5386 ANIMAL PHYSIOLOGY. 
When a subject makes some signal in response to a stimu- 
lus, we recognize three parts to the entire chain of events: 1. 
The time occupied in the passage of the afferent impulses in- 
ward along certain lengths of nerve from a peripheral sense- 
organ. 2. The time taken up by the processes of the central 
cells before the efferent nervous discharge takes place. 3. The 
time consumed by the passage of the efferent impulses from 
the center to the muscle involved. The whole interval is termed 
the reaction-time, while the second constitutes the reduced re- 
action-time. ; 
As the first and third probably vary but little, it is highly 
probable that the difference in the reaction-time observable in 
different individuals, and very much modified by the condition 
at the moment (as fatigue), and especially by practice, is trace- 
able to the central cells. In popular language, some persons 
are,as compared with others, slow thinkers. This factor is the 
“personal equation,” so called. There are, of course, many 
sources of error in such calculations, but approximate results 
of value may be reached. It would appear that the reaction 
period for tactile is shorter than for visual or auditory sensa- 
tions, while that of vision is longer than for hearing. The 
respective periods have been set down as about 4 of a second 
for vision, ¢ for audition, and 4 for feeling. 
The central processes may be reckoned to take (for percep- 
tion and volition) about 7, of a second. 
If discriminations have to be made—so as to decide, e. g., 
whether it is the right or the left side of the body that has 
been touched—a longer time is, of course, required, and the re- 
action period in this case also varies greatly. It has been set 
down as occupying from gy to 4 of asecond. From these con- 
siderations, it will be plain that “the lightning-like rapidity 
of thought” is a rather extravagant figure of speech. 
if 
FUNCTIONS OF OTHER PORTIONS OF THE BRAIN. 
Certain parts of the encephalon are spoken of as the basal 
ganglia, prominent among which are the corpus striatum and 
the optic thalamus. 
The Corpus Striatum and the Optic Thalamus.—The corpus 
striatum consists of several parts, the main divisions being an 
intra-ventricular portion or caudate nucleus, and an extra- 
ventricular part or lenticular nucleus. 
Between these lies the internal capsule, through which 
