PHYSICAL PROPERTIES OF THE URINE. 377 



OBSERVATION SECOND. March 2lst. 

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



- 2d " neutral, < ; 1022. 



- 3d " neutral, " 1025. 

 4th - acid, " 1027. 

 " 5th " acid, " 1030. 



These variations do not always follow a perfectly regular course, since 

 they are liable to temporary modification from accidental causes during 

 the day ; but their general tendency corresponds with that given above. 



The acidity of the urine is also liable to vary from temporary causes, 

 owing to the introduction of organic substances with the food which 

 give rise to alkalescence in the animal fluids. The salts of the organic 

 acids, such as the lactates, acetates, malates, and tartrates, when taken 

 into the stomach and absorbed by the circulation, are replaced by 

 carbonates of the same bases, and appear under that form in the urine. 

 When these salts, or the fruits and vegetables which contain them, are 

 taken in large quantit}^ the urine becomes alkaline from the presence 

 of the carbonates. The use of summer fruits, therefore, though they 

 may have an acidulous taste, is followed by alkalescence of the urine. 

 The effect thus produced may be manifested in a very short time; 

 according to the observations of Lehmann, the urine sometimes becom- 

 ing alkaline within a quarter of an hour after taking a little over 15 

 grammes of sodium acetate. 



It is evident, therefore, that when the specific gravity or the acidity 

 of the urine is to be tested, either in health or disease, it will not be 

 sufficient to rely upon the examination of a single specimen. The nor- 

 mal variations in specific gravity during the day do not usually exceed 

 the limits of 1015 as a minimum and 1030 as a maximum; but either 

 of these would be unnatural if continued during the whole twenty-four 

 hours. All the different specimens 'of urine passed during the day 

 should therefore be collected and examined together. The average 

 specific gravity thus obtained will represent the normal daily density 

 of the excretion. 



The daily volume of the urine is also to be taken into account. The 

 total amount of solids discharged by the urine in health is from 50 to 

 60 grammes per day ; and this quantity of solid material is dissolved in 

 about 1200 cubic centimetres of water. This gives an average daily 

 quantity and an average specific gravity of the urine, as the measure of 

 the excretory process during twenty-four hours. 



Both the quantity of the urine and its mean specific gravity are 

 liable to vary somewhat in different individuals, or even in the same 

 individual from day to day. Ordinarily, the water of the urine is more 

 than sufficient to hold all the solid matters in solution ; and its propor- 

 tion may therefore be diminished by temporary causes without the 

 production of turbidity or the formation of a deposit. Under such cir- 

 cumstances, the urine merely becomes deeper in color, and of higher 

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