There were 119 episodes, one reel each. The episodes were released every Saturday, starting on 14 November 1914 through 17 February 1917.
Helen Holmes played the character "Helen" in the first 48 episodes. Then Holmes and director J.P. McGowan quit together. They were replaced on episodes 49-119 by Helen Gibson as "Helen" and James D. Davis as director.
Based on an article in Moving Picture World, Helen Holmes is believed to have taken over direction of the episode "Escape from the Fast Freight" after credited director J.P. McGowan was involved in an accident that landed him in the hospital. It's extremely likely that Holmes worked uncredited as a director on other parts of this film series.
Helen Holmes and Leo D. Maloney are believed to have co-directed Episode 13, "The Escape on the Fast Freight," released February 6, 1915.
Although many film reference books refer to this as a serial, it's more like what today would be called a series. In many of the earliest serials, each episode's story was self-contained.