188 
PSYCHOLOGY: D. MACKENZIE Proc. N. A. S. 
contain uracil. At least we found no evidence of its presence in the prod- 
uct which we investigated. We have succeeded, however, in isolating 
in a pure condition the two pyrimidines, thymine I and cytosine II. 
NH CO N CNH2 
II II 
CO CCH3 CO CH 
I II ' I II 
NH CH NH CH 
I II 
Both pyrimidines were obtained in sufficient quantity for analysis and 
their constitution further established by the color reactions^ character- 
istic of these two compounds, respectively. The two products isolated 
were compared with the pyrimidines obtained by synthesis and found to 
agree in every respect in chemical and physical properties. The further 
study of the chemistry of tubercle bacillus is in progress and the results of 
the investigation just finished will soon be published in The American 
Review of Tuberculosis and the Journal of Biological Chemistry. 
1 Wheeler and Johnson, /. Biol. Chem., 3, 1907 (183). Johnson and Baudisch, /. 
Amer. Chem. Soc, 43, 1921 (2670) and Ber., 55, 1921 (18). 
THE RELATIVE SENSITIVITY OF THE EAR AT DIFFERENT 
LEVELS OF LOUDNESS 
By Donald MacKknzie 
Research Laboratories of the American Telephone and Telegraph Company 
AND the Western Electric Company, Incorporated 
Read before the Academy, April 25, 1922 
The threshold sensitivity of the ear for tones of various frequencies 
has been studied by many investigators. In order to determine the rela- 
tive sensitivity at higher intensity levels, an alternation phonometer has 
been devised which permits balancing two tones of different frequency 
for equality of loudness. 
The apparatus (fig. 1) consists of two vacuum tube oscillators, in- 
dependently controlled, which through a relay commutator alternately 
supply current to a sound generator (either thermal or electromagnetic). 
The commutator is a polarized telegraph relay, driven at a suitable speed 
from another such relay. The commutating relay is adjusted to give a 
contact time of 1/25 second on each side, with a silent interval of 1/1000 
second required for armature travel between contacts. This device 
differs in principle from the flicker photometer in that fluctuations in 
intensity are not caused to disappear and subjective fusion of the tones 
compared does not take place.* The interval (2/1000 second) through 
which auditory sensation persists after cessation of the physical stimulus 
