190 M. M. Garver—Periodic Character 
that the expression “think twice” is literally true, and tha 
the variation 7s entirely cerebral.” The matter can probably 
be best presented in the form of an hypothesis, supporting it 
by what proofs may be at hand. The hypothesis is this: 
ae cerebral portion of the nervous system is continually 
rying in its activity, waxing and waning between ‘certain 
fimita, periods of maximum activity following periods of mini- 
mum activity at the rate of 86 to 60 times per secon 
The first proof in support of this view is that it offers a 
to which attention was called in the preceding article. For, if 
voluntary movements must also be periodic in character—it 
being impossible, according to the hypothesis, for a voluntary 
impulse to originate during a period of minimum activity or 
rest. The fact that the periods are not more sharply defined 
is not conclusive proof of the non-existence of such cerebral 
variations, for there is evidence to show that the periods are 
omewhat variable in different individuals, and in the same 
individual under different circumstances. For instance, it is 
generally conceded that the — does not work so well after 
a hearty meal as before. Here are two series of experiments, 
one of — was taken pimadately before dinner, the other 
soon a 
Garver, “hand to hand.” 
BEFORE DINNER. 
16 it 18 19 20 21 22 23 vib. 
16 17 18 19 20 21 22 
16 17 18 19 20 2] 
16 7 18 19 21 
17 19 21 
17 19 21 
19 _ 
The numbers below the line are the answers to the signals 
and show the time expressed in etal of the tuning-fork, 
one vibration being equal to ;4, of asecond. An evident 
preference 3 is shown for the numbers 17, 19, “OL. 
Garver, “hand to hand.” 
FTER DINNER. 
1G. 30 30 10 20 2b ge ao. 2k 2b 62 2T 88.29 vib. 
16 15 13 ke 200 2k Us oe A 25 86. 8 
it 28 19 "20° 21 23 26 29 
18 19 20 23 
18 19 20 23 
18 219. 26 
18 29 20 
19 
