170 
FACTS AND REASONINGS CONCERNING THE 
HETEROGENOUS EVOLUTION OF LIVING 
THING S* 
N all ages it has been believed by many that Living things 
| of various kinds could come into being de zove, and without 
ordinary parentage. Much difference of opinion has, however, 
always prevailed as to the kinds of organisms which might so 
arise. And, although received as an article of faith by many 
biologists—perhaps by most—in the earlier ages, this doctrine or 
belief has, in more recent times, been rejected by a very large 
section of them, Definitely to prove or disprove the doctrine in 
some of its aspects is a matter of the utmost difficulty, and there 
are reasons enough to account for the wave of scepticism on this 
subject, which has been so powerful in its influence during the 
last century. The notions of the ancients were altogether crude, 
and founded upon insufficient proofs. It was not in their power 
to settle such a question; and when the inadequacy of the 
evidence on which they had relied became known, then much 
doubt was thrown also on the truth of the conclusion at which 
they had arrived. All this was natural enough. When, there- 
fore, about a century ago, the rude microscopes of the time began 
to reveal a multitude of minute organisms whose existence had 
been hitherto unsuspected ; when more facts became known 
concerning the various modes of reproduction amongst living 
things ; and, above all, when the philosophical creeds of the day 
were supposed to be irreconcilable with such a doctrine, then a 
growing scepticism in the minds of many gradually developed 
into an utter disbelief in the possibility of the occurrence of what 
was called ‘‘ spontaneous generation.” 
This was the state of things anterior to and during the time of 
the celebrated controversy between the Abbé Spallanzani and 
John Needham. Then it was that the former of these two 
champions, with the view of accounting for phenomena which 
would otherwise have necessitated his admission of the doctrine 
which he rejected, recklessly launched upon the world the A1//o- 
thesis that multitudinous, minute, and almost metaphysical 
“‘cerms” existed everywhere- -ready to burst into active Life and 
development whenever they came under the influence of suitable 
conditions. Armed with this all-powerful Passpermic hypothesis, 
Spallanzani argued against the conclusions of Needham. His 
views on this subject were supported by the still more extrava- 
gant theories of Bonnet. The doctrine of ““L’ Emdottement des 
germes” was the production of an unbridled fancy, and might, 
perhaps, never have been elaborated, had not the Leibnitzian 
doctrine concerning ‘‘ Monads,” as centres of force and activity, 
been already in existence, and at the time all-powerful in the 
philosophical world. 
The controversy which was initiated by these two pioneers in 
microscopical research they were unable to terminate—the enigma 
which they sought to solve has, since their time, still pressed 
for solution, and still the tendency has been to solve it after one 
or other of the modes by which they attempted to account for 
the occurrence of the phenomena in question, It is and has been 
contended, on the one hand, that Living things can originate 
de nove, and without ordinary parentage ; it is contended, on the 
other, that this is impossible—that every Living thing is the 
product or off-cast of a pre-existing Living thing, and that those 
which appear to arise de szove have, in reality, been produced by 
the development of some of the myriads of visible or invisible 
“germs” which pervade the atmosphere. 
Now it is obvious, that of these two opposing doctrines, the one 
must be true and the other false : either Living beings can origi- 
nate de nove, or they cannot. Solongas any doubt remains upon 
this subject, we have to confess our ignorance concerning one of 
the very first principles of Biology. In the whole domain of 
Science, moreover, it is scarcely possible to propose a question 
which is more replete with interest than that which asks whether 
Living things can be evolved de xoz0. If settled in the affirma- 
tive, what light will be thrown upon the past and present history 
of our globe! How must our notions concerning Life, health, 
and disease be influenced in one way or the other by its solution ! 
Without entering into the history of the long controversy 
* This paper was originally intended for presentation to the Royal Society, 
but it was finally not presented, when I understood that, owing to the accu- 
mulation of many papers and other causes, no evening could be allotted on 
which it might be read and discussed. Its appearance 7” ex/enso, and at 
once, was thought preferable to the reading of its mere title before the Royal 
Society, with the probability of a very considerable delay in its publication, 
NATURE 
[Fune 30, 1870 
which has taken place upon this subject—details of which may 
be found in the works of Pouchet* and Pennetier,+ and in the 
writings of Pasteurt{—lI shall, before describing my own experi- 
ments and their results, merely relate as briefly as possible what 
conclusions have been come to concerning the degree of heat to 
which inferior organisms may be subjected with impunity, and 
what temperature, on the other hand, has been invariably found 
to be fatal to them. T*ortunately there is at present much 
unanimity of opinion on this subject. As a result of numerous 
investigations which have been communicated to the French 
Academy, and to the Société de Biologie during the last ten 
years, we find that both the advocates and the opponents of 
heterogeny are, within certain limits, pretty well agreed on this 
most important aspect of the: question. The many disbelievers 
and opponents of heterogeny who took part in these investigations, 
naturally desired that the power possessed by inferior organisms, 
both animal and vegetable, of withstanding the destructive in- 
fluence of high temperatures, should be shown to be as high as 
possible. We may, therefore, with much safety, assume that 
the limits of vital resistance could not then be shown to be higher 
than that which these experimenters were compelled, after fre- 
quently repeated investigations, to ascribe to such inferior 
organisms. 
In dry air or in a vacuum, organisms are capable of withstand- 
ing a notably higher temperature than when they are immersed 
in fluid. According to the direct observations of M. Pasteur, 
the spores of certain fungi belonging to the family A/ucadinee, 
seem to possess this tenacity of life to a very great extent ; but 
even these, he says, though they still remain capable of germinat- 
ing after having been raised, fora few minutes in dry air or 7” 
vacuo, to a temperature of from 120° to 125° C., lose this power 
absolutely and entirely after an exposure for half an hour, under 
similar conditions, to a temperature varying from 127° to 130°C. 
And the labours of the commission (consisting of the following 
members—MM. Balbiani, Berthelct, Broca, Brown-Séquard, 
Dareste, Guillemin, and Ch, Robin) appointed in 1869 by the 
Société de Biologie, to inquire into the subject, led them to the 
conclusion that the lower animals which were the most tenacious 
of lifes—the rotifers, the ‘*sloths,” and the anguillules of tufts of 
moss or lichen—succumbed at even a much lower temperature than 
this. In dry air or zz vacuo, therefore, we may look upon the 
temperature of 130°C, for thirty minutes, as marking the extreme 
limit of vital endurance under such conditions, so far at it has 
been hitherto possible to fix such a limit. There is, at present, 
no evidence forthcoming to upset this conclusion. When im- 
mersed in fluids, however, the power possessed by the inferior 
organisms of resisting the destructive influence of heat is not 
nearly so great. Comparatively few, whether animal or 
vegetable, have been found capable of resisting a temperature 
of 75°C. ; and with regard to that of 100°C., it has been 
admitted, by MM. Claude Bernard and Milne-Edwards, by M. 
Pasteur, and by all the other most influential opponents of the 
doctrines of heterogeny, that such a temperature, even for one 
minute, has always proved destructive to all the lower organisms 
met with in infusions ||—so far as these had been made the sub- 
jects of special and direct experimentation. And, amongst all 
the diversity ef form presented by the lowest Living things, there 
is so much of uniformity in property—living matter, as we know 
it, agrees in so many of its fundamental characters—that biolo- 
gists and chemists alike may feel a reasonable assurance as to 
the probable universality of any such rule which has been proved 
to hold good for a very large number of organisms, more 
especially when, amongst this large number of cases, no excep- 
tions have been encountered. 
Practically, however, it will be found that, in order to appre- 
ciate the bearings of the experiments which I shall have torelate, 
it will be necessary for us more especially to know what are the 
limits of vital resistance to high temperatures, possessed by 
spores of Vungi on the one hand, and by éacteria and vibrios on 
the other. 
I am not aware of any experiments tending to show that sfores 
of Fungi can survive after exposure for even a few seconds in 
fluids raised to a boiling temperature (100° C.) ; whilst, on the 
* Hétérogeniz, Paris, 1859. + L’Origine de la Vie, Paris, 1868. 
t Annales de Chimie et de Physique, 1862. 
§ This extreme tenacity of life is perhaps due in part to the chitinous 
integument with which such animals are provided. . 
|| It is quite fairto make this limitation, since we are only concerned with 
the origin of such organisms. Seeds of higher plants, provided with a hard 
coat, may—especially after prolonged periods of desiccation—germinate 
even after they have been boiled for a long time in water. 
