356 INSECT PESTS. 



eat of their employer's good cheer ; and yet it pays to 

 keep horses, and it pays to keep and feed servants: 

 neither could in fact be done without; and so, if we 

 may venture to say it, and to uphold what is rank 

 heresy in the eyes of many farmers, so do the birds 

 pay to keep about one's dwelling and about one's 

 farm. 



That they consume a certain amount of valuable 

 property, like the horses and the workmen, there can 

 be no doubt ; but if they do, the farmer gets value 

 for it in the destruction of injurious insects. For re- 

 member, if we have spoken of pestilences among the 

 animal creation, we have also to record the fact that 

 disease, in other words pestilence, is equally liable to 

 destroy the vegetable productions of the earth; they 

 are afflicted with various forms of " blight" as it is 

 called. These are the pestilences of plant life, which 

 rage even with a higher rate of mortality than the 

 " Black Death" ever did in the purlieus of London, of 

 Florence, or of Constantinople. We need cite but two 

 instances of it: viz., the potato disease (or plague) in 

 Ireland, and the vine disease in France and elsewhere. 



Both are due to parasitic growths the first to a 

 minute fungus known as the " Peronospora Infestans, " 

 and the second to an insect called the " Phylloxera 

 Vastatrix" f But then most, perhaps all of our human 

 maladies, are due to the same set of causes. This has 

 been well pointed out by Budd, and others, in what 

 is known as the " Germ Theory of Disease" and the 

 existence of malignant organisms in modern pathology 

 termed " Microbes. " This of course lands us in a vast 



* Encycl. Brit., 9th Edit., Vol. xix., page 597. 



- Ibid., Vol. xxiv., page 329. 



