Injeclion Preparation of the Tracheal System 
of Insects. 
By 
August Krogh. 
(From the Laboratorj- of Zooiihysiology, Copenliageii Universily.) 
In the course of a series of investigations of the mechanism 
of tracheal respiration I have found it necessary to work out a 
metho’d for injection and isolation of tracheæ. As the method adop- 
ted may possibly be of use also for anatomical purposes I take 
this opportunity of describing it somewhat more in detail than I 
should think it desirable to do in connection with the physiological 
research for which it was primarily intended. 
The principle — which is not new — of the injection method 
is to remove as completely as possible the air contained in the 
tracheæ by exhaustion with a filter pump and to immerse the ani- 
mal in a coloured injection fluid, which is forced in through the 
spiracles by a slowly established air pressure on the fluid. When 
the injection is complete the animal is opened along a suitable 
line and the tissues or as much of them as may be desirable are 
removed by digestion in a suitable fluid which will not attack the 
injected tracheæ. 
Technique. After a number of trials I have found the best 
substance for injection of tracheal systems to be a mixture of paraf¬ 
fin, beeswax, colophonium and turpentine stained as deeply as pos¬ 
sible with alkanna. The substance must be of a lipoid nature, 
because most spiracles are very effectively protected against the 
entrance of water and watery mixtures.-) The substance is pre- 
h These will be published at a later date probably in Zeitschr. fiir allg. 
Physiologie. 
Compare P. Portier: Mécanisme qui s’oppose å la pénétration de l’eau 
dans la syslerne trachéenne. (C. R. Soc. Biol. T. 61, 1909, p. 422). 
