78 ILLUSTRATIONS FROM WINE AND BREAD. 



Illustration a ^ e l en gth ^ tmie without undergoing any change ; but if 

 from the mak- a puncture be made in it to give the air access, it rapidly de- 

 ine ' teriorates. The precise change taking place is perhaps bet- 

 ter understood by observations on the expressed juice of this fruit. If 

 grapes be pressed beneath the surface of quicksilver, and the juice be col- 

 lected in an inverted jar, without ever coming in contact with the atmos- 

 pheric air, it may be kept for a long time without any apparent change ; 

 but if a small quantity of air, or only a single bubble of oxygen is per- 

 mitted to enter the jar, and the temperature is that of a summer's day, an 

 intestine commotion or fermentation at once ensues, carbonic acid escapes, 

 alcohol arises in the liquid, and the sugar which was in the grape-juice 

 disappears. But the quantity of sugar thus capable of being destroyed 

 is limited, and a point is eventually reached at which no. more sugar can 

 be decomposed, and no more carbonic acid set free. 



The juice of the grape contains a nitrogenized principle resembling al- 

 bumen. It is this which is in reality the active body. So long as ox- 

 ygen is excluded, this nitrogenized substance remains unaltered, but the 

 moment the air finds access, a change begins. The sugar which is pres- 

 ent in the juice becomes involved in the movement going on, which is 

 propagated by degrees to all its atoms, dividing each into two well-known 

 and well-marked bodies. The period at which no farther change takes 

 place in portions of sugar 'which may have been purposely added is 

 when the nitrogenized principle has disappeared. 



Carbonic acid and alcohol are the two substances arising in this de- 

 composition. Their mode of origin is obvious when it is understood 

 that one atom of sugar can be so divided as to yield four of carbonic acid 

 and two of alcohol. In this artificial instance, the subdivision is even 

 more complex than that which occurs in duodenal digestion, in which the 

 sugar atom is subdivided into two equal and symmetrical parts, two 

 atoms of lactic acid. In the following formulas, (1) represents the case 

 of vinous production, (2) that of duodenal digestion : 



(1) ..... C 12 H 12 13 =4 (C0 2 )+2 (C 4 H 6 OJ. 



(2) ..... C 13 H 13 13 =2(C 6 H 6 6 ). 



Second, of bread. If, in the preceding case, a transmuting nitrogen- 

 T11 ized body breaks the sugar atom so that alcohol is one of the 



Illustration J ,. & .., -,,. 



from making products, and upon this principle all wines and intoxicating 

 bread. liq uors are made, the instance now presented is of far more 

 interest to the well-being of man. The use of wine undoubtedly adds 

 not only to social enjoyment, but sometimes conduces to health a ben- 

 efit, alas ! often attended with a thousand ills. Not so with bread, em- 

 phatically and truly described as the staff of life. 



The making of wine and of leavened bread are two of the oldest chem- 



