Page:Life in Motion.djvu/159

Rh hydrogen, as in water, sugar is said to be a carbo-hydrate; or, as one might phrase it, it is hydrated carbon. Suppose, as 1 now do, we pour some strong sulphuric acid, which has a great affinity for water, upon a bit of lump sugar, you see the lump soon becomes a black mass of carbon or charcoal. This group of carbo-hydrates includes the various kinds of sugars, starches, and gums. Carbo-hydrates are always present in a diet. They abound in rice, sago, potato, and bread, and in vegetable matters used as foods.

I need hardly demonstrate to you that milk contains butter. Butter is a mixture of various fats, and as fats are soluble in ether, it is easy to make an ethereal solution of the fat of milk by shaking up milk with ether, after adding a little caustic potash to it and keeping it moderately warm. In this long tube you see a layer of ether holding fat in solution, floating on the top of the fluid. Fat also consists of carbon, hydrogen, and oxygen, but in proportions different from those in which these elements exist in the carbo-hydrates. It contains no nitrogen. Fatty matter must always exist in a diet suitable for sustaining life.