Trehalose, or mycose, a disaccharide occurring in Syrian manna, is decomposed by trehalase into two molecules of glucose:

C12H22O11.2H20= 2C6H12O6 + H2O

The enzyme trehalase, which produces this decomposition, was discovered by Bourquelot in Aspergillus niger and other moulds.

Melibiose, obtained from melitriose as already mentioned, is converted, according to Fischer and Lindner, and Bau, by a bottom fermentation yeast extract, but not by a top fermentation yeast extract, which contains the enzyme melibiase, into glucose and galactose :

C12H22O11+ H2O

Melibiose.

= C6H12O6C6H12O6

Glucose.

Galactose.

It is also hydrolysed by lactase (Fischer and Armstrong).

Gentiobiose was lately obtained from gentianose by Bourquelot and Hérissey, but not in a crystalline form; according to these observers, it is a definite compound resembling maltose, and is hydrolysed by an extract of Aspergillus niger into two molecules of glucose :

C12H22O11+ H2O = 2C6H12O6

The osones of the disaccharides maltose and melibiose have quite recently been shown by Fischer and Armstrong to be capable of undergoing hydrolysis by ferments in the same way as these disaccharides themselves, with the formation of the same products; these compounds can thus be used in the place of their disaccharides for testing their behaviour with regard to the action of ferments.

These investigators have also synthesised three new disaccharides, which have been called glucosidogalactose, galactosidoglucose, and galactosidogalactose, since they think that their constitution is very similar to that of the glucosides. These three disaccharides are decomposed by emulsin into their constituents, but only two of themgalactosidoglucose and glucosidogalactose-are fermented by bottom yeasts; top yeasts have no action on them at all. Galactosidoglucose in properties very closely resembles melibiose, and it is very probable that these two disaccharides are identical.

Fischer and Armstrong have further obtained a fourth diasccharide, isolactose, by the action of lactase upon a mixture of glucose and galactose. This is another case of synthetical ferment action. As regards its behaviour to ferments, this disaccharide occupies a position between lactose and melibiose. Another disaccharide was formed when lactase acted upon a solution of glucose alone, the synthesising power of this enzyme being here again shown.

These investigators have shown that emulsin also is capable of exerting a synthetic action, since they obtained a disaccharide as the result of its action upon a mixture of glucose and galactase, as in the case of lactase.

CHAPTER IV.

CHANGES IN THE MONOSACCHARIDES.

THE members of the first group of monosaccharides undergo various changes as the result of fermentation. The oldest known change is that called alcoholic fermentation, which glucose especially undergoes, together with fructose, both of which are formed, as before stated, by fermentation from cane sugar. The history of this fermentation process is very interesting, as the whole subject begins with it.

From the very earliest times it has been known that sweet liquids, if exposed to the air and allowed to stand, become cloudy and turbid, and bubbles of gas rise to the surface, which give the appearance of boiling to the liquid. The term "fermentation" was first applied to this change, on account of this appearance of boiling, but it was soon also applied to all changes where any effervescence took place, especially to the process of putrefaction, the terms putrefactio and fermentatio being used synonymously. A froth forms on the liquid, and a sediment, or "lees," in it; later, the whole settles to the bottom, leaving the liquid clear. After the process of apparent boiling is over, the liquid will no longer be sweet, but will have a spirituous smell and taste, owing to the presence of the

substance now known as alcohol. The earliest idea of the nature of this process is found in the writings of Basil Valentine, about the end of the fifteenth century, and was to the following effect: The scum, which is formed in the process, imparted an internal inflammation to the liquid, so that a purification was thereby determined; from this it is seen that he supposed that the alcohol was present in the liquid before the fermentation began. The gas evolved, which gives the boiling appearance, was thought to be the same as ordinary air; but van Helmont, in the following century, pointed out that this gas resembled that sometimes found in caves and wells, and he termed it "gas sylvestre." In 1682 Becher observed that this change occurred only in saccharine liquids, and he considered the alcohol to be a product of the reaction. He thought that the presence of air was necessary to start the process, which, in his opinion, was analogous to combustion; a distinction was also made between fermentation and putrefaction, and between true alcoholic fermentation and acid fermentation, e.g. the production of lactic acid. Some twenty years before this observation, Willis had put forward a new view of this change. It had already been found that the scum was necessary for the process, and this scum had been called a ferment; this ferment was supposed to be possessed of a motion peculiar to itself, which it transmitted to the fermentable matter. Stahl, a little later, also held this view, but considered, in addition, that the fermentable matter consisted of an unstable union of salt, oil, and earth; by the internal motion caused by the ferment, these particles were separated from one another, only to combine together

again to form more stable molecules, consisting of the same principles, but in other proportions.

Another century elapsed before any real light was cast upon the nature of this process; then Lavoisier took up the investigation of the changes, which was the first work of a really scientific character upon the subject. Instead of using the juices of fruits which had been employed before, he worked with a solution of cane sugar. This substance he regarded as a vegetable oxide made up of two bases, carbon and hydrogen, brought into the state of an oxide by a certain proportion of oxygen; these three elements were in such a feeble state of equilibrium that only a slight force was necessary to destroy their connection. He made analyses of the sugar, the alcohol, and the carbon dioxide, the results of which are to be found in his "Elements of Chemistry." The change is explained as a mere separation of the elements into two portions, the one being oxygenated at the expense of the other, in order to form carbon dioxide, whilst the other is deoxygenated and converted into the combustible substance called alcohol. The conclusion is that, if it were possible to reunite the alcohol and the carbon dioxide, sugar would be again formed. Though his analyses were far from correct, yet he approached very nearly to the truth.

Twenty years later, Gay Lussac and Thénard, and De Saussure, made more accurate analyses of cane sugar, which supported Lavoisier's view. The formula C12H12012 was given to sugar, and the following equation expressed the change:

C12H120122C4H6O2 + 4CO2

It was pointed out in 1828, by Dumas and Boullay,