AIR AND WATER. 67 



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

 to August to such an extent that flasks at the end of August 

 and the beginning of September are frequently infected with 

 these organisms, after which a decrease takes place. The 

 Saccharomycetes which are found at other times of the year in 

 the atmosphere may be regarded as unimportant in numbers 

 and accidental in occurrence. As most species of the Sac- 

 charomycetes have in all probability like Saccharomyces 

 apiculatus their winter quarters in the earth, and their 

 propagation areas on sweet succulent fruit, the latter must be 

 considered as the most important source of contamination. 

 During the same season bacteria are also found in the largest 

 numbers. This constitutes a real danger in technical opera- 

 tions, since wort, when spread in a thin layer on the open 

 coolers, is exposed to a source of contamination from the 

 atmospheric germs. 



Bacteria are found in the flasks in somewhat greater 

 number than the Saccharomycetes, whilst the moulds occur 

 in still greater numbers. Amongst the latter Cladosporium 

 and Dematium are especially prevalent in gardens, and after 

 these Penicillium ; whilst Botrytis, Mucor, and Oidium occur 

 less frequently. 



After Hansen had thus demonstrated which of the micro- 

 organisms existing in the open air are capable of developing in 

 flasks with sterilised wort, he proceeded to communicate the 

 results of his examination of different parts of the brewery. 



When grains (draff) are allowed to stand in the open air, 

 they evolve, as is well known, acid vapours, and since they 

 always harbour a rich growth of bacteria when they remain 

 exposed for a short time, the question naturally presents 

 itself, what is the condition of the air in the neighbourhood 

 of heaps of grain ? It was found that only 30 per cent, of the 

 flasks opened in these areas became infected, and of these 

 3-6 per cent, with Saccharomycetes and 2-4 per cent, with 

 bacteria, whilst parallel experiments in the garden gave a 

 contamination of about 44 per cent., of which 8-5 per cent, 

 were bacteria. The air near the grains thus contained fewer 

 bacteria than the air in the garden. The most abundant 

 contamination was that of moulds, as in all other localities. 



