636 R. M. STRONG 
bottles were mounted in dishes which contained wax in order to 
prevent them from being upset. The glass tubing used was of 
uniform diameter, and the ends which projected inside the cham- 
bers were carefully rounded so that they might present no dis- 
cernible differences In appearance. This tubing had an inside 
Text fig. D; Air pressure apparatus (not designed by the writer); ¢’, upper tank; 
t’’, lower tank; r. t., rabber tube which connected the tanks; s. c., stop cock. 
diameter of about 5.6mm. One only of the small bottles was used 
to contain the odorous material, and it was disconnected after 
each set of experiments to be put away until the next series of 
experiments were begun. Food (a mixture of canary seed, mil- 
let, and wheat with a small admixture of ground charcoal and 
oyster shells) was placed for each series of four experiments in 
