104 SANITARY ENTOMOLOGY 



There is a rule which receives much support, that a given reaction 

 or stage of development is accomplished at an almost constant total 

 effective temperature, which is the multiple of time units by temperature 

 units accumulated above the zero of effective temperature. Since the 

 zero varies with the humidity, the total effective temperature obtained 

 by this rule does likewise. We must therefore reword the rule to read: 

 A given reaction or stage of developvient is accomplished at any given 

 mean humidity at a constant total effective temperature, which is the 

 mvltiple of effective time units by temperature u/nits accumulated within 

 the zone of effective temperatures at a given atmospheric pressure. 

 To compute this one* must first eliminate all tim'" temperature, 

 and humidity which was noneffective, whether at the top or bottom of the 

 scale. For instance, if at 60% humidity the temperatures 63° to 85° 

 are effective, and during the day the temperature ranged from 50° to 90°, 

 but only during eight hours at the effective temperatures ; we must 

 multiply the period 8 hours by the mean temperature experienced be- 

 tween 65° and 85°, considering 65 as and 85 as 20. The result is 

 the total effective temperature of that day. Adding these total effective 

 temperatures during the total period of the stage, we obtain the total 

 effective temperature necessary to bring about the perfection of the 

 stage. Necessarily this is a very complicated proposition, requiring 

 very careful computations. Nevertheless, once worked out we can es- 

 tablish laws of control which are of utmost value. 



Some of the following lectures will refer to the principles laid dow^l 

 in this lecture and lines of research will be suggested leading toward 

 control measures. The charts (figs. 8, 9) should be studied in connec- 

 tion with the lecture. 



