Due to
World War II the publication of the journal stopped in 1943 with volume 49. Publication was resumed in 1949 with the volume numbering starting again at 1. In order to distinguish between the identical numbered volumes, volumes in the first publishing period are referred to as the first series whereas the later volumes are called second series.
Before volume 51 of the second series the journal was called Tôhoku Mathematical Journal, with a circumflex over the second letter of Tohoku.
Kümmerle, Harald (2018), "Hayashi Tsuruichi and the success of the Tôhoku Mathematical Journal as a publication", in Ogawa, T.; Morimoto, M. (eds.),
Mathematics of Takebe Katahiro and History of Mathematics in East Asia, Advanced Studies in Pure Mathematics, vol. 79, Tokyo: Mathematical Society of Japan, pp. 347–358
Oda, Tadao (2011), "The first hundred years of the Tohoku mathematical journal", Tohoku Mathematical Journal, Second Series, 63 (4): 461–470,
doi:10.2748/tmj/1325886276,
MR2872951