Lemon juice is deleterious and should be eschewed

I'm finally reading a book I bought years ago: The Four Adventures of Richard Hannay by John Buchan, who's generally considered the father of the spy thriller. The second chapter of the second novel, Greenmantle, contains this sentence:

The kettle was simmering by the fire, the night was raw, and it seemed the hour for whisky punch.

This got me wondering what sort of whiskey punch Richard Hannay, a Scot who moved to South Africa when he was six, would have made in 1915 London.

Poking about a bit on the net brought me to a footnote by R. Shelton Mackenzie in his edition of the Noctes Ambrosianae. Commenting on a mention of "het whisky toddy," he writes:

The mystery of making whisky-punch comes with practice. The sugar should be first dissolved in a small quantity of water, which must be what the Irish call "screeching hot." Next throw in the whisky. Then add a thin shaving of fresh lemon peel. Then add the rest of the water, so that the spirits will be a third of the mixture. Lastly, -- Drink! Lemon juice is deleterious and should be eschewed.

What is called "Father Maguire's receipt for making Punch," is more simple than the above. It runs thus, -- First put in your sugar, then add the whisky – and every drop of water after that spoils the punch!

Glasgow Punch is cold. To make a quart jug of it, melt the sugar in a little water. Squeeze a couple of lemons through a small hair-strainer, and mix. This is Sherbet, and half the battle consists in its being well-made. Then add old Jamaica rum, in the proportion of one to six. Finally, cut two limes in two, and run each section rapidly round the edge of the jug gently squeezing in some of this more delicate acid to complete the flavor. This mixture is very insinuating and leaves those who freely take it, the legacy of splitting headaches, into the day - use of which they can enter the next morning!

Of hot punch, however, though containing double the quantity of alcoholic spirit, it is boastingly said, "There is not a headache in a hogshead of it." In the rural parts of Scotland, at the harvest-home, I have seen the punch made in small wooden tubs which, as made to contain the fourth part of a bolt of corn, is called a firlot. The quantity of this punch those men can and do drink in Scotland, is wonderfully large. At the "Noctes," it will be noticed the punch is always hot.

I would not have thought that Glasgow punch would have rum instead of whiskey, but Gavin D. Smith explains it in the entry for "whisky punch" in his A-Z of Whisky:

As [David] Daiches explains [in A Wee Dram], "When Lowlanders drank whisky in the eighteenth century they usually made it into toddy (whisky, hot water, and sugar) or punch (whisky, hot water, sugar, and lemon)."

The earliest reference to punch made with whisky occurs in Captain Edward Burl’s Letters from a Gentleman in the North of Scotland to his Friend in London (1754), "When they chuse to qualify it for Punch they sometimes mix it with Water and Honey, or with Milk and Honey." The first attestation of the term "whisky punch" is in Burns' poem "Scotch Drink" (1785).

In Glasgow rum punch was popular as a result of the city's trade with the West Indies, but in Edinburgh whisky was always the spirit used.

I had not come across the "whisky toddy + lemon = whisky punch" formula before. Smith's article on "toddy" is well worth reading; I will spoil it by quoting this recipe by a non-toddy-drinker:

First, you put in whisky to make it strong; then you add water to make it weak; next you put in lemon to make it sour, then you add sugar to make it sweet. You put in more whisky to kill the water. Then you say, "Here's to you" -- and you drink it yourself.