SIR DAVID BREWSTER ON THE CAUSE AND CURE OF CATARACT. 13 



portion of the aqueous humour, and either supply its place by injecting distilled 

 water, or leave it to nature to supply a more healthy secretion. In order to cure 

 the second kind, we must supply the place of the discharged humour with a solu- 

 tion of albumen ; or, as in the first case, leave to nature the production of a more 

 albuminous secretion. 



These views have received a remarkable confirmation from recent experi- 

 ments on the artificial production and removal of cataract in the eyes of animals. 

 Dr Kind, a German physiologist, whom I met at Nice in 1857, informed me that 

 he had produced cataract in guinea-pigs, by feeding them with much salt, and that 

 the cataract disappeared when there was no salt in their food. More recently, 

 Dr Mitchell,* an American physician, produced cataract by injecting syrup into 

 the subcutilar sacs of frogs ; and Dr Richardson f did the same by injecting 

 syrup into the aqueous chamber of the recently dead eye of a sheep. In the ex- 

 periment of Dr Mitchell, the cataract was removed from the living eye of the 

 frog by surrounding the animal with water ; and in that of Dr Richardson, the 

 cataract was removed from the dead eye of the sheep by replacing the syrup with 

 distilled water. 



Neither Dr Mitchell nor Dr Richardson seem to have been acquainted with 

 my experiments on the changes in the lens after death, published in 1837, and 

 with the theory of the cause and cure of cataract there referred to ; nor with the 

 distinct statement of it published in 1836, ^ and twenty years later, in 1856.§ 

 Dr Rtchardson, however, has borne ample testimony to its practicability and 

 safety, when he suggests, almost in my own words, " that it would be worth 

 while, in the earliest stage of cataract in the human subject, to let out the aqueous 

 humour, and to refill the chamber with simple water." And he has borne a 

 still stronger testimony to its value by congratulating " Dr Mitchell in having 

 been the earliest experimentalist to elucidate the synthesis of cataract, and to 

 take the first steps towards a rational interpretation of the disease." 



The tendency of the human crystalline lens to indurate or soften, by a defect 

 or excess of water in the aqueous humour, 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 at that age, between 40 and 60, and often much earlier, when the lens 

 experiences that change in its condition which requires the aid of spectacles. 

 This change commences at one part of the margin of the lens, where its density 

 is either increased or diminished. Its action in forming a picture on the retina 

 thus becomes unsymmetrical, and vision is sensibly impaired. But when the 

 change has taken place round the margin of the lens, its symmetrical action is 



* American Journal of tlie Medical Sciences. January 1860. 



f Medical Times and Gazette. March 31, 1860. 



| Report of the British Association, 1836, p. Ill ; and 1837, p. 12. 



§ North British Review, vol. xx. p. 167. November 1856. 



