ftS$ WENT A TtOft. 543 



proved an ignis fatuus instead of & pharos to some of his 

 followers. 



. ^m the alcoholic leaven, and sometimes seriously 

 with the latter. They are the weeds of this 



I have said that our air is full of the germs of ferments 

 differing fron 

 interfering with 



microscopic garden which often overshadow and choke the 

 flowers. Let us take an illustrative case. Expose milk to 

 the air. It will, after a time, turn sour, separating like 

 blood into clot and serum. Place a drop of this sour milk 

 under a powerful microscope and watch it closely. You 

 see the minute butter-globules animated by that curious 

 quivering motion called the Brownian motion. But let 

 not this attract your attention too much, for it is another 

 motion that we have now to seek. Here and there you observe 

 a greater disturbance than ordinary among the globules; 

 keep your eye upon the place of tumult, and you will 

 probably see emerging from it a long eel-like organism, 

 tossing the globules aside and wriggling more or less 

 rapidly across the field of the microscope. Familiar with 

 one sample of this organism, which from its motions receives 

 the name of vibrio, you soon detect numbers of them. It 

 is these organisms, and other analogous though apparently 

 motionless ones, which by decomposing the milk render it 

 sour and putrid. They are the lactic and putrid ferments, 

 as the yeast-plant is the alcoholic ferment of sugar. Keep 

 them and their germs out of your milk and it will continue 

 sweet. But milk may become putrid without becoming 

 sour. Examine such putrid milk microscopically, and you 

 find it swarming with shorter organisms, sometimes asso- 

 ciated with the vibrios, sometimes alone, and of ten 'mani- 

 festing a wonderful alacrity of motion. Keep these 

 organisms and their germs out of your milk and it will 

 never putrefy. Expose a mutton-chop to the air and keep 

 it moist; in summer weather it soon stinks. Place a drop 

 of the juice of the fetid chop under a powerful microscope; 

 it is seen swarming with organisms resembling those in 

 the putrid milk. These organisms, which receive the 

 common name of bacteria,* are the agents of all putre- 

 faction. Keep them and their germs from your meat and 



* Doubtless organisms exhibiting grave specific differences aro 

 grouped together under tliis common name. 



