EXCRETION. 475 



ethereal sulphates. The extent to which they are present is taken as a meas- 

 ure of the extent of intestinal putrefaction; their presence can be deter- 

 mined by various tests. Of these compounds the one generally tested for is 

 potassium indoxyl sulphate or indican. If [hydrochloric acid and a small 

 quantity of potassium chlorate be added to suspected urine, the indican if 

 present will be separated into indoxyl and potassium sulphate. The former 

 compound will then be oxidized and form indigo blue. The depth of the 

 color is indicative of the quantity present and the extent of the intestinal 

 putrefaction. 



Inorganic Salts. Sodium and potassium phosphates, known as the 

 alkaline phosphates, are found in both blood and urine. The total quantity 

 excreted daily is about 4 grams. Calcium and magnesium phosphates, 

 known as the earthy phosphates, are present to the extent of i gram. Though 

 insoluble in water, they are held in solution in the urine by its acid constitu- 

 ents. If the urine be rendered alkaline, they are at once precipitated. 

 Sodium and potassium sulphates are also present to the extent of about 2 

 grams. The phosphoric and sulphuric acids which are combined with these 

 bases enter the body for the most part in the foods, though there is evidence 

 that they also arise by oxidation in consequence of the metabolism of proteins 

 which contain phosphorus and sulphur. Sodium chlorid is the most 

 abundant of the inorganic salts. It is derived mainly from the food. The 

 amount excreted is about 15 grams in twenty-four hours. 



THE KIDNEYS. 



The kidneys are the organs engaged in the excretion of the urinary 

 constituents from the blood. Each resembles a bean in shape, is from 10 

 to 12 centimeters in length, 2 in breath, and weigh from 144 to 170 grams. 

 They are situated in the lumbar region, one on each side of the vertebral 

 column behind the peritoneum, and extend from the eleventh rib to the crest 

 of the ilium. The anterior surface is convex, the posterior surface concave. 

 The latter presents a deep notch the hilum. The kidney is surrounded by 

 a thin smooth membrane composed of white fibrous and yellow elastic 

 tissue; though it is attached to the surface of the kidney by minute processes 

 of connective tissue, it can very readily be torn away. The substance of the 

 kidney is dense but friable. 



Upon making a longitudinal section of the kidney it will be observed that 

 the hilum extends into the interior of the organ and expands to form a 

 cavity known as the sinus, in which are found the blood-vessels, nerves, and 

 duct (Fig. 216). This cavity is mainly occupied by the upper part of the 

 renal duct, the ureter, the interior of which is termed the pelvis. The ureter 

 divides into several portions which terminate in small caps or calyces which 

 receive the apices of the pyramids. The parenchyma of the kidney consists 

 of two portions: viz: 



1. An internal or medullary portion, consisting of a series of pyramids or 



cones, some twelve or fifteen in number, which present a distinctly 

 striated appearance. 



2. An external or cortical portion, half an inch in thickness and distinctly 



friable in character. 



