CHAPTER. XI. 



examination of air, soil, and water. 



Air. 



The air, as is well known, contains in suspension, mineral, animal,, 

 and vegetable substances. The mineral world is represented 

 by such substances as silica, silicate of aluminium, carbonate and 

 phospate of calcium, which may be raised from the soil by the 

 wind, and particles of carbon, etc., which gain access fi-om acci- 

 dental sources. Belonging to the animal kingdom we find the 

 debris of perished creatures, as well as, sometimes, living animals. 

 The vegetable world supplies micrococci, bacilli, and other forms 

 of the great family of bacteria, spores of other fungi, pollen seeds, 

 parts of flowers, and so forth. The air of hospitals and sick rooms 

 has been found to be especially rich in vegetable forms ; fungi 

 and spores have been stated to be present in particularly large 

 numbers in cholera wards ; spores of tricophyton have been dis- 

 covered in the air of hospitals for diseases of the skin, and of achorion 

 in wards with cases of favus. The tubercle bacillus is said to have 

 been detected in the breath of patients suffering from phthisis. 



These points indicate that, in addition to the interest for the 

 micro-biologist, considerable importance, from a hygienic point of 

 view, must be attached to the systematic examination of the air, 

 A knowledge of the microbes which are found in the air of marshy 

 and other vinhealthy districts, and in the air of towns, dwellings,, 

 hospitals, workshops, factories, and mines, will be of practical value. 



Miquel, who has particularly studied the bacteria in the air, 

 has fovind that their number varies considerably. The average 

 number per cubic metre of air for the autumn quarter at Mont- 

 souris is given as 142, winter quarter 49, spring quarter 85, and 

 summer quarter 105. In air collected 2,000 to 4,000 metres above 

 the sea-level, not a single bacterium or fungus spore was found, 

 while in 10 cubic metres of air from the Rue de Rivoli (Paris) the 

 number was computed at 55,000. 



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