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The fraction of cod-liver oil which inhibits the Carr and Price reaction for vitamin A is different from the better known unsaturated acids of cod-liver oil. The inhibiting power disappears completely after hydrogenation.

From the unsaponifiable matter of cod-liver oil a fraction has been isolated with strong inhibitory action upon the growth of Mycobacterium tuberculosis in vitro, using the fluid medium of Sauton with and without addition of serum albumin. The fraction was toxic to guinea pigs and therefore could not be studied effectively in experimental tuberculosis in these animals.

1. The unsaponifiable fraction of cod-liver oil contains substances which in a concentration of 2 μg per ml of Sauton's medium have a marked inhibitory action on the growth ofM. tuberculosis D328 and the virulent strain A30. 2. Saturated and unsaturateda-glycerylethers are very probably responsible for this activity. 3. Addition of blood serum albumin to the medium gives an important reduction of the growth inhibition by these substances. 4. With analogous fractions of margarine, butter, yolk and beef dripping growth inhibition could not be obtained. 5. The presence of dead Mycobacteria reduces the observed growth inhibition considerably. A quantitative relationship exists between the amount of dead bacteria added and the amount of inhibitor which is neutralised. It could be shown that the inhibitor is adsorbed by the added bacteria. Each bacterium binds 4×107 molecules. Supposing adsorption as a monomolecular layer, this means 1 molecule to about 20 A2 of the bacterial surface. 6. The glycerylether fraction of cod-liver oil (fraction 5) which inhibits in a concentration of 1 μg/ml of Sauton's medium the growth of virulent tubercle bacteria has no favourable action on tuberculosis in guinea-pigs in a daily dose of 25 mg given per os or by subcutaneous injection. Indeed the substance is toxic and oral administration to healthy guinea-pigs causes hyperaemia of the intestinal mesenterium, swollen mesenterial lymphglands and growth of connective tissue (sometimes followed by strangulation of the intestine).

IT has been demonstrated1–5 that prolonged and vigorous saponification of the mixed free acids of fish-liver oils causes remarkable changes in their chemical structure and in the absorption in the ultra-violet. When saponifying the acids of cod liver oil in this way, I observed a remarkable change in the Carr and Price reaction of these acids.

FOR the determination of vitamin A by means of the reaction of Carr and Price, the blue colour of the mixture is estimated with the Lovibond tintometer. If analysed by the spectroscope, the blue mixture shows two absorption-bands at 572μμ and 610μμ respectively (Morton). The blue colour depends only on the intensity of the 610 band.

IT has been shown1 that traces of substances like furan, indol and skatol inhibit strongly the intensity of the absorption band of vitamin A with antimony trichloride at 620 mµ. In cod liver oil, there must be such an inhibitor, because after saponification a much stronger Carr and Price reaction is obtained with the unsaponifiable fraction.