276 FRAGMENTS OF SCIENCE. 



film, round it the bacteria will pirouette and wabble 

 until its oxygen has been absorbed, after which all 

 their motions cease. Precisely the reverse of all this 

 occurs with the vibrios of butyric acid. In their case 

 it is the peripheral organisms that are first killed, the 

 central ones remaining vigorous while ringed by a zone 

 of dead. Pasteur, moreover, filled two vessels with a 

 liquid containing these vibrios ; through one vessel he 

 led air, and killed its vibrios in half an hour ; through 

 the other he led carbonic acid, and after three hours 

 found the vibrios fully active. It was while observing 

 these differences of deportment fifteen years ago that 

 the thought of life without air, and its bearing upon 

 the theory of fermentation, flashed upon the mind of 

 this admirable investigator. 



We now approach an aspect of this question which 

 concerns us still more closely, and will be best illustrated 

 by an actual fact. A few years ago I was bathing in 

 an Alpine stream, and returning to my clothes from 

 the cascade which had been my shower-bath, I slipped 

 upon a block of granite, the sharp crystals of which 

 stamped themselves into my naked shin. The wound 

 was an awkward one, but being in vigorous health at 

 the time, I hoped for a speedy recovery. Dipping a 

 clean pocket-handkerchief into the stream, I wrapped it 

 round the wound, limped home, and remained for four 

 or five days quietly in bed. There was no pain, and at 

 the end of this time I thought myself quite fit to quit 

 my room. The wound, when uncovered, was found 

 perfectly clean, uninflamed, and entirely free from 

 matter. Placing over it a bit of goldbeater's-skin, I 

 walked about all day. Towards evening itching and 

 heat were felt ; a large accumulation of matter followed, 

 and I was forced to go to bed again. The water- 



