404 URINE. 



different; even under purely physiological conditions, that no 

 definite estimate can be made of it. The quantity of water which 

 permeates through the kidneys is entirely independent of the 

 quantity of solid urinary constituents which are simultaneously 

 secreted ; although, according to Becquerel's observations,* which I 

 am able perfectly to confirm, large quantities of water may simul- 

 taneously carry off a large amount of solid constituents with the 

 urine; that is to say, when large quantities of water have been drunk, 

 more solid constituents are generally carried off by the urine in the 

 twenty-four hours than when but little drink has been taken. But 

 the quantity of water which passes off in the urine depends upon 

 such various reasons, that the causes of its diminution and increase 

 in this fluid cannot always be determined, even under purely 

 physiological relations. These controlling causes are more especially 

 the quantity of water drunk, or absorbed, in the bath, the nature of 

 the stools, and the more or less copious transpiration, which again 

 depends upon the external temperature, the degree of moisture of 

 the atmosphere, bodily exercise, and many other internal and 

 external causes. 



Much obscurity long prevailed as to the cause of the acid 

 reaction of the normal urine, which was originally referred to 

 lactic and even to acetic acid ; but this subject has at length been 

 set at rest by Liebig, who has shown that the acidity of normal 

 urine can alone depend upon acid phosphate of soda. Thus, for 

 instance, when ordinary phosphate of soda (which, as is well 

 known, yields an alkaline reaction) is dissolved in water, and the 

 solution is gradually treated with uric acid, which exerts no 

 reaction on vegetable colours, a fluid is obtained, which, on heat- 

 ing, reddens litmus paper, and on being cooled deposits a white 

 crystalline powder, which exhibits under the microscope the most 

 beautiful groups of prismatic crystals of urate of soda. Since so 

 extremely weak an acid as uric acid can abstract from the phos- 

 phate of soda a portion of its base, we can hardly deny that 

 stronger acids, such as hippuric, lactic, and sulphuric acids, may, 

 immediately after their formation by the metamorphosis of animal 

 matter, convert neutral phosphate of soda into an acid salt, in 

 which form it then passes into the urine, together with the 

 already formed sulphate, lactate, and hippurate of soda. If this 

 mode of explanation be applied to the acidity of every species of 

 urine, freshly discharged urine would not saturate a larger amount 

 of base than would correspond with the quantity of phosphate of 

 * S^neiotique des Urines, &c. Paris, 1841. 



