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THE MONTHLY BULLETIN. 



A STUDY OF FUMIGATION METHODS FOR KILLING GROUND 



SQUIRRELS. 



By JOHN S. BURD and G. R. STEWART. 



INTRODUCTION. 



In the problem suggested by the title, two general methods may be 

 used: (1) Applying a given method in squirrel-infested areas and 

 observing its apparent effects in decreasing the number of animals; 

 (2) Working with individual animals to determine their susceptibility 

 to the fumigant, the time necessary to kill, and other conditions neces- 

 sary to bring about the desired result. The first method will not furnish 

 a very exact determination of the percentage of squirrels killed; how- 

 ever, it does meet a very practical condition, namely, that it complies 

 with conditions actually existing in the field. So many statistical 

 studies concerning the general effect of fumigants have been made by 

 the first method that it was felt that the best procedure was to follow 

 the second method, and it may be of interest to readers of this pub- 

 lication to learn of the results obtained in the application of such a 

 method. 



VALUE OF CARBON DISULPHID AS A FUMIGANT. 



Because of the well-known practical value of carbon disulphid as a 

 fumigant, we have devoted considerable attention to a study of its 

 effect on squirrels, both in the exploded and unexploded condition. 

 We have found that 2 per cent of carbon disulphid in air kills a normal 

 animal in somewhat less than 20 minutes, and that a greater strength 

 does not seem to be proportionately more effective. This means that 

 if the animal can be kept in contact with the 2 per cent gas for 20 min- 

 utes, death may be expected. If it is practicable to bring the animal 

 in contact with the gas at all, the maintenance of this strength for 

 20 minutes is quite feasible. A strength of 1 per cent carbon disulphid 

 does not normally kill animals in less than one hour. During the course 

 of an hour it is to be expected that there is much greater opportunity 

 for the gas to escape, so we have no hesitation in stating that a much 

 higher efficiency will unquestionably be obtained if 2 per cent gas is 

 used for 20 minutes, than if attempts are made to use a 1 per cent gas 

 and hold it for a longer period. All of these statements apply to 

 unexploded gas both in closed containers and artificial burrows. 



We have obtained practically the same results with the exploded 

 carbon disulphid when the animals were kept in closed containers. The 

 reason why the exploded gas acts the same as the unexploded gas is 

 clear from a chemical study made by us. When the carbon disulphid 

 is exploded there is formed a comparatively large volume of sulphur 

 dioxid which is less poisonous than is the original carbon disulphid. 

 On the other hand, a small proportion of carbon monoxid is also formed 

 when carbon disulphid is exploded. Carbon monoxid is highly toxic, 

 and apparently it is sufficiently toxic to compensate for' the fact that 

 some of the carbon disulphid is changed to sulphur dioxid. 



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