488 Entomological Methods 
For killing, cyanide is perhaps most generally useful: benzene is 
apt to make the tubes sticky, and chloroform tends to stiffen insects 
killed with it, but either is useful in damp seasons when the delique¬ 
scence of cyanide may become a nuisance. It is much better to use 
several fairly small tubes than one large and heavy killing-bottle. 
The diagram (Fig. 2) gives a suggestion for a tube which could be 
used with any killing-agent and be easily re-charged. If cyanide and 
Fig. 2. The cartridge is seen below separated from the main tube by two layers of gauze 
seccotined on to a ring of cork. 
plaster of Paris is to be employed, a piece of tube of similar bore is 
used as a mould in which a cyanide “ cartridge ” can be cast, the tube 
being lined with paper, and the cartridge when set pushed out of the 
tube and inserted in the killing-tube. Small lumps of cyanide wrapped 
in soft paper may be used instead, or cotton-wool wetted with benzene 
or chloroform. Rubber corks are attacked by the two latter substances, 
but not by cyanide. When insects have been killed in rainy seasons it 
is better to put them with some pieces of soft paper into pill-boxes 
rather than into glass tubes, as they run less risk of getting wet and 
spoilt. A number of living insects in a tube with paper will often keep 
