Limitations on the Equivalent Cardiac Generator

This paper is a critical summary of the implications of potential theory in electrocardiography with particular attention to the “inverse problem.” It is emphasized that potential measurements on the human torso serve to determine only the multipole coefficients of the heart sources and that no additional information is available. An interpretation of these coefficients with respect to the actual electrophysiological sources is considered further on the basis of distribution theory.     

Ventricular septal defect with bidirectional shunting: Mathematical considerations

Previously proposed formulae for the quantitative estimation of bidirectional shunts across ventricular septal defects require determination of the oxygen contents of mixed venous, pulmonary artery, pulmonary venous, and aortic blood. Because these formulae do not take into account the mixing of oxygenated with unoxygenated blood within the ventricles, their use must result in underestimation of shunt flows in each direction. A mathematical model for a ventricular defect is examined, in which it is assumed that mixing of blood occurs in each of six sites in the venae cavae or right atrium, right ventricle, pulmonary artery, left atrium, left ventricle, and aorta. A total of fourteen streams of blood can flow from one to another of these mixing sites. As long as complete mixing occurs in the six specified mixing sites, any degree of mixing or non-mixing of the various streams is permitted. From the equations characterizing the model, formulae are derived in which the shunt flow in each direction is expressed in terms of the oxygen contents in the six mixing sites and the fractions of blood which enter the shunt from either side without prior mixing in a ventricular mixing site. The previously reported formulae, which apply when no ventricular mixing is allowed to occur, lead to theoretical minimum values for the shunt flows in each direction. At the opposite extreme where all the shunting blood is required to mix in a ventricle before entering the shunt, formulae for maximum possible shunt flows are also obtained. The absolute values for the left-to-right and right-to-left shunt flows, which must lie somewhere between the theoretical maximum and minimum values, cannot be computed from blood gas data alone. This work was supported in part by grant HE-07563 from the National Heart Institute of the National Institutes of Health and grants-in-aid from the American and North Carolina Heart Associations and the Life Insurance Medical Research Fund. Work completed during tenure as U.S.P.H.S. post-doctoral fellow.     

METHOD FOR COMBINED ULTRASTRUCTURAL AND BIOCHEMICAL ANALYSIS OF NEURAL TISSUE

No significant change was found in the electrolytes and lipids of the brain analyzed after glutaraldehyde fixation by perfusion of laboratory animals; such fixation also satisfactorily preserves neural tissues for electron microscopy. The brains of normal and tumor-bearing C3H mice, Wistar rats, and New Zealand rabbits were studied. Little difference was found in the dry weight and the content of sodium, potassium, total lipid and lipid fractions, and in the sulfate space (S³⁵O₄) between specimens from unperfused and perfused animals, whether normal or tumor-bearing. The results suggest the possibility of using selected regions of the nervous system, dissected after fixation, for chemical study and at the same time characterizing similar regions morphologically with the electron microscope.     

The settling of female Haematopota insidiatrix austen (Diptera, Tabanidae) on cloth screens

The response of female Haematopota insidiatrix towards cloth screens is considered as part of the host-finding behaviour. When black, dark grey, light grey and white cloths were compared as regards attractiveness, more flies settled on the black than on the other shades. When a screen was carried horizontally flies settled on the under surface but not on the upper surface and more flies were caught. A black screen with three white stripes was progressively less attractive as the width of these stripes was increased. Even narrow white stripes reduced the catch, particularly if they were horizontally arranged. When differently sized black screens were compared, fewer flies were caught on the smaller ones. Flies settled on the lower part of a screen, as they do on a host animal. When a screen was divided so that its lower half was white and its upper half black, fewer flies settled on it than on the all-black reverse side (control). Conversely, with black below white approximately the same number of flies were caught on this as on the black control side of the screen. At temperatures below 19°C and humidities above 77% R.H., more flies settled on the sunny than on the shaded side of the screen. At higher temperatures and lower humidities this preference was reversed.

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Zusammenfassung Die Reaktion der weiblichen Haematopota insidiatrix auf Stoffschirme wird als ein Teil des Verhaltens bei der Suche nach einem Wirtstier betrachtet. Beim Vergleich von schwarzen, dunkelgrauen, hellgrauen und weissen Stoffen in Beziehung auf ihre Anziehungskraft setzten sich mehr Fliegen auf die sxhwarzen Stoffe als auf anders getönten. Wenn ein Schirm horizontal getragen wurde, setzten sich die Fliegen auf die untere Seite doch nicht auf die obere Seite. Ausserdem stieg die Anzahl der gefangenen Fliegen. Ein schwarzer Schirm mit drei weissen Streifen versehen übte um so weniger Anziehungskraft aus, je breiter die Streifen gemacht wurden. Selbst enge weisse Streifen verminderten die Anzahl der gefangenen Fliegen, besonders wenn sie horizontal angebracht waren. Wenn Schirme von verschiedener Grösse herumgetragen wurden, fingen sich auf den kleineren Schirmen weniger Fliegen. Die Fliegen setzten sich auf den unteren Teil der Schirme genau wie sie es bei Wirtstieren machen. Wurde ein Schirm in eine untere Hälfte (weiss) und eine obere Hälfte (schwarz) geteilt, so liessen sich weniger Fliegen darauf nieder als auf der ganzschwarze Rückseite (Kontrolle). Im umgekehrten Falle, (untere Hälfte schwarz, obere Hälfte weiss) wurde ungefähr dieselbe Anzahl von Fliegen auf dieser Seite wie auf der völlig schwarzen Rückseite gefangen. Bei Temperaturen unter 19°C und einen relativen Feuchtigkeit von über 77% setzten sich mehr Fliegen auf die sonnige Seite als auf die beschattete Seite des Schirmes. Bei höheren Temperaturen und niedrigerem Luftfeuchtigkeitsgehalt war diese Vorliebe umgekehrt.