Health may be defined as a satisfactory condition of nutrition, strength, and power of endurance.

In considering how such a satisfactory condition can be produced we shall have to treat of the albumens of the food, their sources, characters, digestibility and the amounts of force and urea derived from their metabolism in the body.

In far off olden times, when man was a more natural and less refined animal than at present, Nature managed the whole business for him, and he either died or attained to a satisfactory condition of health and nutrition without knowing how or why.

But when later on he began to control some of the conditions of his own nutrition without having obtained a thorough comprehension of all their bearings, he here, as in so many other points of contact with Nature, upset her scales and balances without being prepared to substitute any more satisfactory ones in their place, and suffered in con-sequence from many unexpected and terrible results of his rashness.

And even now many men are attempting to carry the diet of youth on into middle life and age, or the diet that was quite correct for an active outdoor life into a life of sedentary office work in a town; or if they fall into neither of these errors they are generally completely ignorant with regard to the relative value and importance of foods, so that they either starve themselves on vegetables or herbs containing little or no albumen, or, on the other hand, over-feed themselves on the most concentrated albuminous foods.

Now to prevent such mistakes and to substitute a certain amount of scientific precision for the previous rule of thumb methods is the object of this little book, and so we may say that the first essential of nutrition is the supply to the blood of sufficient albumen to replace that transformed into urea in the production of force.

If food is withheld urea goes down and down, and with it falls the power of producing force in active exercise.

Fig. 1 shows in a curve the hourly excretion of urea in the sixteenth, fifteenth, fourteenth and earlier hours of a fast, no food having been taken since 8.30 p.m. on the previous day.

We see, then, that in the hour ending at 8 a.m., urea is a little above 13 grains and it rises in the hour ending at 9 a.m. to a trifle above 14 grains; this is probably the result of the exercise involved in the acts of washing and dressing.

Effects of fasting and food on the excretion of urea.

Fig. 1. - Effects of fasting and food on the excretion of urea.

At 10 it falls, and at 11 is only about 12.5 grains, but at 12 it rises again nearly to 14 grains as the result of some exercise, only to fall more quickly and decidedly down to 11 grains at 1 p.m. At 1.5 food is taken and at 2 there is a rise, but only a slight rise, to 11.5 grains; at 3, however, the full effect of the meal begins to be felt and it rises with a bound to 16.7 grains per hour. The total for the day being a little over 400 grains, or 17 grains per hour.

We see, then, from this figure, that the effect of withholding food for sixteen hours is a steady fall of urea (only the latter part of which we see here), from 17 grains or more per hour down to 11, but this fall is broken from time to time by the effects of exercise, which appears to call out some albumen or nitrogen from some reserve store, about which more presently.

We also see that with this fall of urea there is a steady corresponding diminution of strength and power of endurance, that is, of force production, and that with the rise of urea, which at 3 p.m. follows the taking and digestion of food, there is an equally marked rise of general strength and power.

We see, then, that the excretion of urea is the measure of the force available, and that its falls and rises accurately register the conditions of the nutrition, strength, and endurance of the body.

We know also that this urea is generally obtained from the nitrogen in the form of albumen contained in food, that there is also a certain amount of stored albumen in some of the tissues, and that in prolonged starvation, nitrogen is further provided by destruction of the tissues themselves, this being accompanied by a definite daily decrease in body weight.

We shall see that such loss of body weight is an exact measure of the albumens consumed, and of the urea and force produced from them.

So that when the condition arrives that there is no more albumen available for absorption, no more reserves and no food, urea and force alike cease to be produced, and life comes to an end.

From this we may conclude that urea excreted is an exact measure of force produced, and that albumen available is also an exact measure of the force that can be produced (see also chap. iv.).

We shall see also as I have already suggested in "Uric Acid"1 as the result of other researches, that those who believed that strength could be got out of food containing no nitrogen, and that urea was therefore not an absolute measure of strength and power, had flaws in their premisses which seriously affected the value of their conclusions.

I mention this here because the relation between urea, albumen and force, is the keynote of this volume; but I shall have much further evidence to bring forward on the subject in the pages that follow.

1 "Uric Acid as a Factor in the Causation of Disease." Fifth Edition. J. and A. Churchill. London: 1900. Pp. 335, 340.

Further, by watching my own excretion of urea for many years (see details in "Uric Acid") as well as on all kinds of diets, I have come to the conclusion that given a sufficient amount of albuminous food, which can be digested and metabolised in the body into sufficient urea, I can produce force proportional to that urea, without much regard to the quantities of other non-albuminous foods taken.