24 THE FLOATING-MATTEE OF THE AIR. 



the external world. And what could that something be 1 

 The dipping of the instrument in oil, and the subsequent 

 precautions, prevented the entrance of oxygen. Or even if 

 you allowed that a few atoms of the gas did enter, it would 

 be an extraordinary assumption to make that these could 

 in so short a time effect such changes in so large a mass 

 of albuminous material. Besides, the pyogenic membrane 

 is abundantly supplied with capillary vessels, through which 

 arterial blood, rich in oxygen, is perpetually flowing ; and 

 there can be little doubt that the pus, before it was evacu- 

 ated at all, was liable to any action which the element 

 might be disposed to exert upon it. 



On the oxygen theory, then, the occurrence of putrefac- 

 tion under these circumstances is quite inexplicable. But 

 if you admit the germ theory, the diiSculty vanishes at 

 once. The canula and trocar having been Ipng exposed to 

 the air, dust will have been deposited upon them, and will 

 be present in the angle between the trocar and the silver 

 tube, and in that protected situation will fail to be wiped 

 oft' when the instrument is thrust through the tissues. Then 

 when the trocar is withdrawn, some portions of this dust will 

 naturally remain upon the margin of the canula, which is 

 left projecting into the abscess, and nothing is more likely 

 than that some paiticles may fail to be washed off by the 

 titream of out-flowing pus, but may be dislodged when the 

 tube is taken out, and left behind in the cavity. The germ 

 theory tells us that these particles of dust will be pretty 

 sure to contain the germs of putrefactive organisms, and 

 if one such is left in the albuminous liquid, it will rapidly 

 develop at the high temperature of the body, and account 

 for all the phenomena. 



But striking as is the parallel between putrefaction in this 

 instance and the vinous fermentation, as regards the greatness 

 of the effect produced, compared with the minuteness and the 

 inertness, chemically speaking, of the cause, you will natu- 

 rally desire further evidence of the similarity of the two 

 processes. You can see with the microscope the torula of 

 fermenting must or beer. Is there you may ask, any 



