USE OF BACTERIA IN THE ARTS. . 47 



ive tissues so much that the bones may be readily 

 cleaned of flesh. 



Citric acid. Bacterial fermentation is em- 

 ployed also in the ordinary preparation of citric 

 acid. The acid is made chiefly from the juice of 

 the lemon. The juice is pressed from the fruit 

 and then allowed to ferment. The fermentation 

 aids in separating a mucilaginous mass and mak- 

 ing it thus possible to obtain the citric acid in a 

 purer condition. The action is probably similar 

 to the maceration processes described above, al- 

 though it has not as yet been studied by bacteri- 

 ologists. 



BENEFITS DERIVED FROM THE PRODUCTS OF 

 BACTERIAL LIFE. 



While bacteria thus play a part in our indus- 

 tries simply from their power of producing de- 

 composition, it is primarily because of the prod- 

 ucts of their action that they are of value. 

 Wherever bacteria seize hold of organic matter 

 and feed upon it, there are certain to be devel- 

 oped new chemical compounds, resulting largely 

 from decomposition, but partly also from con- 

 structive processes. These new compounds are 

 of great variety. Different species of bacteria 

 do not by any means produce the same com- 

 pounds even when growing in and decomposing 

 the same food material. Moreover, the same 

 species of bacteria may give rise to different 

 products when growing in different food mate- 

 rials. Some of the compounds produced by such 

 processes are poisonous, others are harmless. 

 Some are gaseous, others are liquids. Some 

 have peculiar odours, as may be recognised from 

 4 



