106 THE FLOATING -MATTEE OF THE AIR. 



The rapidity of development in an infusion infected 

 by either a speck of licjuid containing Bacteria, or by a 

 drop of distilled water, is extraordinary. On the 4th of 

 January I dipped a thread of glass almost as fine as a hair 

 into a cloudy turnip-infusion, and introduced the tip 

 only of the glass fibre into a large test-tube containing 

 an infusion of red mullet : twelve hours subsequently 

 the perfectly pellucid liquid was cloudy throughout. A 

 second test-tube containing the same infusion was in- 

 fected with a single drop of the distilled water furnished 

 by Messrs. Hopkin and Williams; twelve hom-s also 

 sufficed to cloud the infusion thus treated. Precisely 

 the same experiments were made with herring infusion, 

 with the same result. In the winter season several days' 

 exposure to warmed air are needed to produce this effect 

 with air-germs. 



On the 31st of December a strong infusion was pre- 

 pared by digesting turnip in distilled water at a tem- 

 perature of 120° Fahr. It was divided between four large 

 test-tubes, in one of which the infusion was left unboiled, 

 in another boiled for five minutes, in the two remain- 

 ing ones boiled and, after cooling, infected with one 

 drop of beef-infusion containing Bacteria. In twenty- 

 four hours the unboiled tube and the two infected ones 

 were cloudy, the unboiled tube being the most turbid of 

 the three. Tlie infusion in the unboiled tube was pecu- 

 liarly limpid after digestion ; for turnip it was quite 

 exceptional, and no amount of searching with the micro- 

 scope could reveal in it at first the trace of a living 

 Bactenum; still germs were there which, suitably 

 nourished, passed in a single day into Bacterial swarms 

 without number. Five days failed to produce an effect 



matter between the germ and its environment ; and this inter- 

 change must obvioualy depend upon the character of the encom- 

 passing liquid. 



