RESPIRATION AND EXCRETION 



337 



again. The proper watering of streets before they are swept is 

 also an important factor in health. Much dust is composed largely 

 of dried excreta of animals. Soft-coal smoke does its share to 

 add to the impurities of the air, while sewer gas and illuminating 

 gas are frequently found in sufficient quantities to poison people. 

 Pure air is, as can be seen, almost an impossibility in a great city. 



How to get Fresh Air. As we know, green plants give off in 

 the sunlight considerable more oxygen than they use, and they 

 use up carbon dioxide. The air in the country is naturally purer 

 than in the city, as smoke and bacteria are not so prevalent there, 

 and the plants in abundance give off oxygen. In the city the 

 night air is purer than day air, 

 because the factories have stopped 

 work, the dust has settled, and 

 fewer people are on the streets. 

 The old myth of " night air" 

 being injurious has long since been 

 exploded, and thousands of people 

 of delicate health, especially those 

 who have weak throat or lungs, 

 are regaining health by sleeping 

 out of doors or with the windows 

 wide open. The only essential in 

 sleeping out of doors or in a room 

 with a low temperature is that the body be kept warm and the 

 head be protected from strong drafts by a nightcap or hood. 

 Proper ventilation at all times is one of the greatest factors in 

 good health. 



Change of Air. Persons in poor health, especially those having 

 tuberculosis, are often cured by a change of air. This is not always 

 so much due to the composition of the air as to change of occupa- 

 tion, rest, and good food. Mountain air is dry, and relatively 

 free from dust and bacteria, and often helps a person having tuber- 

 culosis. Air at the seaside is beneficial for some forms of disease, 

 especially hay fever and bone tuberculosis. Many sanitariums 

 have been established for this latter disease near the ocean, and 

 thousands of lives are being annually saved in this way. 



HUNTER, CIV. BI. 22 



A sleeping porch, an ideal way to 

 g6t fresh air at night. 



