84 



BACTERIA IN THE AIR 



even ultra-microscopic cells obey the law of gravitation. This is equally 

 true in the limited areas of a laboratory or warehouse, and in the open 

 air. At high altitudes, the air may be looked upon as practically 

 germ-free, although here again the lighter spores of the mould fungi 

 may cause them to be carried by air currents to a very great height. 

 In the recent researches of Dr Jean Binot of the Pasteur Institute,* 

 100 litres of air taken at the summit of Mont Blanc did not contain 

 a single microbe, and the total number of organisms varied between 

 4 and 11 per metre cube (1000 litres). An examination of the air of 

 the iaterior of M. Janssen's Observatory, situated on the highest 

 point of Mont Blanc, and taken in two different rooms, gave, on the 

 other hand, 540 and 260 organisms per metre cube. The gradual 

 increase of the number of organisms as descent to lower level takes 

 place is of interest. Thus 6 per metre cube were found in the Grand 

 Plateau, 8 at the Grand Mulct, and 14 at the Plon de I'Aiguille. 

 Upon the Mer de Glace 23 organisms were found, and 49 at Montan- 

 vert. Graham Smith found that at the top of the Clock Tower of 

 the Houses of Parliament in London there was only about one-third 

 of the number of bacteria found at the ground level.f 



4. Air Currents. — Miquel, Pasteur, Cornet, and other workers 

 have shown that the presence of micro-organisms in air depends in 

 part upon air currents, winds, etc. In the month of August, with 

 the wind from the south, i.e. blowing from the country citywards, the 

 number of organisms was found by Miquel to be 40 in the Mont Souris 

 Pare around the Observatory, while at the same moment a record of 

 14,800 was obtained in the 4th Arrondissement, which may be taken 

 as the centre of Paris, and comprises the surroundings of Notre Dame 

 and of the Hotel de Ville. In the month of June, on the other hand, 

 with the wind blowing from the KE., i.e. across the city towards 

 Mont Souris, the numbers were, in the 4th Arrondissement, 10,000 per 

 metre cube, and in the Park of Mont Souris itself, 1180 per metre cube. 



The seasonal variations of the organisms present in the air are 

 also worthy of note, and depend chiefly upon dust and air currents. 

 The following table shows the mean over a period of ten years in the 

 air taken at Mont Souris : — 



* Communication ci VAeadimie des Sciences de Paris, 17 Mars 1902, 

 t Jour. ofHyg., 1903, p. 513. 



