1893.] 



lire 2 in the Blood of Birds, fyc. 



483 



in mammalian blood, and that the urate of ammonium is a subsequent 

 product of the union of urea with some other principle or principles, 

 glycine probably being one of them. Consequently, it is not neces- 

 sary that uric acid should be present in the blood of uric-acid-excreting 

 animals : in health, in fact, it is not detectible. When it is present, 

 its presence is a result of its having been absorbed after formation in 

 the kidneys or elsewhere. 



With regard to the first proposition but little need be said, as most 

 physiologists will agree with the statements it contains. With 

 regard to the second, the case is very different, as the views therein 

 enunciated are totally at variance with those which are held at the 

 present time. The statement that the ultimate metabolism in the 

 uric- acid-excreting animals is identical with that which takes place 

 in mammals requires for its establishment the constant presence of 

 urea in their blood. And I was led to seek for urea by my views on 

 the production of uric acid, and from a recollection of having obtained 

 urea from the blood of a turkey some few years ago. If no urea 

 exists in the blood of birds, my theory falls to the ground. In this 

 paper, therefore, I have laid special stress on the presence of this 

 principle and the relative amounts contained in the blood of the two 

 classes of animals discussed. 



The statement that urate of ammonium is synthetically produced 

 from this urea can easily be shown to be not only possible, but very 

 probable ; as likewise can the fact that it is not produced within the 

 blood itself, but is formed, at least chiefly, in the kidneye. We have 

 already spoken of the changes which take place when urea is intro- 

 duced into the system of birds, whether by the stomach or otherwise, 

 and certain experiments which I have made tend to indicate that 

 glycine is, at any rate, one of the principles which plays a part in the 

 building up of urate of ammonium. In the case of small birds, 

 feeding on canary seed and water, the throwing out of the white 

 urate of ammonia was observed hour by hour, and the quantity 

 noted. When the seed was taken away — water only being left — the 

 amount of the urate rapidly diminished. The exhibition of sugar 

 did not increase the urate, but when a mixture of urea and glycine 

 was given the amount of the urate was rapidly increased, whereas 

 urea given alone at this period of the fasting produced little or no 

 effect in the production of urate of ammonium. I do not, however, 

 lay too much stress on these observations, as they were not suffi- 

 ciently numerous, nor were the amounts weighed with sufficient 

 accuracy. 



From this theory it follows also that, though there is no need for 

 uric acid to be present in the blood of animals which secrete it, the 

 presence of urea is absolutely essential. 



One of my observations is to this effect : — The blood of a goose 



