44 MICRO-ORGANISMS AND FERMENTATION. 



air at the moment of opening, Erlenmeyer flasks were also 

 used to give supplementary information, for which purpose 

 they were allowed to remain in the same locality for some 

 length of time, in some cases as long as 48 hours. 



After these preliminary remarks we will give a brief 

 summary of the results obtained by Hansen. 



He confirms the statement first made by Pasteur, that 

 the air at neighbouring points, and at the same time, may 

 contain different numbers and different varieties of organ- 

 isms ; and he found that this rule also holds good for places 

 lying close together in the same garden. Hansen states, 

 as other characteristics of the distribution of micro-organisms, 

 that those forms, for instance, which in the first half of July 

 commonly occurred under the cherry trees in the garden, 

 were in the latter half of the same month entirely absent 

 from the same place; further, that organisms which atone 

 time were found under the cherry trees, but not under the 

 grape-vines, were to be found later only under the latter ; as 

 a proof of the inequality of distribution of the organisms, it 

 is shown that the flasks opened in the same place in the 

 same series of experiments often had the most diverse 

 contents. 



The experiments with the vacuum flasks have further 

 taught us that the micro-organisms of the air often occur 

 in groups or clouds, with intermediate spaces, which are 

 either germ-free or only contain quite isolated germs. As 

 the organisms are not generated in the air, but have their 

 place of growth on the earth, it follows that their presence in 

 the air must be dependent on the condition of the surface of 

 the ground, which again depends, in certain respects, on the 

 weather. 



ffansen's numerous analyses have further proved that the 

 Saccharomycetes occur comparatively seldom in the dust of 

 the air. Their number in the air increases from June to 

 August in such a way that the flasks at the end of August 

 and the beginning of September are frequently infected 



