Sebe. 15, 1870] 
NATURE 
403 
is hard to imagine what the fine sieve formed by the cotton-wool 
-could have stopped except minute solid particles. Still the 
evidence was incomplete until it had been positively shown, 
<first, that ordinary air does contain such particles; and, 
secondly, that filtration through cotton-wool arrests these par- 
ticles and allows only physically pure air to pass. This de- 
-monstration has been furnished within the last year by the re- 
-markable experiments of Professor Tyndall. It has been a 
«common objection of Abhiogenists that, if the doctrine of Biogeny 
-is true, the air must be thick with germs ; and they regard this 
as the height of absurdity. But Nature occasionally is ex- 
ceedingly unreasonable, and Professor Tyndall has proved that 
this particular absurdity may nevertheless be a reality. He has 
‘demonstrated that ordinary air is no better than a sort of stir- 
-about of excessively minute solid particles ; that these particles 
are almost wholly destructible by heat ; and that they are strained 
off, and the air rendered optically pure by being passed through 
cotton-wool. 
But it remains yet in the order of logic, though not of history, 
-to show that among these solid destructible particles there 
really do exist germs capable of giving rise to the development 
-of living forms in suitable menstrua. This piece of work was 
done by M. Pasteur in those beautiful researches which will 
ever render his name famous ; and which, in spite of all attacks 
upon them, appear to me now, as they did seven years ago,* to 
-be models of accurate experimentation and logical reasoning. 
He strained air through cotton-wool, and found, as Schroeder 
and Dusch had done, that it contained nothing competent to 
-give rise to the development of life in fluids highly fitted for 
that purpose. But the important further links in the chain of 
evidence added by Pasteur are three. Inthe first place he sub- 
jected to microscopic examination the cotton-wool which had 
«served as strainer, and found that sundry bodies clearly recog- 
nizable as germs, were among the solid particles strained off. 
Secondly, he proved that these germs were competent to give 
rise to living forms by simply sowing them in a solution fitted 
-for their development. And, thirdly, he showed that the in- 
“capacity of air strained through cotton-wool to give rise to life, 
was not due to any occult change effected in constituents of the 
air by the wool, by proving that the cotton-wool might be dis- 
-pensed with altogether, and perfectly free access left between 
the exterior air and that in the experimental flask. If the neck 
_of the flask is drawn out into a tube and bent downwards ; and 
if, after the contained fluid has been carefully boiled, the tube 
‘is heated sufficiently to destroy any germs which may be present 
‘in the air which enters as the fluid cools, the apparatus may be 
left to itself for any time and no life will appear in the fluid. 
The reason is plain. Although there is free communication be- 
“tween the atmosphere laden with germs and the germless air 
in the flask, contact between the two takes place only in the 
“tube ; and as the germs cannot fall upwards, and there are no 
currents, they never reach the interior of the flask. But if the 
-tube be broken short off where it proceeds from the flask, and 
-free access be thus given to germs falling vertically out of the 
air, the fluid which has remained clear and desert for months, 
becomes, in a few days turbid and full of life. 
These experiments have been repeated over and over again 
by independent observers with entire success ; and there is one 
-very simple mode of seeing the facts for oneself, which I may as 
well describe. 
Prepare a solution (much used by M. Pasteur, and often 
-ealled ‘‘ Pasteur’s solution’’) composed of water with tartrate of 
‘ammonia, sugar, and yeast-ash dissolved therein.t Divide it 
into three portions in as many flasks; boil all three for a 
“quarter of an hour; and, while the steam is passing out, stop 
the neck of one with a large plug of cotton-wool, so that this 
also may be thoroughly steamed. Now set the flasks aside to 
cool, and when their contents are cold, add to one of t!.e open 
ones a drop of filtered infusion of hay which has stood for 
-twenty-four hours, and is consequently full of the active and ex- 
cessively minute organisms known as Bacteria. Ina couple of 
lays of ordinary warm weather the contents of this flask will 
be milky from the enormous multiplication of Bacteria. The 
other flask, open and exposed to the air, will, sooner or later, 
become milky with Bacteria, and patches of mould may appear 
in it ; while the liquid in the flask, the neck of which is plugged 
with cotton-wool, will remain clear for an indefinite time. I 
*“Tectures to Working Men on the Causes of the Phenomena of 
Organic Nature,” 1863. ‘ iz Ge E 
* ¢ Infusion of hay treated in the same way yields sitnilar results ; but as it 
contains organic matter the argument which follows cannot be based upon it. 
have sought in vain for any explanation of these facts, except 
the obvious one, that the air contains germs competent to give 
rise to Bacteria, such as those with which the first solution has 
been knowingly and purposely inoculated, and to the mould- 
fungi. And 1 have not yet been able to meet with any adyo- 
cate of Abiogenesis who seriously maintains that the atoms of 
sugar, tartrate of ammonia, yeast-ash, and water, under no in- 
fluence but that of free access of air and the ordinary tempera- 
ture, rearrange themselves and give rise to the protoplasm 
of Bacterium. But the alternative is to admit that these 
Bacteria arise from germs in the air; and if they are thus pro- 
pagated, the burden of proof that other like forms ar2 generated 
in a different manner, must rest with the assertor of that propo- 
sition. 
To sum up the effect of this long chain of evidence :— 
It is demonstrable that a fluid eminently fit for the develop- 
ment of the lowest forms of life, but which contains neither 
germs, nor any protein compound, gives rise to living things in 
great abundance if it is exposed to ordinary air, while no such 
development takes place if the air with which it is in contact is 
mechanically freed from the solid particles which ordinarily 
float in it and which may be made visible by appropriate means. 
It is demonstrable that the great majority of these particles are 
destructible by heat, and that some of them are germs or living 
particles capable of giving rise to the saine forms of life as those 
which appear when the fluid js exposed to unpurified air. 
It is demonstrable that inoculation of the experimental fluid 
with a drop of liquid known to contain living particles gives rise 
to the same phenomena as exposure to unpurified air. 
Andit is further certain that these living particles are so minute 
that the assumption of their suspension in ordinary air presents 
not the slightest difficulty. On the contrary, considering their 
lightness and the wide diffusion of the organisms which produce 
them, it is impossible to conceive that they should not be sus- 
pended in the atmosphere in myriads. 
Thus the evidence, direct and indirect, in favour of Biogenesis 
for all known forms of life must, I think, be admitted to be of 
great weight. 
On the other side the sole assertions worthy of attention are 
that hermetically sealed fluids, which have been exposed to great 
and long-continued heat, have sometimes exhibited living forms 
of low organization when they have been opened. * 
The first reply that suggests itself is the probability that there 
must be some error about these experiments, because they are 
performed on an enormous scale every day with quite contrary 
results. Meat, fruits, vegetables, the very materials of the most 
fermentable and putrescible infusions are preserved to the extent, 
I suppose I may say, of thousands of tons every year, by a method 
which is a mere application of Spallanzani’s experiment. The 
matters to be preserved are well boiled in a tin case provided 
with a small hole, and this hole is soldered up when all the air 
in the case has been replaced by steam. By this method they 
may be kept for years without putrefying, fermenting, or getting 
mouldy, Now this is not because oxygen is excluded, inasmuch 
as it is now proved that free oxygen is not necessary for either 
fermentation or putrefaction. It is not because the tins are 
exhausted of air, for Vibriones and Bacteria live, as Pasteur has 
shown, without air or free oxygen. It is not because the boiled 
meats or vegetables are not putrescible or fermentable, as those 
who haye had the misfortune to be in a ship supplied with un- 
skilfully closed tins well know. What is it, therefore, but the 
exclusion of germs? I think that Abiogenists are bound to 
answer this question before they ask us to consider new experi- 
ments of precisely the same order. 
And in the next place, if the results of the experiments I refer 
to are really trustworthy, it by no means follows that Abiogenesis 
has taken place. The resistance of living matter to heat is known 
to vary within considerable limits, and to depend, to some extent, 
upon the chemical and physical qualities of the surrounding 
medium. But if, in the present state of science, the alternative 
is offered us, either germs can stand a greater heat than has been 
supposed, or the molecules of dead matter, for no valid or intel- 
ligible reason that is assigned, are able to rearrange themselves 
into living bodies, exactly such as can be demonstrated to be 
frequently produced in another way, I cannot understand how 
choice can be, even for a moment, doubtful. 
But though I cannot express this conviction of mine too 
strongly, I must carefully guard myself against the supposition 
* For a full account of the most recent series of experimen of this descrip- 
tion see Dr. H. C. Bastian’s paper in Nature, No, xxxv., p. 170; No, 
xxxvi., p. 193; and No, xxxvii., p, 219.—Enp, 
