FERMENTATION. 273 



ring 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 essen- 

 tial 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 vegetable, reducing such matter, 

 with a rapidity otherwise unattainable, to innocent 

 carbonic acid and water. Furthermore, 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 neces- 

 sary 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 observation. 



A drop of the liquid containing those small organ- 

 isms 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-glass of the 

 microscope should come very close to the organisms. 

 Round 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 appro- 



