500 URINE. [CHAP, xxxiv. 



with diseases of the kidneys, an&leads to the development of coma, which is 

 often fatal. Urea has been detected in the blood of patients suffering from 

 cholera, and once by Dr. Garrod, in that of a gouty patient. In the serous 

 fluids poured out in various parts of the body, in cases of kidney disease, as 

 well as in several of the secretions, such as the saliva, &c., it has been found 

 in large quantity. Dr. Owen Kees has met with it in milk, and the same ob- 

 server, and Wohler, have found it in the liquor amnii, an observation, how- 

 ever, which others have failed to confirm. It has been detected in the 

 aqueous and vitreous humours of the eye. 



There can be little doubt that urea is formed in the blood by the action of 

 oxygen upon lith-ic acid, creatine, and, possibly, upon some of the matters 

 comprehended under the indefinite term of extractive matter. In a state of 

 health it is so rapidly separated from the circulating fluid, in its passage 

 through the kidneys, that its presence is not easily recognized ; but, in animals 

 in which these organs have been extirpated, it accumulates in sufficient 

 quantity in the blood to be detected with facility. Urea cannot be extracted 

 from the muscles, although it is probable that the greater quantity excreted 

 is formed from the effete materials produced by muscular action, since the 

 quantity of urea is so much increased by exercise, and is also produced, al- 

 though only non-nitrogenous food be taken. At the same time, it is almost 

 certain, that if an amount of nitrogenous food greater than is required by the 

 wants of the system, be taken, the excess becomes converted into urea, and 

 is eliminated from the system by the kidneys.* 



Uric or Lithic Acid (C, H 4 N 4 O 6 ) is always present in healthy urine, and 

 exists in the proportion of about one part in a thousand. It may very readily 

 be obtained by the addition of a few drops of hydrochloric acid to a portion 

 of the urine placed in a conical glass vessel. After the lapse of a few hours, 

 the uric acid is found deposited in the form of small crystalline grains, 

 adhering to the sides or collected at the bottom of the glass. Uric acid pre- 

 pared in this manner is always highly coloured, which arises from the cir- 

 cumstance of its having a great aflinity for the colouring matter of the urine. 



Uric acid exists in healthy urine in combination with soda, and perhaps 

 also with ammonia and lime ; as these salts are only present in small quantity 

 they are held in solution, but in the urine of patients suffering from fever, 

 they often form an abundant deposit, which, in this country, is generally 



* It has lately been advanced by Dr. Frerichs, that in cases in which the 

 urea is prevented from being eliminated from the blood, either by the extir- 

 pation of the kidneys (as in his experiments upon animals), or in cases 

 in which the functions of these organs have been impaired by disease 

 (as in certain forms of Bright's kidney), this substance is resolved, whilst in 

 the circulating blood, into qarbonate of ammonia ; the presence of which, 

 according to this observer, gives rise to the coma which so frequently carries 

 off patients in an advanced state of renal disease. We should, however, state, 

 that this view has not yet received confirmation from the experiments of 

 others. That a considerable quantity of urea may be present in the blood 

 without giving rise to any serious symptoms, we can affirm from actual expe- 

 riment ; but, at the same time, we consider that there is sufficient evidence 

 to prove that the coma, in many cases of kidney disease, is dependent upon 

 the presence of urea. We have tested the breath of a few patients suffering 

 from this form of coma in King's College Hospital, and have also examined the 

 blood, but have failed to demonstrate the presence of carbonate of ammonia. 



