BACTERIA IN INDUSTRIES 



405 



There are many different 

 bacteria which grow in milk. 

 A group attacks milk sugar 

 and produces lactic acid, 

 which results in souring. 



A similar process takes place in preparing linen fibers. Linen 



comes from the flax plant. If the flax is cut and thrown into pits 



and kept damp, certain bacteria will decay 



the cementing materials which hold the 



tough, strong fibers together. These fibers, 



when separated, are used for the manufac- 

 ture of linen. This process of obtaining the 



fibers of flax is known as retting or rotting. 



There is an artificial process of retting which 



is not as successful as the natural water 



process. The natural process is used in 



Ireland and produces a fine grade of linen. 



The artificial process, used in the United States, consists of an 



acid treatment for loosening the fibers. It is much quicker than 



the natural method, but less perfect, since the acid may roughen 



the flax fibers. 



Bacteria are valuable in curing tobacco. The tobacco stalks 



with the leaves are piled into great heaps or hung from racks and 



allowed to sweat and then ferment at a fairly low temperature. 



This gives to tobacco its special flavor. 



In tanning leather, the hides are soaked, scraped, and limed or 



treated with acids to remove the hairs. The lime is removed, 



and the hides are put into solutions of tan- 

 bark. During these processes, certain bac- 

 terial fermentations take place, which make 

 the leather soft and pliable. 



Bacteria in agriculture. Large quantities 

 of the nitrates from the soil are built into 

 proteins and protoplasm by the plants. 

 In fruit juices bacteria "When thcsc plants are removed, they take 



change alcohol to acetic '■ ^ ^ i/ 



acid. with them the nitrogen in the form of 



protein and protoplasm. The nitrogen of the soil would be 

 exhausted in a comparatively short time if there were no ways 



