The average quantity of urine is usually subnormal, even when large quantities of water are consumed, and is generally 300 c.c. less than the amount consumed. The loss of water by the lungs, skin, and kidneys exceeds that ingested, due to the fact that water is being manufactured through the tissue breakdown. The reaction is acid, and becomes increasingly so from day to day, because of the formation of sulphuric, phosphoric, oxybutyric, diacetic, and uric acids. The specific gravity varies, sometimes being below normal.

Less than the normal 85-88 per cent. of urea is formed, and more than the normal 2-5 per cent. of ammonium. This is accounted for by the formation of the above acids by tissue disintegration, and as there is not enough fixed alkali with which they may combine, they enter into union with a part of the ammonia which is formed by decomposition of the protein, and so the formation of urea is prevented.

It might be thought that fasting was a favourable opportunity for ascertaining the precise quantity of endogenous uric acid, but it is to be remembered that the organism is chary of using the nuclein from which purins are formed, and hence much more is manufactured on a full diet than during starvation. Besides this, some of the purin bodies produced by decomposition of nuclein are converted into urea, and one must not forget the possibility of the synthetic production of uric acid, or the small quantity formed from the hypoxanthins of muscle. A ready method of estimating the nuclein decomposition is to combine the purins with the phosphoric acid excreted; but this is not available here, an accurate result being impossible on account of the large excretion of phosphoric acid due to the breakdown of bone.

In addition to carbon dioxide, water, sulphates, and urea, creatinin is now recognised as one of the products formed from the disintegration of proteins. Under normal conditions about 1 gram of creatinin is excreted in twenty-four hours, the exact amount depending upon the nature of the food. Folin has shown that the absolute amount of creatinin eliminated in the urine on a meat-free diet is a constant quantity, differing in individuals, but quite independent of the quantitative changes in the total amount of nitrogen excreted. The amount, indeed, is fairly constant from hour to hour and from day to day. Although its formula, C4H7N3O, is comparable with that of creatin, C4H9N3O2, minus one molecule H2O, it is not derived from the creatin of the muscular tissues of the organism nor from muscle ingested as food. It has been supposed that it is the expression of some special metabolic process in muscle, a process upon which the efficiency of muscular activity may depend.

Creatin is not present in normal urine, but is present in the urine during starvation, in acute fevers, in women during involution of the uterus, and in conditions where there is rapid loss of muscle. Its fate in the normal body is unknown, although it is conjectured that it may be converted into urea, yet creatin injected into the blood does not follow this course, but undergoes excretion as such. Creatinin excretion is quite independent of diet and exercise, and Folin believes that it is the expression of the extent of endogenous metabolism and is manufactured in the liver and not the muscles.

Mellanby, again, has shown that it is not present in muscle at all, even after prolonged work, and advances the hypothesis that the liver manufactures creatinin out of certain products of protein katabolism; that these are carried to the muscle, combining with water, thus forming creatin; and that when saturation has taken place, excess of creatinin is then excreted by the kidneys.

In fasting, creatinin is undoubtedly diminished proportionately to the lessened tissue disintegration.

The mineral salts are likewise excreted proportionately to the tissue breakdown. They are unable to remain in the circulation, as the kidney is ever on the watch to remove any excess.

The chlorides in the urine, being chiefly derived from the food, are diminished in quantity more than the other salts, because the tissues contain very little sodium chloride. Normally there should be in the urine one part NaCl to two parts urea, and the daily excretion of NaCl should amount to about 12 grams. If several grams be found in the urine during fasting, it is being derived from ingested food or drink, as the tissues could not supply so much. Cetti on the tenth day excreted .6 gram, Breithaupb on the sixth day .35 gram, Succi on the tenth day .51 gram, which was reduced to .36 gram on the eleventh day.

On a normal diet the ratio sodium: potassium:: 64: 36 obtains, but the proportion of potassium may be much increased by eating a large quantity of flesh which is rich in that salt. During fasting, the muscles and glands which supply the nutriment being rich in potassium and poor in sodium, the ratio is reversed, more potassium than sodium being excreted, and this is a fairly absolute proof of genuine complete fasting. On the seventh day Cetti excreted 2 grams potassium and only .7 gram of sodium, whilst on the eighth day Succi excreted 3.7 grams potash to 1.9 grams of sodium.

The relation of phosphorus to nitrogen in muscles and glands is 66:1, but this proportion is reduced in the urine of starvation, because a larger relative amount of phosphorus from the breakdown of bone is excreted.

More magnesia than lime is excreted in the urine of a normal man, because animal food and most vegetables are poor in lime and rich in magnesia. In fasting, an increase takes place in the excretion of lime, because bones contain more lime than magnesia, and because it is cast off by the kidney instead of by the bowel, as in normal cases. This is accounted for by the fact that the faeces are deprived of the lime that would be ingested in the food, and the presence of abnormal acids in the blood helps to dissolve more lime salts, and so they are excreted by the kidney.

The urine of fasting people always contains acetone bodies, both acetone and diacetic acid and even β oxybutyric acid being detected on the second day. It is now well recognised that acetonuria depends on a diminished supply of carbohydrate food and a proportionate decrease of the carbohydrates decomposed as compared with the fat destroyed. In Cetti's case, before the fast, only .075 gram acetone could be discovered in the urine, and in Breithaupt's urine the amount was too small to be capable of estimation. On the tenth day of Cetti's fast, however, .671 gram, and on the sixth day of Breithaupt's fast .506 gram of acetone appeared in the urine. Acetone is usually excreted by the breath, but during fasting it appears almost entirely in the urine. On the second day after the termination of the fast in both the above-mentioned cases the urinary secretion reverted to the normal condition, showing the sensitiveness of the body to a supply of carbohydrates.