SCOPE OF THE PROBLEM 



Glomerulus 



Thin segment 



Proximal 

 tubule 



Figure 1 A nephron, the functional unit of the kidney. [Front 

 S?nith, H. W., The Physiology of the Kidney, Oxford, New York, 1937; 

 with pennission.'] 



Distal 

 tubule 



No adequate consideration of the role of secretion in the func- 

 tion of the multicellular organism, whether marine or terrestrial, can 

 be provided to the student of transport within the space of the 

 present volume. Everywhere one turns in the study of life func- 

 tions, whether to respiration, digestion or excretion, or to special 

 senses such as vision or hearing, he will find relevant aspects of secre- 

 tion. The student who is not already informed of the great scope 

 and interest of the subject should be referred to a textbook of gen- 

 eral physiology. 



7 



