120 THE GROUNDWORK OF SCIENCE

We have spoken of " the circulation " as the function of the

organs which compose the " circulating system." But over

and above that great stream of life there is a minute circula-

tion which takes place within each smallest particle of the

body's substance (just as it takes place in unicellular animals),

for the sake of which multitudinous microscopic streamlets

the great sanguineous current may be said to exist.

Respiration consists in the gaseous exchange to which

our breathing organs minister. But it is not in that con-

spicuous respiratory process which is evident to our senses

that the process really consists. It is in the minute gaseous

interchange which takes place in the ultimate and intimate

components of the body's substance.

Similarly, " secretion " is a process of formation, by organs,

from the blood of products which did not previously exist as

such within it. It is thus analogous to the power by which

the various tissues that compose the body are enabled to add

to their own substance from the life-stream which bathes

them, though their substance does not exist as such in

that stream. Thus the process of assimilation in which

alimentation culminates is analogous to secretion.

Having thus, in the briefest manner, noticed the most

essential facts concerning various bodily functions, we may

next turn to our special subject in this chapter the functions

of the nervous system. In the first place, it is by the agency

of this system that all the other organic activities of the

human body are carried on. Without its aid all nutrition,

growth, circulation, respiration, and muscular motion would

not exist, just as its activity would be arrested were it not

nourished by a sufficient supply of duly-constituted blood.

But besides organic activities, this system also ministers

to, and is necessary for, sensation, and, therefore, for know-

ledge, seeing, once more, that the latter is impossible for

us except as following upon sensation. The nervous system

We have spoken of " the circulation " as the function of the

organs which compose the " circulating system." But over

and above that great stream of life there is a minute circula-

tion which takes place within each smallest particle of the

body's substance (just as it takes place in unicellular animals),

for the sake of which multitudinous microscopic streamlets

the great sanguineous current may be said to exist.

Respiration consists in the gaseous exchange to which

our breathing organs minister. But it is not in that con-

spicuous respiratory process which is evident to our senses

that the process really consists. It is in the minute gaseous

interchange which takes place in the ultimate and intimate

components of the body's substance.

Similarly, " secretion " is a process of formation, by organs,

from the blood of products which did not previously exist as

such within it. It is thus analogous to the power by which

the various tissues that compose the body are enabled to add

to their own substance from the life-stream which bathes

them, though their substance does not exist as such in

that stream. Thus the process of assimilation in which

alimentation culminates is analogous to secretion.

Having thus, in the briefest manner, noticed the most

essential facts concerning various bodily functions, we may

next turn to our special subject in this chapter the functions

of the nervous system. In the first place, it is by the agency

of this system that all the other organic activities of the

human body are carried on. Without its aid all nutrition,

growth, circulation, respiration, and muscular motion would

not exist, just as its activity would be arrested were it not

nourished by a sufficient supply of duly-constituted blood.

But besides organic activities, this system also ministers

to, and is necessary for, sensation, and, therefore, for know-

ledge, seeing, once more, that the latter is impossible for

us except as following upon sensation. The nervous system