THE RHYTHMIC NATURE OF LiFE 



Frank A. Brown, Jr. 

 Northwestern University 



The living organism is never in true physicochemical equilibrium. It 

 maintains a steady state which consists of continuous variations about 

 some specific mean. For the most part our ignorance is great, not only as 

 to the factors which regulate the mean level, but also as to those factors 

 which continuously return the organism to the mean from its repeated 

 fluctuations from it. It is not surprising that in such a system rhythmicities 

 and cycles appear more the rule than the exception. Cycles such as con- 

 tractile vacuole pulsations, spontaneous neuron discharge, and heart beat 

 are well known and their mechanisms are being gradually elucidated by 

 physiologists. These will not be the topic of this discussion. Rather, I shall 

 consider rhythms and cycles of much lower frequencies, those that parallel 

 or are even induced by rhythmic factors of the external environment di- 

 rectly or indirectly related to the changing relations of the sun and moon. 



These are the daily, tidal, monthly, and annual cycles. Rhythms of these 

 frequencies are, as we shall see, concerned in the maintenance of the 

 organism's steady state over days, months, and even generations. Though 

 the dependence of the invertebrate animals on such rhythms appears to be 

 particularly heavy, the evidence now suggests that these animals are simply 

 utilizing a nearly universal vital property. Since our knowledge of the 

 nature of this property is being derived from investigations of a wide 

 variety of animals and plants, I shall feel free to refer often to organisms 

 other than the invertebrates. 



Let us first view the problem in a very general light. Great strides were 

 obviously made in man's never-ending attempts to become the master 

 of his environment when he invented the clock, and perfected a workable 

 calendar. Have you ever pondered what would be the outcome were all 

 clocks and other time-measuring devices suddenly to become nonexistent 

 in our civilization? There would be a complete collapse of most systems 

 of communication and transportation. Our whole complex technological 

 era would virtually disappear overnight. Precise timing enters into the 

 manufacturing processes of innumerable essential materials which have 

 become part of our daily mode of living. Even colleges and universities 

 as we know them could not exist. Without clocks and calendars the proba- 

 bilities are almost nil that I would have arrived here at this time to deliver 

 this address or that anyone would have been in the room waiting to hear 



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