Print advertisements for Langtry's Pharmacy date back to the 1950s and they were in the government Register of Pharmacies in 1960. Online records suggest that Langtry's shop was demolished in 1975 (however, they moved at least once based off Kete documents) MAVtech has another Langtry's slide from a similar era as this one which advertises Kodak photographic film (also searchable on Kete) as well as one advertising perfume. 

The 1966 Encyclopaedia of New Zealand stated that a pharmacist had two years of academic training followed by a two year apprenticeship- but the University of Otago was about to launch a bachelors degree which would cut the apprenticeship down to one year. This combination of a degree and a one year internship is still used today- although the University of Auckland also offers a relevant degree.

Public appeals like this one were screened during cinema intermissions by placing the slide into a special holder in the projector for a couple of seconds (any more and the slide would crack!).

Many of these 'appeal' slides (and ones advertising upcoming film screenings) had a blank space at the bottom for the projectionist to add the latest details in removeable ink. Some blank slides were kept on hand for 'on the spot' messages like an appeal for a doctor if there was a medical emergency in the cinema.

Compared to many of MAVtech's advertising slides this one is quite basic- but it would have gotten it's message across well. It probably dates to the 1950s/1960s- long before we had a national blood donation service, hence the lack of logos.

In the time before the internet 'watching the papers' was a great way to get the word out....