No longer white mice for bad air warning board of British submarines according to the Dutch magazine Marineblad dated 1908-1909 no. 5

An item reported that the British Admiralty ordered that the white mice on board of submarines which were used as a warning for the danger of (dangerous) gasses were to be removed. On 13th July was a gas accident on board of the submarine HMS A9 but then were already the mice removed.