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Volume 27(5);  May 15, 1941
Astronomy
Two Interesting Nuclei of Planetary Nebulae: IC 418 and NGC 40
P. Swings and O. Struve
Proc Natl Acad Sci U S A. 1941 May 15; 27(5): 225–229.
PMCID: PMC1078311
Chemistry
Radioactive Carbon as an Indicator of Carbon Dioxide Utilization: V. Studies on the Propionic Acid Bacteria
S. F. Carson, J. W. Foster, S. Ruben, and H. A. Barker
Proc Natl Acad Sci U S A. 1941 May 15; 27(5): 229–235.
PMCID: PMC1078312
Relation between Genes and Carotenoids of the Tomato
A. L. LeRosen, F. W. Went, and L. Zechmeister
Proc Natl Acad Sci U S A. 1941 May 15; 27(5): 236–242.
PMCID: PMC1078313
Mathematics
On the First Variation of the Dirichlet-Douglas Integral and on the Method of Gradients
Richard Courant
Proc Natl Acad Sci U S A. 1941 May 15; 27(5): 242–248.
PMCID: PMC1078314
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