144 LIVE DUST. 



and pulverized may form part of the common dust. The dust 

 that you wipe from your eye, or is caught by the mucus of 

 the nasal passages, may, instead of being made of clean soil, 

 be from the excreta of horses, decayed leaves, wood, grass, etc. 

 Indoors we are constantly making dust by wearing out our 

 clothes. Many of the tiny particles that we see floating in 

 the sunbeams are bits of cotton or woolen fibers. Shake any 

 garment in a beam of light to see how much dust is given off, 

 and how easily. The worn-off particles of our shoes, books, 

 floors, all contribute to the ever-present dust. 



Now, this dust (so far as it is mere dead, dry matter, not 

 considering it as a poison) is irritating to the lungs and res-> 

 piratory passages. There is provision, as we have seen, for 

 catching and getting rid of a good deal of it. 



But still much is taken into the lungs. Examination shows 

 that the lungs have many black specks from particles of car- 

 bon, etc., that have become lodged, and are of no benefit, to 

 say the least. 



LIVE DUST. 



Bad as this dead dust is, the injury from it is slight com- 

 pared to that from live dust. We know that certain seeds 

 float in the air, carried along by the wind. But these are 

 comparatively heavy, and soon sink to the ground. 



We all know pollen. At certain seasons it forms, in the 

 vicinity of cornfields for instance, a considerable part of the 

 dust. This is alive. It will grow if it falls on the right kind 

 of a surface, the stigma of the right plant at the right time. 

 Such dust will not grow in our bodies. We do not furnish a 

 soil in which it can grow. It merely adds to the amount of 

 irritating dust. 



We have seen puff-balls give off a cloud of dust when they 

 are crushed. Here, again, this dust is composed of live Spores, 



