Note 308 — Chapter XIV

K. Brandt (“Über den Nitratgehalt des Ozeanwassers and seine biologische Bedeutung,” Abh. d. kais. Leop. Carol. deutsch. Akad. d. Naturfoscher., 1915) accounts for this fact by the assump­tion that through the greater activity of the denitrifying bacteria in the tropical waters the amount of available nitrates is here comparatively smaller than in the polar oceans. The writer fully appreciates the importance of this fact but nevertheless is inclined also to see a limiting factor in the enormously rapid decline of the dura­tion of life at the upper temperature limits.