a long time unless lie also do a large amount of muscular work—unless he do much more work of this sort than the great majority of human beings are willing or able to do. Fat and butter and oily matter generally, on the other hand, require no digestion, in the proper sense of the word. They are converted into an emulsion—which is no more than a mechanical mixture like cream, by the action of the pancreatic and duodenal juices chiefly, and by the action of the bile partly, and this emulsion passes directly into the general circulation of the blood through the lacteals directly, without going the round of the portal circulation and the liver, as albuminose has to do. Fat and butter and oily matters generally are fuel ready-made, or which only need to be emulsified in order to be in this case; and they have this advantage also—that they are burned up in the system, without leaving behind them, so to speak, any ash like urea. And, as force-producing agents—if the capacity for oxidization may be taken as a measure—the value of fat and oil is almost double that of fibrine or albumen.
C. I can see that I may have been taking too much lean meat and too little toast; I can also see that I may have been especially wrong in avoiding fat and butter; but I do not see how to set to work to reform mv doings.
M. What you have to do, first of all, is to bear in mind that the daily loss which has to be made good by food, in a man of medium stature and in moderate work, amounts to 4,800 grains of carbon and 300 grains of nitrogen, and that, in round numbers, lean meat contains 11 per cent of carbon and 3 per cent of nitrogen, and bread 30 per cent of carbon and 1 per cent of nitrogen.
C. Is it so?
M. Yes. The daily rate of wasting of the system which I have mentioned is that which is brought to light by very many observations, carried on by many persons in various ways, with a view to regulate the food-rations of soldiers and sailors and prisoners, and other ration-fed people; and as to the proportion of carbon and nitrogen in lean meat and in bread the evidence is sufficiently conclusive.
C. Upon these data I can easily calculate how much meat and bread I really want if I choose to live wholly on meat or bread, and how the meat and bread ought to be apportioned if I take meat and bread together.
M. The calculation is ready made for you, and the result shows very plainly that you must mix your lean meat and bread in certain proportions if you care to feed without wasting good food. In order to replace the daily loss of 4,800 grains of carbon by lean meat, the quantity of meat you must take is 43,637 grains, or rather over 6 pounds a quantity which contains 1,009 grains of nitrogen in excess of the 300 grains actually wanted. In order to replace the daily loss of 300 grains of nitrogen by bread, the quantity of bread you must take will be 30,000 grains, or about 4 pounds—a quantity which ex-
