THE KIDNEYS. SECRETION OP URINE. 601 



a well-marked acid reaction. When it is left to itself for some time, slight 

 nebulae, consisting of mucus, are formed in it; and these gradually descend to 

 the bottom. Soon afterwards, an unpleasant odor is developed; instead of an 

 acid, an alkaline reaction is presented, in consequence of the decomposition of 

 the urea into carbonate of ammonia; and a precipitation of earthy phosphates 

 then takes place. A turbidity may occur, however, on the simple cooling of 

 the urine, without any such departure from its normal composition as would 

 properly constitute disease ; this being due to the precipitation of urates of soda 

 and ammonia, under the conditions formerly specified ( 56). If the urine be 

 turbid, however, when it is passed from the body, having a temperature of 98 

 or 100, it must be considered as abnormal. The average Quantity of urine 

 passed during the 24 hours, has been variously estimated : it differs, of course, 

 with the amount of fluid ingested, and it is influenced also by the external tem- 

 perature ; a much smaller amount of the superfluous fluid of the body being set 

 free from the skin in winter than in summer, and a larger proportion being car- 

 ried off by the kidneys. Probably we shall be pretty near the truth, in estimat- 

 ing the amount (with Dr. Prout) at from about 30 oz. in summer, to 40 oz. in 

 winter, for a person who does not drink more than the simple wants of nature 

 require. The Specific Gravity comes to be a very important character, in various 

 morbid conditions of the urine : and it is therefore desirable to estimate it cor- 

 rectly. This also is liable, of course, to the same causes of variation; since, 

 when the same amount of solid matter is dissolved in a larger or smaller quantity 

 of water, the specific gravity will be proportionably lower or higher. The ave- 

 rage, according to Dr. Prout, in a healthy person, taking the whole year round, 

 is about 1020; the standard rising in summer (on account of the greater dis- 

 charge of fluid by perspiration) to 1025 ; and being lowered in winter to 1015. 

 Simon, however, states the average specific gravity at no more than 1012. It 

 will depend, in each individual Case, upon the amount of fluid habitually ingested, 

 as compared with that dissipated by cutaneous exhalation ; and it will also vary 

 with the period that has elapsed since the last introduction of liquid into the 

 stomach. From these and other causes, the proportion of solid matter in 1000 

 parts of Urine may vary from 20 to 70; and hence the various recorded analyses 

 of this liquid present very wide diversities in the proportions of its solid consti- 

 tuents. These discrepancies, however, being chiefly due to the fluctuating amount 

 of water, become very much less (as Simon 1 pointed out) when we calculate the 

 proportion which each principal component bears to 100 of solid residue; as is 

 shown in the following Table : 



Berzelius. Lehmann. Simon. Marchand. 



Urea .... . 45.10 49.68 33.80 48.91 



Uric Acid ... . 1.50 1.61 1.40 1.59 



Extractive matter, Ammonia-sa ts, \ qfi qn 9 o Q r A<> n <?9 4Q 



and Chloride of Sodium > 36 ' 30 28 ' 95 42 ' 60 32 ' 49 



Alkaline Sulphates 

 Alkaline Phosphates 



10.30 11.58 8.14 10.18 

 6.88 5.96 6.50 4.57 



Phosphates of Lime and Magnesia . 1.50 1.97 1.59 1.81 



We shall presently find the causes of some of the variations even here shown, 

 to lie in the nature of the ingesta, and in the amount of exercise taken by the 

 individual. 



639. The most important of those organic constituents of the Urine, whose 

 presence may be directly traced to the metamorphosis of the azotized components 

 of the tissues and of the blood, is evidently that which, from its being the prin- 

 cipal cause of the characteristic properties of the secretion, is termed Urea. 

 This substance, as already shown ( 52), exists preformed in the Blood ; being 



1 "Animal Chemistry," translated by Dr. Day, p. 405, Am. Ed. 



