Friedrich von Muller1 was the first to affirm that the number of grams of ammonia eliminated by an organism during twenty-four hours might be used as an indicator of the intensity of acid formation within the body. Infection of the bladder leading to ammoniacal fermentation has sometimes caused erroneous deductions to be drawn from experimental data. Murlin and Bailey2 found that the bladder, especially in women, could be irrigated to advantage with a warm saturated solution of boric acid in order to avoid this complication.

To understand the conditions under which ammonia appears in the urine, one must understand the mechanism by which the blood is constantly held at a point the very slightest degree on the alkaline side of neutrality.

Distilled water is absolutely neutral in reaction, that is to+ say, the number of free H ions is equal to the number of free hydroxyl ions OH.3 A normal solution of hydrochloric acid contains 1 gram of free hydrogen ions in a liter of water, whereas in pure distilled water only one-ten-millionth of a gram of free hydrogen ions is present. Solutions are acid which have more than one-ten-millionth of a gram of hydrogen ions in a liter. They become alkaline when the hydrogen ion concentration falls below this point, which for convenience may be written 10 -7. Thus, when the hydrogen ion concentration is one part in one hundred million or 10 - 8 the hydroxyl concentration represents one-millionth normal alkaline solution. The hydrogen ion concentration of the blood varies between 10-7 (which it reaches only in severe acidosis) and 10 - 8, which is attained only after the administration of alkalies.

1 Muller: "von Leyden's Handbuch der Ernahrungstherapie," 1903, i, 261. 2 Muller and Bailey: "Archives of Internal Medicine," 1903, xii, 288. 3 Consult Michaelis: "Die Wasserstoffionenkonzentration," Berlin, 1014.

The addition of one-millionth of a gram of hydrogen ions (which would be contained in 36.5-millionths of a gram of hydrochloric acid) to a liter of water would change its hydrogen ion concentration of 10-7 to one of less than 10-6. Some cells cannot live in this concentration of acid.

In order to abolish cumbersome numbers, such as 0.35 X 10-7, Sorensen suggested that the negative exponent be used as a whole number. This is called the hydrogen ion exponent or:

The last figure given above represents an alkaline solution of three ten-millionths normal, or the equivalent of 0.000012 grams of NaOH dissolved in a liter of water. This is the usual alkalinity of the blood, and though so slight that it may almost be called neutrality is yet of definite importance.

McClendon,1 after careful experimentation, concludes that the normal PH of venous blood is 7.5, with a range between 7.45 to 7.55. The extreme difficulty of the technic renders the reports of many experimenters only relatively accurate.

The use of logarithms as expressive of acidity requires a little practice to accustom oneself to think, for example, that Ph = 5.70 represents a solution whose acidity is half that represented by PH = 6. Also, it must be remembered that the smaller the figure, the higher the concentration of hydrogen ions.

To Lawrence J. Henderson2 belongs the credit of the following analysis: The proper action of physiologic processes depends on the accurate adjustment and preservation of temperature, molecular concentration, and neutrality. Within the organism there is a constant formation of acid substances, principally carbonic, sulphuric, and phosphoric acids, which immediately combine either wholly or in part, according to their several avidities, with the basic constituents of the protoplasm and blood. In pathologic conditions β-oxybutyric acid and aceto-acetic acid claim their share of base. Metabolism, therefore, operates to lower the unvarying alkaline reaction of the blood. This reaction, according to Henderson, is maintained under conditions in which 89 per cent, of the phosphates of the blood are dibasic, as in Na2HP04, and 11 per cent, monobasic, as NaH2P04; and in which 93 per cent, of the carbon dioxid is present as in NaHC03, and 7 per cent, free as free C02. Henderson states that the arrangement of these four substances in the blood is such that the whole system surpasses in efficiency any possible closed aqueous solution of like concentration for preserving the hydrogen ion concentration of the blood at the normal of 0.3 X 10-7.

1 McClendon and Magoon: "Journal of Biological Chemistry," 1916, xxv, 669.

2Henderson, L. J.: "Ergebnisse der Physiologie," 1909, viii, 254; "Journal of Biological Chemistry," 1911, ix, 403.

If an acid be introduced into this system, not only may monosodic phosphate be formed from disodic phosphate or additional amounts of C02 dissociated from sodic bicarbonate, but both these acid substances may be eliminated by the kidney and lungs respectively, thereby maintaining the reaction at a normal level. The high diffusibility of these acid products assists in this regulation.

If alkali increases in the system, this though converted into bicarbonate must necessarily be accompanied by a large increase in osmotic pressure. The elimination of an alkaline urine corrects this.

Carbonic acid is lost through the lungs without loss of alkali to the body.

Phosphoric and sulphuric acids are removed from the blood by the kidney in the forms of NaH2P04 and Na2S04. If they were removed in other forms the urine would be intensely acid. The ordinary acid formation in the human organism corresponds to between 600 and 700 c.c. of N/10 acid solution daily.1 On account of the bases in combination the actual PH in 222 specimens of urines for twenty-four hours from 16 individuals showed an average value of 5.98, the range being between 5.1 to 7.2 For a short period the urine may be as alkaline as 7.4. Blatherwick3 finds the average PH of 30 urines of vegetarians to be 6.63. The titratible acidity appears to be a function of the ionized hydrogen present, and is almost wholly due to the excess of primary phosphate over secondary phosphate.