384 THE EXCRETIONS OF THE BODY 



376. The reducing power of normal urine corresponds to a 0.15-0.6-per-cent 

 solution of dextrose. 



Heller's test (cf. page 69) is commonly used to demonstrate proteid in the 

 urine. A urine which does not give this reaction is generally regarded as free 

 of proteid. And yet there is proteid, chiefly serum albumin, even in such urine. 



12. The inorganic constituents of the urine on a normal diet amount to 

 about 25 g. per day. For the most part they come from the ingested food, 

 and consequently decrease in fasting. Naturally their percentages vary 

 greatly ; hence the following table is only for the purpose of giving a general 

 idea of the average quantities: 



Sodium chloride, NaCl 15.0 g. per day 



Sulphuric acid, H 2 SO 4 2.5 g. " 



Phosphoric acid, P 2 O 5 2.5 g. " 



Potassium, K 2 O 3.3 g. " 



Magnesium, MgO 0.5 g. " 



Calcium, CaO 0.3 g. " 



Other inorganic substances 0.2 g. " 



Besides these the urine contains 4-5 vols. per cent of C0 2 which for the 

 most part is physically absorbed, but occurs also in the form of acid car- 

 bonates. 



13. Accidental constituents. The urine may contain either in solution or 

 suspension a large number of different bodies coming from substances ingested 

 for one reason or another, or originating from abnormal processes in the body. 

 I shall merely enumerate the most important of these: 



(a) Blood, blood pigments and their derivatives; blood corpuscles, hemo- 

 globin, methasmoglobm, hsematin, melanin, etc. 



(&) Bile acids, bile pigments, and their transformed products. 



(c) Leucin, tyrosin, and dioxy-phenyl-acetic acid, C 6 H 3 (OH) 2 .CH 2 .COOH. 



(d) Proteid. 



(e) Sugar. 



(jO Acetic acid, /3-oxybutyric acid and acetone. 



(g} Drugs, either as such or as transformed products. 



2. THE EXCRETION OF URINE 



In no other secreting organ are the peculiarities of structure so significant 

 for a conception of its function as in the kidney. It is therefore necessary 

 to discuss the microscopic structure of the kidney here somewhat in detail. 



A. STRUCTURE OF THE KIDNEYS 



The larger branches of the renal artery (Fig. 143) run along the outer sur- 

 face of the pyramids to their base and there form an anastomosing network. 

 From this network branches pass toward the surface of the kidney (radial 

 arteries), and others pass off in tufts toward the pelvis of the kidney. The 

 individual branches of the latter run between bundles of urinary tubules in the 

 pyramids. 



The radial arteries send out small branches, vasa afferentia, which soon break 

 up in the so-called glomeruli of the Malpighian corpuscles presently to be 



