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XXIV. On a nevo Meirnbrarie in the Eye. 5j/George Hunsley 

 Fielding, Member of the Royal College of Surgeons in Lon- 

 don, Member of the British Association for the Advancement 

 of Science, Curator of Comparative Anatom]) to the Hull 

 Literary and Philosophical Society, Sfc. Sfc* 



A CCORDING to the accounts we find in standard ana- 

 ■^^^ tomical works, we are taught to believe that the Pig- 

 menlum nigrum of the eye is placed immediately behind, and 

 in contact with the retinaf. We are further taught that the 

 colour of this pigment varies greatly in different animals, and 

 that it is of a very light colour, or even wanting, in the night- 

 prowling animals %. 



_ Now, the membrane I have discovered is immediately be- 

 hind, and in contact with the retina: it presents a fine co- 

 loured appearance, which varies in different animals ; and is of 

 a very light colour in the night-prowling animals. It is evi- 

 dent, therefore, that what I term a membrane, is usually 

 esteemed to be a pigment. To prove that it is a membrane 

 will be the object of the present paper. 



1st. What are the nature and properties of the pigment of 

 the eye ? It is a mucous substance combined with carbona- 

 ceous matter on which its colour depends § ; it stains white 

 paper; it is removeable by washing || ; no known chemical 

 agent has any power either to alter or remove its colour f. 



Take a section of a beast's eye from which the whole of the 

 humours and the retina have been carefully removed : you will 

 find a brilliant spot of coloured surface which was evidently 

 immediately behind the rethia. The colour will generally be 

 found to be blueish-green, with frequently a tinge of yellow, 

 the circumference round this spot (which spot varies in size, 

 from occupying three-fourths to less than one-fourth of the 

 hollow of the globe,) is of a deep blue. 



Now take a piece of white paper and apply it to the blue 

 or green part, you will obtain no stain ; wash, it with water, 

 you will not remove the colour, nor stain the water: — here 

 then are two easy proofs that its colour is of a different nature 

 from that of the true pigment of the eye. 



But it may be said, that what I am describing is the Tape- 

 turn; and if so, unless we are to regard tapetum and pigmen- 

 tum as synonymous terms (which Cuvier, Richerand, John 



* Communicated by the Author: — This paper is an abstract of part of 

 one read before the late Meeting of tlie British Association for tiie Ad- 

 vancement of Science, at Oxford. 



t Hell, Fyfe, Monro, Shaw, &c.&c. t Bell, Fyfe, &c. § Young. 



II I^ell. t Bi^i,.,t. 



Third Series. Vol. 1. No. 2. Aw ",2 Q 



