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form of energy, or some other property of matter as yet unknown, 
which is peculiar to living substance and the living organism?’ 7 This 
is the ultimate problem of biology. The mysterious properties of 
living substance have appealed alike to the philosophers of ancient 
days and modern times. Yet, as Johnstone states in his Philosophy 
of Biology, the ordinary person unacquainted with the results of 
physiological analysis has probably no doubt in his mind that the 
human body is animated by a principle or agency which has no 
counterpart in the inorganic world, and the same might even be said 
of the anatomist, naturalist, and physicist unacquainted with details 
of physiological inquiry. 
We biologists have, as our duty, to explain all that is possible 
of such explanation by those forms of energy and properties of 
matter that so far have been known to us. A general knowledge 
of the beautiful co-ordination met with in Nature might, and very 
often does, lead to the belief that something more than the physical 
forces is present to animate and sustain the dust of which we are 
made. Let us see then to what view the results of our combined 
knowledge lead us to-day. 
The earliest attempts to explain the phenomena of life have been 
lost with the knowledge of the ancients. In the period 460-370 B.C., 
however, the followers of Hippocrates believed that an agent — 
the pneuma — controlled all vital phenomena in the organism. In the 
years that followed, two controlling powers were considered neces- 
sary — the vital spirits resident in the heart and the animal spirits 
which had their abode in the brain. Much more definite information 
can be gathered if we pass to the period A.D. 131-200, when Galen, 
the first physiologist, formulated a doctrine which, with his other 
works, remained untouched, unshaken and controlling, through the 
long slough of the middle ages. Galen was also a believer in the 
spirits as the cause of all phenomena in the living body. He added, 
however, another of these ruling powers — the Natural Spirits — to 
the two already mentioned. This third factor was supposed to reside 
in the liver! 
The nature of the spirits is not exactly indicated, but it must not 
be assumed that this early physiologist regarded them as entirely 
metaphysical. 
Through thirteen hundred years of stagnation and decay 
must we pass until the night once more gives way to the light of 
learning, and we reach the dawn of modern times. By a strange 
coincidence the particular branch of the new learning with which 
we are to-night concerned was heralded by the works of one Andreas 
Yersalius, who was educated at Louvain. Louvain University was 
of great renown even in 1530. Who could have foretold that it would 
have been left for the German race, most arrogant concerning learn- 
ing, to demolish that kind of culture they have not yet attained? 
I have not time to do more than mention the work of Yersalius. We 
