Royal Society. 421 



readily detected three hours after the administration of the dose, 

 even when it was so small as 10 grs. 



From an experiment described in the paper, it was shown, that bj' 

 a simple combustion of ammonia out of the body, as well as in the 

 body, nitric acid was produced. From other experiments it appears 

 that urea, also, l)y oxidation, whether in the body or out of the body, 

 gives rise to nitric acid. 



Having found that nitric acid was produced more readily and fre- 

 quently than had been supposed to be the case, the author was led 

 to try whether combustions in the atmosphere without ammonia 

 could not give nitric acid. The presence of this acid was, in con- 

 sequence, detected in the products of the combustion of alcohol, of 

 coal, of a wax candle, and of hydrogen. 



As this led to the supposition that nitric acid might exist in rain- 

 water at all times, experiments were made on the rain-water col- 

 lected on wet days in London, and the presence of nitric acid was 

 discovered by the starch an<l also by the indigo test. 



The conclusions the author comes to from his experiments are: — 



1. That the action of oxygen takes place in the body, not only on 

 hydrogen, carbon, sulphur and phosphorus, but also on nitrogen. 



2. That in all cases of combustion, out of the body and in the 

 body, if ammonia be present, it will be converted partly into nitric 

 acid. 



3. That the nitrogen of the air is not indifferent in ordinary cases 

 of combustion, but that it gives rise to minute quantities of nitric 

 acid. 



He further remarks, that the production of nitric acid from am- 

 monia in the body adds another to the many instances of the action 

 of oxygen in man ; and that the detection of nitric acid in the urine 

 may lead to the conclusion, that the blood is being freed from am- 

 monia, or from substances closely related to it, as urea, or possibly 

 caffeine and other alkaloids. 



2. " Description of a Muscle of the striped variety, situated at 

 the posterior part of the choroid coat of the Eye in Mammals, with 

 an explanation of its mode of action in adapting the Eye to distinct 

 vision at different distances." By George Rainey, Esq., M.R.C.S. 

 Communicated by Joseph H. Green, Esq., F.R.S. Received De- 

 cember 21, 1850. 



Respecting this muscle, the author observes that it occupies about 

 the posterior two-thirds of the choroid coat, its fibres lying in dif- 

 ferent planes, the most superficial being immediately beneath the 

 membrana pigmenti, the deepest extending almost as far as the vasa 

 vorticosa; that these fibres ])ass in different directions, some going 

 from before to behind, and others intersecting these at various an- 

 gles : altogether they receive the pigment membrane, the retina and 

 the vitreous humour as into a cup. 



From the connection of these fibres with the choroid coat, the 

 author calls them the choroid muscle. He has not been able to trace 

 them nearer to the ciliary ligament than about two-thirds of the di- 

 stance from the centre of the choroid to the border of the cornea. 



