GENERAL CHARACTERISTICS OF THE URINE. 225 



fectly clear, and remains so if care is taken to prevent the access of 

 micro-organisms. If left exposed to the air, however, bacterial 

 decomposition soon takes place. Ammonia appears in the free state, 

 and as a consequence of the change in reaction certain constituents 

 of the urine are precipitated and render the liquid turbid. Sooner 

 or later they settle to the bottom, but owing to the presence of 

 innumerable micro-organisms the supernatant fluid remains cloudy. 

 Such urine is said to have undergone ammoniacal decomposition. 



A formation of sediments, aside from the light cloud which de- 

 velops in every urine on standing for a short while, may, however, 

 also occur in the absence of micro-organisms. In the winter-time it 

 is a common experience to see the entire volume of urine become 

 turbid when kept in a cold room. This is owing to the fact that 

 the urates of the urine are very much less soluble in cold than 

 in warm water, and are hence thrown down. On standing, they 

 soon settle to the bottom, and the supernatant liquid remains clear 

 so long as bacterial decomposition does not occur. A similar forma- 

 tion of sediments is observed if the reaction of the urine is alkaline, 

 owing to the presence of fixed alkali in contradistinction to free 

 ammonia. This may at times be observed after a large meal, or 

 after the administration of sufficiently large amounts of alkalies as 

 such, or of substances which are oxidized to alkaline carbonates 

 within the body. In such an event the urine may be clear when 

 first passed, but after standing a short time it becomes turbid, 

 and deposits a sediment of phosphates and carbonates of the alka- 

 line earths. The change is, no doubt, due to an escape of the 

 carbon dioxide which was present in solution. But here also the 

 supernatant liquid is clear. 



In herbivorous animals, by which an alkaline urine is passed 

 habitually, the liquid is turbid when discharged. In man the pas- 

 sage of a turbid urine is always abnormal, excepting during the 

 first days of life, when cloudy urine is the rule. This is largely 

 referable to desquamated epithelial cells and relatively large amounts 

 of urates. 



While the urine of all mammalian animals is liquid, the lower 

 animals excrete a urine that is more or less solid. In birds 

 and reptiles, for example, in which the ureters end in a common 

 cloaca with the rectum, the excrements appear in the form of a whit- 

 ish pasty material. A gelatinous urine is observed in turtles. 



The color of the urine in man normally varies from light yellow 

 to dark amber, and is largely influenced by the concentration of the 

 secretion and its reaction. Acid urine is thus always darker than an 

 alkaline urine, and the color is naturally lighter when the secretion 

 is abundant than when scanty. A gradual darkening of the urine 

 is observed when the material is kept for some time and access of 

 micro-organisms is prevented. 



Deviation from the normal color is notably observed in disease, or 

 following the administration of various drugs, but may also occur iu 

 15 



