418 PHILOSOPHICAL TRANSACTIONS. [aNNO 1753. 



lated mertly to procure an easy separation of the crystalline from the vitreous 

 humour: but they are difficult to the operator, fatiguing to the patient, and, he 

 should hope, altogether needless, if the knife be used in the manner which he 

 has recommended : for whether the capsula of the crystalline be nothing more 

 than the duplicature of the membrane of the vitreous humour, or whether it be 

 a proper coat, which is also covered by the membrane of the vitreous humour ; 

 in either case, since by compression the crystalline advances with so much facility 

 through the pupil, it will be easily seized by the knife, and removed from the 

 vitreous humour, with its inveloping membrane : whereas, in making an inci- 

 sion on the surface of the crystalline, and wounding its capsula, the crystalline 

 will frequently slip out of the capsula, which will be left behind : and in fact 

 this has happened to M. Daviel, who advises pincers, and other instruments, to 

 extract the remaining membrane. But he observes, in regard to the capsula of 

 the crystalline, that should the humour slip out of it, before it be seized by the 

 knife, it possibly will waste ; for in milky cataracts, when the fluid is discharged, 

 the membrane in length of time wastes : whole cataracts, with the inveloping 

 membrane likewise, sometimes waste : and in one of his patients, the crystalline, 

 from the mere pressure in the operation, burst out of its capsula, which he left 

 in the eye ; but in some weeks it entirely wasted. However, if the removing of 

 the capsula should, by future experience, be found necessary, it may be conve- 

 niently done by the curette ; one of the instruments M. Daviel recommends for 

 that purpose/ This instrument may be also used for the extraction of a cata- 

 ract, which has been broken to pieces by the couching needle in a former opera- 

 tion, and for the removal of the capsula of a bag-cataract, when the fluid only 

 has been discharged, and the bag remains behind ; but it will be most eminently 

 useful in detaching the crystalline from the back part of the iris, when any portion 

 of it happens to adhere : which circumstance would render the operation fruit- 

 less, without such a precaution. 



It had not happened, in any of the cases treated, that either during the ope- 

 ration, or after the operation, the iris had been pushed forwards, or insinuated 

 itself through the wound of the cornea, forming a staphyloma ; but M. Daviel 

 speaks of it as an occurrence he had met with, and says it may easily be replaced 

 by the small spatula. 



Mr. S. hopes that when this operation is more generally practised, ingenious 

 men will render it still more perfect : and he should not be surprised, if the use of 

 a speculum oculi should hereafter be esteemed an improvement : but then it must 

 be contrived so, as that it shall not compress the globe of the eye ; or, if it does, 

 the operator must be careful to remove it in the instant the incision is making, 

 lest, by continuing the pressure after the wound is made, all the humours should 

 suddenly gush out. 



