321 
between 40® and 50®. The injection substance gradually melts 
and the animals sink to the bottom, if they are suitably weighted. 
Otherwise they will usually remain floating. When the substance 
is completely melted the screw clip 
(3) is closed and the filterpump dis- 
connected and stopped. By means 
of the clip (4) connection is estab- 
lished with the washbottle (6) which 
contains a little water. (5) is a 
thermometer tube of the narrowest 
possible bore (0.1 mm or less). 
When the clip (4) is opened slightly 
air should bubble in very slowly 
through the washbottle, and the ani¬ 
mals will sink to the bottom and 
become injected. The most impor- 
tant point in the technique is the 
slow increase of the pressure which 
secures a complete filling of the 
tracheal system. After about half an 
hour the clip can be opened a little 
more, but the injection should never 
be completed in less than an hour. 
When the pressure has risen to the 
normal the bottle is disconnected 
and opened, and the injected ani¬ 
mals are fished out and quickly 
cooled under water. After complete 
cooling the injection substance stick- 
ing to the outsides can be removed 
with ether. 
After the injection the specimens 
can be treated in various ways. The 
insect larvæ, with which I have exclusively dealt, have been 
mounted on slides by means of picein: The slide is cautiously 
heated over a small flame and one side is completely covered with 
a good layer of picein into which the under side of the animal is 
stuck. When the picein has set by cooling I have opened the 
Fig. 2. 
Magnification 1..S. 
/ 
