The British Museum provides the following gloss on the above ad:
John Lawson Johnston was a butcher in Edinburgh, although he was originally from Canada. He invented a beverage made from extract of beef that was advertised as a healthy alternative to alcohol. It was called ‘Fluid Beef’ and hot water was poured onto it to create the drink. He opened a factory in London in 1886 and produced a more concentrated version of the drink, calling it Bovril.