106 THE FLOATING-MATTEE OF THE AIR. 



The rapidity of development in an infusion infected 

 by either a speck of liquid 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 hours 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. The 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 

 Bacterium ; 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 obviously depend upon the character of the encom- 

 passing liquid. 



