DIURNAL VARIATIONS OF THE URINE. 351 



quantity of water is often so much diminished that it is no longer 

 sufficient to retain in solution all the solid ingredients of the urine, 

 and the urate of soda is thrown down, after cooling, as a fine red 

 or yellowish sediment. So long, however, as the variation is con- 

 fined within strictly physiological limits, all the solid ingredients 

 are held in solution, and the urine remains clear. 



There is also, in a state of health, a diurnal variation of the urine, 

 both in regard to its specific gravity and its degree of acidity. 

 The urine is generally discharged from the bladder five or six 

 times during the twenty-four hours, and at each of these periods 

 shows more or less variation in its physical characters. We have 

 found that the urine which collects in the bladder during the 

 night, and is first discharged in the morning, is usually dense, 

 highly colored, of a strongly acid reaction, and a high specific 

 gravity. That passed during the forenoon is pale, and of a low 

 specific gravity, sometimes not more than 1018 or even 1015. It 

 is at the same time neutral or slightly alkaline in reaction. Toward 

 the middle of the day, its density and depth of color increase, and 

 its acidity returns. All these properties become more strongly 

 marked during the afternoon and evening, and toward night the 

 urine is again deeply colored and strongly acid, and has a specific 

 gravity of 1028 or 1030. 



The following instances will serve to show the general characters 

 of this variation : 



OBSERVATION FIRST. March 20th. 

 Urine of 1st discharge, acid, sp. gr. 1025. 

 " 2d " alkaline, " 1015. 



" 3d " neutral, " 1018. 



" 4th " acid, " 1018. 



" 5th " acid, " 1027. 



OBSERVATION SECOND. March 2lst. 

 Urine of 1st discharge, acid, sp. gr. 1029. 

 " 2d " neutral, " 1022. 



" 3d " neutral, " 1025. 



" 4th " acid, 1027, 



" 5th " acid, " 1030. 



These variations do not always follow the perfectly regular 

 course manifested in the above instances, since they are somewhat 

 liable, as we have already mentioned, to temporary modification 

 from accidental causes during the day ; but their general tendency 

 nearly always corresponds with that given above. 



It is evident, therefore, that whenever we wish to test the specific 



