W. F. Cooper and W. A. B. Walling 167 



into the choice of a form which was convenient to handle, and obtain- 

 able in quantity through the greater part of the year. Muscid larvae 

 conform to these conditions, and as insecticidal methods of dealing 

 with these, particularly in connection with the maggot-fly pest of 

 sheep, and the dissemination of disease by house-flies, have been the 

 subjects of much attention in recent years, one or other of these appeared 

 to be eminently suitable. 



The problem of the Maggot-fly pest is one which specially appeals 

 to us, and, as the subject of the relation of the House-fly to the trans- 

 mission of disease has been adequately dealt with by others, it was 

 decided to use the larval form of one of our English Maggot-flies as a 

 subject for experiment. The larva of Calliphora vomitoria, the common 

 Blue-bottle, is readily obtainable at all times from dealers in anglers' 

 requisites and consequently was selected as the most convenient species. 



We realise that the most satisfactory manner of attacking the 

 Maggot-fly problem would be in the nature of field experiments on the 

 actual species, but the preliminary sorting out of likely chemicals is 

 carried out most conveniently in the laboratory, so that it is only 

 necessary to experiment with a small selection when the opportunity 

 for field experiments presents itself. 



The most obvious means of protecting sheep against the ravages of 

 the Blow-fly are (a) the application to the fleece of some substance 

 repellent or distasteful to the flies ; Lavender Oil has been recommended 

 in this category : (b) the application to the fleece of some compound 

 actually poisonous to the Blow-fly or its larva. Our experiments fall, 

 therefore, under these two main divisions. 



As is usual in this class of investigation, very variable and contra- 

 dictory results have been encountered. These are due to unknown or 

 uncontrollable conditions, and such sources of error can only be eliminated 

 by repetition of the experiment under slightly varying conditions. 



The appearance of a Chalcid fly, which attacked the larvae in our 

 later experiments, and, it is to be feared, seriously vitiated the results, 

 unfortunately prevented us from confirming many of the results 

 obtained, and this must be our excuse for publishing results obviously 

 incomplete, and, in many respects, unsatisfactory. It is hoped, never- 

 theless, that the results obtained will serve as some guide to further 

 work, especially in the direction of field experiments. 



The actual manner in which the Blow-fly larva is killed by an 

 insecticide, whether by absorption through the skin, ingestion, by 

 suffocation due to the blocking of the spiracles, or by some other means, 



