464 
DE. W. EOBEETS ON BIOGENESIS. 
boiled an hour, became turbid from Bacteria in three days ; the other four, boiled for 
periods varying from two to five hours, remained permanently sterile. 
5. July 15, 1873. — Six plugged bulbs, charged with hay-infusion alkalized with 1*4 
per cent, of liquor potassse, were boiled together in a can of saturated brine for various 
periods from fifteen to ninety minutes. One of the bulbs was withdrawn from the 
boiling brine every quarter of an hour. The boiling-point of the brine was 109° Cent. 
The first bulb, withdrawn at the end of the first quarter of an hour, became fertile, 
all the rest remained permanently barren. 
6. July 30, 1873. — Nine plugged bulbs, divided into sets of three each, were charged 
with hay-infusion alkalized to three different degrees. The first set was alkalized with 
one per cent., the second with two per cent., and the third with three per cent, of 
liquor potassee. These were all boiled together in a can of saturated brine. One bulb 
of each set was withdrawn from the boiling brine at the end of fifteen minutes, one of 
each set at the end of twenty-five minutes, and the remainder at the end of thirty- 
five minutes. The bulbs of the first set (those which were alkalized with one per 
cent.) all proved fertile in three days ; the other six remained permanently barren. 
This last experiment showed that hay-infusion alkalized with one per cent, of liquor 
potassse possessed an immensely greater power of resistance to sterilization by heat 
than infusions alkalized with two and three per cent. 
7. July 14, 1873. — Six plugged bulbs, charged with hay-infusion alkalized with T4 
per cent, of liquor potassse, were slowly heated in a can of oil up to a temperature of 
125° Cent., and maintained at that temperature for periods varying from five to thirty 
minutes. All of these remained permanently barren. 
In all the above-described experiments of the three groups, the sterilized liquids and 
mixtures, whether they were sterilized by a few minutes’ boiling in a plugged flask, 
or by one or more hours exposure in a plugged bulb to the heat of boiling water, or 
by exposure to the still higher temperature of boiling brine or heated oil, immediately, 
and without exception, recovered their fertility when exposed to the contamination of 
unfiltered air or of ordinary water. Their susceptibility in this respect did not differ 
whether the preparations had been kept for months or even years, or whether they had 
only been kept a few days. 
The following were the general conclusions drawn from the experiments : — 
1. Organic liquids and mixtures are capable of being permanently sterilized by the 
heat of boiling water. Some are sterilized by an exposure to this heat for a few 
minutes, others require an exposure of twenty to forty minutes, and others an exposure 
of one, two, or several hours. A slight difference in the aggregation of the materials or 
a slight difference in their reaction was sufficient to alter very greatly the amount of 
heat required for their sterilization. 
2. There appeared to be two factors of equal importance in the process of steriliza- 
tion, namely, the degree of heat and the duration of its application. These two factors 
were mutually compensatory, in such fashion that a longer exposure to a lower tempe- 
