OF TREATMENT IN SURGERY 57 



bent necks.] Observe, then, what inference is to be drawn from this remarkable 

 fact. There has been nothing in the bent tubes that could by possibility inter- 

 fere with the transit of any of the gases of the atmosphere. At first, indeed, 

 they contained some drops of condensed aqueous vapour ; but these in a few 

 days disappeared, the tubes being dried by the air passing through them, and 

 I beg you particularly to observe that, in the instance before you, the tube is 

 open and dry from end to end. Every atmospheric gas, therefore, in whatever 

 proportion it may exist, must have daily passed unchanged into the flasks to 

 exert upon the putrescible urine an}- influence of which it was capable ; yet 

 no putrefaction has occurred. The urine has remained absolutely free from 

 putrefactive changes for half a year, though exposed during the whole of that 

 time to the action of all the gases of the atmosphere, perpetualh' renewed. 

 Surely we are safe in drawing the inference that, in the case of this putrescible 

 substance at least, the atmospheric gases alone are incapable of inducing 

 putrefaction. What is it, then, that is essential to putrefaction of urine by 

 atmospheric influence which the bent tubes have arrested ? It cannot be anv 

 of the gases ; but it may be, it must be, some particles suspended in them, some 

 dust, which the angles of the tubes might arrest mechanically. And this con- 

 clusion, inevitable as it is from the consideration of the flasks with bent necks, 

 is confirmed b}^ comparison with the other in which the orifice, though narrower, 

 was purposely so arranged as to afford a better chance for the introduction of 

 particles of dust, and in which accordingly chemical changes soon declared 

 themselves in the contained liquid. 



This experiment has an equally clear bearing upon the question of equi- 

 vocal generation, essentially involved in the germ theory of putrefaction. It 

 illustrates strikingly what appears to be the truth ; namely that even the lowest 

 and most minute forms of life with which we are conversant, do not arise spon- 

 taneously in organic substances as the result of the operation of the atmospheric 

 gases upon them, but take their origin from definite particles or germs, the 

 offspring of pre-existing organisms. For, on the one hand, we have seen that 

 this liquid, which is a most favourable nidus for such development, has remained 

 for half a year free from any change in its appearance such as even microscopic 

 organisms would produce, though exposed freely during that long period to 

 the influence of air unchanged except in the circumstance that it has been 

 filtered of suspended particles. And, on the other hand, this same liquid 

 similarly situated in every respect, except in the fact tliat particles floating in 

 the atmosphere might gain access to it, soon presented, even to the naked eye, 

 two distinct kinds of vegetation, each springing from a definite point, and grow- 

 ing steadily from that point, but incapable of taking origin in any other part 



