INDUSTRIAL APPLICATIONS 113 



injurious when present at this stage, and indeed only at this stage. 

 S. ellipsoideus II. is the stronger of the two species. Whilst upon this 

 particular subject, we may add that in 1883 Hansen demonstrated 

 that these much-dreaded turbidities and other beer diseases may be 

 due to mixtures of two yeasts, even though each of them by itself 

 gives a faultless product. 



The Industrial Application of Bacterial Ferments 



We may commence our brief category of the industrial application 

 of bacteria by referring the reader to fermentations, like the acetous 

 (which results in the manufacture of vinegar), the alcoholic (alcoholic 

 beverages), the lactic acid (souring of milk for dairying purposes, 

 cheese, etc.), the butyric (resulting in butyric acid), and those fer- 

 mentations occurring in the soil and improving the fertility of land 

 for farming purposes. With the principal facts concerning each of 

 these applications of bacteria to industrial processes we have dealt 

 elsewhere. It remains for us to mention other spheres of industry 

 where bacteria are, whether we recognise it or not, playing a leading 

 rolfj. Their industrial effects are often secondary to vital processes. 

 For instance, in securing their food bacteria break down organic 

 material and bring about chemical and physical change. Now this 

 power which organisms have of chemically destroying compounds 

 may, or may not, be of primary importance, but there can be no doubt 

 that many of the products which arise as a result are of an importance 

 in the world which it is difficult to over-estimate. Perhaps the most 

 remarkable examples occur in soil and in milk. But other illustra- 

 tions which will at once occur to the reader are the maceration 

 industries. For example, linen, as is well known, is produced from 

 flax. The flax stem is made up of cellular substance, flax fibres and 

 wood fibres ; the latter are of no service in the making of linen, but 

 the whole is bound together by a gummy, resinous substance termed 

 "the central lamellae" (an intermediate inter-cellular substance 

 consisting probably not of pectose, but of calcium pectate). The 

 solution of this cementing substance can be brought about by 

 chemical means by treating the plant with very dilute sulphuric 

 acid and then neutralising the adherent acid by a weak alkali bath 

 (Bura). But it can also be solved by the process known as retting. 

 There is dew-retting and water-retting. The former is practised in 

 Russia, and consists in spreading the flax on the grass and exposing 

 it to the influence of clew, air, rain, and light. The result is a soft 

 and silky fibre. Water-retting is the method more commonly 

 adopted, and is accomplished by means of steeping the flax in bundles, 

 roots downwards, in tanks or ponds, with appliances so arranged as 

 to keep the flax below water. In ten to fourteen days, according to 



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