276 BOARD OF AGRICULTURE. [Pub. Doc. 



were to be enclosed in a glass case, where it would be sup- 

 plied with abundance of sunlight, with filtered water and 

 sterilized air and soil deprived of all pathogenic germs or 

 eggs of noxious insects, no canker worm or caterpillar or 

 gypsy moth or any other pest could possibly molest it, and 

 its leaves and flowers and fruit would mature and ripen in 

 fairness and beauty. This is the principle of isolation. 



There is also a great similarity in the methods of spread 

 of infectious diseases and of insect pests ; and, while there 

 is a similarity in the general group of infectious diseases to 

 that of insect pests, there are also many points of specific 

 diflTerence. 



Influenza, for example, spreads with amazing rapidity, 

 and attacks great tracts of country in a few hours" time. It 

 appeared in Boston about Dec. 19, 1889, and in less than a 

 week had also appeared in nearly every city of the northern 

 States. One class of diseases, cholera and typhoid fever, 

 spreads through the medium of water supplies ; another 

 class, including small-pox and scarlet fever, by means of 

 the air and by actual contact. The spread of consumption 

 is favored l)y the presence of dust difiused through the air 

 of rooms and carrying with it the germs of disease. 



So, too, in agriculture, the various insect pests differ in 

 the method of their spread. The female canker worm 

 ascends the trunks of trees in the warm days of late autumn 

 or early spring, and lays her eggs on the twigs, to be 

 hatched in the months of May or June. Hence the mode 

 of prevention is to place a barrier upon the trunks of the 

 trees, which shall hinder the insects from gaining access to 

 the branches. So with the American tent caterpillar. This 

 insect lays its eggs upon the small outer twigs of the trees, 

 in bunches of several hundred eggs in each, carefully var- 

 nishing the bunches to protect them from the weather. 

 Destruction of these bunches or belts of eggs, or of the 

 young caterpillars as soon as they are hatched, is the only 

 practical mode of dealing with them. 



Again, the same substances which destroy noxious insects 

 are also used in medicine as disinfectants, and the careful 

 study of their action will advance the cause of agriculture. 

 The farmer who carefully applies the right form of insecti- 



