Jan. 2, 1920.] Agricultural Gazette of N.S.W. 13 



The Utility of Poison Gases for Pest 



Extermination/ 



In connection with the general iinpression that rabbits and other vermin 

 might easily be exterminated by the use of gas, it may be pointed out, in the 

 first place, that though in the last two years of the war at least twenty — 

 anl usually twice that number — of gas attacks were made per month against 

 the Germans, and that though thousands of gas shells were fired, the enemy's 

 troops were not exterminated by it. So many factors that tend to neutralise 

 the eflfects of the gas come into play that enormous quantities of it are 

 required to produce the designed effects. 



The first consideration in the use of lethal gas in large quantities is the 

 consideration (a) of the operator's life, and (b) of human, animal, and plant 

 life in the vicinity. The protection of the former is simple, and consists of 

 the respirator ; as to the latter, much care and ingenuity is required. Trees 

 and shrubs do not suffer very much, unless the concentration is very great ; 

 but crops and grass are affected. The grass turns yellow quickly, though 

 only the part above ground is destroyeil, unless the concentration is very 

 great, and then the whole plant dies. Light concentrations blowing once or 

 twice across a field of French beans, for instance, ruins the plants, though 

 they may struggle along for some time. In France, when firing gas shell 

 when the wind was blowing toward us, the artillery instruction was to the 

 effect that the range should not be less than 1,000 to 2,000 yards beyond our 

 front line, the distance depending on the gas used. In some of the cloud gas 

 attacks men were killed at distances varying fi-om 3 to -5 kilometres (about 

 2 to 3 miles) from the point of emission of the gas, and casualties were caused 

 at distances up to 9 kilometres. With a small projection of gas, however — say, 

 200 projectiles, each containing 30 lb. of gas — there would be very little danger 

 to persons -5 kilometres down-wind, especially if they were notified of the 

 danger. 



If gas were projected against flying foxes, it would have to be taken into 

 account that a great many wild animals in the area would suffer, and especi- 

 ally those living in the low scrub or on the ground. The gases used are 

 heavy, and, unless a fair wind is blowing, they keep low down and run to the 

 lower ground and into trenches much as water would. 



Character of the Different Gases. 



The second consideration would be the kind of gas to be used. If it were 

 to be used in cloud form, the number available would be practically limited 

 to two — chlorine and phosgene. The most deadly cloud gas used in the war 



* Cominled from particulars kindly supplied by Major H. W. Wilson, O.B.E., M.C., 

 lately Chemical Adviser .5th Army, and Corps Gas Officer, A.I.F., in reply to an inquiry 

 from the Under Secretary and Director of Agriculture as to the possibility of poison 

 gases being useful for the extermination (in particular] of rabbits and flying foxes. 



