20 INTRODUCTION. 
and functions in our rapid sketch: and hasten to place before our 
readers a view of the whole. 
The functions performed by animals may be brought into two 
chief classes. One class comprises the vegetative, the other the 
animal functions. The first are so called because they occur 
equally in plants, and are also, on that account, called organic 
functions. The last are peculiar to animals, and therefore are 
called animal functions. 
To the organic functions belong Nutrition in the widest sense, 
and Propagation. ‘To nutrition belong three systems: namely, that 
of Circulation, that of Assimilation, and that of Secretion. Respi- 
ration is a part of the system of secretion: for the object of respi- 
ration, like that of secretion, is the elimination of effete matter, its 
volatilization, or its separation in a more fixed form: and both, in 
this way, support that unceasing interchange of matter by which 
the circle of vital phenomena is characterised. 
By means of these functions, which together are comprehended 
by the name of Nutrition, the lite of the individual is secured and 
provided for. Other functions have reference to the life of the 
species, and ensure its existence after the death of the individual. 
These functions constitute Propagation, of which a part are dis- 
charged by the male individual, viz. the secretion of the impreg- 
nating fluid (semen), and its conveyance to germs capable of 
development. These germs are prepared and protected by the 
female individual, and on the union of these functions depends the 
being of the Embryo, the development of which is the final purpose 
of propagation. 
To the animal functions also belong three systems: viz. the 
nervous system, that of the organs of sense, and that of the organs 
of motion. 
The food, when solid, is comminuted by means of the jaws and 
teeth, or, when fluid, is imbibed. It is then conveyed into the in- 
testinal canal, which ordinarily has an expansion called the stomach. 
Here and at other parts of the intestinal canal different solvent 
fluids are secreted for assisting the conversion of the food. The 
nutrient part of the food is thus separated from the rest and taken 
up by the surface of the inner wall of the canal consisting of 
formative tissue: the remainder is rejected as unfit for the support 
of the creature. 
