726 PRELIMINARY OBSERVATIONS. 



temperature at which water boils, by alcohol, by acids, salts of 

 mercury, sulphurous acid, chlorine, iodine, bromine, by aro- 

 matic substances, volatile oils, and particularly empyreumatic 

 oils, smoke and a decoction of coffee, these bodies in some 

 cases combining with the ferments or otherwise effecting their 

 decomposition. 



The following are additional instances of fermentation. The 

 smell and taste which distinguish wine from all other fermented 

 liquids depend upon cenanthic ether, which contains a peculiar 

 acid ; and those of spirits from corn or potatoes upon a peculiar 

 oil, the oil of potatoes. Both of these substances are produced 

 in fermentation, the former probably from the tartaric acid of 

 the wine, the latter by a simultaneous decomposition of the 

 cellular tissue of the grain or potato. The oil of potatoes has 

 all the characters of an alcohol (page 813). The production of 

 this oil is completely prevented in the fermentation of beer, by 

 the presence of an aromatic substance, the volatile oil of hops. 

 In the fermentation of the Hcrba centaurium minorius, a plant 

 which possesses no smell, a true ethereal oil is formed, of a 

 penetrating agreeable odour. The leaves of tobacco, when fresh, 

 have little or no smell, and when distilled, yield a white, fatty, 

 crystallizable substance (nicotianine), which contains no nitro- 

 gen and is quite destitute of smell. But when the same plant, 

 after being dried, is moistened with water, tied together in 

 small bundles, and placed in heaps, a peculiar process of decom- 

 position takes place. Fermentation commences, and is accom- 

 panied by the absorption of oxygen ; the leaves now become 

 warm and emit the characteristic smell of prepared tobacco and 

 snuff. When the fermentation is carefully promoted, and too 

 high a heat avoided, this smell increases and becomes more 

 delicate; and after the fermentation is completed, an oily 

 azotised volatile matter, called nicotine, is found in the leaves. 

 This substance which possesses all the properties of a base, 

 was not present before the fermentation. The different kinds 

 of tobacco are distinguished from one another, like Manes, by 

 having very different odoriferous substances, which are gene- 

 rated along with the nicotine (Liebig). 



M. Liebig also ascribes the morbific action of matters of con- 

 tagion and miasms, to their operation as ferments. He applies 

 the law already quoted to organic substances forming part of 



