In a previous paper (Journ. Ment. Sci., April, 1928, p. 269) the writer has pointed out that a culture tube of tyrosine bouillon, if inoculated from the fæces of a healthy person, incubated for forty-eight hours and distilled, will be found to contain not more than 0.008% of phenol, or at most 0.015%. If, on the other hand, similar cultures are made from mental patients they will contain 0.02 to 0.03% of phenol in one half of the persons examined. In all these cases the phenol is formed by the action of bacteria on the tyrosine in an alkaline medium. The most important phenol-producing bacterium in the insane is B. Morgani, which can be demonstrated in 25% of acute cases, while B. phenologenes, Berthelot, is found in a smaller number. The paper referred to dealt with the toxic effects of B. Morgani and the results of vaccination with this organism. In the present paper another aspect of the matter will be considered, namely, the production of tyramine from tyrosine by intestinal bacteria, and whether poisoning by this substance may be a cause of mental disturbance.