156 BOARD OF AGRICULTURE. [Pub. Doc. 



acted in a very sluggish way, and a large portion of them 

 eventually disappeared without development to maturity. 

 What the future is to bring about in regard to them is as yet 

 an unsolved problem, and what precautions should be taken 

 I am at a loss to know, on account of the want of a full 

 knowledge of their habits. 



I come now to the subject of insecticides, by means of 

 which we are enabled to exterminate, suppress or minimize 

 the insects and their injuries. For this purpose the various 

 insects may be divided into two classes, known as leaf-eaters 

 and sap-suckers. Their habits arc so different that an agent 

 that would be fatal to one is of no value in the case of the 

 other. For the class of leaf-eaters, nothing has been brought 

 forward equal in value to arsenic in some form. If this 

 substance is spread upon the leaves, the insect in consuming 

 them is obliged to take the poison, and is thus destroyed. 

 The result of multiplied experiments in the past few years 

 has developed the fact that for this purpose the arsenic must 

 not be in a soluble condition. If it is, it cannot be applied 

 in sufficient strength to kill the insect without seriously 

 injuring the foliage. This rules out arseuious acid, which 

 is the common white arsenic, as it is entirely soluble in water. 

 London purple, which is a compound of arsenic and lime, is 

 to a considerable extent soluble and open to the same 

 objection in a less degree only than the white arsenic. We 

 are therefore obliged to fall back upon Paris green, which 

 is a compound of arsenic and copper. This is in the form 

 of an exceedingly fine precipitate, and is entirely insoluble 

 in water. It is a very heavy substance, which settles at 

 the bottom of the liquid in a brief time, and requires almost 

 constant agitation to keep it in suspension while being used. 

 This mixture is applied by means of something that will 

 deliver it in a very fine spray, so as to wet the entire foliage, 

 each liny droplet of water holding in suspension one or more 

 particles of the poisonous arsenite. The water at once 

 evaporates, and leaves the poison upon the surface of the 

 loaf, where it remains some days unless washed ofFby rain. 



It is of course entirely inappropriate to make use of this 

 agent before the foliage Itegins to develop, as at that time 

 no insect will be affected by it. It might be supposed that 



