806 DR ALISON’S OBSERVATIONS ON 
which result from it, and of the period when it must have been first exerted on 
the earth’s surface, enables us to assert with confidence, that by means of it, 
the whole organised creation has been, as Dumas expresses it, the offspring of 
the air; and that it was by enabling the rays of the sun to excite this action 
in certain particles of matter, existing in the atmosphere, but destined to be 
either the first specimens, or the first germs of vegetable life, that ‘“‘ a beneficent 
God,” to use the striking expression of LAvoIsIER, “has strewed the surface 
of the earth, first with organized structures, and then with sensation and 
thought.” 
In proceeding farther to inquire into the laws of Vital Affinity, we must 
always keep in mind the general arrangement or classification, long ago made 
by Dr Prout, of all the organic compounds, of which any organized structures, 
vegetable or animal, are composed, into three groups or classes, the Saccharine or 
amylaceous, the Oily, and the Albuminous ; and the important observation, I be- 
lieve first made by him, that the food of most animals contains all these com- 
pounds, and that no complex animal structure can be maintained without the 
concurrence of at least two of these kinds of compounds in its food. 
I do not think it is going too far to say that we have now a general know- 
ledge of the laws or conditions under which all these compounds are formed in 
living bodies, taking the starch formed from carbonic acid and water as the foun- 
dation of all. But we perceive farther, that that these laws, varying in diferent 
parts of the same structure, and at dierent times in the same paris, and being of 
transient duration in all, are liable to an influence of time and of place, and in 
animals to a farther influence of mental changes, which is quite analogous to the 
vital actions, both of muscular and nervous organs, but is strongly contrasted 
with the uniformity of the laws that determine the changes of inorganic matter. 
And if this be so, we may assert that considerable progress has been made, both 
in establishing and in illustrating the doctrine of vital affinity, as a first principle 
in physiology. 
I. The formation of Oil or Fat in living bodies is, perhaps, that part of the che- 
mical processes there carried on, which is now the best understood, and the study 
of which gives us the clearest insight into the nature of vital affinities. We need 
not enter into any of the simply chemical questions as to the mode of combination 
of the fatty acids and bases in the different kinds of fat; it is sufficient for our pur- 
pose to observe that they are found very generally, though very variously disposed, 
in almost all vegetables and animals, and even in the earliest stages of their ex- 
istence; the store of nourishment contained in the seed and in the egg, contain-— 
ing a proportion of fatty matter. And though there is considerable variety in 
the different kinds of fat or oil, they all differ from the varieties of starch, by 
having a much smaller proportion of oxygen, and, of course, a larger proportion 
