Flasks thus prepared were maintained at a warmth vary- 
ing from 50° to 90° Fahr. for long periods — many weeks 
and months — some in the dark and some exposed to the 
light, with the following results. 
I. Simple filtered infusions of animal or vegetable tissues 
— a very considerable variety were tried — boiled over the 
flame for five or ten minutes, in flasks previously plugged 
with cotton wool, remained permanently barren. This 
result was absolutely invariable. 
II. More complex mixtures — milk, neutralized or alkalized 
infusions of vegetable and animal tissues, similar albuminous 
and gelatinous solutions, mixtures containing fragments of 
animal or vegetable substances or cheese — yielded variable 
results. In none of them did fungoid growths make their 
appearance — but monads and bacteria frequently appeared 
in abundance. 
This seemingly contradictory result was inferred to be 
due to the ineffective application of the heat in the process 
of direct boiling over a flame. It was found that many of 
these more complex mixtures frothed excessively when 
boiled — brisk ebullition could not therefore be maintained 
— particles were spurted about on the sides of the flask, and, 
in this way, apparently escaped effective exposure to the 
heat. Even when the boiling was prolonged for 20 or SO 
minutes the results were still uncertain — sometimes the 
flasks remained barren — sometimes they became turbid 
and swarmed with bacteria. 
III. By the second modification of the experiment much 
more constant results were obtained — the flasks remained 
almost always permanently barren — and the few exceptions 
were found to be due to some imperfection in the conduct of 
