The Necessity of Pure Air for Health. 249 



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to breathe. From direfl observation, it has been proved 

 that any diminution in the quantity of oxygen is followed 

 by grave symptoms, and also that the human body is 

 not adapted to breathe any increase in the proportion 

 without discomfort. 



By exa£l analysis air has been found to contain— 



1. Oxygen, by volume ... ... ... 20*94 



2. Nitrogen ... ... ... ... 79*02 



3. Carbonic acid gas ... ... ... '04 



4. Water. In varying quantities depending princi- 

 pally on the temperature. In this colony there is always 

 a large quantity, the difference in the dry and wet 

 bulb thermometers being slight. 



5. Ammonia, in the form of carbonates, chlorides and 

 sulphates. 



6. Ozone, an allotropic form of oxygen, and to which 

 the stimulating properties of the air are attributed. 

 The amount varies very much, being small in quantities 

 in towns, and laige on mountains and at sea. 



7. Salts of sodium, which are found every-where. 



8. Pollen of grasses and flowers. Here when the cane 

 arrow is drying, I have noticed small pieces of the plume 

 in the hospital wards, brought from the cane fields to 

 windward of the town. 



9. Dust of all sorts, as can be seen at any time in a 

 dark room in the beam of sun light, thrown through a 

 chink in the shutter, 



10. And from time to time under special conditions, 

 various other foreign bodies are to be found, as for 

 instance, sand at sea, a distance of 600 miles from land. 



1 1. Finally also, at times, organic impurities of various 

 kinds, both living and dead. These vary very much as 



