This journal provides immediate access to some articles. Volume 19(4); April 1933 Astronomy On the Distribution of Galaxies PMCID: PMC1086010 Chemistry Influence of Intensive Desiccation on Certain Physical Properties of Benzene PMCID: PMC1086011 Genetics On the Sterility of the Interracial Hybrids in Drosophila Pseudoobscura PMCID: PMC1086012 A Further Study of Blood Groups of the Rabbit PMCID: PMC1086013 Inbreeding and Homozygosis PMCID: PMC1086014 Inbreeding and Recombination PMCID: PMC1086015 Geology Hyænodontidæ of the Upper Eocene of California PMCID: PMC1086016 Mathematics An Analytic Closed Space Curve Which Bounds No Orientable Surface of Finite Area PMCID: PMC1086019 Regular Differential Systems of the First Order PMCID: PMC1086020 Note on a Metrically Transitive System PMCID: PMC1086021 Application of Poincaré's Sweeping-Out Process PMCID: PMC1086022 Geometry of Two-Component Spinors PMCID: PMC1086023 Physics The Effect of Helium on the Continuous and Secondary Spectra of Hydrogen PMCID: PMC1086017 K Series Spectrum of Tungsten PMCID: PMC1086018 Corrections Some Remarks Concerning Schrödinger's Wave Equation PMCID: PMC1086024 Corrects: Some Remarks Concerning Schrödinger's Wave Equation. Proc Natl Acad Sci U S A. 1933 March; 19(3): 339–344. Cretaceous Orbitoidal Formanifera from the Gulf States and Central America PMCID: PMC1086025 Corrects: Cretaceous Orbitoidal Formanifera from the Gulf States and Central America. Proc Natl Acad Sci U S A. 1932 October; 18(10): 611–616. Journal Matter Original table of contents page Administrative content — journal masthead, notices, indexes, etc. | ||