350 AN ADDRESS ON 



were in almost entire ignorance of the various species of bacteria, and there was 

 no reason then to doubt that any of them getting into a wound would produce 

 serious mischief. Happily, however, we now know the case to be really extremely 

 different. It is but a small proportion of these organisms which are capable 

 of doing mischief in surgery ; and even such species as do produce injurious 

 effects, when they develop in wounds, are by no means always sure of gaining 

 a footing when introduced into them. This depends upon two circumstances. 

 In the first place, we have learned that although putrid blood teems with bacteria 

 of various kinds, some of them in the highest degree pathogenic, normal blood- 

 serum is by no means a very favourable soil for the growth of bacteria, provided 

 that they are in an attenuated condition — not in too strong a dose. I may 

 illustrate what I mean by a simple experiment. If we draw blood, with anti- 

 septic precautions, say from a horse or from an ox, into purified stoppered 

 bottles, and simply place them in a stove at the temperature of the human body, 

 the blood remains permanently unaltered. If we dip the point of the finest 

 needle into already putrefied blood and touch the blood in one of those bottles 

 with the needle so contaminated, and replace the bottle in the stove, to an abso- 

 lute certainty within twenty-four hours the blood is foul and putrid throughout. 

 But if, instead of applying the putrid blood in substance, I mixed it with an 

 abundance of sterilized water, so as to diffuse the bacteria widely, at the same 

 time washing them of their products, I found that a small drop of this diluted 

 putrid blood, though it contained abundance of bacteria, failed for days together 

 to induce putrefaction. The grossly putrid material — if I may so speak — 

 inevitably causes putrefaction in the blood, but the washed and widely diffused 

 bacteria are unable to do so.^ 



Then there is another even more important point, and that is that the 

 living animal body has the power of defending itself against microbes introduced 

 into it, chiefly, as it appears, by the process of phagocytosis, which Metchnikoff 

 has revealed ; so that if the micro-organisms are not introduced in too large 

 a dose, they are consumed by the wandering cells. These two great truths, then, 

 have been taught us by advancing science : that normal serum is not a good 

 soil for the development of attenuated microbes, and that bacteria introduced 

 among the tissues, if in not too concentrated a form, are disposed of by phago- 

 cytosis. The result is that microbes in the form in which they are present in 

 the air are unable to develop in our wounds ; and thus we are able to disregard 

 in our operations the once dreaded atmospheric dust. 



Hence we may dispense entirely with irrigation, whether in the form of the 

 spray, which was a kind of irrigation, or in any other ; in fact, our operations 



^ See Transactions of the International Medical Congress, 1881, vol. ii, p. 372 (p. 281 of this volume). 



