LETTER OF TRANSMITTAL.

U.S. DEPARTMENT OF AGRICULTURE,

BUREAU OF CHEMISTRY, Washington, D. C., January 15, 1909.

SIR: I have the honor to submit for your inspection and approval a report on a phosphorus metabolism experiment conducted by F. C. Cook under the supervision of the Chief of Bureau. The report covers an experiment in rabbit feeding, extending over a period of six months, during which organic and inorganic phosphorus were fed, and includes calcium, magnesium, and total and ether-alcohol soluble phosphorus balances. At the conclusion of the experiment, complete analyses were made of the bodies of the rabbits, also of normal rabbits, which furnish some valuable data. Although the number of experiments is limited, the complete review of the literature bearing on the subject, which is included in this paper, greatly enhances its value and the interest both in this country and abroad in the relative value of the organic and inorganic forms of phosphorus, iron, etc., in the body economy makes the issuance of this contribution on the subject advisable.

I recommend that the manuscript be published as Bulletin 123 of the Bureau of Chemistry.

Respectfully,

Hon. JAMES WILSON,

Secretary of Agriculture.

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II. W. WILEY, Chief.

ILLUSTRATIONS.

PLATE I. Liver sections of organic-phosphorus-fed rabbit No. 1. Fig. 1.-Magnification 60 diameters. Fig. 2.-Magnification 175 diameters.... II. Liver sections of organic-phosphorus-fed rabbit No. 2. Fig. 1.-Magnification 60 diameters. Fig. 2.-Magnification 175 diameters.... III. Liver sections of inorganic-phosphorus-fed rabbit No. 4. Fig. 1.-Magnification 60 diameters. Fig. 2.-Magnification 175 diameters...

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METABOLISM OF ORGANIC AND INORGANIC

PHOSPHORUS.

REVIEW OF THE LITERATURE.

Much work has already been done on phosphorus metabolism, both in regard to the inorganic and organic forms of phosphorus, and many investigations have been recorded showing the advantages of the various organic forms, such as lecithin, glycero-phosphoric acid, phytin, etc. Most of this work has been done abroad, although some has been published in this country, notably the researches of Jordan, Patten, and Hart; a Mendel and Underhill; and Le Clerc and Cook. It seemed advisable, therefore, to present a general survey of the contributions previously made on this mooted question.

PHOSPHORUS COMPOUNDS.

In speaking of phosphorus compounds, Bunged states that certain of them probably should be regarded as essential organic food substances for man; also that in all animal and vegetable tissues, in every cell are found two complex organic compounds which are rich in phosphorus, namely, the lecithins and the nucleins.

According to the recent recommendations of the joint committee of the American Physiological Society and the American Society of Biological Chemists on protein nomenclature, the word "proteid" should be abandoned and the word "protein" should designate that group of substances which consists essentially of combinations of a-amino acids and their derivatives.

The conjugated proteins are divided into (a) nucleo-proteins, (b) glyco-proteins, (c) phospho-proteins, (d) hemoglobins, (e) lecithoproteins. The nucleo-proteins are compounds of one or more protein molecules with a nucleic acid. The phospho-proteins are compounds of the protein molecule with some, as yet unidentified, phosphorus-containing substance other than a nucleic acid or lecithin. The lecitho-proteins are compounds of the protein molecule with lecithins (lecithans, phosphatids).

a Amer. J. Physiol., 1906, 16: 268.

b Ibid., 17: 75.

J. Biol. Chem., 1906, 2: 203.

d Physiologic and Pathologic Chemistry, 2d ed., 1902.

LECITHINS.

The lecithins are ester compounds which may be regarded as having been formed by the union of one molecule of glycerol with two molecules of a fatty acid (stearic acid, palmitic acid, or oleic acid), one molecule of phosphoric acid, and one molecule of cholin, with the loss of four molecules of water. The formula for lecithin is CHNPO. The lecithin radical contains one atom of nitrogen for every atom of phosphorus.

Cholin is an ammonium base, the composition of which is accurately known. When heated it splits into glycol (ethylene alcohol), and trimethylamin. Its synthesis corresponds with this decomposition. Wurtz a produced it by the action of ethylene oxid and water on trimethylamin. In the animal kingdom cholin has, up to the present time, been found only in lecithin. It was first obtained. by Strecker from the bile, which contains lecithin, and hence was called cholin. Liebreich found it among the products of the decomposition of phosphorus compounds from brain tissue. Diaconow d showed that it was a product of the decomposition of lecithin. In the new tissues of plants cholin is found in other combinations as well as in lecithin. At present but little is known about the part which the lecithins play in the vital functions.

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An important question is whether the lecithins of the body tissues are produced from the lecithins of the food or by synthesis from other materials such as fat, protein, and phosphoric acid. It has been ascertained from experiments on artificial pancreatic digestion that the lecithins take up water and readily split up into glycerophosphoric acid, fatty acids, and cholin. It is not yet known whether this decomposition is complete in normal digestion, or a portion is absorbed unchanged, and if so, how large a portion; whether only the undecomposed part, when absorbed, can be utilized in the building up of the tissues, or the products of decomposition which are absorbed again become united; or finally whether lecithin may also be formed from other material. The absorption of lecithin or of its products of decomposition is complete, according to Bunge, as he states that neither lecithin nor glycero-phosphoric acid can be found in the feces. More recent work, however, by Long seems to show that the feces sometimes contain lecithin in considerable quantities. The presence of lecithin in milk, eggs, and many other foods indicates that this substance is essential in nutrition.

d Centrbl. med. Wissensch., 1868, 6:97, 434.

e J. Amer. Chem. Soc., 1906, 28: 704; Long and Johnson, ibid., 1499.