6 
Transactions Texas Academy of Science. 
composed of the same chemical elements that are also composing lifeless 
things. Their vitality is from moment to moment sustained by the in- 
haling of outside air. And without the incorporation of foreign alimen- 
tary substances they themselves become soon reduced to lifeless matter, 
into which state they all eventually wholly dissolve. Furthermore, with- 
out the exquisitely attuned incitement of nature-revealing light, all 
w r ould be indiscriminate darkness to every kind of living creatures. And 
wdthout the rhythmic touch of serial vibrations we would all be steeped 
in eternal silence. Indeed, it can be rightly maintained that the entire 
organization of living beings, down to their minutest structures, is func- 
tioning solely in more or less direct interaction with outside agencies, 
and in more or less important relations to the same. 
But, though all this is undoubtedly true, there exist, nevertheless, no 
more striking, no more trenchant distinctions in nature than those obtain- 
ing between living beings and lifeless things. The most salient of these 
distinctions is perhaps the power of animals, and also of many plants, 
to move themselves; whilst all lifeless things, in order to be moved, have 
passively to aw r ait the impact of influences external to them. Besides, 
many more profound, if less salient, distinctions characterize living 
beings in contrast to non-living things. Living beings transform lifeless 
material into living substance, and coerce the same into definitely organ- 
ized structures. They reproductively grow from tiny germs to specific 
adult stature. They propagate their own kind. They render outside 
nature in various ways subservient to their individual wants. In all this, 
and in much more, to their innermost core, living beings essentially dif- 
fer from lifeless things. 
No wonder that, in attempts at explaining the manifestations of life, 
special hyperphysical forces or powers have from time immemorial been 
invoked as actual agencies of the singular and marvelous phenomena of 
vitality. Not long ago it seemed unthinkable, even to professional biolo- 
gists, that mere physical principles, such as are applied to the interpreta- 
tion of lifeless nature, could possibly account for the minutely intricate 
organization, and the aimful vital activities, of bodies found physically 
to be composed of nothing but a few well-known chemical elements. 
Some vitalizing essence, force, or agent was, therefore, held to inhabit 
living bodies; quickening them, fashioning their organs, and directing 
their functions. 
Most biologists of the first part of the last century still adhered in some 
form or other to the ancient hypothesis of a vital principle. Johannes 
Mueller, for instance, the revered teacher of Helmholtz, Du Bois-Rey- 
mond, Virchow, Haeckel, and many other prominent biologists, whose 
lectures I attended in my early student days, believed still in the ex- 
