ON DUST AND DISEASE. 



185 



wool, c, moistened with glycerine ; then a thin layer of 

 diy wool, c' ; then a layer of charcoal fragments ; and 



FIG. 5. 



RCOriONAi I ELCVATIOH 



SECTION N A 3 



Of HO T T HI COV K 



finally a second thin layer of dry cotton-wool. The 

 succession of the layers may be changed without pre- 



