4 2 4 TEXT-BOOK OF PHYSIOLOGY. 



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 proteids 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. 



he kidneys are the. organs engaged in the excretion of the 

 urinary constituents from the blood. They resemble a bean in shape, 

 are from 10 to 12 centimeters in length, 2 in breadth, and weigh from 

 L444oH^e- 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 sub- 

 stance of the kidney is dense but friable. 



Upon making a longitudinal section of the kidney it will be ob- 

 served 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. 192). 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 por- 

 tions 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 twelye-pr fifteen in number, which present a dis- 

 tinctly striated appearance. 



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



tinctly friable in character. 



The Histology of the Kidney. The kidney is composed of a 

 connective-tissue framework supporting secreting tubules, blood- 

 vessels, lymphatics, and nerves, all of which are directly connected 

 with the removal of the urinary constituents from the blood. The 

 kidney is structurally a rnmpp^rirl tnKni^r ftlarH If the apex of 

 each pyramid be examined with a lens, it will present a number of 

 small orifices which may be regarded as the beginnings of the urinifer- 

 ous tubules. From this point the tubules pass outward in a straight 

 but somewhat diverging manner toward the cortex, giving off at 



