330 PHYSIOLOGY AT THE FARM. 



sugar four or five parts of barley. Thus the distillers, by 

 mixing a portion of unmalted barley with their malt, obtain a 

 wort equally sweet with that furnished by an equal weight of 

 malt. 



The mode of action of diastase in changing starch into dex- 

 trine, as well as the mode of action of yeast in changing sugar 

 into carbonic acid and alcohol, is still involved in obscurity. 

 The two actions, nevertheless, are in some sort analogous. 

 Both are ferments, and their effect in a measure depends on 

 their decomposition. Moist yeast and moist diastase both very 

 rapidly undergo decomposition. The opinion which has arisen 

 of late as to fermentation is, that the formation of each of the 

 compounds concerned depends on a particular stage of decay 

 in the ferment, attended " with the development of fungi or 

 organisms of a kind varying in each particular stage with the 

 products obtained." In appears that the process of fermenta- 

 tion may be prevented in any organic liquid by such isolation 

 from the atmosphere as shall prevent organic germs thence 

 obtaining access to the substance under experiment. 



Inulin. In the roots of many plants, such as those of dahlia 

 (Dahlia frustranea, Dahlia superflua), of elecampane (Inula 

 helenium), meadow saffron (Colchicum autumnale], of dande- 

 lion (Taraxacum dens leonis), and of chicory (Chicorium inty- 

 lus), there is a variety of starch known by the name of inulin. 

 It is a white, pulverulent, inodorous, tasteless substance, in- 

 soluble in alcohol, sparingly soluble in cold water, but readily 

 soluble in hot water, from which it is deposited again on cool- 

 ing in a pulverulent form. Its solution produces left-handed 

 rotation upon a ray of polarised light. By long boiling it ac- 

 quires the characters of a gum ; with iodine it gives a yellow 

 colour ; dilute acids, with the aid of heat, change it first into 

 dextrine and then into grape-sugar. 



Gum, or Arabine. Gum-arabic is the type of gum. The 



