INFLUENCE OF ENVIRONMENT 259 



albumin and hemoglobin. Under possible attractive agents, he studied 

 pepsin, dextrose (fermented), peptone, ammonium carbonate, ammo- 

 nium carbonate (1 to 1,000), glycerin, sugar solution, valeric acid 

 (strong), valeric acid (weak, one per cent), lactic acid, indol (0.1 per 

 cent sol.), skatol (0.1 per cent sol.), vaseline (blue seal), rancid olive 

 oil, and shark liver oil. Under the head of other agents produced by the 

 human body, he studied breath, temperature, moisture, carbon dioxide, 

 carbon dioxide and moisture, carbon dioxide and temperature, carbon 

 dioxide and ammonia. 



The upshot of these studies may be stated as follows : ". . . combina- 

 tions of carbon dioxide, ammonia, moisture and temperature, such as 

 appear in the human breath are the most attractive materials found." 

 Rudolfs concludes that carbon dioxide and ammonia play the important 

 role in attracting mosquitoes. 



Since the completion of Rudolfs' work the writer has used ammonium 

 carbonate and carbon dioxide in connection with regular mosquito 

 traps and found that while either increases the trap catches, carbon 

 dioxide produces far greater increases than ammonium carbonate. It 

 seems that the evolution of ammonia from the ammonium carbonate 

 reaches concentrations that are repellent. 



In September, 1933, an attempt was made to measure the effect of 

 carbon dioxide as an attractant. Two regular vertical mosquito traps 

 were set up in Dayton, New Jersey, about 150 feet apart. By prelimi- 

 nary operation minor but not consistently different catches were taken 

 in those two traps. A tank of COo was secured and copper pipe run from 

 it to the selected trap. This pipe passed through a coil located just 

 above the frosted bulb, thence through a water bottle, and thence to 

 the peak of the cap of this selected trap. The passage of the gas 

 through the coil above the lamp bulb was designed to heat it and the 

 passage of it through the water was designed to moisten it. As gas 

 bubbled through the water and was delivered just above the peak of 

 the trap it filtered down over the peak and some, but not all of it, was 

 caught by the air stream blowing into the trap and carried with this 

 air stream out through the trap in the direction of the ground. 



Operation of both traps began each day at 7 :00 p.m. and continued 

 until 7 :00 a.m. Delivery of the carbon dioxide through the selected trap 

 began each day at 7 :00 p.m. and ceased at 9 :00 p.m. One trap ran with 

 a twenty-five-watt frosted bulb as the sole attractive agency while the 

 other trap ran with a twenty-five-watt frosted bulb as did the first but 

 in addition for the period from 7 :00 p.m. to 9 :00 p.m. each evening had 

 carbon dioxide gas distributed over its hood. (See Table IX.) 



