58 THE FLOATING-MATTER OF THE AIR. 



smallpox, a small quantity of which will in the long 

 run produce the same effect as a large one. 



§ 7. Turnip-Infusion. 



Turnip-juice had a special interest for me in con- 

 sequence of the important part it plays in the experi- 

 ments of heterogenists. I turned to it with the anxious 

 desire to learn whether the statements made concerning 

 it were correct. 



The conditions laid down as to the strength of the 

 infusion, the temperature to be maintained during the 

 process of digestion, and the time it was to be maintained* 

 were scrupulously adhered to. Thus the turnip was cut 

 into thin slices, and digested for four hours in a beaker 

 of water immersed in a water-bath kept at a tempera- 

 ture close to 120°Fahr. The infusion was then carefully 

 filtered, introduced through a pipette into its case, and 

 boiled there for five minutes. Six protected test-tubes 

 were charged with the infusion on the 24th of Sep- 

 tember, while six other tubes were placed on a stand 

 outside, and exposed to the common air of the labora- 

 tory. 



On the 27th the exposed tubes were distinctly 

 turbid, and on microscopic examination were found 

 peopled with Bacteria. The protected tubes, on the 

 contrary, were perfectly clear. A little distilled water 

 had been added to one of the outer tubes. The germi- 

 nal matter, whatever it may be, must have been 

 copious in the water ; for the tube to which it was 

 added far exceeded the other two in the rapidity of life- 

 development. On the 30th this tube contained Bacteria 

 in swarms, of small size, but of astonisliing activity. 

 Tlie other tubes also were fairly charged with organisms, 



' Bastian, ' Beginnings of Life,' vol. i. p. 357, note. 



