430 BIOLOGY FOR BEGINNERS 



2. A slight continuous movement of air through the whole 

 room, without perceptible draughts. 



3. A sufficient degree of heat to keep the body in comfort, usu- 

 ally 68 to 70 degrees. 



4. A moderate amount of moisture in the air so that it will 

 neither interfere with evaporation from the skin, nor yet tend to 

 dry it. 



5. The removal of chemical impurities and odors; the amount 

 of CO 2 should not exceed .06 per cent. 



6. The removal of excess moisture which is especially great in 

 crowded rooms. 



" Fresh air " is not necessarily cold air as some people seem to 

 think, though for sleeping rooms, the temperature should be 

 lower than in living quarters. Extreme cold is not an advantage 

 even in sleeping rooms, except in cases of tuberculosis, and many 

 people subject themselves to dangerous exposure in this way. 

 Air should be pure, cool, and abundant, but there is no virtue in 

 extreme coldness. 



Dust Removal. Dust carries bacteria, hence air should be as 

 free from it as possible. This means replacing the broom and 

 feather duster by the vacuum cleaner and oiled dust cloth. Rugs 

 and hard- wood floors should take the place of the permanent carpet. 

 Smooth walls, simple furniture, and few hangings offer less oppor- 

 tunity for the accumulation of dust. Sprinkling, oiling, and 

 flushing the streets attain the same result for out-door dust. 



Hygiene of the Eyes. The human eye is such a delicate and 

 necessary structure that its care should be emphasized, but just 

 because it is so complicated, no rules can be made which will 

 properly safeguard this most valuable sense organ. The one safe 

 procedure is to have the eyes examined by a competent expert 

 from time to time, even if no defect appears to be developing. 



Reading in poor light, or at evening when the light is gradually 

 failing, is a common error. Almost as bad is the use of too bright 

 light directly facing the eyes, or reflected from too shiny paper in 

 books. Long continued use of the eyes on very fine print or sew- 

 ing causes severe strain, just as in continued use of any other organ. 



