ZOOLOGY AND BOTANY, MIOROSCOPYj ETC. 511 



The action of gases on tJhe spores depends on the acid character 

 of the products to which they give rise, and the behaviour of these 

 products towards the envelopes of the spores. Nitrogen peroxide is 

 more active than chlorine, which in its turn is far more active than 

 sulphurous anhydride or hydrogen sulphide. The two latter do not 

 kill the spores, but simply delay their development. Ozonized air, con- 

 taining 3-4 per cent, of ozone, has no appreciable effect on the spores. 



Purity of Air in Alpine Regions. Eesistance of Aerial Bacteria 

 to Cold. — Some experiments were conducted by M. de Freudenreich 

 in 1883 * to determine the relative purity of the air at different heights 

 in the Swiss Alps and in the plains. The air was aspirated in known 

 quantities through sterilized cotton wool in Miquel's cultui"e tubes. 

 These tubes were duly sealed and returned to Dr. Miquel for distribu- 

 tion in culture fluids. Out of 2700 litres of air taken at heights from 

 2000 to 4000 metres above the sea they furnished neither bacteria 

 nor mildew spores capable of rejuvenescence in neutralized beef- 

 broth. From 2400 litres taken at the middle of the Lake of Thun 

 there were obtained several mildews and two micrococci. This lake 

 is about 560 metres above the sea. Near the Hotel Bellevue at Thun, 

 from 2400 litres of air taken one metre above a large prairie, resulted 

 five schizophytes. In a room in the hotel from 100 litres of air 

 resulted six bacteria. 



Put into another form, the tabulated results would stand for 

 10 cub. m. of air drawn at different dates in July and August as 



1. At an altitude varying from 2000 to 4000 



metres 



2. Upon the Lake of Thun (560 metres) .. 8 



3. Near the Hotel Bellevue (560 metres) .. 21 



4. In a room of the hotel 600 



5. At the Park of Montsouris, Paris .. .. 7,600 



6. In the Eue Eivoli, Paris 55,000 



Thus the air of the lake appeared about three times less charged 



with germs than that which circulated close to the ground, and this 

 last was purer by 360 times than the air analysed the same days at 

 Montsouris. 



To test the resistance of bacteria to cold, ten closed tubes con- 

 taining several kinds of atmospheric bacteria were experimented on. 

 Six were exposed during thirty-six hours to a slowly decreasing 

 temperature of — 10° to — 100° C. The sealed tubes remained for 

 more than four hours at the lower temperature. It was found, as in 

 previous experiments, that several kinds of bacteria incapable of 

 resisting for two hours a temperature of 70° C. supported this 

 excessive degree of cold. Some appeared to have aged, that is to say, 

 that when sown afterwards in nutritive broths their rejuvenescence 

 required three days, whilst previously they only needed about twenty- 

 four hours. 



Further experiments f in the summer of 1884 by M. de Freuden- 

 reich yielded the following results. Out of 2000 litres of air taken 



* Semaine Medicale, Oct. 11, 1883. 



t Arch. Sci. Pbys. et Nat., sii. (1884) pp. 365-87. 



