472 
DE. W. EOBEETS ON BIOGENESIS. 
have ever been actually seen and identified. The ingenious attempts of Pasteuk and 
others to demonstrate germs in the air are manifestly illusory. Like them I have 
repeatedly collected air-dust and found abundance of molecules, circles, spheres, and 
particles of various kinds under the microscope ; but these could not be identified as 
true spores, nor distinguished from particles of inert dust. Indeed the objects sought 
after are so minute and so wanting in characteristic forms, that such a search, with our 
present instruments, appears well-nigh hopeless*. 
But although an obscurity hangs over the precise nature of these particles, the reality 
of their existence is not doubtful ; nor is it doubtful that the ordinary development of 
Bacteria and Torulce is directly due to their agency. These fundamental propositions 
of the panspermic theory may be regarded as the expression of acquired facts in 
science. 
I come now to deal with those cases which have hitherto proved a stumbling- 
block to the general acceptance of the panspermic theory — namely, the development of 
Bacteria (without the possibility of fresh infection) in liquids and mixtures which have 
been subjected to a boiling heat. 
It is truly, as Dr. Hughes Bennett has remarked, a “ violent assumption ” that living 
particles can survive a boiling heat. Nevertheless it is an assumption that may be justified 
both on grounds already supplied in the preceding sections and by direct experiment. 
The a priori argument stands thus: — Take milk. It has been shown that pure milk, drawn 
without extraneous contamination from the teat, has no germinating power. The ger- 
mination of ordinary milk is therefore due to imported germs ; and if the same milk 
still germinate after boiling in closed vessels, this must be due to the survival of these 
germs. Or take the case of egg-albumen. Uncontaminated egg-albumen does not ger- 
minate when mixed with sterilized water. But if pieces of boiled white of egg be mixed 
with ordinary water, the mixture invariably germinates after boiling (in a plugged flask) 
for ten or fifteen minutes. This can only be explained by supposing that the germs 
contained in the ordinary water have survived the boiling. 
But this point was tested by direct experiments with hay-infusion. Two series of 
experiments were made — A and B. 
A. In the first section it has been shown that alkalized hay-infusion will germinate 
after exposure for more than an hour to the heat of boiling water, but if the heat be 
continued for two or more hours permanent sterilization is effected. In the course of 
my experiments a considerable number of bulbs containing alkalized hay-infusion, 
sterilized in this way, had accumulated on my hands. These bulbs were plugged with 
* A striking illustration of the minuteness of the spores of certain organisms is given in a remarkable 
paper on the life-history of a cercomonad by Dallingek and Drysdale in the Microscopical Journal for August 
1873. The spores of this organism were so minute that they could not be individually recognized even with 
the Jjj objective. They could only be recognized with this high power as seen in enormous aggregation and 
motion in a mass. With a magnifying-power of 2500 diameters they were only just visible as the minutest 
dots. 
