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insecticide as it is called, is applied evenly over the surface in the 

 form of a fine spray or powder by various machines made ex- 

 pressly for the purpose. The arsenical poisons are the common 

 remedy for the biting insects and among the various compounds, 

 Paris green has been the standard one. Paris green is usually 

 applied in milk of lime. The lime in the mixture has the prop- 

 erty of ofi'-setting the burning qualities of the Paris green. In 

 low grade Paris green there is a large excess of free or water 

 soluble arsenious oxid which wall have a direct injurious effect on 

 the foliage of the plant and give it the appearance of having 

 been burned. The Paris green to be harmless to tne plant should 

 be practically insoluble in water. The finely divided crystals are 

 only in suspension in the spraying mixture and for this reason, 

 constant agitation of the liquid is necessary during the process 

 of spraying. These crystals, though insoluble in water, are 

 soluble in the digestive juices of the intestines of the insect and 

 thus death is brought about by an absorption of the poison 

 One of the more recent arsenical poisons is seemingly better 

 suited to the Hawaiian conditions than Paris green. This com- 

 pound is an arsenate of lead. Paris green, as has been said, is 

 quite likely to burn the foliage, especially if it is of low grade 

 or is not used with lime ; it is easily washed away by showers 

 and being not easily seen when used alone, is difficult to apply 

 evenly over the surface of the plant. On the other hand, the 

 arsenate of lead is entirely insoluble in water, thus obviating any 

 danger of burning the foliage, it is white in color, thus insuring 

 an even coating over the plant, and is quite adhesive, not being 

 easily washed away by showers. These properties of the arsenate 

 of lead in the freshly prepared wet form make it preferable to the 

 less adhesive though more acttive Paris green. The arsenate of 

 lead is now^ on the market in paste form, ready for immediate 

 use. Such preparations are for sale in Honolulu. 



Insecticides for siickincr insects (gases, contact poisons and ex- 

 ternal irritants) : Since those insects feeding upon the juices and 

 sap of plants do not swallow portions of the plant itself but gain 

 their food by inserting the beak or proboscis through the epidermal 

 layers into the tissues, it is to be seen that they would not be af- 

 fected by a poison placed on the surface. Therefore in fighting 

 the insects belonging to this second class, other methods must be 

 employed. The methods are to kill the pests by applying to their 

 bodies an external irritant or contact poison, and by submitting 



