The Digestibility of Fats. We have now come to the last group of the real Coal foods, namely, the fats. Fats are the "hottest" and most concentrated fuel that we possess, and might be described as the "anthracites," or "hard coals" of our Coal foods. They are, also, as might be expected from their "strength" or concentration, among the slowest to digest of all our foods, so that, as a rule, we can eat them only in very moderate amounts, seldom exceeding one-tenth to one-sixth of our total food-fuel. It is not, however, quite correct to say that fats are hard to digest, because, although from their solid, oily character, they take a longer time to become digested and absorbed by the body than most other foods, yet they are as perfectly and as completely digested, with the healthy person, as any other kind of food. Indeed, it is this slowness of digestion which gives them their well-known staying-power as a food. Their Place in our Diet. The wholesomeness of fats is well shown by our appetite for them, which is very keen for small amounts of them--witness, for instance, how quickly we notice and how keenly we object to the absence of butter on our bread or potatoes. To have our "bread well-buttered" is a well known expression for comfort and good fortune; yet a very little excess will turn our enjoyment into disgust. Fat, and particularly the cold fat of meat, "gags" us if we try to eat too much of it. Fortunately, most of these fat-foods are quite expensive, pound for pound, and hence we are not often tempted to eat them in excess. Within proper limits, then, fats are an exceedingly important and useful food--a valuable member of the great family of Coal foods. The Advantages of Fat as a Ration. The high fuel value and the small bulk of fats give them a very great practical advantage whenever supplies of food have to be carried for long distances, or for considerable lengths of time, as in sea voyages and hunting and exploring trips. So that in provisioning ships for a long voyage, or fitting out an expedition for the Arctic regions, fats, in the shape of bacon or pork, pemmican,[9] or the richer dried fishes, like salmon, mackerel, and herring, will be found to play an important part. Fats also have the great advantage, like the starches, of keeping well for long periods, especially after they have been melted and sterilized by boiling, or "rendering," as in the case of lard, or have had moderate amounts of salt added to them, as in butter.