Carbon dixoide (C02) content in the muscle of the mackerel (Scomber japonicus) during putrefaction was measured.
(1) The quantity of C02 produced and accumulated in the sample of fish muscle increased quick to some degree in process of time, and then gradually decreased after the complete spoilage of the fish muscle. Accordingly, the C02 content of fish muscle might to be of little significance as a better index of the freshness of the fish flesh.
(2) A large amount of C02 was produced by microbial actions, while a little amount of the gas was produced by muscle's autolysis.
(3) Though the optimum pH for decarboxylases are on the acidic side, not a small quantity of CO2 was produced in fish muscle also at an alkaline pH. In this connection, it was discussed that microbial decarboxylases were inducible enzymes, and that they might therefore produce C02 to some extent on the alkaline side if such substrates as free amino acids were present in sufficient amounts, as it was often the case in a putrefying fish flesh.