VIII BIOGENESIS AND ABIOGENESIS 241 



definition ]:eaclies the exquisite perfection of our 

 modem achromatic lenses, hardly suffices for the 

 mere discernment of the smallest forms of life. 

 A speck, only gV^^ ^^ ^^ ii^ch in diameter, has, at 

 ten inches from the eye, the same apparent size 

 as an object loooo th of an inch in diameter, 

 when magnified 400 times; but forms of living 

 matter abound, the diameter of which is not more 

 than xo-o-cro-^^ of an inch. A filtered infusion of 

 hay, allowed to stand for two days, will swarm 

 with living things among which, any which 

 reaches the diameter of a human red blood- 

 corpuscle, or about 3^0*^^ ^f ^n inch, is a giant. 

 It is only by bearing these facts in mind, that we 

 can deal fairly with the remarkable statements 

 and speculations put forward by Bufifon and 

 Needham in the middle of the eig^hteenth 

 century. 



When a portion of any animal or vegetable 

 body is infused in water, it gradually softens and 

 disintegrates; and, as it does so, the water is 

 found to swarm with minute active creatures, the 

 so-called Infusorial Animalcules, none of which 

 can be seen, except by the aid of the microscope ; 

 while a large proportion belong to the category of 

 smallest things of which I have spoken, and 

 which must have looked like mere dots and lines 

 under the ordinary microscopes of the eighteenth 

 century. 



Led by various theoretical considerations which 

 202 



