EXCRETION BY THE KIDNEYS 



477 



The pigments of the blood and bile and some of their derivatives are 

 of common occurrence in the urine in disease. Hcsmatoporphynn has 

 not only been found in some pathological conditions, but is constantly 

 present in minute traces in normal urine. Certain drugs e.g., sulphonal 

 cause an increase in its amount. In paroxysmal haemoglobinuria, 

 methcsmoglobin, mixed with some oxy haemoglobin, is found in the urine in 

 large amount; and it is worthy of note that it is not formed in the urine 

 after secretion, but is already present as such when it reaches the bladder. 



In the rare condition termed alkaptonuria, a body, alkapton, now 

 known to be identical with homo gent isinic acid, C 6 H 3 .(OH) 2 CH 2 -COOH, 

 a dioxyphenylacetic acid, is present. The urine becomes dark brown 

 on the addition of an alkali, or simply on exposure to air. It gives 

 Fehling's test for sugar. The substance has relations to the aromatic 

 amino-acids tyrosin and phenyl-alanin, and when either of these is 

 given to a person suffering from alkaptonuria, the amount of alkapton 

 excreted is increased. We may suppose, therefore, that in this con- 

 dition the normal decomposition of these products of proteolysis is 

 interfered with. 



Ferments. The urine contains traces of proteolytic and amylolytic 

 ferments (Fig. 185). These may be easily separated from it by putting 

 a little fibrin, which has the power of fixing (adsorbing) enzymes, into 

 the urine. 



Of the inorganic constituents of urine the most important and 

 most easily estimated are the chlorine, phosphoric acid, and sul- 

 phuric acid. 



Fig. 185. Pepsin in Urine. Diastatic Ferment in Urine. 

 At Different Times of the Day (Hoffmann). 



Chlorine. Much the greater part of the chlorine is united with 

 sodium, a smaller amount with potassium. The chlorides of the urine 

 are undoubtedly to a great extent derived directly from the chlorides 

 of the food, and have not the same metabolic significance as the organic, 

 and even as some of the other inorganic constituents. But it is note- 

 worthy that in certain diseased conditions the chlorine may disappear 

 entirely from the urine, or be greatly diminished e.g., in pneumonia, 

 and in general in cases in which much material tends to pass out from 

 the blood in the form of effusions (p. 508). 



Phosphoric Acid. The phosphoric acid of the urine is chiefly derived 

 from the phosphates of the food, but must partly come from the waste 

 products of tissues rich in phosphorus-containing substances, such as 

 lecithin and nuclein. The phosphoric acid is united partly with alkalies, 

 especially as acid sodium phosphate, and partly with earthy bases, as 

 phosphates of calcium and magnesium. The earthy phosphates are 

 precipitated by the addition of an alkali to urine, or in the alkaline 



