you will see that this will take place when you heat it; and in this way you have a proof that glucose exists in the mixture. I told you just now that the liver contained a quantity of sugar. I may say that I believe it has been demonstrated that the liver does not contain sugar itself, but it contains a matter which is so easily converted into sugar, that the instant you expose it to the air it becomes changed into sugar, and this matter is contained in the blood. This sugar-forming substance may, however, be collected from the liver, and, under the name of glycogene, has been separately exhibited. We do not yet know exactly from what this substance in the liver is formed in the food, but there seems to be little doubt, from observations made when the hepatose presents itself in disease in abundance in the blood, that cane sugar and starch mainly contribute to its production.

Although I have not had time to dwell on it, I need hardly impress on you what an interesting chapter in the physiology of life this discovery of sugar in the liver has opened up. We are evidently on the verge of discovering the causes of those remarkable morbid states of the system which have been known so long, in which the blood is poisoned by an immense accumulation of sugar. The sugar, then, surcharging the blood, has been evidently produced for the purposes of combustion and oxidation, the failure of which has caused its accumulation in the blood, and its elimination in an undecomposed form.

The ultimate action of all forms of sugar in the system is the same. We have seen that starch can only be absorbed as it is converted into sugar. The

advantage, then, of sugar over starch, as an article of diet, appears to lie in the facility with which it can be absorbed into the blood. It is supplied to the young of all the higher forms of mammalia in their mother's milk, and its sweetness seems adapted to the instinctive tastes of children, who may always, with advantage, be allowed a free use of it in their food. At the same time what is good for children may not be so advantageous for fathers and mothers. Sugar readily enters into decomposition, forms other compounds, especially lactic acid, and sets in operation other dangerous changes in the food. Hence the dyspeptic, the gouty, the rheumatic, and the corpulent must be warned against it. Those who take alcoholic beverages need but little of it, whilst the teetotaller may be allowed its unrestricted use.

I have just a few concluding remarks to make on substances resembling starch and sugar, and which enter into our daily food, although it is very doubtful if they act on the system in the same way as starch and

sugar.

Dextrine is formed in plants whilst starch is passing into the composition of sugar. Like sugar it is soluble in water, but not sweet. It is obtained from barley whilst being malted.

Gum may be regarded as fixed dextrine; it is soluble in water, but is incapable of being converted into sugar, and has no sweet taste. Although gum enters largely into some kinds of food, it does not enter the blood, or act as an aliment. It may be therefore properly regarded as an accessory food. Sugar is added to it, and it is used in the manufacture of lozenges. These

are flavoured with various substances, as in the case of the Pâté de Jujubes.

Liquorice is found in many plants, but it is separated from the juice of the Liquorice Plant (Glycyrrhiza glabra). Like gum it is soluble in water, and has the sweet taste of sugar. It differs from sugar in not being fermentable. It is obtained from the root of the Liquorice Plant in the form of an extract, and comes to this country in solid sticks, which are sold under the name of "Spanish Juice." This is boiled down and refined, and sold under the name of "refined or pipe liquorice." The liquorice plant is cultivated extensively at Pontefract or Pomfret, in Yorkshire, and a manufacture of the liquorice is carried on in that town. The liquorice is made into cakes, which are called "Pomfret cakes." Liquorice, like gum, does not act as an aliment in the system.

Manna is another sweet substance, soluble in hot water, but not capable of fermentation. It is obtained for medicinal purposes from a species of ash, the Fraxinus Ornus. Several other plants yield manna, and it is used in some countries as an article of diet. Its value is, however, doubtful. This substance has sometimes been supposed to be the "manna" of Scripture, but the putrescent nature of that substance, and the absence of dietetical properties in the substance in question, renders this supposition exceedingly doubtful.

IN this lecture I shall continue my observations on that class of foods which are now known by the name of heat or force-giving.

This group may very well be divided into-first, those which contain starch and sugar, of which I have already spoken; and, secondly, those which contain oil or fat.

There is a great difference in the chemical composition of oils and fats, as compared with starch and sugar, which can be easily made apparent.

Taking, then, the composition of starch and sugar as carbon 12, hydrogen 10, and oxygen 10, which would express generally the composition of starch and sugar; or, taking the real weights, carbon 72, hydrogen 10, and oxygen 80, the quantity of carbon in

starch and sugar would be nearly half their whole weight.

Now, if we take oil, we shall find the difference is very great. Taking all those substances which are indicated by the term oil, which are called fats, butters, lards, suets, greases, and tallows, their composition will be this-carbon 11, hydrogen 10, and oxygen 1. Thus you see, in the starch and the sugar, the hydrogen and the oxygen are just in the proportions in which those two elements form water; but if we take the fat and the oils, you will find a large quantity of the hydrogen to spare, and very little oxygen in these bodies at all. Oxygen, then, is not in the proportion in which it forms water with hydrogen, so that you see in an oil or fat, instead of having only half the bulk, as in the case of the carbon of starch and sugar, you have actually nearly the whole mass for combustion, 66 of carbon and 10 of hydrogen out of the 77 parts of oily matter. Now, this is a practical point of importance, for where you are substituting fat for starch or sugar, there you ought to substitute a very much less quantity. The proportion of the combustible elements in fat, as compared with starch and sugar, is as 2 to 1, so that you ought to take as a substitute for 1 pound of butter, 2 pounds of starch or sugar. It must, however, be recollected that sugar is more easily taken up into the system, and more available than starch.

Now, this oily matter, of which we have to speak, is used not only as an article of diet, but it is extensively employed in the arts.* I would remind you that *See Lecture on Soap, in Uses of Animals.