THE COMPOSITION AND CHARACTERS OF THE URINE 1161 



passages. In concentrated urine a deposit occurs on cooling. This deposit 

 dissolves when the urine is warmed, and consists of urates. Under 

 certain circumstances urine is turbid as it is passed, but in this case the 

 turbidity generally consists of earthy phosphates and is not cleared up 

 by heating. 



The colour of the urine varies with its concentration. After severe 

 sweating the amount of water excreted by the kidneys is small, and the 

 urine is therefore concentrated and of high colour. After copious draughts 

 of liquid the urine may be very pale and dilute. 



Ordinary urine has an aromatic odour, but this varies largely with the 

 character of the food. Many food substances give characteristic odours, 

 which may depend on alterations undergone by them in their passage 

 through the body. 



The specific gravity of the urine is proportional to its concentration. 

 Normally it is 1016 to 1020, though it may rise as high as 1040 or sink as 

 low as 1002. 



The molecular concentration of the urine is almost always greater than 

 that of the blood. Its osmotic pressure may be measured by determining 

 the depression of freezing-point. The A of urine normally varies between 

 0-87 and 2-71 (A of blood = 0-56). After copious draughts. of water the 

 depression of freezing-point in the urine may be less than that of- serum, and 

 may be as small as 0*25. 



The reaction of urine is generally described as acid. It is acid to litmus 

 and to phenolphthalein. This is due to the fact that neutral constituents 

 of the food give rise to acid end-products in metabolism. The sulphur of 

 proteins is converted into sulphuric acid and the phosphorus of lecithin 

 into phosphoric acid. There is thus a predominance of acid radicals over 

 bases in ordinary urine. This statement however applies only to man and 

 to carnivora. In the food of herbivora there is a predominance of alkaline 

 bases. Vegetable acids, e.g. tartaric, malic, and citric acids, undergo 

 oxidation to carbonic acid in the body, so that their bases leave the body as 

 alkaline carbonates. The urine of such animals therefore contains an 

 excess of alkaline carbonates, and is alkaline in reaction and froths on the 

 addition of an acid. If a herbivorous animal be starved so that it has to 

 live on its own tissues, it becomes for the time, so to speak, carnivorous, 

 and its urine becomes clear and acid. The urine of man can be made 

 alkaline by the ingestion of large quantities of vegetables or fruits. Under 

 such circumstances the urine as passed is generally turbid from the presence 

 of precipitated earthy phosphates. In determining the reaction of urine it 

 is usual to adhere to one indicator, e.g. phenolphthalein, and to give the 

 acidity in terms of decinormal acid, naming the indicator used. The 

 acidity (i. e. the concentration of H ions) can also be determined by the 

 electrical method. In this way Hoeber found the acidity of human urine 

 to vary between 4-7 X 10 ~ 7 and 100 x 10 ~ 7 . On the average it was 

 49 X 10 ~ 7 in the litre. 



THE AVERAGE COMPOSITION OF THE URINE. Several analyses 



