RELATION TO THE HOUSEHOLD 



219 



or in other damp, sheltered situations. There is a small 

 poison gland connected with the mandibles which, how r - 

 ever, are incapable of piercing the human skin. Nor is 

 the poison sufficient in quantity and character to cause 

 any appreciable trouble, even if by any combination of 

 circumstances the jaws could be forced into the flesh. 



Among the true insects the lowest or most primitive 

 order, the Thysanura, are represented in houses by 

 several species. In the cellar 

 of the farm-house where veg- 

 etables and other provisions 

 are stored in quantity, they 

 occur wherever it is damp 

 and wherever the least sus- 

 picion of decay occurs. There 

 are here several species of 

 bristle-tails and spring-tails; 

 small wingless creatures, 

 soft -bodied, with indefinite 

 mouth parts, that feed only 

 where a way is opened to 

 them by other things; but 

 when that way is opened 



their feeding promotes the decay that first gave them 

 entrance, and by their numbers they may become 

 troublesome. Remembering their fondness for damp 

 places the free use of lime and thorough ventilation 

 will serve to disperse them. Some are so lowly organ- 

 ized that the tracheal breathing system is not fully 

 developed and oxygen is absorbed through the damp 

 skin. To such creatures dryness is fatal. In cities 

 and towns few of these insects are found, and prac- 

 tically only two species of "bristle-tails," or "fish- 

 moths" or "silver-fish" occur. One of these species 

 is quite tough in texture, somewhat convex, evenly 



FIG. 102. A spring-tail or 

 Podurid. 



