Polarization in the Crystalline Lens after DeatJi, 23 



conceived nii^ht takie place, after d^ath, when the lens was 

 allowed to indurate in the air, or was preserved in a fluid me- 

 dium. After many fruitless experiments I found that distilled 

 water was the only fluid which did not affect the transparency 

 of the capsule, and my observations were therefore made with 

 lenses immersed in that fluid. The general polarizing struc- 

 ture of the crystalline in the sheep, horse, and cow, consists of 

 three rings, each composed o^ four sectors of polarized light, 

 thjs two innermost rings being positive like zircon, and the 

 outermost negative, like calcareous spar. In other cases, 

 especially when the lenses were taken from older animals,ybMr 

 rings were seen, the innermost of which was positive as before, 

 and the rest negative and positive in succession. 



I now placed a lens which gave three rings, in a glass trough 

 containing distilled water, and I observed the changes which 

 it experienced from day to day. These changes were such as 

 I had not anticipated; but though I have observed and de- 

 lineated them under various modifications, I shall confine 

 myself at present to the statement of the general result. There 

 is a black ring between the two positive structures or lu- 

 minous rings. After some hours' immersion in distilled water, 

 this black ring becomes brownish, and on the second day after 

 the death of the animal, a. faint blue ring of the first order 

 makes its appearance in the middle of it, and its double re- 

 fraction, as exhibited by its polarized tint, increases from day 

 to day, till the tint reaches the white of the first order. Si- 

 multaneously with this change of colour, the breadth of this 

 new ring gradually increases, encroaching slightly upon the 

 inner positive ring, but considerably upon the second positive 

 ring; so that the black or neutral ring which separates the 

 two positive structures, and in the middle of which a new lu- 

 minous ring is created, divides itself into two black neutral 

 rings, the one advancing outwards, and diminishing the breadth 

 as well as the intensity of the second series of positive sectors, 

 and the other advancing inwards, and diminishing the breadth 

 and intensity of the inner or central sectors. While these 

 changes are going on, the outer luminous or negative ring ad- 

 vances inwards, encroaching also on the seco7id positive ring. 



Upon examining the character of the new luminous ring, 

 the development of which has produced all these changes, I 

 found it to be negative, so that at a certain stage of these va- 

 riations we have a positive and a negative doubly refracting 

 structure succeeding each other alternately, from the centre 

 to the circumference of the lens, such as I have often observed 

 in lenses taken from animals of greater age, and examined 

 immediately after death. 



