230 SPEEDS OF SOME PROCESSES IN BIOLOGICAL SYSTEMS 



exhaled, with the same loss of heat per gram of water. Respiration then be- 

 comes important, especially when the air is dry and/or cold. 

 Urine and feces contribute a small fraction to daily heat loss. 



Heat Loss from the Body Under Various Conditions 



Table 8-1 1 illustrates that the escape valve for excess heat may be any one 

 of the several methods of heat loss and will vary for different activities. The 

 very important role of the skin as a heat insulator and as a water supplier 

 to the surface, and the role of cover and clothing now become clear. 



To sum up: the maintenance of constant body temperature is a very re- 

 markable example of the "steady state." In Chapter 7 we illustrated heat- 

 producing reactions — chemical, physical, mechanical, etc. In this chapter 

 we have discussed the rates of heat-producing reactions and the rate of heat 

 loss. In the steady state there is continuous flow — and the rate of "waste" 

 heat production is exactly balanced by the rate of heat loss, no matter what 

 the ambient conditions. So it is with literally hundreds of processes in the 

 living thing. 



FORMAL SIMILARITY AND INTEGRATION OF THE FIVE PROCESSES 



The method of presentation used in this chapter permits us to summarize 

 in a table the factors upon which the rates of the five processes depend, and 

 to note their similarities and differences. Since each of the processes was dis- 

 cussed individually, no comment on Table 8- r 12 and its extension, Table 

 8-13, will be made now. other than to ask the reader to note that the classi- 

 cal driving force and the role of the activated complex are both stated ex- 

 plicity. The reader should consider these tables to be a memory aide, which, 

 if understood, will give him a powerful grasp of the nature of each of these 

 important processes occurring within the living system. 



In the living thing, these processes are not separate and distinct, isolated 

 from one another. On the contrary, at every spot in the body probably three 

 or more are simultaneously operative. For instance at some point each 

 moment, a chemical reaction, requiring the transport in of reactants and the 

 transport out of products, produces heat which must be removed if the 

 steady state is to be maintained. As is the trend now in engineering kinetics' 9 , 

 the future of biophysical kinetics lies in the study of the integration and con- 

 trol of rates of all the relevant processes proceeding in so orderly a manner 

 within the framework of the steady state. Motivation for the ultimate mas- 

 tery of biophysical kinetics is clear enough: deviations from the steady state 

 are diseases, the most vicious of which today has the popular generic name 

 "cancer." Some aspects of the all-important subject of control are discussed 

 in Chapters 10 and 1 1, following (next) an important chapter on the biologi- 

 cal effects of the ever-increasing ionizing radiation of our environment. 



