THE NITROGENOUS EXCRETION. URINE. 3/1 



commonly formed which appear as precipitates. The alkali- 

 earth phosphates are the bodies usually thrown out in this 

 way. 



But disturbances in the equilibrium may result from changes 

 of temperature also, and precipitation occur because of the 

 simple cooling of the warm voided urine. Many of the pecu- 

 liar urate sediments are forrned in this way. Sometimes the 

 separation of sediment begins in the bladder or ureters and 

 this sediment may take the form of hard concretions or calculi. 

 In years past numerous attempts have been made to explain 

 the formation of these deposits, especially as they occur within 

 the body. The theoretical explanations given have been in 

 general far from satisfactory, and the most recent studies have 

 only gone to show the complexity of the problem. It is now 

 coming to be recognized that we have here one of the most 

 difficult problems of physical chemistry, which like other ques- 

 tions of chemical equilibrium in solution may be approached 

 only through elaborate studies. The beginning of such stud- 

 ies may be seen in some of the valuable papers which have 

 been published in the last few years on the solubility of uric 

 acid and its salts, and the degrees of dissociation which obtain 

 in the various solutions. As yet these matters are scarcely in 

 condition for elementary presentation. 



The recognition of the general character of the sediments 

 from urine is most readily effected by the aid of the micro- 

 scope, which is explained in text-books of urine analysis. 



THE REDUCING POWER OF NORMAL URINE. 



On account of the presence of some of the bodies described 

 in the last few pages normal urine exhibits a certain reducing 

 action toward metallic solutions. At one time this was 

 ascribed to traces of carbohydrates present, but later doubt was 

 thrown on this conclusion and the presence of even traces of 

 sugar-like bodies was denied by most writers concerned with 

 the question. With the development of greater accuracy in 

 the methods of detecting sugars, especially through the aid of 



