stem, and there
certainly are a very great number of them, do not allow us to recognise
a unity anywhere else than in our own consciousness. An anatomical or
physiological unity has at least as yet been nowhere demonstrated.

When we talk of life we mean vital activity. Now, every vital action
supposes an excitation or irritation. The irritability of the part is
the criterion by which we judge whether it be alive or not. Our notion
of the death of a part is based upon nothing more or less than
this--that we can no longer detect any irritability in it. If we now
proceed with our analysis of what is to be included in the notion of
excitability, we at once discover, that the different actions which can
be provoked by the influence of any external agency are essentially of
three kinds. The result of an excitation or irritation may, according to
circumstances, be either a merely functional process, or a more or less
increased nutrition of the part, _or_ a formative process giving rise to
a greater or less number of new elements. These differences manifest
themselves more or less distinctly according as the particular tissues
are more or less capable of responding to the one or other kinds of
excitation. It certainly cannot be denied that the processes may not be
distinctly defined, and that between the nutritive and formative
processes, and also between the functional and nutritive ones there are
transitional stages; still, when they are typically performed, there is
a very marked difference between them, and considerable differences in
the internal changes undergone by the excited parts.

In inflammation all three irritative processes occur side by side.
Indeed, we may frequently see that when the organ itself is made up of
different parts, one part of the tissue undergoes functional or
nutritive, another formative, changes. If we consider what happens in a
muscle we see that a chemical or traumatic stimulus produces a
functional irritation of the primitive fasciculi, with contraction of
the muscle followed by nutritive changes. On the other hand, in the
interstitial connective tissue which binds the individual fasciculi of
the muscle together, real new formations are readily produced, commonly
pus. In this manner the three forms of irritation may be distinguished
in one part.

The formative process is always preceded by nutritive enlargement due to
irritation of the part, and has no connection with irritation of the
ner