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Volume 7(7);  July 1921
The cover of the journal
Biology
An Unidentified Base among the Hydrolytic Products of Gelatin
Donald D. Van Slyke and Alma Hiller
Proc Natl Acad Sci U S A. 1921 July; 7(7): 185–186.
PMCID: PMC1084845
Note on the Economic Conversion Factors of Energy
Alfred J. Lotka
Proc Natl Acad Sci U S A. 1921 July; 7(7): 192–197.
PMCID: PMC1084847
Genetics
Linkage Variation and Chromosome Maps
A. H. Sturtevant
Proc Natl Acad Sci U S A. 1921 July; 7(7): 181–183.
PMCID: PMC1084843
Genetical and Cytological Proof of Non-disjunction of the Fourth Chromosome of Drosophila Melanogaster
Calvin B. Bridges
Proc Natl Acad Sci U S A. 1921 July; 7(7): 186–192.
PMCID: PMC1084846
The Behavior of Homologous Chromosomes in a Triploid Canna
John Belling
Proc Natl Acad Sci U S A. 1921 July; 7(7): 197–201.
PMCID: PMC1084848
The Prediction of Annual Egg Production from the Records of Limited Periods
J. Arthur Harris, W. F. Kirkpatrick, and A. F. Blakeslee
Proc Natl Acad Sci U S A. 1921 July; 7(7): 213–219.
PMCID: PMC1084851
Paleontology
Origin and History of the Bear Family in the Western Hemisphere, with Particular Reference to the Relation of This Question to Problems of Geographical History
John C. Merriam
Proc Natl Acad Sci U S A. 1921 July; 7(7): 183–185.
PMCID: PMC1084844
Physics
The Destruction of Phosphorescent Zinc Sulfides by Ultra Violet Light
Leonard B. Loeb and Lloyd Schmiedeskamp
Proc Natl Acad Sci U S A. 1921 July; 7(7): 202–207.
PMCID: PMC1084849
Acoustic Pressure Distributions, Chiefly in Reservoirs and in Pipes
Carl Barus
Proc Natl Acad Sci U S A. 1921 July; 7(7): 207–213.
PMCID: PMC1084850
Journal Matter
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