574 FRAGMENTS OF SCIENCE. 
power, nothing is seen in the muddy liquid; but regarded 
with a magnifying power of a thousand diameters or so, 
what an astonishing appearance does it present! Leeuwen- 
hoek estimated the population of a single drop of stagnant 
water at 500,000,000: probably the population of a drop of 
our turbid infusion would be this many times multiplied. 
The field of the microscope is crowded with organisms, 
some wabbling slowly, others shooting rapidly across the 
microscropic field. They dart hither and thither like a 
rain of minute projectiles; they pirouette and spin so 
quickly round, that the retention of the retinal impression 
transforms the little living rod into a twirling wheel. And 
yet the most celebrated naturalists tell us they are vege- 
tables. From the rod-like shape which they so frequently 
assume, these organisms are called " bacteria " a term, be 
it here remarked, which covers organisms of very diverse 
kinds. 
Has this multitudinous life been spontaneously generated 
in these six flasks, or is it the progeny of living germinal 
matter carried into the flasks by the entering air? If the 
infusions have a self-generative power, how are the sterility 
and consequent clearness of the fifty-four uninjured flasks 
to be accounted for? My colleague may urge and fairly 
urge that the assumption of germinal matter is by no 
means necessary; that the air itself may be the one thing 
needed to wake up the dormant infusions. We will 
examine this point immediately. But meanwhile I would 
remind him that I am working on the exact lines laid 
down by our most conspicuous heterogenist. He distinctly 
affirms that the withdrawal of the atmospheric pressure 
above the infusion favors the production of organisms; 
and he accounts for their absence in tins of preserved 
meat, fruit, and vegetables, by the hypothesis that fermen- 
tation has begun in such tins, that gases have been gener- 
ated, the pressure of which has stifled the incipient life and 
stopped its further development.* This is the new theory 
of preserved meats. Had its author pierced a tin of pre- 
served meat, fruit, or vegetable under water with the view 
of testing its truth, he would have found it erroneous. In 
well-preserved tins he would have found, not an outrush of 
gas, but an inrush of water. I have noticed this recently 
* Beginnings of Life, vol. i., p. 418. 
