In a study of the changes induced in foods by ionising radiations the destruction of thiamine in meat has been measured as one indication of chemical change. Under a given set of conditions the breakdown is related to the dose of radiation. The effect of varying the internal and external environment a t the time of irradiation has been studied. Freezing to -75" has been found to be the most effective method of preventing the destruction of thiamine.

COLEBY et a1.-IONISING RADIATIONS AND MEAT. V I I 483 which occurs when herring are heat-processed is caused by (a) gelatin which is derived mainly from the skin, ( b ) ammonia which is produced from unknown sources during heat processing and (c) unidentified nitrogenous components which yield ammonia under conditions of acid hydrolysis and which may be associated with the connective tissue proteins of the skin. I t is not known whether the conversion of collagen to gelatin is important with regard to flavour. Gelatin itself is comparatively tasteless, but under the processing conditions used for herring, considerable degradation of the gelatin to smaller peptide fragments may occur. This aspect requires further study. There is no doubt, however, that the production of gelatin is important , with regard to the texture of the fish. The herring is held together structurally by the connective tissue of the skin, muscle and bone. The conversion of this to gelatin with consequent loss of holding ability results in the cooked fish being softer and more liable to break up on handling. Therefore measurement of hydroxyproline production (itself an index of the degree of conversion of collagen to gelatin) may serve as an objective method for measuring the tendency for the fish to break up after heat processing. The possibility is being investigated of using this method in studies of factors which may effect the firmness and appearance of canned herring.Raw pork and beef have been irradiated with z hIeV electrons at controlled temperatures from 7 -18' t o -196". Appearance, odour and flavour were assessed by a taste panel, the destruction of glutathione was estimated chemically ; and the extent of the survival CJf the bacteria determined. In each case, a relation t o the temperature of irradiation was observed similar t o t h a t previously recorded for thiamine. There was little effect between 18" and oo ; but a rapidly increasing protection from oo t o -zoo, with a smaller increase down t o -196':. Experiments in the range 0" t o -lo0, in which destruction of glutathione was the criterion, indicated that protection began when ice separated from the tissue.

A method is described for the quantitative measurement of oxygen tension in tissue using flush-ended gold and platinum electrodes in conjunction with a transistor amplifier. A circuit is also given for automatic recording. The difficulties involved are noted and the techniques used to surmount these problems described. A satisfactory method was devised to grind electrodes with reproducible ends. The variables involved in biological systems were overcome by the use of several electrodes. Suitable apparatus was designed to calibrate the electrodes against known mixtures of oxygen in nitrogen and 5% CO 2 . The medium used for this purpose was an artificial extracellular fluid (A. E. F.) which was maintained at physiological pH by the CO 2 . The oxygen cathode gave a current directly proportional to oxygen tension and had a temperature coefficient of 2% per 1 °C. The current voltage curve showed no plateau with flush-type electrodes unless these were large or coated with collodion. Addition of the normal concentration of protein did not significantly alter the current. More than 2% of added protein reduced the current, whole blood had little effect, and haemoglobin exerted an effect comparable with its protein value. Glutathione reduced the current. The problem of diffusion of oxygen on to a flush type of electrode was examined theoretically and conclusions were tested by experiment: ( a ) by using compressed cotton wool and A .E .F. as a diffusion medium; ( b ) by comparison of flush-ended and recessed electrodes in vivo and in rats’ limbs perfused with calibration fluid and M/1000-NaCN at 0 to 2 °C. The oxygen consumption of the flush-type electrode was calculated and found to be negligible compared with that of the block of tissue which formed its diffusion zone. The extrapolation from calibration conditions to conditions in vivo is therefore valid. Using this information it has been possible to express diffusion current measurements found in tissue in terms of oxygen tension.

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