398 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1959 
There are also many powerful drugs and poisons which are known 
to slow down living processes greatly. One of these is cyanide. None 
of these ordinary depressing drugs, though the doses may be so great 
as barely to permit the organism to survive following their removal, 
will in any manner slow down the rhythms. These extraordinary 
relative immunities of the rhythms of plants and animals to tempera- 
ture and drugs certainly begin to strain one’s confidence that they are 
wholly inside the living things. And what sort of autonomous series 
of reactions could possibly be imagined in which the organism, with 
all its transformations occurring during that year, could possibly 
provide information as to just when one year had elapsed, even when 
not harrassed by drugs or freezing temperatures? Even a comparably 
resistant 24-hour cyclic mechanism is virtually impossible to conceive 
in any conventional terms of chemistry or biology. 
And philosophically it is very difficult to imagine the living organ- 
ism as possessing an internal clock, wholly independent of all external 
factors, of the remarkable absolute precision it must have to account 
for the rhythmicities. On the other hand, if the organism had, even 
while in the so-called “constant conditions,” daily, lunar, and annual 
rhythms being impressed upon it by external physical factors, these 
might constitute the fundamental clock system which could pace, or 
provide reference rhythms, for the labile biological rhythms possess- 
ing approximately the same frequencies. Some biologists, forgetting 
that they first made the quite arbitrary assumption that the biological 
rhythmic processes and the clocks which time them are one and the 
same thing, claim as already proven that the clocks need no external 
information through the demonstration that the rhythms are freely 
modifiable and often have periods other than the natural ones. It 
might be recalled, however, that using our ordinary pocket or wrist 
watches, set to the correct time of day and running at their usual speed, 
we can readily change the pattern of a precise daily behavior pattern, 
or time accurately a 22- or a 26-hour rhythmically recurring event, 
both of which capacities we would probably lose forthwith were our 
watches suddenly to be taken from us. 
The temperature independence of the frequencies of the organismic 
rhythms was a very difficult fact for physiologists to credit, especially 
since the general consensus was that the timing of the cycles was exclu- 
sively inside the organisms. This was an apparent evasion of a time- 
honored rule of physiology. But this spectacular fact became demon- 
strated unequivocally so easily and in so many laboratories that it was 
necessary that the problem be faced. The reaction of most investiga- 
tors was to begin to postulate various kinds of hypothetical mecha- 
nisms by which organisms might have internal clocks that would per- 
haps do this. A few such speculations have been advanced in the 
literature of the past two years. 
