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POPULAR SCIENCE MONTHLY. 



a twenty-five minute trip from Broadway to Lafayette Avenue, showed 

 over 1,600 colonies after a thirty-six-hour incubation at 85° F. Plates 

 exposed for one hour in the surgical and gynecologic operating rooms 

 at the Johns Hopkins Hospital showed, respectively, 65 and 58 colonies 

 after incubating 48 hours at 100 degrees. These comparative studies 

 are suggestive, and the studies in the caverns and sanitarium demon- 

 strate that with optical purity or freedom from atmospheric dust, we 

 have air that is practically free from bacteria. 



Fig. 4. Showing Flag benkath the Ceiling carried out Horizontally by the Inflow 

 OF Cavern Air. Also the flame of the candle deflected by the outflow of air from the bedroom. 



But in spite of the bacteriologic purity of the air in Limair Sani- 

 tarium, I am sure many will protest against breathing the polluted, 

 moldy emanations from a source never penetrated by the rays of the 

 sun. I must confess this was my first impression, and the same 

 prejudice has been expressed by many friends with whom I have con- 

 versed. But what are the facts, and what is the condition of the 

 caverns' air? In the first place the air is not stagnant. In any part 

 of the caverns the guide's candle, if placed on the floor or on the ledge 

 of a wall, shows by the deflected flame a very decided current of air. 

 Owing to the differences in temperature, there is a constant inter- 

 change of air between the caverns and the outside world. This circu- 

 lation takes place through many natural filters distributed over the 

 hillside in the form of crevices in the rock, which have become filled 

 by porous soil. Both air and water are cleansed in passing through 

 these earth filters. If there be any open fissures for the admission of 

 unfiltered air, its organic particles would soon be deposited on the 

 damp caverns' walls. The action of water passing over and causing 

 the slow dissolution of such a vast surface of limestone can not but be 



