II 6 BACTERIA. 



molecular vibration, such wave rate and length being trans- 

 mitted through the whole body of material to be inverted. 

 In fact, that the addition of the invertin is simply the light- 

 ing of the spark that fires the whole train. There is some- 

 thing very fascinating in this theory, and it certainly explains 

 many, otherwise, obscure chemico-physical questions con- 

 nected with these two subjects inversion and fermentation. 

 We see at any rate that part of the process takes place 

 entirely outside the yeast-cells, and may go on even when the 

 organisms that produce the inverting material have been killed 

 or completely removed. There are other similar examples 

 of conversion by purely chemical means, as, for instance, 

 where, on the addition of a dilute acid, such as sulphuric 

 acid at a certain temperature, starch is converted into glucose, 

 the heat and the acid setting up such molecular vibration 

 amongst the molecules composing starch, that in the dilute 

 acid there is a rearrangement of molecules, water is taken up, 

 and by hydration of the starch glucose is produced. In 

 this case the conversion takes place much more rapidly and 

 completely at a temperature of 130 C. than at 100 C. 



In a similar manner glycogen may be converted into 

 a sugar that will reduce Fehling's solution. This process 

 goes on in the liver and other organs and tissues of man and 

 animals, in which, probably, the secretions of the cells take 

 the place of the sulphuric acid and the high temperature, 

 or of the protoplasm of yeast and other vegetable cells. 

 Let us now, however, see what relation the yeast-cells 

 themselves (as apart from their products) are supposed to 

 bear to the real process of fermentation. If it were possible 

 to obtain an absolutely pure solution of sugar, i.e., a solution 

 containing no nitrogenous elements of any kind, and if we 

 were to place in this a minute quantity of yeast, we should 

 find that a very slight fermentation might take place i.e., 

 there would be an almost inappreciable diminution in the 

 quantity of sugar present ; a small quantity of alcohol and 

 carbonic acid gas would be developed, but very shortly the 

 process Avould stop, and there would be no marked increase 

 in the number of yeast-cells found in the whole solution. If 

 now we were to add a small quantity of nitrogen in the form 

 of an albuminoid substance and a certain quantity of ex- 

 tractives and salts, such as are found in the ashes of burnt 

 yeast, there would very quickly be observed a very different 



