
300 THE EVOLUTION OF LIFE 
as depending upon certain alterations in the putre- 
factwe process.” Prof. Hueppe of Prague has also 
quite recently expressed the very similar view that 
the origin of all common infectious diseases is 
‘phylogenetically traceable to putrefactive pro- 
cesses,” 
If we turn again to one of the best modern books 
on this subject, the ‘‘ Principles of Bacteriology,” by 
Lehmann and Neumann, we find the following 
important statements (1901, pp. 118-119), ‘The 
division of bacteria into pathogenic and non-patho- 
genic, etc., as is still always done in text-books, 
has failed absolutely. We can understand and 
know the pathogenic varieties only if we study 
simultaneously the non-pathogenic, from which the 
former have once originated and still always origt- 
nate.’ They say also, “We certainly believe it 
belongs to the future to convert varieties of bacteria 
into others in a manner scarcely to be imagined 
to-day. The forms of the Micrococcus pyogenes 
are convertible into each other; the Bacterium 
pyecaneum and Bacterium fluorescens can indeed 
almost certainly be converted into each other; and 
similar statements regarding typhus and coli, diph- 
theria and pseudo-diphtheria, etc., are always still 
looked upon with scepticism, but the possibility, 
nay even the probability, can scarcely be contested 
any more.” 
Let me now cite a few illustrations of these 
1 Harben Lecture, in 7he Journal of State Medicine, Nov. 1903, 
p- 641. 
