TWO NEW WORLDS 



of some 1200 such molecules would reach from 

 one end of it to the other. But we also know 

 that the molecules do not all touch each other. 

 The specific gravity of the spore is nearly equal to 

 that of water, and in water the molecules are 

 sufficiently widely apart to allow of their free 

 motion about each other. No doubt the various 

 parts of the cytoplasm, nucleus, and cell-wall of 

 the spore consist of various intricate groupings 

 and aggregations of molecules ; but, on the average, 

 we may estimate that the molecules are half a pp, 

 apart, so that a cubic space of J cubic pp goes to 

 each molecule. Since the radius is about 200 /^ 

 the volume of the spore is -JrV, or 33,500,000 

 cubic pp. Multiplying this by eight, we get 268 

 million as the number of molecules constituting the 

 spore. 



This number, roughly approximate as it is, 

 enables us to draw the important conclusion that 

 no living organism contains less tJian a hundred 

 million molecules. 



When, therefore, we penetrate further into the 

 realms of ultra-microscopy, we leave life behind, 

 and have to do with none but unorganised matter. 

 We can perceive the presence of objects down to 

 about 20 fjifji in diameter, which cannot contain 

 more than about 50,000 molecules. Beyond that 

 limit, even the most recent optical devices fail us, 

 and we must fall back upon the visualising powers 



