THE CANADIAN ENTOMOLOGIST. 397 



I believ'd to proceed from the same Cause that produced 

 Blights, i.e., from Insects; I have therefore, in answer to 

 your Request endeavour'd to recollect what I have from time 

 to time observ'd relating to that Case. 



After five pages of miscellaneous discussion which concludes 

 with the belief "that the most nauseous Vapour of itself will not 

 cause any Distemper that is Epidemical," the letter continues: 



It seems that the Plague proceeds from some other Cause, 

 and that I suppose to be Insects of thatextraordinary smallness 

 that they are not to be discern'd by the naked Eyes; they are 

 so light that they float in the Air, and so are suck'd in with 

 the Breath. Such insects not being among us commonly, 

 but only when they are either brought to us from some remote 

 place by the Wind, or hatch'd or nourish'd by some Intemper- 

 ance of Air or from poisonous Vapours rising from Boggs, 

 Ponds, Ditches or some such unwholesome Funds of stagnating 

 Water. 



These Insects are various, according to the Nature of the 

 Water or Air they are bred in; their Eggs being first laid by 

 some flying Animals, which are then hatch'd, and passing 

 through the several Changes common to Insects, at length 

 take Wing; and being drawn in with the Breath, may perhaps 

 be either kill'd in our Bodies and cause violent Ferment in 

 the Juices, or else finding proper Nourishment, they breed in 

 the Lungs, Stomach, or other parts within us, and probably 

 may occasion those Biles and Breakings out in the tender 

 parts of the Body that are called Plague-sores. 



But these Insects, are some of them so extremely small, 

 that they are only capable of being discern'd with good micro- 

 scopes; and when they are winged, and so quite perfected, 

 may perhaps in Swarms be carried from one Country to 

 another by the Wind : It is Insects of several Kinds and Colours, 

 which causes the Surface of Waters to appear sometimes 

 Green, Red or Black; which last Colour in Water is observ'd 

 by the Herdsmen to poison the Cattle that drink of it; and 



