256 THE SCHOOL OP REAUMUR 



Malpighi had found this a troublesome operation, but 

 Rdaumur discovered that soaking the caterpillar in 

 alcohol coagulates the fluid silk, and makes it so firm 

 that the glands can be removed entire. E^aumur dis- 

 courses upon the physical properties of silk with great 

 animation, for here his technical knowledge of glues, 

 resins, and varnishes furnished him with many useful 

 notions. Silk, he says, is remarkable for three properties ; 

 it sets instantly when exposed to the air ; when once it 

 has set, it is not softened by water or any other natural 

 solvent ; lastly, it is not softened by heat. It is easy 

 to see how the value of silk, not only to the insect, 

 but to ourselves, is enhanced by these peculiarities. 

 Edaumur in his easy conversational way slips from one 

 topic to another, and gives many bits of curious informa- 

 tion that one does not look for in a chapter on cater- 

 pillars. Here is a single specimen. Many rocks, he 

 says, are soft when first exposed, and only harden as 

 they dry. When they have once become thoroughly 

 dry, water does not easily penetrate them again. Fresh- 

 wrought slates can be split into thin laminae, but when 

 the water has been allowed to escape they no longer 

 split with the same facility. A little later he treats us 

 to an entertaining discussion on the possibility of 

 manufacturing thin sheets, not composed of threads, 

 but with a perfectly smooth and bright surface, fit to 

 take paint or gilding. Some of the packets made out 

 of sheets of gelatine to hold sweetmeats perfectly realise 

 E^aumur's notion. 



He gives an interesting account of the alimentary 

 canal, the heart, and the air-tubes of a caterpillar. 

 Here he owes much to Malpighi, though he has looked 

 into everything for himself. He thinks that air enters 

 into the body of an insect by the spiracles, but does not 



