56 THE FLOATING-MATTER OF THE AIR. 



five minutes in the brine-bath, and abandoned to the air 

 of the case. A series of exposed tubes containing the 

 same infusion, similarly treated, was placed beside the 

 protected ones. On the 4th all the outside tubes were 

 muddy and swarming with Bacteria, Schroeder and 

 Cohn have shown that different colours are produced by 

 different kinds of Bacteria. In the three exposed tubes 

 here referred to a yellow-green pigment was developed. 

 More than three months after its preparation, the 

 infusion, considerably diminished by evaporation, re- 

 mained in all the protected tubes as clear as at first, 



§ 5. Beef -Infusion, 



A beef-steak, after having its fat removed, was cut 

 up into small pieces, and digested for three hours at a 

 temperatm-e of 120° F. The liquid was then poured 

 off, boiled, and filtered. It was as, clear and colourless 

 as pure water. On the 4th of October it was introduced 

 into three tubes protected by a chamber of 451 cubic 

 inches capacity. It was boiled for five minutes in a 

 brine-bath. Three exposed tubes, containing the same 

 infusion, were placed beside the protected ones. On the 

 5th the exposed tubes showed signs of haziness, on the 

 6th they were turbid, of a green colour, and filled with 

 Bacteria, They have maintained for months their mud- 

 diness, colour, and swarming life. 



While the exposed beef-infusion putrefied in this 

 way, all the protected infusions rer)iained perfectly 

 sweet and clear, 



§ 6. Haddock-Infusion, 



The haddock was cut up and digested on the 24th 

 of September; it was afterwards introduced into six 

 tubes, protected by a chamber. On boiling, its albumen, 



