638 R. M. STRONG 
in place of the odor containing bottle. When a relatively strong 
solution of ammonia was used, all of the htmus paper strips turned 
blue in the course of a few minutes, those in the corners changing 
last. When solutions produced a diffusion of ammonia gas which 
seemed to be at all comparable in strength with the odor of oil 
of bergamot, so far as such a comparison could be made, a semi- 
circular area of diffusion was indicated by the litmus paper. 
The radu of this area converged at the entrance of that chamber 
where the ammonia gas emerged, and its front extended out to 
the region of the exhaust funnel. The writer stretched himself 
on the floor inside the enclosure and attempted tests of the odor 
diffusion with his own olfactory organs. Musk and violet sachet 
powder were smelled with difficulty and only at the entrance 
where these odors were emerging. The odor of oil of bergamot 
was detected as far as eighteen inches from the point of emergence. 
The odor was not strong beyond a foot or less from the entrance 
of the chamber from which the odor was emerging. 
Of course these experiments afford only indirect evidence con- 
cerning the size and form of the area in which the odor might be 
expected to be effective. However, the behavior of the birds 
and of some rats in the enclosure, when considered in connection 
with the tests mentioned above, have convinced me that the odor 
localization was sufficient to enable an animal which would be 
capable of odor discrimination to determine the compartment 
from which the odor emerged in the experiments. White rats 
appeared to have no difficulty in locating the source of the odor. 
Choice of subjects. It was obviously necessary in using such 
apparatus that only tame and tractable birds be employed. 
Of various species which were considered, ring-doves seemed to 
be most suitable. The writer had on hand a number of hybrids 
between the white and blonde ring-doves Turtur alba and T. 
risorius which were unusually tame; four vigorous males were 
chosen. Unfortunately, the habits of ring-doves do not suggest 
that they have any use for a sense of smell. Their food consists 
mostly of seeds which have practically no odor for the human 
olfactory sense. Nevertheless, their great docility, convenient 
size, and adaptiveness to cage life made them preferable, in the 
