THE MANUFACTURE OF OTHER FERMENTED PRODUCTS. 465 



which destroy nitrates and produce ammonia; variations in these various 

 factors account for variations in the characteristics of tobacco. 



PREPARATIONS AND CONSERVATION OF MISCELLANEOUS PRODUCTS. 



INDIGO. This dye was formerly made only from certain species of 

 Indigofera, principally /. tinctoria. This plant contains a glucoside 

 indican, which by fermentation and oxidation yields indigo. 



The plants are placed in water at a temperature of 25 to 35 and 

 undergo a spontaneous alkaline fermentation which splits up the indigo 

 into a sugar (indiglucin) and indigo white .which remain in the solution. 

 This solution is then thoroughly aerated and the indigo white oxidized 

 into indigo blue which is insoluble and forms a sediment. This sediment 

 is dried and constitutes the old indigo of commerce. 



Many bacteria are found in the fermenting liquid, but the cause of 

 transformation has been shown to be a specific form, Bacillus indigogenus, 

 closely related to Friedlander's pneumonia bacillus. It is strongly 

 aerobic and surrounded by a gelatinous envelope. 



Retting. The separation of the fibers of flax, hemp, ramie and 

 similar plants is brought about by a complex spontaneous fermentation. 

 The plants are either left on the surface of grassy meadows exposed to 

 alternate wetting and drying or immersed in water. In either case, 

 the tissues are gradually disintegrated by microbial action, more rapidly 

 in the wet process. 



The fermentation, principally bacterial, is due to many species. 

 Several have been described as being the principal agent in the process 

 but it is probable that the effects are due to the united action of several, 

 both aerobic and anaerobic. 



Among the forms to which the retting has been attributed are-B. amylobac- 

 ter of van Tieghem, an anaerobic form which attacks the pectic matters 

 and to some extent the cellulose. Granulobacter pectinovorum of Bey- 

 erinck and van Delden, also anaerobic, transforms the pectic matters 

 into sugars which it decomposes, producing butyric acid. Many other 

 forms have been described and part of the work has been ascribed to 

 Mucor, Penicillium and various molds. 



Cultures of Granulobacter pectinovorum and other forms have been 

 successfully used to hasten the process. 



Tanning. In the manufacture of leather the hides are first soaked 

 30 



