MR. F. W. F. ARNAUD, the Public Analyst for the Borough of Portsmouth, delivered a lecture on this subject at the Town Hall on April 27. The lecturer commenced his address by stating that many of the objections to the use of certain preservatives which he might have occasion to put forward were not necessarily his own individual objections, but were the objections of many scientific men who had dealt with all sides of this difficult subject. There was a tendency on the part of some people to regard preservatives as disinfectants, but disinfectants and antiseptics were two different things. A disinfectant not only retarded the growth of microbes, but actually killed them, while an antiseptic preservative merely retarded their growth or formation. Two common antiseptics were sugar and salt. It had been contended that a small dose of a chemical preservative was preferable to a dose of microbes. The effect of a preservative was not to kill the life already present, but to prevent the free multiplication of the organisms present, and the swallowing of a dose of preservative did not necessarily prevent the swallowing of a dose of microbes. There were many old forms of preserving food, such as the use of sugar for fruit and condensed milk; of vinegar for vegetables; and the process of smoking for bacon and fish, smoke being very destructive to microbes; but the oldest form of preservation was the process of salting meat and fish. Another form of preservation was the method of preventing the access of air to perishable articles, as in the cases of eggs and lard. Then there was drying, as in the case of fruit, and chilling, or freezing, as in the cases of meat, milk, poultry, and fish. The temperatures employed for freezing food varied considerably, and depended chiefly upon the length of time during which storage was necessary. If it were only desired to keep meat for a week or two, a low temperature was not necessary, but one of 40 deg. F. was sufficient. Any cooling process was equivalent to the use of a great deal of chemical preservative. A cooling to 50 deg. P. was equivalent to the addition of boric acid to the extent of .05 per cent. At a normal summer temperature of 70 deg. P., two microbes would produce 62,100 in the course of twenty‐four hours; hence the necessity for cooling articles of food. The drawback to most of these methods of preservation was that sugar, salt, and cold were not applicable in every case. Exclusion of air and subsequent sterilisation had their drawbacks also. When sterilisation was complete and the air was exhausted, no putrefaction could take place, and the food should remain indefinitely unchanged. In the matter of tinned meat, the drawback lay chiefly in the failure to ensure complete sterilisation, and in the dissolving of tin, and occasionally lead, from the metal enclosing the food. In the case of tinned meat putrefaction to any considerable extent could be easily recognised by the blown condition of the tin and an absence of the inrush of air when the tin was pierced. Such food was a source of great danger, and if eaten the meat was liable to give rise to ptomaine poisoning—which was occasioned by eating the poisonous products produced by various bacteria. The danger of metallic poisoning could be largely overcome by the use of glass or earthenware vessels. Preservatives in use at the present time were: Benzoates, fluorides, formalin, salicylic acid, sulphites, saccharin, and beta naphthol, generally used singly, though there were some very complicated preservatives on the market. With reference to the use of salt and sugar as preservatives, little or nothing could be said against their use, for sugar was in itself a food and had a well‐known food value. Salt, too, was an essential constituent of our food, for without the elements of which it was composed we could not exist. Naturally, the assimilation of a large quantity of salt was not desirable, but it could not be urged, as, for instance, in the case of boric acid, that it was a substance foreign to the constituents of the human organism, for it was indispensable. Boric acid, however, played no part in any of the essential life processes.
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Jan 1, 1912
Thomas Joseph Nolan + 1
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