The Necessity of Pure Air for Health. 253 



has a clear idea of the transference of the atoms of the 

 element. 



We have seen what the air is composed of, how this 

 composition is maintaiiiedj and I have mentioned that 

 this equilibrium is disturbed when numbers of human 

 beings are crowded together in houses, villages and 

 towns. But this last requires to be dealt with in some 

 detail ; a more exa6l description of these impurities, both 

 as to quantity and quality, is necessary. A fuller state- 

 ment of the diseases produced must be made, and we 

 must study the methods by which in this colony the 

 standard purity of the air may be maintained so that 

 the conditions laid down in the beginning may not be 

 violated. It is to this problem of maintaining the air 

 (oxygen) undefiled that sanitarians have devoted a great 

 part of their time. In the Northern countries it is the 

 commonest as well as the most difficult problem. It 

 meets one on every side, involving as it does all the 

 larger surroundings of man, from the proper arrangement 

 of street, the proper building of houses, (even to the 

 details of the materials used), to the minutest points 

 of house cleaning and removal of refuse. But we, living 

 in the tropics, have the problem in some ways much 

 simplified from the fa6l that the temperature is com- 

 paratively a constant one, so that no provision is re- 

 quired for warming the air before breathing it, and that 

 the wind blows for the greater part of the year from one 

 quarter of the Compass. Hence all we have to do is to 

 put a sufficiently large inlet on the windward side of our 

 houses, and an outlet on the other, in order to permit the 

 natural method of ventilation to come into play. 



From dire6t observation on man in health it has been 



112 



