A NEW MICROCOSM 7 



can determine with a very considerable degree of 

 accuracy the number of molecules which go to 

 make up a living organism. 



One of the smallest infusoria known is the Monas 

 Dallingeri, which is only ^ibm in. in diameter. At 

 a certain stage of the life-history of this organism, 

 two individuals combine and fuse into one, and 

 after six hours' incubation give rise to a large 

 number of spores whose size is not accurately 

 known, but which cannot be more than ^Jro in- 

 Each of these spores is an independent living 

 individual. 



It is not at all difficult to arrive at an estimate 

 of the number of molecules which go to make up 

 spore, but before doing so, it will be worth 

 while to translate our dimensions into the metric 

 system. The unit adopted in measuring objects 

 of the size of a wave-length of light is the micro- 

 inilliinutre, or millionth of a millimetre, denoted 

 by the symbol /*/*. In ordinary microscopic work 

 the micron, /i, or thousandth of a millimetre, is 

 now more generally adopted. It is useful to 

 remember that 25-4 millimetres, or 25,400,000 

 micromillimetres, or 25,400 microns, go to the 

 inch, so that one of the spores under discussion 

 is about half a micron in diameter, or 423 /iyu. 

 Now the average diaim t< r of the nj^truK-s con- 

 aing the substance of the spore has been 

 estimated at 0*3 **, so that we see that a chain 



