RHYTHMIC NATURE OF ANIMALS AND PLANTS—BROWN 399 
In our laboratory, where the complete temperature independence 
was first demonstrated and its implications stressed, our reaction was 
different from that of the others. It seemed to us that the phenomenon 
was so extraordinary that perhaps still another of the sacred tenets 
of physiology was invalid. This other one was the fundamental 
premise of the experimental physiologist that when he keeps his 
organisms in constant illumination, temperature, humidity, and all 
other factors he has conceded to influence them, the organism is truly 
in constant conditions. So time revered was this view that even to 
question it seemed a sacrilege. And we knew when we did it that the 
opposition of tradition would be tremendous to overcome. 
In a sense the view that we took was simply a more sophisticated 
one of the type taken by the numerous skeptics of a decade or more 
ago, when told of the persistence of rhythms in constant conditions. 
They doubted that the investigator had really controlled all daily 
fluctuating factors as well as he thought he had. 
An experiment we performed with oysters had raised similar doubts 
in our minds, too. The U.S. Fish and Wildlife Service had shipped 
us a batch of healthy oysters they had collected in New Haven Harbor. 
Since the tides are, you recall, of lunar-day frequency, we studied in 
the oysters the time of lunar day of maximum opening of their shells 
for feeding in pans of sea water in a photographic darkroom in 
Evanston. For about the first two weeks they opened their shells 
most at the time of high tide in New Haven Harbor; then they ap- 
peared to forget their home tidal times and for the next two fortnights 
they opened their shells almost at the times of lunar zenith and nadir 
in Evanston, a 3-hour time change. These new times were the times 
of maximum gravitational attraction by the moon as it produces the 
well-known lunar tides of our atmosphere. 
In order to examine further the question as to whether the external 
factors were actually controlled, we sought a biological process which 
was common to every living thing. For this we selected metabolism. 
Metabolism underlies all animal and plant activities and thus we were 
no longer limited to the study of special forms. The rate of metab- 
olism could be measured by the rate at which the living thing used 
oxygen. Also, the higher the rate of metabolism, other factors being 
equal, the greater the amount of spontaneous activity displayed by 
an animal, and hence we could also measure metabolic rate by studying 
spontaneous activity. It did not require a very long initial study 
to demonstrate beyond all reasonable doubt that living things, even 
while in so-called constant conditions, had access to outside infor- 
mation as to the time of day (or position of the sun), time of lunar 
day (or position of the moon), time of lunar month, and even time 
of year. 
536608—60——27 
