DR. W. ROBERTS ON BIOGENESIS. 
463 
mum of water for four hours at blood-heat. The infusion was then filtered and diluted 
with ordinary water until it had a specific gravity of 1006. Prepared in this way, hay- 
infusion had the colour of sherry ; it was slightly acid in reaction, and it boiled without 
forming any sediment. When neutralized with ammonia or liquor potassse, it threw down 
a copious sediment which increased on boiling ; this sediment subsided completely on 
standing, and left a perfectly transparent supernatant liquor. This perfect transparency 
permitted the detection of the slightest turbidity from the development of Bacteria. 
Unneutralized hay-infusion, when quite fresh, was easily sterilized by five minutes’ 
boiling in a plugged flask ; but when it was slightly alkalized by ammonia or liquor 
potass®, its resistance to sterilization by heat was increased to a most marvellous degree. 
It could no longer be sterilized even by fifteen or twenty minutes’ boiling in a plugged 
flask, which almost reduced the infusion to dryness by evaporation. By means of the 
plugged-bulb method, however, alkalized hay-infusion could be sterilized without 
difficulty ; but it required more than an hour’s exposure to the heat of boiling water to 
effect this. 
It was found that the maximum resistance to sterilization resided in infusions 
alkalized with about five drops of liquor potass® per ounce (about one per cent.) ; two 
or three drops less than this, or four or five drops more than this, considerably 
diminished this resistance. 
The following experiments will serve to illustrate the high resisting power of 
alkalized hay-infusion to sterilization by heat. In every case the necks of the bulbs 
were filed off above the plug after the experiment, and the bulbs were afterwards placed 
in a warm place. 
1. March 27, 1873. — Seven plugged bulbs, charged with alkalized hay-infusion, were 
boiled in a can of water for fifty minutes. On March 31st, four days after, all were 
turbid and covered with a thick film of Leptothrix- filaments. 
2. March 31, 1873. — Three plugged bulbs, charged with alkalized hay-infusion, were 
boiled in a can of water for two hours. On April 3rd all three were turbid, and covered 
with an abundant film. 
3. April 4, 1873. — Five plugged bulbs (<z, b, c, d, and e) were charged with hay- 
infusion alkalized with 0 - 7 per cent, of liquor potass®. They were boiled in a 
can of water for various lengths of time ; a was boiled for an hour and became turbid 
in four days ; b was boiled for two hours, and d and e for seven hours ; these three 
remained permanently barren. An accident happened to c just before it was put into 
the can ; it was therefore re-charged with the same infusion, but alkalized a little more 
strongly : this one was boiled for three hours, nevertheless it became turbid and covered 
with a film in a few days. This was the most extreme example met with of resistance 
to sterilization with the heat of boiling water. 
4. July 15, 1873. — Five plugged-bulbs, charged with hay-infusion alkalized with 
1*4 per cent, of liquor potass®, were boiled together in a can of water. One of the 
bulbs was taken out at the end of every hour. The first bulb, withdrawn after being 
