Fuly 14, 1870] 
NATURE 
225 
the contrary, he explains the discrepancy between his earlier and 
his later experiments by another supposition altogether. As on 
other occasions, he does not even suggest to the reader that any 
different explanation is possible from that which he adduces. He 
deliberately assumes that the bacteria and vibrios which were 
subsequently found in the milk used in these experiments had 
been derived from ‘‘ germs” of such organisms which either pre- 
existed in or had obtained access to this fluid before it had been 
heated, and also (contrary to the general rule which had been 
previously admitted) he assumed that such supposed pre-existing 
germs were capable of resisting the influence of the boiling tem- 
perature in milk. Nodirect proof of the latter assumption was 
ever attempted, though M. Pasteur did afterwards endeavour to 
bring these exceptional cases under a general law by supposing 
that the results obtained were due to the absence of acidity in the 
fluids employed. Neutral or slightly alkaline fluids might, he 
thought, yield positive results in Schwann’s experiments, because 
the germs of bacteria and vibrios were not destroyed, by the 
boiling temperature in such fluids. 
Such was the very definite statement made by M. Pasteur on 
the faith of a chain of evidence almost every link of which is 
ambiguous. The most direct observations, however, which can 
be made upon this subject (and to the desirability of making 
which he does not even allude) lend not the least support to his 
assumption. On the contrary, they go to confirm the rule which 
had hitherto been generally admitted as to the inability of any of 
these lower organisms to live after an exposure for even a few 
seconds ina fluid raised to a temperature of 100°C. I have again 
and again boiled neutral and alkaline infusions containing very 
active bacteria and vibrios, and the result has always been a 
more or less complete disruption of the vibrios, and the dis- 
appearance of all signs of life inthe bacteria. All their peculiarly 
vital movements have at once ceased, and they have henceforth 
displayed nothing but mere Brownian movements.* 
M. Pasteur approaches the solution of the discrepancy in this 
way. His attention was arrested by the fact that milk was an 
alkaline fluid, because he afterwards ascertained that other 
alkaline fluids also yielded positive results when submitted to 
the conditions involved in Schwann’s experiments. Thus he 
himself helped to overturn the strongest evidence which had 
hitherto been brought to bear against the heterogenists. But, 
this being done, it was necessary for M. Pasteur to explain such 
an occurrence, if he was not prepared to yield his assent to the 
doctrine which he had formerly rejected. He now found, truly 
enough, that the mere alkalinity or acidity of the solution was 
a matter of great importance in these experiments ; he found, 
for instance, that his ‘‘]’eau de leviire sucree,” naturally a faintly 
acid fluid, was always unproductive when submitted to Schwann’s 
conditions unaltered, though it was, on the contrary, always pro- 
ductive if it had previously been rendered neutral or slightly 
alkaline by the addition of alittle carbonate of lime. Facts of 
this kind were observed so frequently as to make him come to the 
conclusion that whilst acid solutions were never productive in 
Schwann’s apparatus, any neutral or alkaline fluids might be, if 
it were otherwise suitable for such experiments. Then came 
the question as to how this was to be explained. It should be 
remembered that M. Pasteur was engaged in investigating the 
problem of the mode of origin of certain low organisms in 
organic fluids, concerning which so much controversy had taken 
place. In this controversy, hitherto, on the one hand, it had been 
contended that the Living things met with derived their origin 
from pre-existing “‘ germs” that had survived all the destruc- 
tive conditions to which the media supposed to contain them had 
been subjected ; whilst, on the other hand, it was contended that 
if the media had been subjected to conditions which (by evidence 
the most direct and positive) had been shown to be destructive 
to the lowest Living things, then such Living things as were 
subsequently discovered in these fluids must have been evolved 
de novo, twas a question, therefore, on the one hand, as to 
the degree of vitality or capability of 1esisting adverse conditions 
peculiar to the lowest Living things; and, on the other, as 
to the strength of the tendency to undergo changes of an 
evolutional character in the organic matter existing in the solu- 
tions, and on the degree to which this molecular mobility could 
persist, in spite of the disruptive agency of the heat to which the 
organic matter might be subjected. When, therefore, after having 
been exposed to a given set of conditions, organisms are not sub- 
sequently found in the fluids employed, this is explicable in one 
of two ways—that is, in accordance with either of the two 
* See what has been previously said on this subject (p. 171). 
opposing views. Either the heat has proved destructive to all 
Living things in the solutions; or else the restrictive conditions 
to which the organic matter in the solutions has been exposed 
have been too severe to permit the occurrence of evolutional 
changes therein. Any person seriously wishing to ascertain 
the truth, and competent to argue, of course would not fail 
to see that he was bound to give equal attention to 
each of these possibilities. He had no right to assume 
that the probabilities were greater in favour of the one 
mode of explanation than they were in favour of the other; 
this was the very subject in dispute—this, it was, which had 
to be proved. When, therefore, it was definitely ascertained 
by M. Pasteur that acid solutions employed in Schwann’s 
experiments yielded negative results as far as organisms were 
concerned, the establishment of this fact was in reality no more 
favourable to the one view than to the other. It is what the 
Panspermatists might have expected, it is true, because—regarding 
it only as a question of the destruction or non-destruction of 
germs—even they had convinced themselves that calcining the 
air and boiling the fluids were adequate to destroy all Living 
things contained in these media ; but, on the other hand, it was 
equally open to the Evolutionists to say that—the restrictive 
conditions employed being so severe—they also were not sur- 
prised at the probable stoppage of evolutional changes and at 
the consequent non-appearance of organisms in the solutions. 
When positive results were obtained, however, the case became 
altogether different. The rule being absolute, so far as it had 
gone—and founded on good evidence, to which M. Pasteur and 
others had assented—with regard to the inability of Living things 
to survive in solutions after these had been raised to the boiling 
temperature for a few minutes ; no one should have attempted to 
set aside this rule, except upon evidence equally direct and equally 
positive, though more extensive, than that upon which the rule 
had been originally founded. Certainly, no one should have 
attempted to set it aside on the strength of indirect evidence, 
which, though equally capable of explanation in accordance 
with either one of the two opposing views, was tacitly repre- 
sented to be explicable only in accordance with one of them. 
Such, however, has been the conduct of M. Pasteur. It 
will, perhaps, scarcely be credited by many that the investiga- 
tions of M. Pasteur, which have had so much _ influence, 
and which have been looked upon by many as models of 
scientific method, should really contain such fallacies. On 
other important occasions, however, his reasoning has been 
similarly defective, though he himself claimed and was believed 
by many to have ‘‘ mathematically demonstrated” what he had 
so plausibly appeared to prove.* 
In the present case, after his experiments with milk in 
Schwann’s apparatus, M. Pasteur ,ascertained that in other 
alkaline or in neutral fluids, even when they had been subjected 
to all the conditions above mentioned, inferior organisms might 
be found more or less quickly. But he also discovered that 
even such solutions no longer yielded organisms if, instead of 
subjecting them to a heat of 100° C, they had been exposed 
for a few minutes to a temperature of 110°C. And it was on 
the strength of two or three other links of such evidence as this 
that M. Pasteur sought to upset the rule with regard to the 
inability of inferior organisms to resist the destructive influence 
of a moist temperature of 100°C. On such evidence as this he 
attempted to raise the possible limit of vital resistance by 10° C., 
and sought to establish the rule that Living organisms might 
survive in neutral or alkaline solutions if these had not been 
raised to a temperature of 110° C. He did not seem to see 
how utterly inconclusive his conclusions were, and that he 
had not so much right to assume that the organisms met with 
in his neutral or alkaline fluids had been derived from ‘‘ germs ” 
which had resisted the boiling temperature, as he or his 
opponents would have had at once to fall back upon 
the counter assumption that the evolutional tendencies of 
neutral or alkaline fluids exposed to high temperatures were 
greater than those of similar fluids when in an acid state— 
and that such neutral or alkaline fluids were, as was now seen, 
capable of overcoming the restrictive conditions in Schwann’s 
experiments and of giving birth to organisms, by permitting the 
occurrence of Life-evolving changes amongst the colloidal mole- 
cules contained therein. He had less right to explain the facts 
as he did, than the evolutionist would have had to explain them 
as above mentioned, because he was thus attempting to upset 
* Tite space at my disposal does not permit of my alluding to these other 
occasions at present, though I shall do so in my forthcoming work, 
