Ixxviii REPORT — 1870. 



But the skill of the microscope-makers of the eighteenth century soon 

 reached its limit. A microscope magnifying 400 diameters was a chef- 

 cVceuvre of the opticians of that day, and, at the same time, by no means 

 trustworthy. But a magnifying-power of 400 diameters, even when de- 

 finition reaches the exquisite perfection of our modern achromatic lenses, 

 hardly suffices for the mere discernment of the smallest forms of life. A 

 speck, only ^^ of an inch in diameter, has, at 10 inches from the eye, the 

 same apparent size as an object , ^^m„ of an inch in diameter, when mag- 

 nified 400 times ; but forms of living matter abound the diameter of which is 

 not more than ^nroinr '^^ ^^ inch. A filtered infusion of hay, allowed to 

 stand for two days, will swarm with living thiiigs, among which any which 

 reaches the diameter of a human red blood-corpuscle, or about .^ .,\ ^ 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 Buifon 

 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 pro- 

 portion belong to the category of smallest things of which I have spoken, 

 and which must have aU looked like mere dots and lines under the ordinary 

 microscopes of the eighteenth century. 



Led by various theoretical considerations which I cannot now discuss, but 

 which looked promising enough in the lights of that day, Buftbn and Need- 

 ham doubted the applicability of Eedi's hypothesis to the infusorial animal- 

 cules, and jS^eedham very properly endeavoured to put the question to an ex- 

 perimental test. He said to himself, if these infusorial animalcules come 

 from germs, their germs must exist either in the substance infused, or in the 

 water with which the infusion is made, or in the superjacent air. Now the 

 vitality of all germs is destroyed by heat. Therefore, if I boil the infusion, 

 cork it up carefully, cementing the cork over with mastic, and then heat the 

 whole vessel by heaping hot ashes over it, I must needs kill whatever germs 

 are present. Consequently, if Redi's hypothesis hold good, when the infu- 

 sion is taken away and allowed to cool, no animalcules ought to be developed 

 in it ; whereas, if the animalcules are not dependent on preexisting germs, 

 but are generated from the infused substance, they ought, by-and-by, to make 

 their appearance. Needham found that, under the circumstances in which 

 he made his experiments, animalcules always did arise in the infusions, when 

 a sufficient time had elapsed to aUow for their development. 



In much of his work Needham was associated with Buflbn, and the results 

 of their experiments fitted in admirably with the great French naturalist's 

 hypothesis of " organic molecules," according to which, life is the indefeasi- 

 ble property of certain indestructible molecides of matter, which exist in aU 

 living things, and have inherent activities by which they are distinguished 

 from not living matter. Each individual living organism is formed by their 

 temporary combination. They stand to it in the relation of the particles of 

 water to a cascade, or a whirlpool ; or to a mould, into which the water is 

 poured. The form of the organism is thus determined by the reaction be- 

 tween external conditions and the inherent acti%'ities of the organic mole- 

 cules of which it is composed ; and, as the stoppage of a whirlpool destroys 

 nothing but a form, and leaves the molecules of the water with aU their 

 inherent activities intact, so, what we call the death and putrefaction of an 

 animal, or of a plant, is merely the breaking up of the form, or manner of 



