How did the old "quarter" gas meters from the late 19th century work?

By putting a quarter in the slot to get gas, as described in this excerpt from a 1908 book.

http://books.google.com/books?id=gU81AAAAMAAJ&pg=PA253&lpg=PA253&dq=quarter+gas+meters&source=web&ots=C2_65zYTMP&sig=p79yOJxMihzafdEmtYYuXxZQA0s

"The danger incident to the use of automatic or 'quarter-in-the-slot' gas meters is also illustrated by the following recent occurrence in New York City, which caused the death of two victims:

"'An automatic gas meter ran out in an apartment after the majority of the household had gone to bed. In the early morning hours someone of the household, after rising, put a quarter in the meter and the gas began to flow through the gas jet in a bedroom, the occupant of which had left the burner open when the gas went out the night previous. Gas filled the room, and the occupant was found unconscious, and after being removed to the hospital, died after several hours. A lady occupying an adjoining bedroom was also overcome by the gas, and likewise died from the effects of gas poisoning.'"