310 bft. WILLIAM ROBERTS. 



pose to lay before you evidence that both these allegations 

 are unsustainable, and to prove that bacteria, like other 

 organisms, arise from pre-existing parent germs, and in no 

 other way, and that they are the actual agents in all decom- 

 position and putrefaction. 



The first proposition I shall endeavour to establish is this ; 

 that organic matter has no inherent power of generating bac- 

 teria, and no inherent power of passing into decomposition. 



I have here placed before you samples of three sets of pre- 

 parations, out of a large number in my possession, which 

 serve to substantiate this proposition. 



The first set consists of organic liquids and mixtures 

 which have been rendered sterile by a sufficiently prolonged 

 application of the heat of boiling water. They are com- 

 posed of infusions of vegetable and mineral substances, frag- 

 ments of meat, fish, albumen, and vegetables, floating in 

 water. They are contained in oblong glass bulbs, and are 

 protected from the dust of the air by a plug of cotton-wool 

 inserted into the necks of the bulbs, but freely pass to its 

 gaseous elements, which pass in and out through the cotton- 

 wool. They are all, as you see, perfectly transparent and 

 unchanged, though most of them have been in my possession 

 for several years. 



The second set consists of organic liquids which have been 

 simply filtered under pressure through unglazed earthenware 

 into sterilised flasks. They include acid and neutralised 

 urine, albuminous urine, diluted blood, infusions of meat and 

 of hay. As these preparations were obtained by a method 

 which is in some respects new, I will describe it to you. A 

 piece of common tobacco-pipe, about six inches long, served 

 as the filter. This was secured by india-rubber piping to 

 the exit-tube of one of the little flasks used by chemists for 

 fractional distillation. The flask is first charged with dis- 

 tilled water, and then a tight plug of cotton-wool is inserted 

 into its neck. The flask is next set a-boiling briskly over a 

 lamp. The steam rushes through the cotton-wool plug and 

 through the tobacco-pipe, clearing both these passages of any 

 germs they might contain. When the water has nearly 

 boiled away, the end of the tobacco-pipe is hermetically 

 sealed with melted sealing-wax. After a little more boiling, 

 the flame is withdrawn and the neck of the flask is instantly 

 closed with a tight vulcanite cork. The apparatus is now 

 ready for action, and the tobacco-pipe is immersed in the 

 liquid to be filtered. When the flask cools, a vacuum is 

 created within it, and this serves as a soliciting force to draw 

 the liquid through the earthenware into the flask. The pro- 



