162 DISSECTION OF THE KIDNEY. 



is the Renal Artery, a branch of the aorta ; and from near the 

 same point the Renal Vein returns the blood from the kidneys, 

 and pours it into the postcaval vein. Through the kidneys is 

 pouring a continuous stream of blood, varying in amount at 

 different times and in different conditions. 



The kidney receives a very large amount of blood for its 

 size, as compared with other organs. The flow to it is made 

 easy by the fact that the renal arteries are relatively wide 

 and short, and take the blood directly from the main current 

 of the aorta. 



When in active work the kidney is distended with blood. 

 The dead kidney, as we study it, is smaller than during life, 

 just as the dead heart is considerably smaller than when alive. 



From the kidney, through the ureter, Urine is continually 

 passing to the bladder. Urine is mostly water, containing 

 urea, salt, and various other substances in small amounts. 

 Urea is a waste matter brought in the blood. If the kidneys 

 are stopped in their action, urea accumulates in the blood, 

 and death soon results; to just the degree that the kidneys 

 fail in performing their duty, just so far must the body suffer. 

 Let us study the structure of the kidney, that we may, in part 

 at least, understand its action. 



For dissection, the sheep's kidney, being a little more simple 

 in structure, is preferable; but a pig's kidney is more closely 

 like that of man. 



Dissection of the Kidney. A class can usually be 

 supplied by asking the butchers a week or two beforehand to 

 save them; or, if near a large slaughtering-house, pigs' kid- 

 neys can easily be obtained. Butchers do not like to remove 

 the kidneys from the sheep's carcass until it is cut up. 



1. Observe the depression in the inner border of the kidney, 

 the Hilum. 



2. From the hilum trace the slender white tube, the Ureter, 



