68 The Microscojpie Germ Theory of Disease. By H, C. Bastian. 
upon the physico-clieniical doctrine of Liebig, some twenty years 
ago. Then a ferment was regarded as a portion of organic matter 
(not necessarily Hving) in a state of molecular change (" motor 
decay "), which, by virtue of its own unstable nature, was capable 
of communicating molecular movement (chemical change) to other 
unstable or fermentable mixtures. This broader notion was pro- 
mulgated by Liebig at a time when less was known than at present 
as to the constant association of low organisms with the processes 
of fermentation and putrefaction. The nature of this relationship 
was, in fact, never adequately grappled with by him. Still, views 
of the kind promulgated by Liebig would not give anything like 
the same support to the germ theory of disease as that afforded 
by the doctrines of Pasteur. Those who have adopted and deve- 
loped Liebig's views now hold that living organisms, though they 
may operate as ferments, act in this capacity merely by virtue of 
the chemical changes which the carrying on of their growth neces- 
sitates ; and that other chemical changes taking place during the 
decay of organic matter may make fragments of it (in the dead 
state) almost equally capable of initiating fermentative changes in 
suitable media ; whilst in either case bacteria or allied organisms 
are prone to be engendered as correlative products. 
In the present day, therefore, two questions seem to need the 
serious consideration of medical men. In the first place, it may be 
asked, Are we justified in relying so strongly upon the analogy 
between fermentation and zymosis? Secondly, we may inquire 
whether the researches by which Pasteur claims to have established 
the sole nature of ferments are so conclusive as they have been 
commonly regarded ? In reply to the first question, certain quali- 
fying considerations will hereafter be stated, though it may be at once 
admitted that the analogy is so strong as to make it likely to continue 
to exercise a very considerable influence upon medical opinion. It 
therefore becomes all the more necessary for medical men to look 
to the foundations of Pasteur's doctrine, if they are not prepared 
blindly to follow his dicta on a subject which is of so much impor- 
tance for medical science. It was with this view that I undertook, 
a few years ago, and shortly after I had been called upon to teach 
pathology, a series of investigations bearing upon this subject. In 
consequence of this work I was compelled, as others had been, to 
refuse assent to the exclusive doctrines of Pasteur concerning the 
nature of ferments. I do not enter upon this discussion now^ I 
maintain, however, that my own investigations and those of others 
show that units of living matter are not sole ferments, since fer- 
mentation and putrefaction may be initiated in their absence, and 
since it can be shown that mere particles or fragments of organic 
matter may act in this capacity. For a brief exposition of the 
grounds of this belief I would refer those interested in the matter 
