1915] on Back to Lister 383 



It is true that both Pasteur and Lister did not fail to recognize 

 that if the air carried the germs it must deposit them upon the sur- 

 face of everything, and that therefore the surface of every soUd and 

 the whole of every liquid must be, or might be, infectious. It is 

 also true that Lister bore this in mind, and acted on the assumption 

 that it was true from the very first. But still it was the air to which 

 he paid and directed most attention— more attention, as we shall 

 see, than it deserved. He probably did not recognize, he certainly 

 did not say, that his precautions with regard to other sources of 

 infection were far more important than those which he took with 

 regard to infection from the air. 



The sceptics and cavillers, the believers in spontaneous genera- 

 tion, kept saying, " Show us your germs in the air.*' They did not 

 doubt that organisms were found in putrefying substances, they could 

 not do that ; but they said that they might be accidental, the result 

 of putrefaction, not the cause of it, and asked for proof that germs 

 existed in the air. Pasteur had tried to meet this objection by 

 filtering the air through gun-cotton, which he afterwards dissolved 

 and submitted the solution to the microscope. There were certainly 

 objects which he was satisfied Avere germs, but the doubters were still 

 unconvinced. 



A few years later, about 1869, John Tyndall, whose eloquent 

 addresses on " Dust and Disease " were listened to with breathless 

 attention in this hall, succeeded in showing to the naked eye of 

 untrained amateurs, the existence of, and the amount of, floating 

 dust in any given sample of air, by passing through it a concentrated 

 beam of light. Next he showed that, if the air was left undisturbed, 

 say in a glass flask, the dust settled, and there was nothing for the 

 beam to illuminate. Then he produced the same result by filtering 

 the air, or by raising to a great heat a piece of platinum wire passing 

 through the flask which burnt up the dust. Finally, he proved, by 

 a series of charmingly simple experiments, that what he called optically 

 pure air was incapable of setting up decomposition in putrescible 

 fluids, whereas optically impure air invariably caused them to de- 

 compose. 



Most of these facts were known to Lister in 1865. All the 

 evidence pointed in the same direction ; and therefore, stated in 

 the simplest way, the problem seemed to be to kill the germs which 

 might have gained access to the wound before it came under treat- 

 ment, and to prevent the air from carrying in others afterwards. 



He first applied what he now called the antiseptic principle to 

 compound fractures, injuries which, above all others, were liable to 

 be followed by those hospital plagues— pya?mia, erysipelas, and 

 hospital gangrene. 



He had to choose between the three recognized methods of 

 excluding the germs— filtration, calcining, and chemical antiseptics — 

 and he naturally selected the last as the most convenient. ThQ first 



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