So that while sugar, starch and oil do, under certain conditions which I shall demonstrate presently, affect to a small extent the production of urea and force, their influence is always indirect, and generally of so little importance that in a purely practical work like the present it may be neglected.

We are now at once met by the question, how much urea and how much albumen are sufficient; and as most physiologists are agreed that good strength and nutrition in adult life can be maintained on about 3 1/2 grains of urea per lb. of body weight per day, and as my own researches (see "Uric Acid," fifth edition, p. 744, et seq.) are in substantial agreement with them, I shall adopt this standard without further consideration here.

Then it is a rough but sufficiently accurate rule that the albumens required to produce any given quantity of urea can be found in grains by multiplying the grains of urea by 3.

So that if we take the weight of any individual in pounds - if there is much adipose tissue either deduct it, or take the body weight (if known) before the adipose tissue was added, - and multiply this by 3 if life is sedentary, and by 3.5 if life is active, we get the urea required, and if this is again multiplied by 3 we shall get the albumens required to produce it.

### Example

A man weighs 160 lbs., but his active weight twenty years ago before he became stout was only 130 lbs., and he is now sedentary; therefore (130 X 3 X 3) = 1,170; and 1,170, or, say 1,200 grains of albumen per day will be required for his proper nutrition and force production.

But if such a man leads, or wishes to lead, a decidedly active life, multiply 130 X 3.5 X 3 and 1,365 grains of albumen would be required each day.

Old people produce much less urea, say down to 2 grains per lb. per day; thus an old man might only require 130 x 2 x 3 = 780 grains of albumen and he would also, of course, produce much less force.

Children, on the other hand, require much more, and may produce 6-8 and even 10 grains of urea per lb.; thus a child of 35 lbs. may require 35 X 10 x 3 = 1,050 grains of albumen per day.

An interesting instance of this came under notice in the case of a boy aged 10, admitted into the Royal Hospital for Children and Women, suffering from albuminuria and having a normal temperature.

He was put on a diet of milk only, by accident he was given 2 1/4 pints, an insufficient quantity of albumens.

On this he lost weight to the extent of 7 lbs. in eleven days, his weight on admission being 53 lbs.

 Now the albumen in 2 1/4 pints milk = 590 grs. And the albumen in 10 ozs. of his own tissues containing say, 18 per cent ..................... = 786 grs. 1,376 grs.

So that we get 1,376 grains of albumen as the quantity this boy required each day, and this divided by 3 gives 458 grains of urea, or 8.6 grains per lb. per day on his original weight of 53 lbs.

Now this is very interesting, as Nature here made up the deficit and told us how much albumen and urea per lb. this boy required, and I have often found children of this age excreting urea to about the quantity thus calculated, and younger ones still more per lb.

As soon as the mistake was discovered the milk was increased, the loss of weight ceased, and the amount lost was slowly regained.

Precisely the same results have often been produced in adults, who for one reason or another have starved themselves, and here again the urea excreted would be found to correspond to the albumens swallowed and the tissues absorbed.

I may remark also that those who starve themselves may feel very bright and well at first, after the usual gastric symptoms of discomfort give way; as they are being nourished on a stimulating flesh diet from their own tissues, and are saving some of the force usually expended on digestion.

But later on, when their reserve of albumens has long been used up, and their tissue albumens begin to get low, they may discover that they have been living on capital which should never have been touched, and which it is difficult to replace; for with all their forces, including that of digestion, at a low ebb, it will take them a comparatively long time to assimilate sufficient albumens to keep the machine working as well as to replace the lost capital. And these considerations sufficiently account for the fact of which I have seen many instances, that those who put themselves on an unaccustomed diet often dangerously diminish their allowance of albumens for some time before they discover that there is anything wrong, and then find great difficulty in getting back to physiological levels.

Thus while 10 grs. of albumen per lb. of body weight is required for an active life, 9 grs. per lb. is about the minimum that an adult can take and continue to take with safety.

Of course in the treatment of disease and for a day or two, much smaller quantities may have to be taken; but whenever this is necessary there should always be a corresponding reduction in the output of force, or there will be a call on the reserves and a loss of weight, which should be avoided if possible.

I mention this 9 grs. minimum specially because I find that people, who do not take care, get below it for a time, by accident or mere want of attention, and then get weak, and being weak perhaps get easily fatigued, and then the fatigue (Physiology And Pathology Of Fatigue) destroys their appetite and power of digestion; and so they go on eating ever less and less, till some of them get to 7 or even 6 grs. per lb. per day, and are on a downward grade which will take them still lower if it is not put a stop to.

The best treatment of this condition is to quickly increase milk or cheese to make up the 9 grs. per lb., and to give a tonic for a time to improve appetite and digestion till the fire burns up again.

And it is because the fire goes down slowly, and the change often escapes notice till more or less serious signs of debility begin to appear, that it is necessary to bestow some care at first to ensure that the proper quantities of albumen are being taken by those who are changing diets.