A technique based on the isotope dilution principle for the measurement of exchangeable body sodium in man has been devised and evaluated by Forbes and Perley (1) and Miller and Wilson (2), and a similar technique for exchangeable body potassium has been developed by Corsa, Olney, Steenburg, Ball, and Moore (3). Once the individual techniques for the measurement of exchangeable body sodium and potassium had been devised, the desirability of carrying out these measurements simultaneously became apparent because of the important biochemical inter-relationships that have been pointed out between these two alkali metals (4-6). Since the metabolic state of a patient may vary considerably during even a relatively short period, single exchangeable body sodium and potassium measurements carried out several days apart are not a satisfactory substitute for simultaneous measurements.Such simultaneous measurements, based on the isotope dilution principle, require at present the separation of sodium from potassium prior to the radioactivity determinations. James, Brooks, Edelman, Olney, and Moore (7) have described a technique for these measurements in which classical chemical methods are used to separate the electrolytes. In the present study we have made use of ion exchange chromatography (8) for the separation. At the outset, our primary concern has been with the reproducibility of this technique for the simultaneous measurements of exchangeable body sodium and potassium in normal young adults."Exchangeability" of sodium and potassium Twenty-four hours has been chosen by previous investigators (1-3, 7) as a satisfactory and convenient equilibration period. Estimated values in man indicate that approximately 82 per cent (1) of the total body sodium and 90 to 95 per cent of the total body potassium (3) are exchangeable in twenty-four hours. These measurements must be considered as preliminary since their accuracy depends on an exact knowledge of rates of electrolyte exchange in all areas of the body, data which are not yet completely available in man. In the case of sodium, bone and brain constitute areas of slow exchange (1, 2, 9), while in the case of potassium, red cell, brain, and bone exchange less rapidly than do other regions of the body (3, 10). Even though the measurement of exchangeable sodium and potassium of the body does not correspond to the total body content of these elements, it does furnish an index of total body sodium and potassium which probably varies directly with total body electrolyte content. EXPERIMENTAL METHOD a) General outlineKnown amounts of radioactive sodium (Na) and of radioactive potassium (K0) are injected intravenously. After a twenty-four hour equilibration period, a blood sample is drawn and sodium and potassium radioactivity and concentration (i.e., specific activity) of the proteinfree serum supernatant are determined. We have described in detail in Part I (8) the use of a sulfonic acid cation exchange resin, Dowex 50, to effect the separation of Na" and KZ in order to measure their ...
Many theories have been proposed to explain the acid-fast property of the tubercle bacillus, but no satisfactory explanation has yet been given. It is suggested that the property is dependent upon the permeability of the cytoplasmic membrane. Evidence will be presented in support of this concept. It will be shown that when the Ziehl-Neelsen technique is employed the dye exists within the cell in two distinct portions: a small portion is bound to the cytoplasm and the remainder is free. The characteristic color of the stained bacillus is due to the free dye which can be removed without altering the acidfast believed that this phenomenon of acidfastness might be based upon the properties of chemicals isolated from the tubercle bacillus or of complexes of these chemicals. At one time there was a general belief that the presence of a wax sheath around the cell was responsible for its peculiar staining characteristics, but this is no longer tenable after the study made by Knaysi (1929). Some authors including Ehrlich thought that acid-fastness was related to the permeability of the cell membrane, but this structure was not clearly defined and experimental evidence was not given. The one point on which there is complete agreement is that the integrity of the cellular structure must be maintained to preserve the acid-fast property.Since our proposed explanation of the mechanism of acid-fastness is based on the function of a cellular structure, a brief review of pertinent information on the cytology of the tubercle bacillus is indicated.The cell wall of the tubercle bacillus has been observed directly with the electron microscope by Mudd and Anderson (1944). Mudd and Mudd (1927) demonstrated the hydrophobic property of the surface of the bacillus. The apparent functions of the cell wall are to protect the cell from mechanical injury and to impart to the cell its characteristic shape. The electron microscopic studies of Mudd, Polevitsky, and Anderson (1942) and Mudd and Anderson (1944) give direct evidence of the cytoplasmic membrane in bacteria. According to Knaysil (1929Knaysil ( , 1938Knaysil ( , 1944Knaysil ( , 1946, who refers frequently to this structure, the membrane of the tubercle bacillus probably consists of lipids and protein. With ordinary technique it appears to be the external boundary of the cytoplasm rather than a separate strtucture. EXPERIMENTAL RESULTSAlthough there is some evidence that the cell wall of the tubercle bacillus retains small amounts of certain other dyes, our observations suggest that this 1 A recent personal communication from Knaysi states that what he referred to as the cell "membrane" in his paper (1929) is now usually known as the cytoplamic membran. 777
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