The Microscopic Germ Theory of Disease. By H. C. Bastian. 67 
material. Throughout all intervening periods such an analogy has 
never been lost sight of ; it has rather been more and more strongly 
dwelt upon. Thus, more than two centuries ago, we find, as has 
been recently pointed out, Robert Boyle, one of our great English 
philosophers, and himself a pioneer in scientific investigation, giving 
strong expression to the then current view : “ He that thoroughly 
understands,” he says, “ the nature of ferments and fermentations 
shall probably be much better able than he that ignores them to 
give a fair account of several diseases (as well fevers as others) 
which will perhaps be never thoroughly understood without an 
insight into the doctrine of fermentation.” Again, in more recent 
times, it was doubtless under the influence of a belief in the same 
analogy between fermentations and the class of diseases of which I 
am about to speak that the term “ zymotic ” was proposed by Dr. 
Wm, Farr, and adopted as a general designation under which nearly 
all these diseases might be included. The consequence of the 
adoption of this nomenclature has been that views as to the nature 
of the infecting something, or contagium , have since been so power- 
fully influenced as to be actually led by views at the time enter- 
tained concerning the nature of ferments — the relationship supposed 
to exist between zymosis and fermentation has indeed been stamped 
and ratified by the very general consent of the profession. 
Omitting for the present any remarks as to the real strength of 
this analogy, I would merely further point out that the foundations 
of the “ germ theory of disease,” in its most commonly accepted 
form, were laid in 1836 and shortly afterwards. The discovery at 
this time of the yeast plant by Schwann and Cagniard-Latour soon 
led to the more general recognition of the almost constant associa- 
tion of certain low organisms with the different kinds of fermenta- 
tions. But it was not till twenty years afterwards that Pasteur 
announced, as the result of his apparently conclusive researches, 
that low organisms acted as the invariable causes of fermentations 
and putrefactions ; that these, in fact, though chemical processes, 
were only capable of being initiated by the agency of living units. 
If, in accordance with this somewhat narrow and exclusive view, 
living units were to he regarded as the sole producers of fermenta- 
tion and putrefaction, then they were sole ferments. The extension 
of this doctrine by medical men to contagious diseases, in face of 
the analogy sanctioned by the use of the term “ zymotic,” became 
only too easy. It was obviously nothing but the logical outcome 
of the two sets of views to hold that low organisms were the true 
contagia, or sole “ germs ” of the so-called zymotic diseases. 
It so happens, therefore, that the very exclusive notion just 
mentioned as to the nature of contagia is at present almost as 
deeply rooted in the minds of the majority of writers on epidemic 
diseases and contagious fevers as was the opposite notion, founded 
