At all times beech-wood is exposed to the attacks of beetles, and it cannot be used, even for household furniture, without being impregnated with some kind of oil or varnish, as a defence against these insects--a very curious fact, for the growing trees are remarkably free from the attacks of wood-devouring insects. Larch being solid, and its juices hot, pungent, and bitter, is rarely affected with the larvæ of insects. Mr. Westwood, Hope Professor of Zoology, Oxford, says: “The insects which in this country are found to be the most injurious from their habit of burrowing into the wood of furniture, belong to three species of beetles, of small size, and cylindrical in form (the better to enable them to work their way through the burrows in the wood), belonging to the family _Ptinidæ_, and known under the systematic names of _Ptilinus pectinicornis_, _Anobium striatum_, and _Anobium tessellatum_. “In the perfect state, the insects of the genus _Anobium_ are well known under the name of the “deathwatch,” as these insects produce the ticking noise occasionally heard in old houses. It is also the _Anobium striatum_ which is so injurious in libraries; the grub burrowing through entire volumes, and feeding upon the paper, and especially the _pasted_ backs of the books. “The destruction of these insects, when enclosed in articles of furniture, is by no means easy, although with care much mischief might be prevented. The saturation of the wood with some obnoxious fluid previous to its being used up in the manufacture of objects of value would be beneficial. “A strong infusion of colocynth and quassia, spirits of turpentine, expressed juice of green walnuts, and pyroligneous acid, have all been proposed. In hot climates the ravages of the _Anobium_ on books have been prevented by washing their backs with a fluid compound of corrosive sublimate (ten grains) and four ounces of alcohol, and the paste used in the book covers is there also mixed with alcohol.” Sir H. Davy and Professor Faraday hesitated to employ corrosive sublimate as a means of preventing the ravages of the bookworm in Earl Spencer’s library, at Althorp, not feeling certain as to whether the quantity of mercury used would affect the health of the inhabitants. Amongst all the combinations of mercury, perhaps the bi-chloride, or corrosive sublimate, is the most terrible poison. It should be remembered that there are two chlorides of mercury--one the proto-chloride, ordinarily known as calomel; the other, bi-chloride, ordinarily known as corrosive sublimate; the respective compositions of which are as follows: