322 FRAGMENTS OF SCIENCE 



with their liquids as clear as filtered drinking water. In 

 six flasks, however, the infusion is found muddy. We 

 closely examine these, and discover that every one of them 

 has had its fragile end broken off in the transit from Lon- 

 don. Air has entered the flasks, and the observed mud- 

 diness is the result. My colleague knows as well as I do 

 what this means. Examined with a pocket-lens, or even 

 with a microscope of insufficient power, nothing is seen in 

 the muddy liquid; but regarded with a magnifying power 

 of a thousand diameters or so, what an astonishing appear- 

 ance does it present! Leeuwenhoek estimated the popula- 

 tion 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 microscopic 

 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 cele- 

 brated naturalists tell us they are vegetables. From the 

 rod- like shape which they so frequently assume, these or- 

 ganisms are called '* bacteria' 7 a term, be it here remarked, 

 which covers organisms of very diverse kinds. 



Has this multitudinous life been spontaneously gener- 

 ated 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 



