386 ADVANCED PHYSIOLOGY 



In the use of gas, care should be taken to prevent any 

 leakage, to adjust the mixture of gas and air at each burner, 

 so as to obtain the most light, and to obviate vitiating the air 

 with unoxidized gas. 



Acetylene gas plants are often placed in private houses, 

 especially in the country; here again leakage should be par- 

 ticularly guarded against, and users should clearly understand 

 its explosive qualities. Kerosene oil may be burned where 

 other artificial illumination is not available, but extreme 

 cleanliness is necessary to prevent bad odors and to secure 

 maximum light. 



In all kinds of illumination, our tendency is to employ too 

 brilliant light and to use too little care in preventing light 

 from shining or being reflected directly into the eyes. From 

 whatever source, light should come from over the shoulder, 

 not from the front or side. 



Artificial Heat.- Stoves are still used for heating houses, 

 even though they are somewhat unsatisfactory for this pur- 

 pose. They are unsatisfactory for several reasons: Dust and 

 dirt accumulate about them; the distribution of the heat in 

 the room is uneven; the floors remain cold above the basement; 

 poisonous gases may escape (from coal stoves) ; and the danger 

 of fires from a number of stoves in one house is increased. 

 Central heating from a furnace obviates all these objections. 

 Each of the different sorts of central heating systems, hot air, 

 steam and hot water, has points in its favor as well as against it. 



Hot Air Furnace: The hot air system brings fresh air into 

 the house, at such temperatures as to obviate cold drafts, 

 and in this respect is a most desirable method of heating; 

 but dust is almost certain to collect in the furnace and delivery 

 pipes, and be brought up in the air current. As winds greatly 

 modify the delivery of hot air to different rooms in the house, 

 the equable distribution of the hot air on cold, windy days 

 is not always possible. 



Steam System: In this system, the steam pressure can be 



