Statistical-Mechanical Studies of the α ⇄ β Transformation in Keratins: II. The Tension-Length Isotherms

In attempting to understand the yield region of the α β transformation in keratins (Astbury and Woods, 1933), we recently proposed a statistical-mechanical model (David and Schor, 1965) which generalized the work done by others on the helix random coil transformation (Zimm and Bragg, 1959; Gibbs and DiMarzio, 1959) (thermal denaturation) to the case of a polypeptide under external tension (Birstein, 1962). We wish now to report the comparison of the quantitative aspects of this model to the observed tension-length isotherms (in the yield region) of Cotswold wool.     

Un nouveau système chromosomique polymorphe chez desLeggada africaines du groupeTenellus (Rodentia-Muridae)

The pigmy-mice belonging to the grouptenellus seem fairly well characterized through the structure of the teeth (M₁). However, the chromosome complement of specimens from Niamey (Niger) is strikingly different from this precedently described bytenellus from Accra (Ghana). In this last station, we had to deal with the “primitive”, complement (2N=36,N.F.=36, sex-chromosomesPR). The sample of Niamey has the following constitution: three males have 33, 33 and 32 chromosomes, the single female has 34. This robertsonian polymorphism is due to the presence either of four acrocentric autosomes, or of one submetacentric and two acrocentrics, or of two submetacentrics. This polymorphism is fundamentally alike to that demonstrated precedently in the groupminutoides. The sex-chromosomes are of primitive type (PR). Two autosomes of medium size are satellited and their metacentricity seems to result from a pericentric inversion increasing theN.F. of two, 38 instead 36.     

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.