BACTERIA. 107 
whooping-cough, typhoid fever, malaria, diphtheria, and leprosy, 
are due to the presence of other forms of Bacteria, but the evi- 
dence in all these cases is at present very incomplete. 
Koch’s last work in this direction has been the investigation 
of cholera from the standpoint of the germ theory. As many 
of you have no doubt seen in the daily papers, he and a few fel- 
low-workers went to Egypt during the late epidemic, and have 
now proceeded to India for the same purpose. If this enquiry 
is crowned with success, the defeat of Arabi will sink into insig- 
nificance before this new Egyptian campaign gu the most 
terrible scourge of modern times. 
The study of these disease-ferments, like every other biolo- 
gical enquiry, brings us face to face with the question—What 
was the origin of these things? Creation or Evolution? Were 
the various species of disease-producing Bacteria specially created 
each in the body of the first man or animal to suffer from the 
disease ; or were they, to begin with, formed by a natural pro- 
cess of change from other species:—for instance, from ordinary 
putrefactive but not disease-procucing Bacteria? We know 
that the higher animals which suffer from the diseases in ques- 
tion came into existence at a comparatively late period of the 
world’s history, and that for long ages after the earth was fitted 
to support animal life there were neither birds nor mammals 
existing upon it. It is further known that the special Bacteria 
which cause disease cannot under ordinary circumstances live 
altogether apart from the animals they infest, so that it may be 
taken as tolerably certain that they came into existence after 
their hosts. The question may therefore be stated thus :—Did 
certain ordinary putrefactive Bacteria undergo gradual changes 
of habit, mode of life, etc., until they became fitted to live .only 
in the blood or other tissues of the higher animals, thus being 
evolved into disease-ferments, or were the latter created anew in 
the tissues? Now, to say that this latter event took place is 
equivalent to saying they were made either out of nothing, or 
out of the materials of the tissues in which they are found, 
either of which, from the purely scientific point of view, is tanta- 
mount to an admission of spontaneous generation; and this, 
as I have already pointed out, is rendered highly improbable by 
the testimony of recent research. 
The tendency of the natural man has always been to evoke a 
miracle to explain any phenomenon beyond his comprehension ; 
the work of men of science has always been to try and bring 
such phenomena within the bounds of natural law. The gospel 
of science, if I may use the expression, is that in this marvellous 
universe of ours there “is no variableness neither shadow of 
turning”; in other words, that there zs an ascertainable Order 
of Nature. 
The great discoveries of Copernicus, Galileo, Newton, Lyell, 
and Darwin, have all tended in the same direction ; all have 
been attacked by those whose faith is so small, or whose i impa- 
tience so great, that they prefer a traditional theory of the uni- 
