MICROBES, OR BACTERIA. 95 



form of yellow patches. It is also found in the albu- 

 men of boiled eggs, in potatoes, etc. (Fig. 52). 





 a 



Fig. 52. Sarcina ventricuU. in different degiees of development 

 (strongly magnified). 



III. THE MICROBE OF VINEGAR, AND ACETIC 

 FERMENTATION. 



Pasteur has shown that the acid fermentation of 

 alcoholic liquids is due to the existence of a special 

 microbe, acting like a ferment, which is developed on 

 the surface of fermented liquors whenever they are 

 abandoned to the contact of the air, in the presence of 

 albuminoid substances. This microbe, which consti- 

 tutes the mother of vinegar, and which is termed 

 Mycoderma aceti, is probably identical with Bacterium 

 lineola, so often present in infusions, in stagnant 

 pools, and even in spring water. It is a true 

 bacterium (Fig. 48). 



The membrane which may be observed on the 

 surface of liquids in course of acetic fermentation is 

 formed of very minute elongated cells, from 1'5 to 3 

 micro-millimetres in length, united in the form of 



