16 Proceedings of the Royal Physical Society. 
The triumphs of surgery, of preventive inoculation, of hygiene 
in relation to specific infective disease, of preservation of food, 
have all had their origin in the knowledge gained during the 
battle which waged around the theory of spontaneous genera- 
tion or generatio equivoca, and although this was ultimately 
proved to be untenable, those who fought so vigorously for it 
came out of the contest defeated, no doubt, but not disgraced, 
for we owe to them and to their attitude of scepticism, and to 
the free, ingenious, and honest criticism which they passed 
on imperfectly conducted experiments, and on vague and 
inadequately supported theories, the fact that the experiments 
of their opponents gradually became not only more convincing, 
but ultimately were perfected ; and if to-day we have reliable 
methods of sterilisation and of obtaining pure cultivations 
of different organisms, it is because nothing was taken for 
granted, because able men were found to take sides in this 
controversy, and to engage in a fight that was fought out to 
the death. 
Gentlemen, I will not weary you with a long description 
of what these micro-organisms are, nor will I enter into the 
oft told story of the development of the germ theory of 
putrefaction and fermentation and of disease; I would only 
have you remember that an enormous amount of work has 
been done to prove that bacteria belong to the animal 
kingdom. It may now, however, be generally accepted that 
they are to be transferred to the domain of the botanist. We 
must remember, however, that they are of a low form of 
protoplasm, and that although in certain cases they may be 
considered as having special functions, the general powers of 
protoplasm are most strongly developed in them, and that 
their specific powers are more readily affected than where 
development is of a higher order. 
A patient accumulation of facts at length made it pos- 
sible to build up a theory that would stand the test of time 
and experiment, and it became easy to prove, by the use of 
new methods, what was at first only a theory, and, by the 
carrying on of fresh experiments, to fill in the gaps that 
were still left. 
As early as 1814, Dr Burrows, in this country, had 
