There is a great diversity of opinion as to the desirability or danger of methods of preserving foods against decomposition. Possibly arbitrarily, it is commonly conceded that preservation by salt, vinegar and oil, and by smoking, is superior to preservation by various other antiseptics. . Physical methods of preservation as by drying, hermetic sealing, subjection to heat before hermetic sealing or for brief preservation without sealing, and refrigeration at 4 degrees C, at which point bacteria cease.to be active or by actual freezing, are universally recognized as harmless except as they change the physical or. chemical characters of food stuffs or allow the impregnation of the foods with toxins or adventitious substances.

The preservation or reclaiming by salting, pickling or smoking of foods already decomposed is obviously to be condemned. Cold storage should not be applied to undrawn poultry, or in general to animal products in which the intestines remain in situ, on account of the impregnation with products of previous internal decomposition. Meats, vegetables, fruits, etc., sometimes seem unaffected by prolonged cold storage, at other times, changes in texture and flavor and perhaps in digestibility occur. There is a common belief that meat should, at least, be kept until rigor mortis has passed off, but that, on the other hand, cold storage for long periods, as months or years, allows all food stuffs to depreciate, even in the absence of demonstrable bacterial changes.

Tainted foods, especially meats, should never be countenanced by the physician, though they are eaten with apparent impunity by some persons. In advising game, fish from a distance and other delicacies for invalids and convalescents, precautions should be taken to insure freedom from decomposition or else plainer foods should be used.

For ambulant patients with no serious impairment of digestion, chemic or mechanic, salted, corned, smoked and pickled meats (the term pickled is often extended to include meats preserved in brine, though it should obviously be limited to preservation by means of vinegar), are often allowable. While as a rule such meats digest more slowly, if properly prepared, they are practically sterile, and, if appetizing, they tend to stimulate digestion. Well boiled or baked smoked ham, and the fat of salt pork or bacon, properly corned and boiled beef, usually digest as well as unprescrved meats of comparable nature.

Fruits, vegetables, meat and fish, sterilized by heat and immediately canned are' especially valuable when fresh products are not available.Economy and convenience have rendered them almost indispensable for domestic use. If good raw material is used, cleanliness is practised throughout the processes of preparation and metal cans and rings for glass cans are free from soluble toxic metals, there is no objection to their free use, and they are even superior, to fresh foods of poor quality or that have been shipped for long distances.

Boric acid, borax, salicylic acid for meats, cider, fruit juices, etc., formalin for milk, hyposulphites for meats and canned vegetables, and indeed, every so-called "chemical " preservative have l)een condemned. On the other hand it has been pointed out that they are not markedly toxic in the small proportions used, and that salt, vinegar, saltpeter and smoke are equally "chemical" and toxic in large dose.