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CHAPTER II. 

 BIOLOGICAL EXAMINATION OF AIR AND WATER. 



THE investigations into spontaneous generation already 

 referred to naturally led to the study of the organisms in air, 

 and after Pasteur, in particular, had demonstrated that air 

 contained, not bacteria only, but also fungi giving rise to 

 alcoholic fermentation, air analyses acquired an interest for 

 the zymophysiologist, and for the fermentation industry. 

 Such comprehensive researches are now available that it has 

 been possible to arrive at an idea of the biological composition 

 of the air on a large scale, and to form a judgment of these 

 conditions in relation to the brewing industry. At first, 

 when it became known that crowds of living germs, capable 

 of development, could occur even in very small volumes of 

 air, there was a natural inclination to exaggerate their effect 

 in practice, and to attribute any excessive growth of disease 

 germs in a fermentation to the direct influence of the air. 



An exhaustive study of the conditions occurring in practice, 

 carried out in recent years under systematic biological control, 

 has shown that this influence had been exaggerated, and that 

 it is possible, even where an air analysis has shown the presence 

 of numerous germs, capable of producing disease in a fer- 

 menting liquid, to suppress the partly dried and weakened 

 germs falling into the liquor by the addition of the excessive 

 number of yeast cells contained in the pitching yeast. 



Large growths of disease-producing organisms were only 

 found in practice if they had been allowed to develop on 

 certain infected areas. The germs in the air are thus only 

 indirectly the cause of disturbances in practice, and under 

 normal conditions can seldom be of importance. 



