758 SPONTANEOUS CONGESTION AND INFECTIOUS DISEASES. 
but which contains neither germs nor any protean 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 same 
forms of life as those which appear when the fluid is exposed to unpurified 
air. It is demonstrable that inoculation of the experimental fluid witli a 
drop of liquid known to contain living particles gives rise to the same 
phenomena as exposure to unpurified air. And it 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, con- 
sidering the lightness and the wide diffusion of the organisms which produce 
them, it is impossible to conceive that they should not be suspended 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 organisa- 
tion 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 con- 
trary 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up when all the air in the case has been replaced by steam.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 have had the misfortune to be in a ship supplied with 
unskilfully 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 experiments 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 intelligible 
reason that is assigned, are able to re-arrange 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 that I intend to suggest that 
no such thing as Abiogenesis ever has taken place in the past, or ever will 
take place in the future. With organic chemistry, molecular physics, and 
physiology yet in their infancy, and every day making prodigious strides, 
I think it would be the height of presumption for any man to say that the 
conditions under which matter assumes the properties we call “ vital ” may 
