536 SECTIONAL TRANSACTIONS .—I. 
presumed that the carbon dioxide has been inactive. Such percentages 
of carbon dioxide have been shown by Jerusalem and Starling and others 
to increase the output of the heart. New experiments are described which 
show that the vasomotor centre has been stimulated, since there is a marked 
increase in the resistance of a limb perfused separately and connected to 
the animal only by nerves. It may therefore be concluded that, since the 
output of the heart is increased and the vasomotor centre stimulated with- 
out causing a rise of blood pressure, the carbon dioxide has caused a 
diminution of peripheral resistance. ‘These results support the view 
previously put forward that the carbon dioxide of the arterial blood has in 
the periphery a dilator action which balances its central effect. 
Prof. H. Harrripce, F.R.S. (12.25) -— 
(a) Variations in skin resistance due to electrical currents. 
Ebbecke found that the resistance of the skin to galvanic currents could 
be decreased either by rubbing the skin or by the continued passage of a 
galvanic current of such strength that whealing was ultimately produced. 
Lewis and Zotterman, using small electrodes, obtained a similar drop in 
resistance which they attributed to breaches in the horny layer, whereas 
Ebbecke has attributed it to stimulation of the living cells which lie deep to 
that layer. 
I have repeated these experiments with electrodes of large area, and I find 
the same fall of resistance. I have noticed, however, that on cessation of the 
galvanic current the skin resistance rises until it reaches a value considerably 
greater than that to which the galvanic current had depressed it. If the 
explanation of Lewis and Zotterman is correct, one must conclude that the 
breaches in the horny layer heal again with very great rapidity. 
(b) An experiment in favour of the resonance theory of hearing. 
A brass disc, about 12 in. in diameter, is provided near its circumference 
with two concentric rows of slots. The inner row consists of ninety-six 
equidistant slots ; the outer row also consists of ninety-six slots, at equal 
distances except for one interval only which is half the distance of each of the 
others, thus introducing a change of phase (a half wave-length). When the 
disc is rotated by an electric motor and a stream of air is directed on to the 
inner row of slots, a continuous musical tone of constant pitch is produced. 
When the stream of air is directed on to the outer row of slots a musical 
tone of constant pitch is heard, but this tone is interrupted once at each 
revolution of the disc when the change of phase occurs. Since the interrup- 
tion effect heard by the ears can be imitated by stopping up two neighbouring 
slots of the inner row, I conclude that this is a true interruption and not, 
for example, a change of pitch of the tone. 
This confirms an earlier conclusion that a change in phase of a musical 
tone causes it to be ‘ out of step ’ with the ear resonators, so that the latter 
first are arrested and then recommence their vibrations. 
(c) Competitive reaction time apparatus. 
A number of neon lamps are connected so that each lamp has a separate 
switch. The lamps and their switches are connected in parallel between 
two buss bars, one of which is connected to one wire of the 200-volt D.C. 
main, the other buss bar being connected to the other wire of the main 
through a suitable resistance (usually 10,000 ohms). The current passing 
