CONCLUSION. 295 
constitutes. contagion, could only be defined by having 
recourse to the term “ catalytic action,’ which merely 
placed the solution of the problem another step back, 
and substituted one unknown thing for another.* The 
parasitic theory will have done much for science if it 
only delivers us from “miasmata,” “effluvia,” and, 
above all, “catalytic action.” As soon as it had been 
shown that miasmata and effluvia, as well as virus, were 
only air-germs—that is, microbes and their spores—a 
brilliant light was thrown on all pathology, of which 
the benefits may be measured by the great work accom- 
plished in this direction within the last ten years. 
This theory has given us Guérin’s protective treat- 
ment of wounds, Lister's antiseptic dressing, and 
Pasteur’s new vaccine, and these three great dis- 
coveries. are enough to render the hypothesis immortal, 
even admitting that it is only an hypothesis. The 
adverse theories, when opposed to the microbian 
theory, can show us no progress effected in science, 
and this suffices to condemn them. 
Moreover, the microbian theory is no longer in 
the primitive stage in which it can be regarded as 
a pure hypothesis, since it has entered the domain 
of positive facts. Before an infectious disease can be 
considered due to the presence of a specific microbe, 
* See, for example, the article Miasmes in Nysten’s Dictionary 
(Littré and Robin, edit. 1864): “ Miasma is constituted by the organic 
substances of the atr, in different stages of catalytic modification.” These 
words are printed in italics by Robin himself. See also the words 
Ejfluves, Catalytiques, Virus, etc., in the same dictionary. 
