of the Crystalline Lens after Death. 193 



the lens exhibited four structures, a negative and a positive one 

 alternating. As these discrepancies appeared in the lenses of 

 animals of the same species, I conceived that they were owing to 

 differences of age or sex, or to some change in the health of the 

 animal. I was therefore led to make new observations in refer- 

 ence to these probabilities, and to observe the phsenomena with 

 additional attention when the structure differed from that which 

 was most common. In these observations I sometimes noticed 

 in the dark or neutral line, which separated two positive struc- 

 tures, something like a trace of an intervening structure, which 

 was either about to disappear, or about to be developed. This 

 conjecture was confirmed by observations on the lenses of a cow 

 eleven years old. 



The lenses, after being carefully taken out, were freed from 

 the adhering portions of the vitreous humour by the gentle ap- 

 plication of blotting-paper, so as not to disturb their internal 

 structure. The lenses were elliptical. Their longest diameter 

 was 0774 inch, their shortest diameter 0747 inch, and their 

 thickness 0*513 of an inch. The first lens which I exposed to 

 polarized light was in the highest perfection, and the symmetry 

 of the optical figure unusually beautiful. I have represented it 

 in Plate V. fig. 1, in which only two structures, or two series of 

 positive sectors, are visible*. The lens was now a day old, and 

 there seemed to be a faint light within the two black rings, espe- 

 cially in the outer one, which was either the remains of an old, 

 or the germ of a new structure. If this were the case, then the 

 anomalous combination of two positive structures would be con- 

 verted into a combination of four structures, in which a negative 

 and a positive one alternated. 



On the following day I prepared the other lens with the same 

 care, and found my conjecture completely verified. In the middle 

 black ring, which was distinctly brownish in the first lens, the 

 negative structure had evidently commenced at one part, and 

 the colour of the whole ring was a brighter brown than in the 

 first lens. In the outer black ring another negative structure 

 had also appeared, and had advanced considerably upon the 

 positive structure. These phenomena I have represented in 

 fig. 2, where the four structures are distinctly seen, the second 



* Upon referring to my earlier observations, I find tbat in botb the 

 leiuei of Jin ox then: was only one structure which was a positive one, and 

 which had not yet divided itself into two structures, as in that of the cow 

 under consideration. There was the appearance of a black space near the 

 margin of the lens, hut the polarized light both within and without that 

 black ring wai positive. 



In tin' Lena of another ox, and of a bull, I found the positive structure 

 separated into two positive structures by a distinct black ring, while an ex- 

 ternal negative structure was clearly developed. 



Phil. May. S. 4. Vol. 3. No. 17. March 1852. 



