320 



Dr. E. K. Martin. 



[Feb. 5, 



the exposed eye from it. Some observers have also attempted to record it in 

 absolute units by expressing it in terms of the universal photometer. 



Whilst this latter method is at first sight more exact, the correlation of 

 observations from various sources would be facilitated by expressing the 

 intensity also approximately in terms of one of its physiological results. As 

 the rdle of strong light in the production of corneal opacity is now well 

 recognised, and the degree of opacity varies pari passu with the quantity of 

 energy absorbed, valuable indication of the intensity of a given source of 

 light from a physiological point of view is afforded by the resultant corneal 

 disturbance — when the exposures are repeated at intervals throughout 

 a considerable period of time. 



2. The Part of the Spectrum mainly Represented in the Source of Light. — 

 From the physiological point of view the spectrum may be divided into heat, 

 visible and ultra-violet rays, each of which require separate consideration. 

 Putting aside the first, the investigation of which is not included in the 

 present work, the absorption by tbe media of the eye must be taken into 

 consideration, since only rays which are absorbed are capable of inducing 

 pathological changes in those media. 



3. Ocular lesions following exposure to lightning, short-circuits of high- 

 voltage currents, and discharge of Leyden jars should be omitted from the 

 discussion of the effects of radiant energy, on account of the impossibility of 

 determining the value of the electrolytic and mechanical (concussion) factors. 



The present enquiry may be divided into three parts : — 



I. The absorption of rays by the media of the eye in the visible and ultra- 

 violet portions of the spectrum. 



II. The histological changes resulting from exposure to light consisting 

 largely of such rays. 



III. The alteration in the iris and ciliary body produced by such rays. 



Young rabbits {i.e. three or four months old) have been employed 

 throughout. 



I. The Absorption of Eays in the Media, of the Eye in the Visible 

 and Ultra-violet Portions of the Spectrum. 



The spectrophotographic method of recording the results was used, and the 

 media were mounted in cells with parallel sides of quartz. The lens was 

 dealt with in two ways : — 



1. Suspended in normal saline and placed at a distance from the slit 

 greater than its focal length, so that a blurred image of the source of light 

 was thrown on the slit. This was necessary to avoid horizontal lines on the 



