446 



SCIENCE 



[Vol. LV, No. 1426 



summer but the men stated that theii- hands 

 and taees became inflamed and swollen especi- 

 ally if there were any cuts. The eyes were 

 often affected also. Lack of time prevented 

 carrying out any experiments but it seems 

 quite probable that the poisoning could have 

 been traced to the Hydras. The dust was com- 

 posed of dried sediment and organic matter 

 and certainly must have contained a high per- 

 centage of Hydra remains. 



This account has been written to call atten- 

 tion to an economic problem in relation to the 

 fishing industry, which awaits study. There 

 would appear to be at least four points for 

 investigation. 



(1) The amount of interference and in- 

 jury caused to the nets by these great growths. 



(2) The question of the poisoning of the 

 fishermen. 



(3) Do these Hydra destroy young fish to 

 any appreciable extent in open water? Beard- 

 sley in 1902 in Bull. U. S. Fish. Comm., vol. 

 XXII, pp. 157-160, recorded the destruction 

 of trout fry by Hydra in a hatchery at Lead- 

 ville, Colo. 



(4) To what extent do these immense num- 

 bers of Hydra reduce the entomostracan food 

 supply of young fish and of mature fish such 

 as the ciscoes? The latter in Lake Erie feed 

 almost exclusively upon Entomostraca and if 

 the Hydra are as abundant throughout the 

 lake as they are along the fifteen miles of 

 shore as described above they must be very 

 serious competitors of these fish in the matter 

 of food. 



Since the above was written Professor Paul 

 S. Welsh of the University of Michigan has 

 informed me that he has been making a special 

 study of Hydra in the Lakes of Northern 



WiLBEET A. Clemens 

 Depaktment of Biology, 

 Univeksitt of Toronto 



A MOSQUITO ATTRACTANT 



Certain facts regarding the possibility of 

 attracting mosquitoes were disclosed in the 

 course of experiments made in 1919 which may 

 have a bearing on mosquito control. Press of 

 other work has prevented further development 



of this project and the following notes are 

 offered for the consideration of those who may 

 care to give the matter further attention. 



A number of possible attractants were tested. 

 Among these were crude mixtures of the com- 

 ponents of perspiration and of blood which 

 seemed to produce faint, en-atic response from 

 the mosquitoes, but it was found that a degree 

 of warmth somewhat above that of the sur- 

 rounding air was highly and consistently at- 

 tractive to a certain percentage of these in- 

 sects. Thus a joint of stove pipe placed in the 

 woods and warmed somewhat by an alcohol 

 lamp, attracted about as many mosquitoes as 

 were attracted by persons in the vicinity. It 

 must be said, however, that in all of our field 

 tests of this attractant the mosquitoes were 

 scarce. 



In most of the laboratory experiments with 

 heat Ciilex pipiens was the species used and 

 the insects were liberated at will, as bred, into 

 a cage about 20 x 20 x 15 inches square having 

 the top and three sides of cheese-cloth, the 

 bottom of wood, and the fourth side of glass 

 for observation. The source of heat was water 

 in a glass flask which was heated by an alcohol 

 lamp. Air bubbled through this water through 

 tubing by means of a pump in connection with 

 a gas bag and was afterwards delivered to a 

 funnel the open face of which, covered with 

 cheese-cloth, was placed very near but not 

 touching the side wall of the mosquito cage. A 

 thermometer was inserted in this funnel. 



As the temperature rose to a point where it 

 exceeded somewhat that of the suiTounding air 

 a sinister beard-like growth would appear on 

 that part of the cheese-cloth wall of the cage 

 covered by the mouth of the funnel. This was 

 produced by the beaks of the mosquitoes which 

 were pushed through the cloth with great per- 

 sistence as long as the current of warm, moist 

 air was kept within certain limits of tempera- 

 ture. There seemed to be no specific optimum 

 temperature but the maximum response oc- 

 curred between 90 and 110 degrees Tahrenheit 

 which represented temperatures from 15 to 30 

 degrees higher than that of the surrounding 

 air. When the temperature reached 120 de- 

 grees less interest was displayed and at 140 

 degrees the mosquitoes were entirely dispersed. 



