. E 



