FOES. 2 7 



perfectly air-tight and if not so, the spores can certainly 

 enter we must try to keep our cases in such a spot 

 that the spores will* not be able to find sufficient 

 moisture to allow them to germinate, and very little 

 moisture is required for such a tiny fungoid growth. 



Many prefer to take the bull by the horns and poison 

 their specimens, which will then be perfectly safe against 

 attacks of either mould or mites. The poison used is 

 mercuric chloride (HgCl.,), commonly called corrosive 

 sublimate, which must be dissolved in spirits of wine 

 (or methylated spirit). A given amount of spirit will only 

 dissolve a certain quantity of the chloride ; if too much 

 is put in, some will remain undissolved at the bottom 

 of the bottle. More spirit must then be added, for a 

 moderately weak solution of mercuric chloride will be 

 sufficient for our purpose. Let the butterflies be steeped 

 in this and then dried in a current of air. The colours, 

 which at first disappear, will return as bright as before, 

 and the specimens will be impregnated with the poison, 

 and may be placed with mites or mould without any 

 fear. There are two drawbacks, however, to its use 

 the hairs and scales are not always as velvety in appear- 

 ance as before its application, and then, corrosive subli- 

 mate is as deadly a poison to men as to mites and 

 mould. Specimens affected with mould should be 

 placed in benzine, and when dried the mould should be 

 rubbed off with a camel-hair brush. 



Fortunately, unlike moths, butterflies are seldom affected 

 with grease ; if any are, they will probably be the Vanessas. 

 Should a specimen that cannot be destroyed, be so affected, 

 probably the best thing to do is to steep it in benzine 

 collas, and, when the superfluous liquid has been taken 

 off with blotting-paper, to sprinkle over it fuller's-earth, 

 magnesia, or French chalk. After leaving it for some 



