GHENEVIX, not long ago, gave us an analysis of 

 the humours of the eye, and I have since examined 

 their composition, together with that of the mem- 

 branes. 



The Sclerotic^, which surrounds the eye on the 

 outside, has the same component parts as the 

 tendons : it dissolves by continued boiling ra wa- 

 ter, and the solution, whilst cooling, hardens into 

 a jelly. The Choroidea, spread over its internal 

 surface, is a similar compound, and in like man- 

 ner dissolves in boiling, with the exception only 

 of its numerous veins,, and the black colouring 

 matter, or pigmentum nigriun,. with which it i& 

 covered. The black substance is indissoluble ra 

 hot or cold water, and also in acids. It is solu- 

 ble, however, in caustic alkali, and the precipi- 

 tate by an acid is somewhat paler. It burns like 

 a vegetable substance, and leaves the same ferru- 

 gineous ashes as the colouring matter of the 

 blood, from which it has, in all probability, been, 

 formed and secreted, the veins of the choroidea 

 transmitting only the colourless parts into the sub- 

 stance of the eye. The Cornea, also, consists of 

 a mass, which by boiling, is converted into a glue. 

 The Iris, on the contrary, has all the chemical 

 characters of a muscle, and its constituent parts 



