148 HUMAN PHYSIOLOGY. 



the skeletal muscles. The active principle of this gland has been isolated 

 by Abel and termed epinephrin or adrenalin. 



EXCRETION. 



The principal excrementitious fluids discharged from the body are the 

 urine, perspiration, and bile; they hold in solution principles of waste which 

 are generated during the activity of the nutritive process and are the ultimate 

 forms to which the organic constituents are reduced in the body. They also 

 contain inorganic salts. 



The urinary apparatus consists of the kidneys, ureters, and bladder. 



KIDNEYS. 



The kidneys are the organs for the secretion of urine; they resemble a 

 bean in shape, are from four to five inches in length, two in breadth, and 

 weigh from four to six ounces. 



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 presenting a deep notch, the hilus. 



The kidney is surrounded by 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 be readily 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 hilus extends into the interior of the organ and expands to form a cavity 

 known as the sinus. This cavity is occupied by the upper, dilated portion 

 of the ureter, the interior of which forms the pelvis. The ureter subdivides 

 into several portions, which ultimately give origin to a number of smaller 

 tubes, termed 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. They present a distinctly striated 

 appearance, a condition due to the straight direction of the tubules and 

 blood-vessels. 



2. An external or cortical portion, consisting of a delicate matrix containing 

 an immense number of tubules having a markedly convoluted appearance. 

 Throughout its structure are found numerous small ovoid bodies, termed 

 Malpighian corpuscles. 



