16 
CURT P. RICHTER 
work directly after eating. Sayings of this nature are fre¬ 
quently apt to be colored by fictions and superstitions, but this 
one seems to be based on fact. If the same curve holds for man 
that holds for the rat it would then seem advisable for man when 
he has work to do, to do it during the period of maximum spon¬ 
taneous activity, that is when the body cooperates, rather than 
during the period of natural inactivity when the body does not 
cooperate. 
III. RELATION OF SPONTANEOUS ACTIVITY TO EXTERNAL TEM¬ 
PERATURE 
Temperature and illumination are factors which are present 
in the environment of all organisms at all times and which can 
never be eliminated. They are vital factors. They are present 
in all situations from the simplest to the most complex, so that a 
thorough knowledge of their relation to activity is of prime im¬ 
portance for the solution of any kind of behavior problems. 
The difficulties of studying the relation of behavior to external 
temperature in animals are many. A rather highly specialized 
equipment and technique for obtaining and controlling tem¬ 
peratures at all levels are absolutely essential. Without them 
conclusive results are obtained only with the greatest difficulty. 
In the present work many different temperature experiments were 
tried, but with the exception of one or two all of them failed to 
give satisfactory results. 
The following experiments deal only with the modifications 
of the normal activity distribution curve, described in the pre¬ 
vious chapter, with relation to external temperatures. The 
conditions of these experiments were essentially the same as for 
the others. The experiments were carried out over long periods 
of constant illumination and constant complete darkness. 
Higher temperatures than the normal 23°C. were obtained by 
means of two electric heaters, while temperatures lower than 
normal were obtained from natural sources during the cold 
months of winter. 
The results of these experiments showed that the characteristic 
shape of the activity distribution curve is very definitely affected 
