It would hardly be fair to devote much more time or space to this object, especially as I have dealt with it most exhaustively1 elsewhere, but, from their popularity and importance, one or two of the systems demand a little more consideration. I am specially thinking of vegetarianism, and the "uric-acid-free" diet so-called, but before referring to them more particularly it will be profitable to direct our attention to a question which may very well in some measure be the explanation of their existence, viz. idiosyncrasy in diet.

Doubtless this is also the origin of the expression that one man's food is another man's poison. We are all acquainted with people who dare not eat oysters, crabs, shell-fish, strawberries, raspberries, or other fruits, without producing nettlerash. It is less usual, however, to find that honey is provocative of vomiting and diarrhoea, but I number among my patients one case of the kind, and many such are on record. Some people indeed are so susceptible to its action, that even a small poultice of honey on the skin will produce these untoward effects.

There is a well-known case of a Spaniard who could not eat meat without vomiting, a woman in whom nutmeg always produced the same effect, and there are many people who cannot taste the least scrap of sugar on account of the violent sickness following its use. Haen always had convulsions after eating half a dozen strawberries, and Gould mentions a family in whom the male members exhibit symptoms of poisoning after eating the same fruit, while, strange to say, the female members are exempt. A little boy of this family was killed by eating a single strawberry.

1See Modern Theories of Diet, by Alexander Bryce.

A case is recorded of a woman in whom vinegar - a gentle styptic - always produced haemorrhage, of a man who always vomited after drinking coffee, and another in whom the slightest dose of manna had a similar effect.

Julia, the wife of Frederick, King of Naples, had such an aversion to meat that she could not carry it to her mouth without fainting, and the anatomist Gavard was unable to eat apples without convulsions and vomiting. Almonds often produce a scarlet rash on the face.

Of all foods, perhaps the one which most frequently gives rise to trouble is the egg. Swelling of the lips, purple spots on the face, vomiting, syncope, and many other alarming symptoms are described by medical writers as following the ingestion of an egg. Sir Morell Mackenzie gave a striking example of idiosyncrasy to eggs transmitted through four generations. The case is far too long to quote in all its details, but was remarkable in that even although the egg was put into coffee, quite unknown to the partaker thereof, it was followed by the most remarkable symptoms. The eye was swollen and wild, the face crimson, the throat contracted and painful - the whole appearance approximating closely to that observed in apoplexy.

Hutchinson speaks of an M.P. who dared not take parsley because sickness and pain in the abdomen, swelling of the tongue and lips, and blueness of the face always supervened quickly thereafter.

Another man could not eat rice in any shape or form without extreme distress, spasmodic asthma being the most violent symptom. On one occasion he took lunch with a friend in chambers, only partaking of bread, cheese, and a little beer. Shortly thereafter he was seized with the usual symptoms of rice poisoning, and it was then discovered that a few grains of rice had been put into each bottle of beer for the purpose of exciting a secondary fermentation.

Figs sometimes cause the most unpleasant itching of the mouth and throat, and split peas have been known to cause the same phenomena in addition to exciting a running of the nose and eyes. Nettlerash has often been excited by eating veal, whilst chocolate in any form always produced sneezing in another case. "Raw-fooders" will doubtless stand aghast at the suggestion of uncooked fruit producing asthma in the case of a lady, cooked fruit inciting no deleterious effects whatever.

The most remarkable case of food idiosyncrasy known to science, however, is that of David Waller, who lived about the year 1780. To him wheaten flour in any form proved to be a noxious poison. He was accustomed to say that of two equal quantities of tartar emetic and flour, although the dose of the former did not exceed that usually prescribed by a medical man, he would much prefer to swallow the tartar emetic than the flour. In two minutes or thereby after partaking of the flour in any form he would have been attacked by a painful itching all over the body, accompanied by violent colic and sickness and continuous vomiting ten times as distressing as that occasioned by tartar emetic. In about ten minutes the itching would be greatly intensified, spreading over the whole surface of his body, continuing for two days with intolerable violence, and lasting for ten days in all. During the last seven days of this period his lungs were seriously affected, he coughed and expectorated vast quantities of phlegm, and really resembled a patient in the last stage of consumption. The odour of wheat sufficed to produce the same distressing symptoms, though in a lesser degree, and for this reason he was in the habit of carrying camphor in his pocket, and as an additional safeguard he practised snuffing. It was only in this manner that life was at all tolerable and he was able to escape from the disastrous effects of the practically ubiquitous wheat.