12 Proceedings of the Royal Physical Socrety. 
minds it appeared, however, that these experiments of Need- 
ham’s left loopholes for other explanations than those which 
he had given, and Bonnet, of Geneva, suggested that the 
vessels used by Needham were not hermetically sealed; that 
an almost invisible opening would be quite sufficient to serve 
as a means of entrance to organisms so minute as those with 
which he was dealing; and that, on the other hand, there 
was a possibility that the germs were so far resistant to 
increase of temperature that they might live through a short 
period (a few minutes only) of treatment with boiling water. 
Abbot Spallanzani followed up, by his wonderful experi- 
ments, the theoretical criticism of Bonnet. After convincing 
himself that organisms did actually develop in unboiled 
infusions, even when the outer air was rigorously excluded, 
he argued that the germs or eggs, as he termed them, of 
micro-organisms might exist on the walls of the vessel, on 
the material of which the infusion was made, or suspended 
in the air within the vessel. To get rid of these germs from 
the vessels, he heated the latter over the fire, then filling 
them rapidly with his infusions, he allowed them to cool, 
and sealed them hermetically. He still found, however, 
that after a few days a number of organisms made their 
appearance. Could the organisms have got in along with 
the air during the process of cooling ? 
To set this question at rest, he made a number of infusions 
in hermetically-sealed flasks, and boiled them for a whole 
hour, with the result that in flasks so treated no organisms 
or traces of their activity could be found; if, however, the 
sealing was in any way interfered with, organisms soon made 
their appearance. From these experiments he concluded 
that living germs were necessary for the development of 
putrefactive organisms. This fact once established, the whole 
question was much simplified, and the principle on which 
it rested was soon utilised in Paris and elsewhere in the 
methods adopted for ensuring the preservation of various 
food-stuffs—methods which, with few modifications, have 
been handed down to the present day. It was, of course, 
objected that Spallanzani had shut out air, and therefore 
oxygen, from his vessels; or that he had so altered the 
