1184 
Journal of Agricultural Research 
Vol. V, No. 25 
checked twice daily by maximum and minimum thermometer and sling- 
psychrometer readings. The means of temperature and humidity are 
based upon these records. In addition to the natural records, a series of 
artificial-cold experiments were conducted at various times, and the 
writer recently conducted an extensive series of artificial-heat experiments 
with definite humidity control in order to determine the effects of heat. 
EXPERIMENTAL METHODS 
Before venturing to present this new interpretation the writer has 
thoroughly discussed it with many prominent workers, and it is now 
proposed for more extensive criticism and elaboration. 
To express the relationship of the two factors, temperature and 
humidity, to insect metabolism, development, and activity, a tempera¬ 
ture scale may be marked off on the vertical line of a sheet of plotting 
paper and a humidity scale from left to right on the horizontal line. 
There are, for any given insect, definite boundaries of atmospheric tempera¬ 
ture and humidity within which the life of the species revolves. There is a 
temperature below which, even for the shortest time, life is impossible— 
the absolute minimum fatal temperature. There is also a temperature 
above which, even for a moment, life is impossible—the absolute maxi¬ 
mum fatal temperature. Absolute dryness is more or less prohibitive 
of life and so is absolute humidity, or saturation, although some insects 
may be adapted better to withstand extremes of humidity than others. 
It is quite possible that the boundaries of humidity may be o and 100 
per cent, or infinitesimally close thereto. 
The diagrammatic figure sought, however, has four definite absolute 
boundaries—the maximum and minimum temperatures and humidities. 
Within the limits which we have thus defined there exist conditions 
under which all the activities of the species reach their maximum effi¬ 
ciency. It has been conceived by most writers that this maximum 
efficiency was reached at a definite point known as the optimum. It 
seems more likely that it will prove to be a zone of humidities and 
temperatures of more or less restricted area. A careful study of the records 
of any species, charting for the time required for each activity and the 
temperature and then similarly for humidity, will disclose temperature 
and humidity points of maximum efficiency. With the boll weevil 
these points lie approximately near 83° F. and 65 per cent of relative 
humidity. 
ZONES OF CLIMATIC RELATIONS 
At any ordinary humidity, starting with the absolute minimum fatal 
temperature, as the temperature increases a longer and longer time of 
exposure is required to kill, until a point is reached at which life con¬ 
tinues indefinitely. This zone of temperatures has been called the 
zone of fatal temperatures. 
