500 CYCLES OF ORGANIC AND INORCiANIC SUBSTANCES 



tendency for all cells to release metabolites into the surrounding 

 medium, both in relatively large (e.g., carbon dioxide) and rela- 

 tively small (e.g., thyroxin) quantities, and to the vital roles 

 which we have come to recognize that such processes play in the 

 life of the individual organism. These roles range from the most 

 subtle internal hormonal coordination to the means whereby the 

 gametes are usually brought together. The latter are essentially 

 external, but they initiate processes of development which are 

 governed by series of chemical inductions. In each of these the 

 release of metabolites by a cell or group of cells fundamentally 

 changes the environment and modifies the reactions and develop- 

 ment of neighboring cells, often at some distance in the body. 

 The whole process is, or should be, a coordinated one, in which 

 during evolution all the cells of the body have become adapted to 

 the existence and metabolic processes of their neighbors. Indeed, 

 it is when this coordination in one way or another breaks down 

 that we consider a body to have become diseased, and this is 

 particularly the case when, in tumerous growth, coordination is 

 lost. Then cells, which should have been dependent and fitted into 

 the general scheme, come to show a progressi\'e "independence" 

 of the specific metabolites which they formerly needed and which 

 coordinated them (e.g., Klein and Klein, 1957). Death is the final 

 independence. 



The life of the normally organized "body" therefore shows us, 

 at the one extreme, how the loss of internal chemical dependence 

 leads to chaos and perhaps even death, while at the other those 

 temporarily isolated parts of the body, the gametes, secrete into 

 the external medium and are mutually influenced thereby. 



Nor need one have in mind merely the gametes. In recent years 

 the work of Raper (e.g., 1957) and others has shown how the 

 sexuality of whole thalli of lower plants may be essentially under 

 external "hormonal" control. In two heterothallic species of 

 Achlya for example, no less than "seven distinct difi'usible agents" 

 take part in a chemical progression which is "a series of morpho- 

 genetically integrated stages in which each stage is initiated and 

 quantitatively regulated by the secretion (s) of the last preceding 

 stage" (Raper, 1957, p. 146). Somewhat similar interrelationships 



