INTRODUCTION XXV 
of Surgery in the University of Glasgow, was constantly speculating on these 
matters, especially on the cause of the putrefaction of the discharges in 
wounds, and during one of his discussions with friends the suggestion was made 
that the perusal of Pasteur’s papers on fermentation and spontaneous generation, 
which had then recently appeared, might be of assistance to him. This sugges- 
tion was fertile, and it may well be imagined how great a revelation to Lister 
were these researches of Pasteur. The oxygen theory of putrefaction, which had 
- seemed to oppose all advance, was at once swept away, and the problem was now 
seen to be not to exclude intangible gases, but to deal with living organic particles 
which could be destroyed and the characteristics of which could be carefully 
studied. . 
It is interesting to note that previous to the appearance of Pasteur’s work 
three papers had been published which really laid the foundation of the germ 
theory and of modern bacteriology ; these were by Schultze in 1836, Schwann in 
1837, and Cagniard-Latour in 1838. The two latter authors brought forward 
a large amount of evidence which satisfied them that the alcoholic fermen- 
tation of grape-juice was due not to oxygen but to the growth in the fluid of the 
Torula cerevisiae. Schwann also studied the putrefactive decomposition of meat- 
juice and other organic substances, and came to the conclusion that it was not the 
gases of the air which caused these changes, but organic particles which floated in 
the air, and could be destroyed by heat. He went further and ascribed all fer- 
mentative processes to the growth of the organisms found in fermenting liquids. 
In 1854 additional evidence was brought forward by Schréder and Dusch, who 
showed that it was not necessary, following the example of previous observers, 
to calcine the air which had access to the flasks, but that putrefaction did not 
occur in organic fluids contained in flasks if the air entering the flasks were 
filtered through cotton-wool. Pasteur finally (1864) completed the proof by 
showing that it was not necessary either to heat the air or to filter it before 
admitting it to properly prepared organic fluids, but that if it were con- 
ducted along a tortuous tube in which the dust could settle before it reached 
the fluid, no change took place in the organic matter. He showed also that if 
flasks containing putrefactive material were left open in a place where the air 
had been undisturbed sufficiently long to allow the dust to settle, as, for example, 
in a cellar, no decomposition took place, nor did any micro-organisms appear in 
the fluids. 
Apart from these researches on the causes of fermentation, much heated 
discussion had gone on for many years as to the significance of the minute 
“animalculae ’ which appeared in decomposing fluids, and the question whether 
these organisms originated de novo from the organic fluids in which they were 
