334 DR ALISON’S OBSERVATIONS ON 
Thus the general fact seems established, that the excretions from the living 
body are only an intermediate stage between the organic compounds, forming the 
animal textures, and the inorganic chemical compounds into which these are ulti- 
mately resolved after death ; and that in the same living body, and in the same 
parts of it, at the same temperature, and when in contact with the same sub- 
stances, the same chemical elements, carbon, nitrogen, hydrogen, and oxygen, 
are continually acting on one another so as to form two distinct sets of com- 
pounds; the one set peculiar to living bodies, always attaching to them certain 
saline and earthy matters, sulphur or phosphorus, and always taking the form of 
cells or fibres, never of crystals,—and building up the organised frame; the other 
set rejecting those adventitious matters, tending always to the crystalline forms, 
and to the same mode of combination of the elements as takes place, under the 
same temperature, where no living structures exist,—and which are always ex- 
pelled from the organised frame. These are facts of such obvious importance, 
so generally observed and characteristic, that the physiologist cannot decline to 
take cognizance of them, and arrange them together, and have some general ex- 
pression for them. It does not appear possible to express these facts otherwise 
than by saying, that the particles of these elements taken into living bodies, are 
under the influence of different chemical laws at different times; which is exactly 
what we mean by saying, that they are first actuated by vital affinities (called 
vital because they are seen only in living structures, and in connection with the 
indications of life), by which the organised structure is gradually formed, and 
afterwards by simply chemical affinities by which it is gradually worn down ; and 
that both are in continual operation during Jife. And thus it appears that the 
chemical change, which always attends the absorption, and discharge by the ex- 
cretions, of all parts of a living body, is simply this.—that they lose their vital pro- 
perties, and become liable to the same affinities among themselves, and the same 
action with the oxygen brought to them by the blood, as prevail in the dead state. 
This inference as to the loss of vital properties, has been stated by several 
authors of late years, in regard to those portions of the living solids which per- 
form distinctly vital actions in a visible or tangible form, as the portions of mus- 
cular fibre or nervous matter, which are employed in vital motions and sensations ; 
but as the facts from which we draw the inference are equally true of bones and 
membranes, and other animal solids, unconcerned in any such vital actions, it 
seems to me necessary to extend the inference to all those portions of matter which 
exhibit in a living body the vital affinities, as well as to those which take on any 
kind of vital movement, or are concerned in any nervous actions. 
That oxygen must be the main agent in effecting the changes of these animal 
compounds, which precede their expulsion in the excretions, is sufficiently proved 
by observing, jirst, that it is uniformly and necessarily applied to them when 
these changes are going on; secondly, that the compounds into which the animal 
