DE. W. EOBEETS ON BIOGENESIS. 
461 
When the bulb was thus charged and sealed, it was weighted with a leaden collar and 
submerged in the semi-upright position (so as to prevent the wetting of the cotton-wool 
plug) in a can full of water. The can was next placed over a source of heat and boiled 
for the required time. The bulb was then withdrawn ; and, when quite-, cold, its neck 
was filed off above the cotton-wool plug as represented in fig. 2, C. Finally, it was set 
aside in the upright position, and maintained at a suitable temperature. 
When it was desired to test the effects of a higher temperature than that of boiling 
water, the can was filled with brine or oil instead of water. 
By this method the materials of the experiment could be exposed for any desired 
time to a desired heat without evaporation, and without the disturbing effects of ebulli- 
tion ; and by subsequently filing off the neck of the bulb above the cotton-wool plug? 
free access of filtered air was provided, so that the conditions most favourable to 
germination were maintained for an indefinite time*. 
In the last four years I have performed several hundred experiments by the “ plugged- 
flask ” and the “ plugged-bulb ” methods, on a great variety of organic liquids and 
mixtures. The flasks and bulbs, after heating, were either placed on a marble slab 
covering a warm-water cistern, which stands in a corner of my room, or they were kept 
in a warm greenhouse. In the former case their temperature ranged from 15° to 
27° Cent., and in the latter from 15° to 32° Cent. 
The following summary exhibits the general results of the experiments. The values 
here given must not, however, be regarded as absolute, but rather as comparative 
and approximative values, which hold good only for the precise quantities, materials, 
and methods of experimenting adopted. The experiments are thrown into three groups 
according to the comparative facility of sterilization exhibited by the various liquids 
and mixtures employed. 
Group I. Substances sterilized by jive or ten minutes ’ boiling in a plugged jlask . — 
The easiest substances to sterilize were infusions of animal or vegetable tissues raised 
to the boiling-point for a few seconds and then filtered. These were, strictly speaking, 
decoctions rather than infusions ; they were sterilized, if quite fresh, by three or four 
minutes’ boiling. In the same category stood solutions of organic salts — citrates, acetates, 
and tartrates, and healthy and diabetic urine. 
Infusions made slowly at blood-heat, and not raised to the boiling-point, generally 
(but not always) required to be boiled for five or ten minutes. Many infusions so made 
let fall a sediment on boiling, and the non-removal of this by filtration appeared to 
increase their resistance to sterilization. It appeared also that the longer the infusions 
were kept before boiling, the greater, as a rule, proved their resistance to sterilization. 
* My experience does not agree with that of Dr. Bastian, that liquids sealed in ebullition are more 
favourably circumstanced for germination than the same liquids under the ordinary pressure of the atmosphere. 
In repeating his experiments I found that the liquids which germinated after being sealed in ebullition, also 
germinated (and much more abundantly) when air was admitted to them through cotton-wool. 
