48 matured 



the air. By this process the normal condi- 

 tions of the air are maintained. 



One decimeter (nearly 4 inches) square of 

 green leaves will decompose in one hour seven 

 cubic centimeters of carbon dioxide, if the 

 sun is shining on them; in the shade the same 

 area will absorb about three in the same time. 



There is another substance in the form of 

 vegetable germs in the air called bacteria. At 

 one time these were supposed to be low forms 

 of animal life, but it is now determined that 

 they are the lowest forms of vegetable germs. 

 Bacteria is the general or generic name for a 

 large class of germs, many of them disease 

 germs. By analysis of the air in different lo- 

 cations and in different parts of the country 

 it has been determined that on the ocean and 

 on the mountain tops these germs average 

 only one to each cubic yard of air. In the 

 streets of the average city there are 3000 of 

 them to the cubic yard, while in other places 

 where there is sickness, as in a hospital ward, 

 there may be as many as 80,000 to the cubic 

 yard. These facts go to prove what has long 

 been well known, that the air of a city fur- 

 nishes many more fruitful sources for disease 

 than that of the country. Some forms of bac- 

 terial germs are not considered harmful, and 

 they probably perform even a useful service in 

 the economy of nature. Within certain limits, 

 other things being equal, the higher one's 



