356 EXCRETION. 



expelled from the body by the same channel. Those substances 

 which tend to unite strongly with the animal matters, and to form 

 with them insoluble compounds, such as the preparations of iron, 

 lead, silver, arsenic, mercury, &c., are least liable to appear in the 

 urine. They may occasionally be detected in this fluid when they 

 have been given in large doses, but when administered in moderate 

 quantity are not usually to be found there. Most other substances, 

 however, accidentally present in the circulation, pass off' readily by 

 the kidneys, either in their original form, or after undergoing cer- 

 tain chemical modifications. 



The salts of the organic acids, such as lactates, acetates, malates, 

 &c., of soda and potassa, when introduced into the circulation, are 

 replaced by the carbonates of the same bases, and appear under 

 that form in the urine. The urine accordingly becomes alkaline 

 from the presence of the carbonates, whenever the above salts have 

 been taken in large quantity, or after the ingestion of fruits and 

 vegetables which contain them. We have already spoken (Chap. II.) 

 of the experiments of Lehmann, in which he found the urine exhi- 

 biting an alkaline reaction, a very few minutes after the administra- 

 tion of lactates and acetates. In one instance, by experimenting 

 upon a person with congenital extroversion of the bladder, in whom 

 the orifices of the ureters were exposed, 1 he found that the urine 

 became alkaline in the course of seven minutes after the ingestion 

 of half an ounce of acetate of potassa. 



The pure alkalies and their carbonates, according to the same ob- 

 server, produce a similar effect. Bicarbonate of potassa, for example, 

 administered in doses of two or three drachms, causes the urine 

 to become neutral in from thirty to forty-five minutes, and alkaline 

 in the course of an hour. It is in this way that certain " anti-cal- 

 culous" or " anti-lithic" nostrums operate, when given with a view 

 of dissolving concretions in the bladder. These remedies, which 

 are usually strongly alkaline, pass into the urine, and by giving it 

 an alkaline reaction, produce a precipitation of the earthy phos- 

 phates. Such a precipitate, however, so far from indicating the 

 successful disintegration and discharge of the calculus, can only 

 tend to increase its size by additional deposit. 



Ferrocyanide of potassium, when introduced into the circulation, 

 appears readily in the urine. Bernard 2 observed that a solution of 



' Physiological Chemisty, vol. ii. p. 133. 



2 Leqons de Physiologie Experiruentale, 1856, p. 111. 



