DECOMPOSITION OF THE URINE. 395 



The first portions of the ammoniacal salt thus produced neutralize a 

 corresponding quantity of the sodium biphosphate, so that the acid 

 reaction of the urine diminishes in intensity. This reaction gradually 

 becomes weaker, as the fermentation proceeds, until it at last disappears 

 altogether and the urine becomes neutral. The production of ammonium 

 carbonate still continuing, the reaction of the fluid then becomes alkaline, 

 and its alkalescence grows more pronounced with the constant accumu- 

 lation of the ammoniacal salt. 



The time at which the alkaline reaction of the urine becomes estab- 

 lished varies with its original degree of acidity and with the rapidity of 

 its decomposition. Urine which is neutral when first passed, as often 

 happens with that discharged during the earlier part of the day, will of 

 course become alkaline more readily than that which has at , first a 

 strongly acid reaction. In the summer, urine will become alkaline, if 

 freely exposed, on the third, fourth, or fifth day ; while in the winter, a 

 specimen kept in a cool place may still be neutral at the end of fifteen 

 days. In cases of paralysis of the bladder accompanied with cystitis, 

 where the vesical mucus is increased in quantity and altered in quality, 

 and the urine is retained in the bladder for ten or twelve hours at the 

 temperature of the bod} r , it may change so rapidly as to be distinctly 

 alkaline and ammoniacal at the time of its discharge. In these cases it 

 is acid when first secreted by the kidneys, and becomes alkaline while 

 retained in the interior of the bladder. 



The first effect of the alkaline condition of the urine, thus produced, 

 is the precipitation of the earthy phosphates. This precipitate slowly 

 settles upon the sides and bottom of the vessel, or is partly entangled 

 with certain animal matters which rise to the surface and form a thin, 

 opaline scum upon the urine. There are no crystals to be seen at this 

 time, but the deposit is entirely amorphous and granular. 



The next change consists in the production of a new salt, the 

 ammonio-magnesian phosphate, by the combination of the ammonia 

 formed from the urea with the magnesium phosphate already present in 

 the urine. The change may be represented as follows : 



Magnesium phosphate. Ammonia. Ammonio-magnesian phosphate. 



MgHP0 4 + NH 3 = MgNH 4 PO, 



The crystals of this salt are very elegant and characteristic. They 

 show themselves throughout all parts of the mixture, growing gradually 

 in the mucus at the bottom, adhering to the sides of the glass, and 

 scattered abundantly over the film which collects upon the surface. By 

 their refractive power they give to this film a peculiar glistening and 

 iridescent appearance, which is nearly always visible at the end of six 

 or seven days. The crystals are perfectly colorless and transparent, and 

 have the form of triangular prisms, generally with bevelled extremities. 

 Their edges and angles are frequently replaced by secondary facets. 

 They are insoluble in alkalies, but are easily dissolved by acids, even 

 in very dilute form. At first they are of minute size, but gradually 



