158 
THE PROGRESS OF NATURAL SCIENCE 
DURING THE LAST TWENTY-FIVE YEARS 
il 
Ns the last quarter of a century, the his- 
tory of the formation of our earth has assumed 
anewaspect. When the Cosvos appeared, the opinion pre- 
vailed that our earth, once a globe of liquid fire, became 
covered with a crust of congealed scoriz, on which, by- 
and-by, the first animal and plant life made its appear- 
ance ; after an almost infinite length of time, during which 
the Silurian, Devonian, Carboniferous, and Permian strata 
were deposited, a terrible catastrophe, affecting simulta- 
neously the whole earth, so completely destroyed the first 
paleozoic life, that not a single species survived the 
universal devastation. Upon the lifeless expanse, it was 
supposed, appeared then, forming the Secondary Fauna 
and Flora, entirely unconnected with and different from 
the extinguished one, until after frequent repetitions of 
the same process at longer or shorter intervals, man 
made his appearance, and along with him all existing 
plants and animals: with him begins the Historical 
Period, whose duration has not exceeded 6,000 years. 
The causes of these world-wide revolutions Geology 
sought in the violent reaction of the molten interior 
against the once extremely slender crust. 
In opposition to these views, the opinion peculiarly 
associated with the name of Lyell has made way, that no 
violent revolutions, returning at intervals, destroyed the 
external structure of the earth and all the life it sustained, 
but that all changes even in the earliest times affected 
only the earth’s surface, and that these could only be the 
results of the same powers of nature which are actively 
at work on the earth at the present time ; and that more- 
over, the gradual, but ever active powers of water, of air, 
and of chemical change, have perhaps had a greater 
share in accomplishing these transformations, than the 
fierce | eat of subterranean masses of lava. The ex- 
plorers of the buried remains of plants and animals show 
it to be impossible that all life in those geological forma- 
tions could have been destroyed simultaneously, for many 
species are common at several stages; in particular 
many existing animals and plants reach far back into 
the primitive world. Man himself could be shown to 
have been contemporary with many extinct species of 
plants and animals, and therefore his age on the earth 
must be extended back to an indefinite period. Man was 
witness to that inundation which buried the plains of the 
old and the new world under the waves of the sea of ice, 
Even in the immediately preceding period, when the sub- 
tropical elephant, rhinoceros, and hippopotamus disported 
themselves in the lignite woods of Middle Europe, have 
traces of mankind been found. Only in the most recent 
times has a foundation been laid for the pre-historic 
records of mankind, by means of which we may be 
able to obtain a knowledge of the state of civilisation, 
weapons, implements, and dwellings of that primitive 
race. 
No book of recent times, Dr. Cohn thinks, has influenced 
to such an extent the aspects of modern natural science, as 
Charles Darwin’s work “On the Origin of Species,” the first 
edition of which appeared in 1859. For even to so late a 
period, was the immutability of species believed in ; so long 
was it accepted as indubitable that all the characteristics 
NATURE 
which belong toany speciesof plants andanimalsweretrans- 
mitted unaltered through all generations, and were under 
no circumstances changeable; so long did the appear- 
ance of new fauna and flora remain one of the impene- 
trable mysteries of science. He who would not believe 
that new species of animals and plants, from the yeast- 
fungus to the mammalia, had been crystallised parentless- 
out of transformed materials was shut up to the belief that 
‘in primeval time an omnipotent act of creation, or, as it 
may be otherwise expressed, a power of nature at present 
utterly unknown, interfered with the regular progress of 
the world’s developments yea, according to the researches 
of D’Orbigny and Elie de Beaumont, twenty-seven diffe- 
rent acts of creation must have followed each other pre- 
vious to the appearance of man—but after that, no more. 
It was Darwin who lifted natural science out of this 
dilemma, by advancing the doctrine that the animals and 
plants of the late geological eras no more appeared all at 
once upon the scene, than those of the preceding epochs 
simultaneously and suddenly disappeared ; on the con- 
trary, these are the direct descendants of former species, 
which gradually in the course of an exceedingly long 
period, through adaptation to altered conditions of life, 
through the struggle for existence, through natural and 
sexual selection have been changed into the new species. 
Professor Cohn does not doubt but that Darwin and 
his school may have over-estimated the reach of the 
explanations given by him to account for the trans- 
mutation of species, and especially the importance of 
natural and sexual selection, but the fundamental fact has 
been established, and will remain so for all future time. 
This fact is that the collective life of the earth, from the 
beginning even until now, and from the fungus-cell up to 
man, represent a single series which has never once been 
broken, whose members through direct propagation have ~ 
proceeded out of each other, and in the course of a vast 
period have been developed into manifold and, on the 
whole, perfect forms. 
The sciences which are concerned with life have during 
late years been cultivated on all sides; even in earlier 
years Cuvier and Jussieu had done as much for zoology 
and botany as the state of discovery in their time per- 
mitted, but since 1858 the boundaries of both kingdoms 
have been widely extended by the labours of i i, 
Huxley, and Pourtalés. 
After referring to the researches of Goethe in the last 
century, and those of Bauer and of Johannes Miiller in 
the present, in reference to the physiology of plants and 
animals, Prof. Cohn says it was only in our own time, 
and first in 1843 in Schleiden’s “ Grundziigen der Wissen- 
schaftlichen Botanik,” that the new principle was followed 
out; the principle, namely, that all vegetable phenomena 
and all the various forms of plants proceed from the life and 
the development of their cells. After Schwann discovered 
that animal bodies also were built up from an analogous 
cell, mainly by Virchow was then developed from this 
principle the modern. cellular physiology and pathology 
which traces the condition both of healthy and diseased 
men and animals back to the life-function of their cells, 
But, as the lecturer says, to attempt to follow out the 
advances made by science in these directions during the 
last twenty-five years would require a large volume, and 
cannot be done in the space of a lecture or an article, 
