Daly's Bartenders' Encyclopedia by Tim Daly (1903, p.77)

0.5 glassclam broth — hot clam brothbase
lime water — Add to fill glass.dilution
  1. Half fill a small bar glass with hot clam broth.
  2. Add lime water to fill the glass and serve hot.

This is a strong reminder that mixed-drink manuals still included openly medicinal broth service as part of bar practice.

Its identity is entirely restorative and functional rather than convivial.

See also: Oyster Cocktail, Beef Tea