VITALITY OF PUTKEFACTIVE ORGANISMS. 217 



there a living layer through which no oxygen could pass 

 to the liquid underneath, which, thus surmounted, 

 remained as clear as water. The observation of these 

 facts, and many others of a similar bearing, suggested 

 inquiry into the effect which the more or less perfect 

 withdrawal of the air from the infusions would have 

 upon the development of life. 



A few experiments with an ordinary air-pump were, 

 in the first instance, made. The necks of a series of 

 pipette bulbs charged with turnip-infusion were drawn 

 out at the middle to a tube of very small diameter. 

 The open end of the neck being connected with the 

 air-pump, the bulbs were exhausted. In some cases, 

 to render the removal of the air more perfect, hydrogen 

 was admitted into the bulb and was afterwards with- 

 drawn by the air-pump. Before they were detached 

 from the pump the bulbs were immersed in lukewarm 

 water. They boiled freely, and after a minute's ebul- 

 lition the narrowed necks were hermetically sealed. 

 The bulbs were then submerged in cold water, which 

 was gradually raised to 212° F. and kept boiling for 

 ten minutes ; they were afterwards removed and placed 

 in a room with a temperature of about 90° Fahr. 



Four bulbs were thus treated in a preliminary expe- 

 riment on the 7th of March. Two of them remain 

 crystal clear to the present hour ; the two others became 

 cloudy, but remained entirely free from scum. The 

 cloudiness, I may add, was barely perceptible, but it 

 was perfectly distinct to the practised eye. 



By such means, however, the removal of the air 

 must have been more or less imperfect, and I therefore 

 resorted to the far more effective Sprengel pump. To 

 connect them with the pump, the bulbs were thrown 

 into the form represented in fig. 21. After the neck of 

 the bulb had been plugged with cotton-wool it was bent 



