As it is the food taken into the body that produces heat and motion, it might at first sight appear an easy matter to determine the amount of heat or of motion which a given weight of a particular kind of food is capable of producing within the animal mechanism. But this performance is not so easy a task as it appears to be. In the first place, all of the food may not be perfectly oxidised, though thoroughly disorganised within the body; secondly, as animals rarely subsist on one kind of food, it is difficult, when they are supplied with mixed aliments, to determine which of them is the most perfectly decomposed. But though the difficulties which I have mentioned, and many others, render the task of determining the nutritive values of food substances difficult, the problem is by no means insoluble, and, in fact, is in a fair way of being solved. Professor Frankland, in a paper published in the number of the _Philosophical Magazine_ for September, 1866, determines the relative alimental value of foods by ascertaining the quantity of heat evolved by each when burned in oxygen gas. From the results of these researches he has constructed a table, showing the amount of food necessary to keep a man alive for twenty-four hours. The following figures, which I select from this table, are of interest to the stock-feeder:-- Weight necessary to sustain a man's life for twenty-four hours. Kinds of Food. Ounces. Potatoes 13·4 Apples 20·7 Oatmeal 3·4 Flour 3·5 Pea Meal 3·5 Bread 6·4 Milk 21·2 Carrots 25·6 Cabbage 31·8 Butter 1·8 Lump Sugar 3·9 These figures show the relative calefacient, or heat-producing powers of the different foods named _outside_ the body; but there is some doubt as to their having the same relative values when burned _within_ the body. The woody fibre of the carrots and cabbages is very combustible in the coal furnace, but it is very doubtful if more than 20 or 30 per cent. of this substance is ever burned in the _animal furnace_. However, such inquiries as those carried out by Frankland possess great value; and tables constructed upon their results cannot fail to be useful in the drawing up of dietary scales, whether for man or for the inferior animals. I may here remark, that in my opinion the nutritive value of food admits of being very accurately determined by the adoption of the following method:--