Jack's Manual by J. A. Grohusko (1910, p.52)

gin — Customer helps himself from the bottle.base
milk — cold milkdilution
  1. Set out a glass with a spoon and a bottle of gin and allow the customer to help himself.
  2. Fill up the glass with cold milk and serve.

The Buffet Blue Book by John H. Considine (1912, p.32)

gin — Customer helps himself from the bottle.base
cold milk — Fill up the glass.other
  1. Hand out the glass with a spoon and the bottle of gin and allow the customer to help himself.
  2. Then fill the glass with cold milk and serve.

Customer-finished plain service is part of the identity.

Bartenders' Guide: How to Mix Drinks by Wehman Bros. (1912, p.35)

gin — Ginbase
milk — Ice-cold milkdilution
  1. Present the bottle of gin, glass, and spoon to the customer, fill the balance with rich ice-cold milk, and serve.

Ice: Ice

See also: Gin and Calamus, Hot Milk Punch