136 ~° ANIMAL PHYSIOLOGY. 
will depend a great deal on the knowledge already possessed of 
chemical and vital processes. 
It is in all probability true that the nature of any vital pro- 
cess is at all events closely bound up with the chemical changes 
involved ; but we must not go too far in this direction. We are 
not yet prepared to say that life is only the-manifestation of 
certain chemical and physical processes, meaning thereby such 
chemistry and physics as are known tous; nor are we prepared 
to go the length of those who regard life as but the equivalent 
of some other force or forces; as electricity may be considered 
as the transformed representative of so much heat and vice 
versa. It may be so, but we do not consider that this view is 
warranted in the present state of our knowledge. 
On the other hand, vital phenomena, when our investiga- 
tions are pushed far enough, always seem to be closely asso- 
ciated with chemical action; hence the importance to the stu- 
dent of physiology of a sound knowledge of chemical princi- 
ples. We think the most satisfactory method of studying the 
functions of an organ will be found to be that which takes into 
consideration the totality of the operations of which it is the 
seat, together with its structure and chemical composition; 
hence we shall treat chemical details in the chapters devoted to 
special physiology, and here give only such an outline as will 
bring before the view the chemical composition of the body in 
its main outlines; and even many of these will gather a signifi- 
cance, as the study of physiology progresses, that they can not 
possibly have at the present. 
Fewer than one third of the chemical elements enter into 
the composition of the mammalian body; in fact, the great 
bulk of the organism is composed of carbon, hydrogen, nitro- 
gen, and oxygen; sodium, potassium, magnesium, calcium, 
sulphur, phosphorus, chlorine, iron, fluorine, silicon, though 
occurring in very small quantity, seem to be indispensable to 
the living body; while certain others are evidently only pres- 
ent as foreign bodies or impurities to be thrown out sooner 
or later. It need scarcely be said that the elements do not 
occur as such in the living body, but in combination form- 
ing salts, which latter are usually united with albuminous 
compounds. As previously mentioned, the various parts which 
make up the entire body of an animal are composed of living 
matter in very different degrees; hence we find in such parts 
as the bones abundance of salts, relative to the proportion of 
proteid matter; a condition demanded by that rigidity without 
