THE VOLATILE PART OF PLANTS. 103 



substances which the chemist can prepare, and to which 

 he gives special designations, are doubtless mixtures, and 

 in most cases contain but a small proportion of the real 

 ferment, which, in a state of entire purity, is unknown. 



Leaven, or Yeast, which has been employed in mak- 

 ing bread, wire and beer for many centuries, contains, or 

 mainly consists of, a microscopic plant of very simple 

 structure (pp. 244-5), which, when placed in a solution of 

 cane-sugar, is able in the first place to cause the "inver- 

 sion " of that substance into the two sugars, dextrose and 

 levulose, and, secondly, to transform both the latter into 

 alcohol and carbon dioxide. The " inverting " effect of 

 yeast upon cane-sugar has been traced to a substance 

 which can be separated from the yeast and obtained as a 

 dry, white powder. The alcoholic fermentation requires 

 the living yeast plant for its accomplishment. Ferments 

 are accordingly divided into the two classes, unorganized 

 and organized. We shall here notice briefly a few unor- 

 ganized ferments or enzymes, as they are also termed, 

 that have been somewhat carefully studied. 



Invertin is obtained from dry, pulverized yeast by 

 heating it to 212 to coagulate albumin and then ex- 

 tracting with warm water. The invertin dissolves, and, 

 by addition of alcohol, is precipitated. Barth thus ob- 

 tained a substance containing 6 per cent of nitrogen 

 which was able, in the course of 48 hours, to transform 

 (invert) 760 times its weight of cane-sugar. Invertin 

 has no effect on starch or dextrin. 



Diastase is the name applied to a substance that may be 

 obtained as a whitish powder from sprouted barley (malt) 

 by extracting with dilute alcohol and precipitation with 

 strong alcohol, which is capable of transforming 2,000 

 times its weight of starch, first into dextrin and finally 

 into maltose and dextrose. The purest diastase prepared 

 by Lintner contained 10.4 per cent, nitrogen and gave 

 reactions for albuminoids, but it had properties besides 



