4 NATURE AND LIFE. 
ated at other poles, and which combine with the first in ex- 
citing in their turn new impulses. Such are the chief. 
noticeable ways in which innervation makes its appearance 
and fulfills its action; a property which, rudimentary, and | 
hardly to be detected in the lower animals, rises in the 
higher ones, and lifts them, too, to so lofty a degree of 
perfection. Whatever may be, as to the rest, the first 
cause of the most striking acts of our life, of the affections 
and the intellect, we feel, will, imagine, and understand, 
only through the means of these nerve-corpuscles distrib- 
uted through cur system, and endowed with that power, 
not paralleled elsewhere, of receiving, transmitting, per- 
ceiving, storing away, and modifying impressions. 
This, then, is one first and fundamental lesson yielded 
by the study of the anatomical elements; the play of ani- 
mal organisms is reduced to four simple essential modes of 
action: nutrition, evolution, contractility, and innervation. 
At once distinct and combined, sometimes intricately in- 
termingled, sometimes visibly separate, consubstantial with 
those anatomical elements by which their existence is made 
known, capable of putting on various and manifold ap- 
pearances, these properties are the springs of all living 
mechanisms. In machines produced by man’s industry, 
one single force goes through many forms to accomplish 
the most various effects. In animals, several different forces 
have for their business, in the midst of a thousand entan- 
glements and intricacies, to insure the perpetuation of the 
species through the full working of the individual. 
We are thus led to speak of the generation of the ana- 
tomical elements. This question is one of twofold gravity: 
In the first place, it abounds in difficulties of every kind, 
so extremely subtile are the observations in the case, so 
prompt the senses to be misled, so ready the mind to be 
deceived. Then it borders.on the most formidable prob- 
lems, not merely of general anatomy, but also of natural 
