Ill 



contain a caustic and venomous liquid; when 

 we recollect, tbat several species of the culex\ 

 are 1*8 line long from the head to the ex- 

 tremity of the corselet (without reckoning the 

 legs) ; lastly, when we consider, that in this 

 swarm of moschettoes and gnats, diffused in the 

 atmosphere like smoke, there is a great num- 

 ber of dead insects, raised by the force of the 

 ascending current, or by that of the lateral cur- 

 rents, which are caused by the unequal heating 

 of the soil ; we are led to inquire, whether the 

 presence of so many animal substances in the 

 air must not occasion particular miasmata. I 

 think, that these substances act on the atmo- 

 sphere differently from sand and dust ; but it will 

 be prudent, to affirm nothing on this subject. 

 Chemistry has not yet unveiled any of the nu- 

 merous mysteries of the insalubrity of the air; it 

 has only taught us, that we are ignorant of many 

 things, with which fifteen years ago we believed 

 we were acquainted, thanks to the ingenious 

 dreams of ancient eudiometry. 



What is less uncertain, and in some sort con- 

 firmed by daily experience, is, that at the Oroo- 

 noko, Cassiquiare, Rio Caura, and wherever the 

 air is very unhealthy, the sting of the moschet- 

 toes augments the disposition of the organs to 



+ For instance, the species which I have named cuiex cya- 

 nopterus. 



