EXAMINATION OF AIR AND WATER. 37 



The questions then arose : What is the nature of these 

 germs floating in the air ? To what degree and extent do 

 they occur in space ? Do their number and nature vary 

 with the different seasons of the year? And, finally, are 

 they really able to effectually interfere with technical 

 operations ? 



It will be of interest to glance at the different methods 

 by which the analyses of air with regard to its germs have 

 been attempted. 



The majority of the analyses of air have been under- 

 taken with the view to obtain some light on the mysterious 

 obscurity which envelops most contagious diseases, nearly all 

 of which are, as is well-known, attributed to the agency of 

 micro-organisms. With regard to the organisms of fermen- 

 tation, these have been investigated chiefly by Pasteur, and 

 later by Hansen. The French savant stated that these 

 germs are always floating about in the air, but that they are 

 present in much larger quantities in the dust which settles 

 on the vessels and apparatus employed. The true alcoholic 

 ferments are present in comparatively small numbers in the 

 air, whilst the germs of mould-fungi are more frequent ; he 

 further showed, as was subsequently done by Tyndall, that 

 the germ-contents of the air vary both with regard to the 

 quantity and the species. These results were obtained by 

 exposing in open, shallow dishes, in different places, beer- 

 wort, wine-must, or yeast-water containing sugar ; after some 

 time their contents were examined for microscopical germs. 

 Pasteur also employed for this purpose the so-called vacuum- 

 flasks, containing nutritive liquids and rarefied air. On 

 opening the flask the air with its germs entered. 



The most important air-analyses undertaken in recent 

 years are, without doubt, those undertaken by Miquel, the 

 director of the laboratory specially arranged for this purpose 

 at Montsouris, near Paris. His fellow-worker, Freudenreich, 

 has also added very valuable contributions to our knowledge 

 in this direction. 



