FERMENTATION AND DISEASE. 147 



which the infusion was inoculated. At the same time the infusion 

 will have passed from a state of sweetness to a state of putridity. Let 

 a drop similar to that which has produced this effect fall into an open 

 wound: the juices of the living body nourish the bacteria as the beef 

 or mutton juice nourished them, and you have putrefaction produced 

 within the system. The air, as I have said, is laden with floating mat- 

 ter which, when it falls upon the wound, acts substantially like the 

 drop. Prof. Lister's aim is to destroy the life of that floating matter 

 to kill such germs as it may contain. Had he, for example, dressed 

 my wound, instead of opening it incautiously in the midst of air laden 

 with the germs of bacteria, and instead of applying to it gold-beater's- 

 skin, which probably carried these germs upon its surface, he would 

 have showered upon the wound, during the time of dressing, the spray 

 of some liquid capable of killing the germs. The liquid usually em- 

 ployed for this purpose is dilute carbolic acid, which, in his skilled 

 hands, has become a specific against putrefaction and all its deadly 

 consequences. 



We now pass the bounds of surgery proper, and enter the domain 

 of epidemic disease, including those fevers so sagaciously referred to 

 by Boyle. The most striking analogy between a contagium and a 

 ferment is to be found in the power of indefinite self-multiplication 

 possessed and exercised by both. You know the exquisitely truthful 

 figures regarding leaven employed in the New Testament. A particle 

 hid in three measures of meal leavens it all. A little leaven leaveneth 

 the whole lump. In a similar manner a particle of contagium spreads 

 through the human body and may be so multiplied as to strike down 

 whole populations. Consider the effect produced upon the system by 

 a microscopic quantity of the virus of small-pox. That virus is to all 

 intents and purposes a seed. It is sown as leaven is sown, it grows and 

 multiplies as leaven grows and multiplies, and it always reproduces 

 itself. To Pasteur we are indebted for a series of masterly researches, 

 wherein he exposes the looseness and general baselessness of prevalent 

 notions regarding the transmutation of one ferment into another. He 

 guards himself against saying it is impossible. The true investigator 

 is sparing in the use of this word, though the use of it is unsparingly 

 ascribed to him ; but, as a matter of fact, Pasteur has never been able 

 to effect the alleged transmutation, while he has been always able to 

 point out the open doorways through which the affirmers of such trans- 

 mutations had allowed error to march in upon them. 1 



The great source of error here has been already alluded to in this 

 discourse. The observers worked in an atmosphere charged with the 

 germs of different organisms; the mere accident of first possession 



1 Those who wish for an illustration of the care necessary in these researches, and of 

 the carelessness with which they have in some cases been conducted, will do well to con- 

 suit the Rev. W. H. Dallinger's excellent " Notes on Heterogenesis," in the October num- 

 ber of the Popular Science Review. 



