PHYSIOLOGY. 



The amount of urine is diminished by reason of profuse sweat- 

 ing, extensive diarrhoea, thirst, diminution in blood-pressure, after 

 severe haemorrhage, and in some forms of kidney disease. 



Increase in urinary secretion (polyuria) is produced by an in- 

 crease in blood-pressure, by imbibing excessive draughts of liquids, 

 by any condition whereby the cutaneous blood-supply is diminished 

 (cold will do this). Polyuria is likewise produced by the administra- 

 tion of drugs which raise arterial tension, as digitalis and alcohol, 

 and by caffeine and sparteine, which stimulate the renal cells. 



The influence of the nervous system upon the secretion of urine 

 is very beautifully demonstrated by cases of hysteria. Hysterical 

 patients void excessive amounts of a very pale, watery urine. 



The specific gravity, as previously stated, averages 1.020; that 

 is, the mean between 1.015 and 1.025. The specific gravity varies 

 inversely to the quantity excreted. When for any reason, not patho- 

 logical, there is polyuria, the mark drops proportionately, register- 

 ing as low as 1.002. As a result of profuse sweating and abstinence 

 from liquids, the mark may reach 1.035 in healthy individuals. 



Acidity. The acidity of the urine is chiefly due to acid phos- 

 phate of sodium. There are two tides in the acidity of the urine. 

 During digestion the formation of the hydrochloric acid in the 

 stomach frees certain bases in the blood, which, when excreted, 

 diminish the acid reaction of the urine. This is called the alkaline 

 tide. The acid tide is after a fast, and hence occurs early in the 

 morning. 



Ordinarily it should be remembered, when taking the specific 

 gravity of urine, that anything below 1.010 should at once excite 

 suspicion of polyuria, with probably albumin; when above 1.030, 

 diabetes mellitus or some febrile condition may be present. 



The urinometer is the instrument used to ascertain the density 

 of any given sample of urine, and is so graduated that, when floating 

 in distilled water, it registers degrees, by which is meant 100Q. 

 The urine is placed in a tall, cylindrical glass of proper width so 

 that the urinometer will not adhere to its sides. After cessation of 

 the oscillations of the instrument, the observer carefully sights along 

 the surface of the urine to note the number registered. This pre- 

 caution is taken because the capillarity along the stem of the instru- 

 ment causes the urine to rise. 



The urine is composed of water in the average proportion of 96 

 per cent., and of substances dissolved in it in the proportion of 4 

 per cent. 



