212 THE INVISIBLE WORLD 



infinitely small microbe, and by this microbe only. 

 Since the world began, not a single case of con- 

 sumption has come from any other cause; so long 

 as the world shall endure, not a single case will 

 originate from any other source. 



The microbe is represented in Fig. 98. It is 

 named Bacillus Tubercle, Bacillus, because that 

 word means a rod, and the microbe is rod-shaped; 

 Tubercle, because in the progress of the disease the 

 microbes form tubercles in the lungs or other organs. 

 Like the individuals in every other species of liv- 

 ing beings, the individuals composing the species of 

 microbes causing consumption, vary in size. Of 

 all the millions generated in the lungs of a single 

 case of this disease, scarcely any two can be said 

 to be exactly the same in size. Their longer diam- 

 eter varies from 2J to 5 micromillimeters. Their 

 shorter diameter is always about one-third of the 

 longer. But, rolled into little balls, each little 

 sphere, on the average, would be about three and 

 one-third micromillimeters in diameter. 



To get something of an idea of the almost in- 

 finite smallness of these little beings, we may find, 

 by a little calculation, how many of them may be 

 packed into the space occupied by a small drop of 

 water, the drop best explains. 



The millimeter is the one twenty-fifth part of an 

 inch. The drop of water, whose diameter is only 

 the one twenty-fifth part of an inch, is certainly a 

 comparatively small drop. 



The micromillimeter is a thousand times less 



