THE EVOLUTION OF THE KIDNEY-* 



Seventy-odd years have elapsed since Claude Bernard first 

 apprehended the fact that the true medium in which we live 

 is neither air nor water, but the blood, the internal medium, 

 that bathes our muscles, glands and brain. This internal en- 

 vironment, as he called it, is a cosmos elaborately isolated 

 from the external world and protected by a variety of phy- 

 siological devices to the end that its composition shall remain 

 unaffected by the sudden and sometimes severe changes that 

 beset the other and unstable cosmos that lies outside our 

 skins.^ 



During the seven decades since Bernard formulated this 

 concept, there has been discovered feature after feature in 

 our milieu interieur to which his concept of physiological 

 regulation must be applied. Vital phenomena involve the 

 interplay of so many physical-chemical factors that only a 

 beginning can be made towards enumerating them. The 

 most important one is, of course, water itself, the chief con- 

 stituent of the blood and tissues; then there are the numerous 

 inorganic salts: sodium, potassium, magnesium, calcium, 

 chloride, phosphate and bicarbonate, the delicate and pre- 

 cisely balanced acid and basic components, glucose and amino 

 acids. This list, though incomplete, is long enough to empha- 

 size the biological importance of the mixture as a whole. The 

 lungs serve to maintain the composition of the blood with 

 respect to oxygen and carbon dioxide, and with this their 

 duty ends. The responsibility for maintaining the composi- 

 tion of the blood in respect to other constituents devolves 



'•'This lecture is based in part on investigations cited in the bibliography, and in part 

 upon unpublished studies of the fish kidney which are now being prepared for publication. 

 A large part of the material upon which these studies are based was collected in 193 while 

 the author was a Fellow of the John Simon Guggenheim Memorial Foundation. 



