CHAPTER II. 
REFLEX ACTION. 
“Pure reflexes are admirably adapted to certain ends. They are 
reactions which have long proved advantageous in the phylum of 
which the existent individual is a representative embodiment. 
Perfected during the course of ages, they have during that course 
attained a stability, a certainty, and an ease of performance beside 
which the stability and facility of the most ingrained habit acquired 
during an individual life is presumably small.”—SHERRINGTON, 
The Integrative Action of the Nervous System. 
The term reflex action is used in a wide and somewhat 
indefinite sense, but it is applied in general to responses of the 
organism which are evoked directly upon the application of 
a stimulus. In a typical reflex we have a sensory or afferent 
impulse set up in some sense organ and proceeding toward 
a ganglion or larger nerve center. From the latter an efferent 
impulse passes outward along a motor nerve, causing a 
muscular contraction. Frequently the impulse is reflected 
back near its point of origin, more or less after the fashion 
in which light may be reflected back to its source from a 
mirror and the reaction occurs in the stimulated part. It is 
from analogy with the reflection of light that the term re- 
flex action is chosen, although the analogy, it must be con- 
fessed, is rather loose, and in some respects misleading. 
When one involuntarily winks the eyes after they are 
suddenly illuminated by a glare of light, impulses are set 
up in the retina which proceed along the optic nerve to the 
brain. Here they traverse certain established connections 
among the fibers, by means of which they become directed 
outward along the motor nerves to the muscles of the eye- 
11 
