38 MICRO-ORGANISMS AND FERMENTATION. 



to the dangers that may arise from the neglect of the requisite 

 considerations alluded to above. 



The discoveries of SPALLANZANI (mentioned in the last 

 chapter), and of later investigators on the generatio spontanea 

 first gave rise to the study of micro-organisms of the air. 

 PASTEUR especially showed that these micro-organisms are 

 of vital importance to the fermentation industries, when he 

 proved that the air contained both bacteria and alcoholic 

 ferments. 



It will be of interest to glance at the analytical methods 

 by which the germ-contents of the air have been determined. 



The majority of the analyses of air have been undertaken 

 with the view of obtaining some light on the 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 fermentation, 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 com- 

 paratively 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 quantity and the species 

 present. These results were obtained by exposing beer- 

 wort, wine-must, or yeast-water containing sugar, in open, 

 shallow dishes, at different places, and examining their 

 contents after some time for microscopical germs. PASTEUR 

 also employed for this purpose the so-called vacuum-flasks, 

 containing nutritive liquids and rarefied air. On opening 

 the flask a sample of gerrn-laden air could be drawn in. 



The most important air-analyses undertaken in recent 

 years are, without doubt, those carried out by MIQUEL, the 

 director of the laboratory specially arranged for this purpose 

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

 has also made valuable contributions to our knowledge of this 

 subject. 



MIQUEL performed his first experiments with a so-called 



