| During sleep | 4·99 | grains. |
| When lying down and half asleep | 5·91 | " |
| When walking at the rate of two miles an hour | 18·10 | " |
| When walking at the rate of three miles an hour | 25·83 | " |
| When turning the tread-mill at the rate of 28·65 feet in a minute | 43·97 | " |
Similar facts are supplied in numbers by these experimentalists, and also by Fick and Winceslaus, and Traube and Parkes, and Pavy, and other excellent observers in this country and abroad; but these three, about the correctness of which there can be no doubt, are sufficient to show that the amount of urea in the urine does not supply the measure of this waste of muscular tissue in muscular action, which has to be repaired by lean meat and other nitrogenous food, and that the food you really want to repair this waste may be carbonaceous rather than nitrogenous—simple fuel, rather than plastic material.
C. I shall, I expect, be quite ready for my dinner when I come back. I may have taken more lean meat than I wanted to keep my muscles in trim; I have not taken more than I seem to want. I have been breakfasting in this way for a long time, and I was never in better trim for a long pull than now. I may be eating too much, but you must allow that I am eating the best kind of food.
M. I do not say that you are not eating the best kind of food; I only say that lean meat is not the only kind of nitrogenous food which will serve your purpose. It is impossible to distinguish between the albuminose or peptone into which fibrine is resolved in the process of digestion and the albuminose or peptone into which albumen, or caseine, or gluten, or legumin, is resolved in this process. It is apparently of little or no moment whether these various nitrogenous articles of food are derived from the world of animal life or from the world of vegetable life. You must allow that an herbivorous animal is not less vigorous than a carnivorous animal; and certainly you would find it difficult to show that man, who can live and thrive under the most dissimilar circumstances upon almost any kind of food, is vigorous in proportion to the amount of meat he contrives to consume.
C. You can hardly wish to depreciate the nutritive value of lean meat.
M. Certainly not. All the nitrogenous substances, animal and vegetable, are resolvable into albuminose in the process of digestion, but not with the same facility in every case. Some of them are digested more easily by some persons than by others; and, besides, there may be differences in the albuminose itself which are recognizable by chemical means. In your own case, lean meat may be more digestible than any other nitrogenous compound, and the albuminose into which it is converted may be more easily assimilated. In another case, eggs or cheese or macaroni may better suit the requirements of the person taking it. I do not venture to lay down a hard and fast rule for you
