652 THE MICROSCOPE. 



able that only the female insects yield a good colouring 

 matter. 



Of all the secretions peculiar to insects, silJc may well 

 be regarded as the most valuable, since it has become as 

 much an essential to the purposes of mankind as to the 

 economy of its producers. The fluid, before it comes in 

 contact with the air, is viscous and transparent in the young 

 larva, but thick and opaque in the more mature. It is found, 

 by chemical analysis, to be chiefly composed of Bombic 

 acid, a gummy matter, a portion of a substance resembling 

 wax, and a little colouring matter. Silk may be placed in 

 boiling water without undergoing any change ; the strongest 

 acids are required to dissolve it; and it has never yet been 

 imitated artificially. More than 500,000 human beings 

 derive tlieir sole support from the culture and manufacture 

 of silk ; and upwards of 200,000/. sterling may be said to 

 be circulated annually by the Silkworm. Then we have 

 large sums of money changing hands from the labours of 

 the useful little Bee ; tons' weight of honey and wax are 

 yearly consumed ; England pays more than 50,000/. for 

 foreign honey and wax, in addition to her own valuable 

 produce. A great variety of scents, which from their 

 agreeable odours are much used in perfumery, are manu- 

 factured from insects. The Spanish Fly is an indispen- 

 sable article in the treatment of certain forms of disease ; 

 and that invaluable agent. Chloroform, was first made 

 from formic acid ; an acid discovered in the Formic ant, 

 and from which it has derived its name. Then there are 

 (rail-nuts, produced by a small fly, for which a substitute 

 could not be found in dyeing and ink-making. 



" Much more extensive and important than any of the 

 foregoing, but, as less palpable, even more disregarded, are 

 the general uses of insect existence. Disease, engendered 

 of corruption in substances animal and vegetable, would 

 defy all the precautions of man, unless these were aided 

 by scavenger- insects, those myriads of flies and carrion 

 beetles, whose perpetual labours, even in our tempered 

 climate — but infinitely more so in warmer regions — are 

 essentially important to cleanliness and health. 



" A use of this nature, and one performed perhaps to an 

 extent we little think of is the purification of standing 



