38 Physiology of the Kidney 



largely upon the kidneys. It is no exaggeration to say that 

 the composition of the blood is determined not by what the 

 mouth ingests but by what the kidneys keep; they are the 

 master chemists of our internal environment, which, so to 

 speak, they synthesize in reverse. When, among other duties, 

 they excrete the ashes of our body fires, or remove from the 

 blood the infinite variety of foreign substances which are 

 constantly being absorbed from our indiscriminate gastro- 

 intestinal tracts, these excretory operations are incidental to 

 the major task of keeping our internal environment in an 

 ideal, balanced state. Our glands, our muscles, our bones, our 

 tendons, even our brains, are called upon to do only one kind 

 of physiological work, while our kidneys are called upon to 

 perform an innumerable variety of operations. Bones can 

 break, muscles can atrophy, glands can loaf, even the brain 

 can go to sleep, without immediately endangering our sur- 

 vival, but when the kidneys fail to manufacture the proper 

 kind of blood neither bone, muscle, gland nor brain can carry 

 on. To quote Bernard again, "In proportion as we ascend the 

 scale of living beings, the organism grows more complex, the 

 organic units become more delicate and require a more per- 

 fected internal environment". It was the view of this physi- 

 ologist that we achieve a free and independent life, mentally 

 and physically, because of the constancy of the composition 

 of our blood. Recognizing that we have the kind of blood 

 we have because we have the kind of kidneys that we have, 

 we must acknowledge that our kidneys constitute the major 

 foundation of our physiological freedom. Superficially, it 

 might be said that the function of the kidneys is to make 

 urine; but in a more considered view one can say that the 

 kidneys make the stuff of philosophy itself. 



Taken as a whole, the human kidney appears to be extra- 



