PHILOSOPHICAL TRANSACTIONS. 



663 



VOL. LXXXVI.] 



termine whether the axis of vision could be elongated by any uniform pressure 

 applied to its coats. 



The experiments were made in the following manner: an eye of a dead subject 

 was carefully removed from the socket, before any change could be produced in 

 consequence of death, and its different diameters were measured by a pair of 

 calliper compasses. As soon as these were determined, a hole was made in the 

 centre of the optic nerve, and a pipe fixed into it, through whicii air could be 

 thrown into the cavity of the eye, so as to distend its coats. While distended 

 in a moderate degree, by compressing with the hand a small bladder, containing 

 air and quicksilver, attached to the pipe, the same diameters were measured 

 again, and compared with those which were taken while in the natural state. 

 These experiments were made by Mr. Muttlebury and Mr. Williams, two very 

 intelligent and dilligent students in surgery, who were filling situations that gave 

 opportunity of making such experiments. They measured the diameters in 

 these 2 states, and marked them on paper, without ascertaining their difference, 

 so that there could be no fallacy in the measurement from any pre-conceived 

 opinion ; and I have every reason to believe there was none from inattention. 



The eye of a boy 6 years old, 45 \ Natural state 



minutes after death J Distended state .... 



The eye of a man 25 years old, 1 \ Natural state 



hour after death J Distended state .... 



The eye of a man 50 years old, ") Natural state 



20 minutes after death J Distended state .... 



From these experiments it appears, that the diameters of the eye do not al- 

 ways bear the same proportion ; sometimes the transverse diameter is the longest, 

 in other eyes it is of the same length as the axis of vision ; but when the coats 

 are distended, the tranverse diameter is diminished, and the axis of vision is 

 lengthened. This change, however, does not take place at all ages, for at 50 it 

 vas not met with. 



In these experiments the pressure was made in the most unfavourable way 

 for producing the greatest degree of elongation in the axis of vision ; it was 

 however the least exceptionable mode for ascertaining that such an efi^ect could 

 take place ; when the pressure is made laterally and from without, the elongation 

 must be still greater ; and the action of the straight muscles is the most advan- 

 tageous that could be imagined for that purpose. This lateral pressure will not 

 only elongate the eye, and increase the convexity of the cornea, but it will pro- 

 duce an effect on the c rystalline lens and ciliary processes, pushing them forward 

 in the same proportion as the cornea is stretched. This is necessary for two 

 reasons ; viz. to preserve the cavity containing the aqueous humour always of 



