VIII BIOGENESIS AND ABIOGENESIS 241 



definition reaches the exquisite perfection of our 

 modern achromatic lenses, hardly suffices for the 

 mere discernment of the smallest forms of life. 

 A speck, only -s-gtln. of an inch in diameter, has, at 

 ten inches from the eye, the same apparent size 

 as an object 10 ^ 00 th of an inch in diameter, 

 when magnified 400 times ; but forms of living 

 matter abound, the diameter of which is not more 

 than TtfThnrth 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 ^-gVo^h of an 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 Buffon and 

 Needham in the middle of the eighteenth 

 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 



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