THE EXCRETION OF WASTE FROM THE BODY 281 



242. The Kidneys. The kidneys are two dark red, bean- 

 shaped organs, somewhat smaller than the fist, which lie on 

 either side of the spinal column just below the ribs. Through 

 the many capillaries of the kidneys, all the blood of the body 

 sooner or later passes and these organs are therefore able to 

 select and remove the wastes it contains. The actual work 



Renal vei 



FIG. 94. Posterior view of the right kidney. (Morris.) 



of excretion is performed by the glandular cells of many small 

 tubes, not unlike sweat glands in structure, which make 

 up the bulk of the kidneys. The material excreted is not 

 merely strained out of the blood. The action is a true excre- 

 tion in which the materials are selected by the cells much as 

 other glandular cells produce their characteristic substances. 

 Some of the substances excreted by the kidneys, however, 



