460 
DR. W. ROBERTS ON BIOGENESIS. 
described prove that there are liquids which germinate after exposure to the heat of 
boiling water for even two and three hours, or after exposure to a heat of 9° Cent, 
above that of boiling water for more than half an hour. 
In pursuing these inquiries it was found that the method of direct boiling over a flame 
in a plugged flask was unsuited to liquids which required a prolonged application of 
heat for sterilization. In the first place, the evaporation that ensued on boiling for 
fifteen or twenty minutes seriously altered the concentration of the materials ; and, 
secondly, this method did not permit an accurate gradation of temperature ; for the 
boiling-point in a plugged flask was observed to rise above the normal temperature of 
ebullition from 3° to 6 9 Cent, according to the tightness of the plugging. 
To obviate these disadvantages another plan was adopted ; and, as most of my experi- 
ments were performed by this method, it is necessary to describe it more particularly. 
It will be referred to as the “ plugged-bulb ” method. 
The “ jplugged-bulb” Method . — An ordinary delivery-pipette, having on it an oblong 
bulb capable of containing 30 to 50 cub. centims., was sealed hermetically at one end 
Fig. 2. The plugged-bulb experiment. 
A. The bulb charged. B. The bulb charged, plugged, and sealed ready for heating. C. The bulb with its 
neck filed off, and set aside to see if it will germinate. The figures are drawn about half the actual size. 
(see fig. 2, A). The materials of the experiment were then introduced into the bulb 
until it was two thirds full. The inside of the neck of the bulb was next wiped dry, 
and a plug of cotton-wool ( a ) was inserted about its middle. Lastly, the neck was drawn 
out above the plug and sealed in the flame, as represented in fig. 2, B. 
