320 
pared as follows: Alkanna root is digested with turpentine for at 
least a week and preferably at a high temperature (30^). The ex- 
tract is filtered oif and so much paraffin (melting point about 50®) 
and beeswax (about equal parts) are dissolved in it that the mel¬ 
ting point is suitably raised. A little colophonium is added to di- 
minish the brittleness of the mixture. 
I have found a melting point about 40® suitable for my pur¬ 
poses. A mixture with a lower melting point will penetrate more 
easily, and if it is desired for instance to inject a cockchafer larva 
Fig. 1. 
through the intact spiracles, coloured turpentine is the only fluid 
which can be used. 
The injection mixture is kept in a wide-necked bottle of about 
250 cc capacity (1, fig. 1) with a ground, tubulated stopper which 
can be connected with a filter pump and evacuated. The animal 
to be injected must be living. It is deeply nårcotized with ether, 
which secures immobility and usually renders ineffective the me- 
canism for closing the tracheæ. In certain cases — e. g. Dytiscus 
larvæ — the narcosis is insufficient to procure access to .the tra- 
cheal system, and it becomes necessary to introduce hairs through 
the spiracles to keep them open. It will often be useful to weight 
the animals with lead wire or soft copper wire. They are there- 
upon put into the bottle containing the injection mixture, the stop¬ 
per is greased so that it becomes absolutely airtight, and the bottle 
is connected with a good filter pump and evacuated. After a few 
minutes the bottle is placed in a waterbath (2) at a temperature 
