374 SISTER MARGARET ANN 



" persistent " rhythms in animals and plants were independent 

 of temperature over wide ranges/' If the rhythms in question 

 were purely chemical reactions, as many physiological processes 

 are, then there should have been proportionate increases and 

 decreases in the rates, for example, of color change, oxygen 

 consumption, and activity in the fiddler crab consequent upon 

 a raising or lowering of the temperature by ten degrees centi- 

 grade. Yet this did not prove to be the case. The rhythms 

 continued unaltered over several successive ten degree increases 

 in temperature. In addition to this, still another finding con- 

 tradicted the concept of purely chemical reactions as the sole 

 explanation of observed periodicities, namely, the fact that 

 these rhythms appeared to be immune to the action of drugs 

 and poisons knowTi to interfere with many different physi- 

 ological reactions, especially those involving enzyme activity. 

 The mechanisms responsible for the rhythms, it would seem, 

 must be regarded as something decidedly more than purely 

 chemical reactions. 



A second unassimilable finding seemed to contradict the 

 assumption of genuinely " controlled " conditions. Many inves- 

 tigators w^ere led to postulate inherent, independent " clocks " 

 in organisms because the rhythms continued in their periodicity 

 under what were considered to be constantly controlled con- 

 ditions of temperature, light, atmospheric pressure and other 

 environmental factors. They accepted this explanation in spite 

 of the fact that there were experimenters through the years 

 who reported data that contradicted the idea of inherent, inde- 

 pendent " clocks." Examples of such data, quoted by Dr. 

 Brown, are the work of Stoppel in a basement in Iceland, 

 Cremer in a deep salt mine in Germany and the two Hempels 

 in Lapland. These experimenters showed that under very 

 constant conditions of this kind the regular observed rhythms 

 were in fact interfered with during the time of the mid-night 



^" Frank A. Brown, Jr., H. Marguerite Webb, Miriam F. Bennett and Muriel I. 

 Sandeen, " Temperature-Independence of the Frequency of the Endogenous Tidal 

 Rhythm of Vca" Physiol. ZooL, XXVII (1954), 345-9. 



