2 FROM FISH TO PHILOSOPHER 



ganic category are the plasma proteins and many smaller 

 molecules such as glucose, the amino acids (the build- 

 ing blocks of proteins), the lipides (the building blocks 

 of fat), and a variety of vitamins and hormones, all of 

 them necessary to the nutrition and operation of the 

 body. This organic category also includes many waste 

 products on their way to excretion. In the inorganic cate- 

 gory are water itself (the major constituent of the plasma 

 and the interstitial fluid, as well as the tissues) and nu- 

 merous salts as represented by sodium, potassium, mag- 

 nesium, calcium, chloride, bicarbonate and phosphate in 

 various combinations, as well as oxygen on its way from 

 the lungs to the tissues for utilization, and carbon dioxide 

 on its way from the tissues to the lungs for excretion. 

 The lungs serve to maintain the composition of the 

 extracellular fluid with respect to oxygen and carbon 

 dioxide, and with this their duty ends. The responsibiHty 

 for maintaining the composition of this fluid in respect 

 to other constituents devolves on the kidneys. It is no 

 exaggeration to say that the composition of the body 

 fluids is determined not by what the mouth takes in but 

 by what the kidneys keep: they are the master chemists 

 of our internal environment, which, so to speak, they 

 manufacture in reverse by working it over completely 

 some fifteen times a day. When, among other duties, 

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

 the blood the infinite variety of foreign substances that 

 are constantly being absorbed from our indiscriminate 

 gastrointestinal tracts, these excretory operations are in- 

 cidental to the major task of keeping our internal en- 

 vironment in an ideal, balanced state. Our bones, mus- 

 cles, glands, even our brains, are called upon to do only 

 one kind of physiological work, but 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, and endanger our sur- 

 vival; but should the kidneys fail in their task neither 

 bone, muscle, gland nor brain could carry on. 



