FEhMENTATlON. 549 



fortuitous ferments of disease. These ferments, which, it 

 is to be remembered, are living organisms, have their 

 activity suspended by temperatures below 10 degrees C., 

 and as long as they are reduced to torpor the beer remains 

 untainted either by acidity or putrefaction. The beer of 

 low fermentation is brewed in winter, and kept in cool 

 cellars; the brewer being thus enabled to dispose of it at 

 his leisure, instead of forcing its consumption to avoid the 

 loss involved in its alteration if kept too long. Hops, it 

 may be remarked, act to some extent as an antiseptic to 

 beer. The essential oil of the hop is bactericidal: hence 

 the strong impregnation with hop juice of all beer intended 

 for exportation. 



These low organisms, which one might be disposed to 

 regard as the beginnings of life, were we not warned that 

 the microscope, precious and perfect as it is, has no power 

 to show us the real beginnings of life, are by no means 

 purely useless or purely mischievous in the economy of 

 nature. They are only noxious when out of their proper 

 place. They exercise a useful and valuable function as the 

 burners and consumers of dead matter, animal and vege- 

 table, reducing such matter, with a rapidity otherwise 

 unattainable, to innocent carbonic acid and water. Fur- 

 thermore, they are not all alike, and it is only restricted 

 classes of them that are really dangerous to man. One 

 difference in their habits is worthy of special reference 

 here. Air, or rather the oxygen of the air, which is 

 absolutely necessary to the support of the bacteria of 

 putrefaction, is, according to Pasteur, absolutely deadly to 

 the vibrios which provoke the butyric acid fermentation. 

 This has been illustrated by the following beautiful obser- 

 vation. 



A drop of the liquid containing those small organisms is 

 placed upon glass, and on the drop is placed a circle of 

 exceedingly thin glass; for, to magnify them sufficiently, 

 it is necessary that the object-gTass" of the microscope 

 should come very close to the organisms. Bound the edge 

 of the circular plate of glass the liquid is in contact with 

 the air, and incessantly absorbs it, including the oxygen. 

 Here, if the drop be charged with bacteria, we have a zone 

 of very lively ones. But through this living zone, greedy 

 of oxygen and appropriating it, the vivifying gas cannot 

 penetrate to the center of the film. In the middle, there- 



