vous system of
the higher animals, by the connections it provides between the
stimulus and the stores of energy in the muscles, is of especial
importance in determining the nature of the response.

Stimuli are necessary to arouse the activity of the organism. Without
any stimulus whatever, it seems likely that the animal would relapse
into total inactivity. It should be said, however, that stimuli, such
as that of hunger, may arise within the organism itself. The stimulus
may be external or internal, but some stimulus is necessary in order
to release the stored energy.

In general, then, a reaction consists in the release by a stimulus of
some of the stored energy of an animal, and the direction of that
energy by the animal's own internal mechanism of nerves and muscles
(and, we may add, bones and sinews) into the form of some definite
response.

{42}

EXERCISES

1. Outline of the chapter, being at the same time a "completion
test". Complete the following outline by filling in the blank
spaces (usually a single word will fill the blank, but sometimes two
words will be better):

A. Definition: A reaction is a response to a ___________.
The stimulus energy stored in the organism, and the __________
has a definite form determined by the organism's own machinery
of ________ and ______.

B. Among very prompt reactions are the reflex and the "simple
reaction". The reflex differs from the "simple reaction" in that:

(1) It usually takes less________.

(2) It requires no___________,

(3) The machinery for it is ________in the organism.

C. The machinery for a reflex consists of:

(1) a________ organ.

(2) a ________nerve.

(3) a nerve ________,

(4) a _________nerve.

(5) a muscle or _________.

D. The sensory and motor nerves consist of ________ which are
branches of ______. The cells for the motor nerves lie in the
________, and those for the sensory nerves lie in two cases in
the _________, and in all other cases in bunches located close
beside the _________or ________,

E. The neurone is the _______ of which the nervous ______ is
composed. It consists of a ________ and of two sorts of
branches, the ________ and the ________. Internally, the neurone
shows a peculiar structure of ________ and ________.

F. Communication from one neurone to another occurs ac