EXPERIMENT STATION BULLETINS. 



653 



In other experiments certain beetles were tried in air. Then the 

 same beetles were used again under the influence of the insecticide, 

 with conditions of temperature, moisture, etc., similar to those of the for- 

 mer trials. Moreover, in order to see if the same results would obtain if 

 unrespired air should continually pass through the vessel containing 

 the insects, the apparatus represented in Fig. 3 was used. In this 



Fig. 3. Another arrangement /or finding the CO2 output of insects under the influence of volatile 



insecticides. 



figure, the arrow represents the direction in which air was drawn by 

 means of an aspirating filter pump connected at "h." An alkaline 

 wash-flask for taking carbon dioxide out of the incoming air is shown 

 at "a." Flask "b" contained a Aveak barium hydrate wash, and into 

 '*c" the absorbent cloth with the insecticide was placed when the 

 effect of its vapors upon carbon dioxide excretion was to be studied. 

 Flasks "e," "f," and "g" contained measured amounts of the standard 

 barium hydrate. In these three flasks all the carbon dioxide which 

 came from the respiration chamber ''d" was caught. Care was taken 

 to start the aspirating pump, after connecting up the apparatus and 

 thus free the latter entirely of carbon dioxide before introducing the 

 standard barium hydrate just previous to the experiment. Air was 

 then kept bubbling slowly during the experiment; but a few minutes 

 before the end, a rapid stream of air was started in order that all 

 carbon dioxide might be carried from the respiration chamber. Table 

 III B. gives results of three experiments carried out in this manner, 

 using the same beetle. 



TABLE III B. 

 CO J excreted by a ledle before and after treatment with gasoline vapor. 

 (See apparatus, Fig. 3.) 



