396 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1959 
By the same token, living things seem also to possess a basic timing 
mechanism indicating the lengths of lunar periods, or a “lunar clock.” 
And since a number of living things are known also in constant condi- 
tions to measure periods of annual length, they appear also to have 
“annual clocks.” These last two kinds of “clocks” we treat in our 
annual calendars with their monthly divisions. Therefore, living 
things behave as if they possessed both “clocks” and “calendars” by 
means of which many vital processes are appropriately timed even 
in the absence of such well-known daily, monthly, and annual changes 
as those of illumination and temperature. 
The characteristics of the rhythmicity in living things of the kind 
that have just been described led many investigators of the phenom- 
enon many years ago to the conclusion that living things possess within 
themselves clock mechanisms that would permit them, when isolated 
from all environmental changes which were conceded to be able to 
influence them, to measure off accurately periods closely corresponding 
to the lengths of the solar day, and other natural periods. In other 
words, there was postulated to be operating in living things a com- 
pletely independent complex of rhythms which paralleled in their 
natural periods the complex known for the external physical environ- 
ment. This view was entertained despite the fact that certain skeptics 
of this view had demonstrated over the years that there were circum- 
stances in which the rhythms of living things could not be shown 
in constant conditions. Stoppel could not observe them in a basement 
in Iceland during the time of the midnight sun; Cremer could not 
find them in a deep salt mine in Germany, nor Hempel and Hempel 
in Lapland during the time of the midnight sun. The investigators 
who discovered these very interesting exceptions claimed or implied 
that the rhythm in the bean seedling or insects which they used 
depended upon rhythmic changes in the environment which still, in 
some manner, pervade all ordinary so-called laboratory constant con- 
ditions. Under these special circumstances, the rhythmic external 
factor was postulated to be not present. 
But biologists, like other scientists, are human and often not always 
quite as fully objective as is commonly believed. It was for them 
easier to rationalize objections to the way an experiment was con- 
ducted, or to claim correctly that no one had yet confirmed the experi- 
ment, than to abandon a hypothesis which, except for these little 
disrupting facts, provided a consistent view. 
At any event, all the evidence at hand seems to suggest the posses- 
sion by living things of a rhythmic phenomenon superficially resem- 
bling a recording system with about one complete circuit per day. 
This system appears capable of having any form of behavior pattern 
impressed upon it, whereafter it keeps repeating this pattern until 
either it fades away or some new pattern is made to replace it. 
