chemical Nature of the Humours of the Eye. 197 
both before and after it has been boiled, and consequently shows 
the presence of gelatine. 
Nitrate of silver causes a precipitate, which is muriate of 
silver. No metallic salts, except those of silver, alter the aqueous 
humour. 
From these and other experiments it appears, that the aqueous 
humour is composed of water, albumen, gelatine, and a muriate, 
the basis of which I found to be soda. 
I have omitted speaking of the action of the acids, of the 
alkalis, of alcohol, and of other reagents, upon this humour. It 
is such as may be expected in a solution of albumen, of gela- 
tine, and of muriate of soda. 
Crystalline Humour. 
To follow the order of their situation, the next of the humours 
is the crystalline. 
This differs very materially from the others. 
Its specific gravity is 1 1 000. 
When fresh, it is neither acid nor alkaline. It putrifies very 
rapidly. It is nearly all soluble in cold water, but is partly 
coagulated by heat. Tannin gives a very abundant precipitate ; 
but I could not perceive any traces of muriatic acid, when I had 
obtained the crystalline quite free from the other humours. It 
is composed,, therefore, of a smaller proportion of water than the 
others, but of a much larger proportion of albumen and gelatine. 
Vitreous Humour. 
I pressed the vitreous humour through a rag, in order to free 
it from its capsules ; and, in that state, by all the experiments 
I could make upon it, I could not perceive any difference 
between it and the aqueous humour, either in its specific gravity. 
