482 



Sir A. Garrod. On the presence of [May 18, 



Uric acid is not found in the blood of healthy mammals. Man, 

 however, is, to some extent, an exception to this rule, for uric acid is 

 often found when the deviation from good health is scarcely percep- 

 tible. This I showed in a paper in the ' Medical Chirurgical Trans- 

 actions,' in 1848. Observations are usually made on the blood of 

 animals which are "killed for food, and these are probably young and 

 healthy ; whereas, when observations are made on man, the chances 

 of his being in perfect health are diminished, since it is usually illness 

 which brings his condition under notice. 



The blood of healthy birds, instead of containing uric acid, as 

 would naturally be supposed, is usually quite free from that sub- 

 stance, except when it has been introduced into the system through 

 the stomach, or by injection. In a paper read before this Society in 

 1884, I showed that the blood of the duck was, for the most part, 

 free from any detectible uric acid, and, in a paper read in 1848, I 

 showed that the blood of a healthy pigeon was entirely free from it. 

 I have recently had occasion to examine most minutely the blood of 

 the goose, the fowl, and the turkey, and have found that, although 

 fairly rich in urea, no uric acid could be separated from it. We may, 

 therefore, conclude that birds may throw out uric acid by the kidneys, 

 although it is not present in their blood. 



Perhaps it will be desirable to mention here that uric acid intro- 

 duced into the stomach of the bird as a soluble urate is absorbed 

 into the blood, which becomes so saturated with it that it can be 

 crystallised out with the greatest ease. 



Uric acid thus introduced into the system is not thrown out by the 

 kidneys, as these organs appear to be incapable of eliminating it, and 

 this applies not only to the bird but to the mammal also. This fact 

 has been proved by the researches of Zabelli. 



Having considered these facts, the correctness of which is capable 

 of being fully established, we are justified, I think, in coming to the 

 following conclusions : — 



First. That in mammalia and other urea-excreting animals the 

 metabolism of the nitrogenised tissues results in the formation of 

 urea as an ultimate product ; that an appreciable and measurable 

 amount of this substance is always found in their blood, and is con- 

 stantly being excreted by the kidneys; and, further, that any cause 

 leading to the decrease of this excretion produces an augmentation of 

 the urea in the blood. It necessarily follows from this that, as stated 

 above, the blood of the renal artery is richer in urea than the blood 

 of the renal vein. 



Second. That in birds and other uric-acid-excreting animals the 

 metabolism of the nitrogenised tissues is exactly the same as in 

 mammals, and that urea is the ultimate product of this metabolism ; 

 that urea is always present in their blood, in quantities not less than 



