462 
DE. W. EOBEETS ON BIOGENESIS. 
This was attributed to the gradual diminution of the acidity of the infusions when they 
were long kept, and to the commencing multiplication of organisms in them. 
The following were the infusions actually experimented on and found conformable to 
the above rule,s : — infusions of beef, mutton, pork, codfish, mussel, carrot, turnip, hay, 
malt, pear, apple, cucumber, cabbage, lettuce, tomatoes, vegetable marrow, and 
parsnep. 
It was found that pieces of carrot, turnip, apple, cucumber, &c. floating in water were 
nearly as easily sterilized as filtered infusions of these substances. But chopped green 
vegetables floating in water (such as kidney-beans, asparagus, cabbage and lettuce, 
and green peas) were very difficult to sterilize by boiling in a plugged flask. Such 
mixtures could be boiled for fifteen or twenty minutes or longer, and yet they almost 
invariably germinated a few days after. Chopped boiled white of egg floating in water 
also behaved in the same way. The singular resistance of green vegetables to steriliza- 
tion appeared to be due to some peculiarity of surface, perhaps their smooth glistening 
epidermis, which prevented complete wetting of their surfaces ; for I found that if they 
were previously thoroughly crushed in a mortar they were sterilized much more easily. 
The difficulty in the case of egg-albumen was presumably due to the alkaline reaction of 
that substance. 
Group II. Substances sterilized by exposure for not less than twenty to forty minutes 
to the heat of boiling water in a plugged bulb. — To this group belonged : — mixtures of 
chopped green vegetables with water (with or without alkali), pieces of flesh-meat, or fish, 
or boiled egg with water, blood, dropsical fluids, milk, albuminous urine, and turnip- 
infusion with cheese. Experiments performed in this fashion often yielded beautiful 
preparations. Owing to the absence of the disintegrating turmoil of ebullition the 
pieces of vegetable or flesh retained their original appearance in the bulbs, and the 
supernatant water preserved its transparency. In the case of egg-albumen and drop- 
sical fluids it was found better, instead of mixing the materials at first with water, to 
proceed as follows: — About two drachms of egg-albumen or dropsical fluid were 
conveyed to the bottom of the bulb by means of a long-necked funnel. The lower 
part of the bulb was then immersed in boiling water until the albumen coagulated 
into a solid cake, then water was introduced and the bulb plugged, sealed, and boiled 
in the usual way. When the experiment was thus performed, the supernatant water 
remained brilliantly limpid and colourless. 
Group III. Substances sterilized by exposure for not less than one or two hours to the heat 
of boiling water in a plugged bulb. — Only one member of this group was encountered, 
namely, superneutralized hay-infusion. Of all the substances examined by me this 
proved to be the most difficult to sterilize. As a large number of experiments were 
made with hay-infusion, and as different specimens of hay differ a good deal from each 
other, a bundle of good meadow-hay was secured, and all the infusions were made with 
this hay, so as to insure as great a uniformity as possible in the materials of the experi- 
ment. The infusion was always made in the same way. The hay was soaked in a mini- 
