68 



tion from, starch. Starch, chemically, is nothing more than carbon, combined 

 wth the elements that compose water in the proportion of six to five. It appears 

 to be the first product of that decomposition of carbonic acid and assimilation of 

 the carbon, which, under the influence of the sun's rays, is continually going on 

 in grooving plants. Starch is the basis from which most other vegetable secretions 

 are formed. It is either used up at once by the plant that secretes it, or it may 

 be laid by for future use ; sometimes in the tuber as in the potato, in the seed as 

 in com, or in pith as sago. Saccharose, the sugar of commerce or cane sugar, is 

 made up, like starch, of carbon and water ; but the proportions differ. Instead 

 of six to five, in saccharose it is twelve to eleven. This sugar is found in the 

 maple and beet ; whenever found it is intended as a store for the future use of the 

 plant at the time when a great and sudden demand is made for the purposes of 

 reproduction. Glucose is the sugar met vidth in the grape and other fruits ; it 

 contains a little more water than saccharose and is more soluble. It is necessary 

 that stored-up starch and saccharose should be altered into glucose before they 

 are used by the plant. This alteration is always prepared for by the laying up of 

 nitrogenous matter in close approximation with the stored material. When the 

 food is wanted, the nitrogenous matter acts as indirect ferment, and causes the 

 starch or saccharose, whichever it may be, to take up an additional quantity of 

 water, and become glucose. Thus the starch stored up in the barleycorn is altered 

 into glucose when heat and moisture bring the nitrogenous matter called diastase 

 (which has been laid up under the cuticle), in contact with it. This process takes 

 place in seeds when they germinate, and is taken advantage of by the maltster. 

 For the same reason the tuber of the potato becomes sweet and transparent from 

 the alteration of its sugar into glucose when growth begins. Again, when sugar 

 cane and beet blossom, a large supply of nutriment is suddenly wanted ; the 

 stored-up saccharose is then digested, that is, altered into glucose, and is carried 

 away in the sap to the reproductive organs, to be there reconverted into starch, 

 and stored up again in the seed. Parsnips, and some other sweet roots that do 

 not blossom in the first year, lay up glucose itself, which is held in reserve till 

 the next summer, then seed is formed, and the root loses its sweetness and 

 coUapses. 



If yeast be placed in water containing air or oxygen, the oxygen gradually 

 disappears, and is replaced by carbonic acid ; a process exactly similar to the res- 

 piration of fishes, continuing day and night, but proportionately more active. 

 The yeast would die when the oxygen was absorbed, but if the glucose be then 

 added, the fungus will abstract from it the oxygen required, and set free carbonic 

 acid and alcohol. Pasteur, who has given great attention to the life history of 

 ferments, has concluded, after many experiments, that a continued supply of oxy- 

 gen, and the combustion it causes, are necessary sources of energy for the develop- 

 ment of vitality in ferment plants. As soon as the cells of yeast have exhausted 

 the glucose in contact with them, they have a tendency to come to the surface and 

 take on their aerial growth, which is simply the formation of spores. Under 

 favourable circumstances some of the cells at the surface may be observed under 



