W. R Cooper and W. H. Nuttall 279 



fre([iientlY so badly scalded that death ensued. By employing an 

 emulsified oil in conjunction with the sodium arsenite and so ensuring 

 complete wetting of the hide, Cooper found that a much lower per- 

 centage of arsenite was sufficient to destroy the ticks and that the risk 

 of scalding was practically removed. The scorching of sprayed trees 

 is not an uncommon occurrence, and it is most probable that the means 

 adopted for the prevention of the scalding of animals would also prove 

 effective in preventing injury to foliage. 



With solid insecticides or fungicides, such as copper carbonate, lead 

 chromate, lead arsenate, etc., which are usually applied, as aqueous 

 suspensions, in the form of a spray, the physical condition of the solid 

 plays a by no means unimportant part in the efficiency of the pre- 

 paration. According to the manner of precipitation, these compounds 

 may be obtained in either a coarse granular state, or as a fine light 

 flocculent precipitate. In the first case, the suspension settles rapidly 

 and requires constant attention in the matter of stirring ; further, it 

 is liable to clog the nozzles of the spray-pump and, in addition, after 

 drying, is apt to fall from the sprayed leaves. On the other hand, a 

 fine, flocculent precipitate has none of these disadvantages. 



These examples will serve to show how very greatly the efficiency 

 of an insecticide or fungicide is dependent upon conditions other than 

 chemical ; they indicate that, as with disinfectants, a chemical assay 

 alone must give a wrong impression of the actual value ; and these are 

 facts which must not be lost sight of in the consideration of the standard- 

 isation of insecticides. 



As a matter of fact, we are only just entering upon the scientific 

 study of the preparation and application of insecticides. That our 

 methods have been too empirical in the past is largely due to the lack 

 of co-operation between the economic entomologist and the chemist; 

 neither can hope to achieve real success alone. It is for the entomo- 

 logist to investigate the various pests, their life history, habits and 

 vulnerability; it is for the chemist to devise and elaborate means of 

 attack, based upon the information supplied by the entomologist and 

 upon the chemical and physical properties of the substances with 

 which he has to deal. 



