PHYSIOLOGIC CHEMISTRY.

BY REID HUNT, M.D., AND WALTER JONES, PH.D.,

OF BALTIMORE, MD.

1

Cystin. Mörner's discovery of two isomeric forms of cystin as hydrolytic products of horn may furnish food for reflection to the artists who are accustomed to draw pictures of the proteid molecule without giving the sulphur atom any consideration. Interest was first given to the manner of the binding of sulphur in the proteids by the researches which were carried on in Liebig's laboratory, and which showed that by boiling proteids with alkalies a part of the sulphur can be split off in such a form as will precipitate lead sulphid from a solution of lead acetate, but that by far the greater part of the sulphur can not be so split off. It is, therefore, not surprising that Abel should find ethyl sulphid in the dog's urine, and that Aldrich should prove the presence of normal butyl mercaptan in the secretion of mephitis mephitica, which feeds only on proteid matter. It will be remembered also that from his researches on the oxidation of proteids with potassium permanganate Maly was led to the conclusion that in each proteid molecule there is one sulphur atom present as an SH group, which is oxidized by the permanganate to an SO,H group. So that if Kossel's assumption be true that the simplest proteids are the protamins which are sulphur-free, and that the sulphur present in ordinary proteids is to be found in conjugated side-chains, then our interest must be directed to the side-chain, for the occurrence of cystin in pathologic concretions is just as stern a fact whether we consider the sulphur of the cystin to be present originally as an essential part of the proteid molecule or not. The question whether the cystin of urinary calculi is to be considered as directly split off from the proteids of the body or as a result of synthetic processes can not be positively answered, but the work of Bauman and Preusse and of Bauman and Goldmann is to show that either cystin or a near relative of cystin occurs normally in slight amount in the urine, and that cystin is an intermediate product in the metabolism of sulphur which can be protected from further decomposition by the ingestion of halogen substitution products of benzene. The work of Mörner, however, seems to take the matter out of the field of argument. Pure defatted horn shavings were placed in a flask which was connected with a wash-bottle containing lead Enough dilute hydrochloric acid was added nearly to fill the flask, and without the introduction of any reducing agent the contents

1 Zeit. f. physiol. Chem., XXVIII, p. 595.

of the flask were heated on a water-bath at from 90° to 95° C. Only a trace of sulphureted hydrogen was given off, and among the products of hydrolysis were found two isomeric forms of cystin whose relative proportions depend upon the length of time during which the hydrolysis is carried on. One of these is ordinary hexagonal levorotatory cystin, and is formed in comparatively large quantity when the hydrolysis is carried on for a week. The substance gives analytic results which correspond to the composition of cystin, and when heated with an alkaline solution of lead acetate, it yields a copious precipitate of lead sulphid. By treatment with tin and hydrochloric acid it can be reduced to a substance which responds to all the color reactions for cystein, and which by oxidation passes back again into cystin, from which the cystein was prepared. Aside from optic properties and crystalline form the two cystins are scarcely to be distinguished from each other; indeed, there is no physical property of the substances which can serve for their separation, and they were to be obtained in comparative purity only by conducting the hydrolysis in such a manner that only one of the two products is formed, heating for 2 weeks having been found most favorable for the production of the needle form and 1 week for the hexagonal. In fact, while the needle-shaped crystals appeared to be an individual, and certainly have the composition of cystin, their specific rotation changes on recrystallization; so that all the preparations obtained were more or less contaminated with an isomeric but optically different cystin. From these and a countless number of qualitative reactions we can not escape the conclusion that the substance is in all respects identical with the hexagonal crystals of cystin which are to be found in urinary calculi. A check test, moreover, showed that the substance is not present as such in horn. On the other hand, when the hydrolysis of the horn shavings is allowed to proceed for 2 weeks, a large yield is obtained of a substance which has the composition of cystin, but which crystallizes in needles. Its chemical reactions and solubilities are practically those of hexagonal cystin; by reduction it is changed into cystein, which is apparently identical with the corresponding substance obtained from hexagonal cystin, but which on oxidation, strangely enough, yields needles of cystin. In addition to these two forms of cystin, cystein is also formed in considerable quantity in the hydrolysis of horn, and especially when the heating is prolonged. Moreover, the formation of cystein is almost entirely prevented by conducting the hydrolysis in an atmosphere of hydrogen, from which Mörner concludes that cystin is the primary product from which cystein is afterward formed by reduction. This work leaves little doubt that in the proteids of horn there is preformed a cystin group, or, at least, an atomic grouping which easily gives rise to cystin and which is accountable, in part at least, for the property which the proteids possess of giving off the so-called reduced sulphur when boiled with alkalies. This is one of the most interesting papers which has appeared since the YEAR-BOOK was last published, and even in the unusually large space which has been devoted to its abstraction it has been found impossible to mention many matters con

nected with what is one of the most interesting cases of geometric isomerism to be found in physiologic chemical literature.

Chemical Relationships of Colloid, Mucoid, and Amyloid Substances. The very remarkable work of Schmiedeberg showed that the chondroitin sulphuric acid of the cartilage is capable by hydrolysis of producing chondrosin, glycuronic acid, and glucosamin; and it has since been found that chondroitin sulphuric acid exists in some form of combination in the amyloid substance. Levene 1 now finds that tendomucin is a combination of a proteid with a nitrogenous ethereal sulphuric acid very similar to chondroitin sulphuric acid, since it yields chondrosin, and that submaxillary mucin, as well as colloid of a colloidal carcinoma, contains very similar or identical ethereal sulphuric acids in combination. The work points very clearly to the conclusion that colloid, mucoid, and amyloid substances are similarly constituted.

Ovarial Mucoid.-Leathes 2 has separated from the liquid of ovarian cysts a reducing substance which he names "paramucosin." This substance has the formula C12H,,NO10, and is considered to be a dihexosamin of some unknown carbohydrate.

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Normal Occurrence of Arsenic in Animals and Its Localization in Certain Organs.-The statement has been made-without, however, adequate evidence that arsenic occurs in all the organs of the body and in all articles of food. Gautier 3 finds most organs (liver, spleen, kidney, marrow, suprarenals, testicles, ete., and blood, urine, and feces) to be free of arsenic, but does find it constantly present in the thyroid of man and other animals; it also occurs in the thymus, brain, mammary glands, and milk, and, in traces, in bone, hair, and skin. The lastnamed structures seem to be the chief channel for the elimination of arsenic. One hundred grams of human thyroid yield on an average 0.75 milligram of arsenic; 1.3 grams of dried thyroid of the dog gave distinct reactions for arsenic. No arsenic could be detected in such articles of food as bread, eggs, and fish, but traces were found in potatoes and some other vegetables. Nucleins were prepared from the thyroid by peptic digestion; all the arsenic was found in these nucleins, the rest of the gland being entirely free of it. The arsenic probably exists in the nuclei in the form of "arsenical nucleins." The iodin was also found in the nucleins; there seems to be some connection between arsenic and iodin in the body, just as there is in the inorganic world. The medicolegal bearings of these observations are obvious; they show that the organs most commonly examined for arsenic in cases of poisoning are normally free of it, but they also show the necessity of examining each organ separately. The method employed by Gautier consisted essentially in destroying the organic matter with nitric and sulphuric acids, precipitating the arsenic with hydrogen sulphid, and applying the Marsh test; 0.0005 mg. in 100 parts of thyroid

1 Arch. Neurol. and Psychopathol., II, p. 571.

2 Arch. f. exper. Path. u. Pharmakol., XLIII, p. 245.

3 Compt. rend., CXXIX, p. 929; cxxx, p. 284; and Bull. Acad. de méd., Dec. 5, 1899.

can be detected in this way. The usual method of destroying organic matter in toxicologic examinations (by means of potassium chlorate and hydrochloric acid) causes most of the arsenic to escape in a volatile form. A very delicate test for arsenic is said to be that of Abba, which consists in allowing Penicillium brevicaule to act upon the substance to be examined and observing the garlic-like odor produced. Scholtz 1 applied this method to the skin, hair, perspiration, and urine, and found that from 0.005 to 0.002 mg. arsenic could be detected. When testing the urine, it is advisable to first remove the odor of this liquid with animal charcoal, as it interferes somewhat with the test.

Titanium in the Animal Organism.-Baskerville 2 found human flesh to contain 0.0325 % of titanic oxid; human bone contains but a trace, while 0.0195% was found in beef-bone.

Iodin in Thymus and Thyroid.-Gley found that the parathyroids of the dog and rabbit contain a relatively greater amount of iodin than do the thyroids of these animals; Mendel 3 finds the same in man, although in the individual examined the thyroid was abnormal and apparently contained an unusually small amount of iodin. Mendel, like some others, finds that the thyroids of new-born children contain not iodin; also that the thymus, when carefully isolated, is free of iodin. According to Charrin and Bourcet, however, the presence or absence of iodin in the thyroid of the new-born child depends largely upon the condition of the mother's health. These authors found iodin (in amounts varying from 0.001 to 0.006% of the dried gland) in the thyroids of 14 children; some of the children had been born prematurely, others had lived a few weeks, but most of them had died during birth at term. Most of the mothers of these children were healthy. No iodin was found in the thyroids of 18 recently born children whose mothers were suffering from various pathologic, especially chronic, conditions.

Uric Acid. Since the appearance of the Hopkins' method for the determination of uric acid in the urine so many criticisms have been offered that one must have a most thorough acquaintance with the literature to be able to make any intelligent use of the method. This method was accepted with eagerness by chemists who had used the exact but laborious method of Ludwig and Salkowski, but the results which were obtained by its use are now known to be incorrect, and in order to obtain results which are useful, the original method must be so far modified that it is scarcely recognizable as the method which Hopkins originally proposed. It will be remembered that Hopkins saturates a known volume of the urine with ammonium chlorid, filters off the precipitated ammonium urate, and washes the precipitate with a saturated solution of ammonium chlorid. The precipitate is then dissolved in water and the uric acid precipitated as such by the addition of hydrochloric acid, and after washing is determined by direct weighing or by titration with a standard solution of potassium permanganate. Hopkins

1 Berl. klin. Woch., XXXVI, p. 913.

2 Jour. Am. Chem. Soc., XXI, p. 1099.

3 Am. Jour. Physiol., III, p. 285. * Compt. rend. d. l'Acad. d. Sci., cxxx, p. 945.