This has probably arisen from experience of the fact that _mineral_ acids do serious mischief, and that alkaline carbonate of potash affords relief. The difference between the organic acids, which are decomposed in the manner I have described, and the fixed composition of the mineral acids, does not appear to have been sufficiently studied by those who prohibit fruit and vegetables on account of their acidity. It must never be forgotten that nearly all the organic compounds of potash, as they exist in vegetables and fruit, are acid. It may be desirable, in some cases, to add a little bicarbonate of potash to neutralise this excess of acid and increase the potash supply. I have found it advantageous to throw a half-saltspoonful of this into a tumbler of water containing the juice of a lemon, and have even added it to stewed or baked rhubarb and gooseberries. In these it froths like whipped cream, and diminishes the demand for sugar, an excess of which appears to be mischievous to those who require much potash. I must conclude this sermon on the potash text by adding that it is quite possible to take an excess of this solvent. Such excess is depressing; its action is what is called ‘lowering.’ I will not venture upon an explanation of the _rationale_ of this lowering, or discuss the question of whether or not the blood is made watery, as sometimes stated. Intimately connected with this part of my subject is another vegetable principle that I have not yet named. This is vegetable jelly, or _pectin_, the jelly of fruits, of turnips, carrots, parsnips, &c. Fremy has named it _pectose_. Like the saline juices of meat it is very little changed by cookery. An acid may be separated from it which has been named ‘pectic acid,’ the properties and artificial compounds of which appear to me to suggest the theory that the natural jelly of fruits largely consists of compounds of this acid with potash or soda or lime. We all know the appearance and flavour of currant jelly, apple jelly, &c., which are composed of natural vegetable jelly plus sugar.