lucrative for manufacturers to produce harmoniums with cases impregnated with chemicals to prevent woodworm and other damaging organisms found in the tropics. At the peak of the instruments' Western popularity around 1900, a wide variety of styles of harmoniums were being produced. These ranged from simple models with plain cases and only four or five stops (if any at all), up to large instruments with ornate cases, up to a dozen stops and other mechanisms such as couplers. Expensive harmoniums were often built to resemble pipe organs, with ranks of fake pipes attached to the top of the instrument. Small numbers of harmoniums were built with two manuals (keyboards). Some were even built with pedal keyboards, which required the use of an assistant to run the bellows or, for some of the later models, an electrical pump. These larger instruments were mainly intended for home use, such as allowing organists to practise on an instrument on the scale of a pipe organ, but without the physical size or volume of such an instrument. For missionaries, chaplains in the armed forces, travelling evangelist etc., reed organs that folded up into a container the size of a very large suitcase or small trunk were made; these had a short keyboard and few stops, but they were more than adequate for keeping hymn singers more or less on pitch. The invention of the electronic organ in the mid-1930s spelled the end of the harmonium's success in the West, although its popularity as a household instrument had already declined in the 1920s as musical tastes changed . The Hammond organ could imitate the tonal quality and range of a pipe organ whilst retaining the compact dimensions and cost-effectiveness of the harmonium as well as reducing maintenance needs and allowing a greater number of stops and other features. By this time, harmoniums had reached high levels of mechanical complexity, not only through the demand for instruments with a greater tonal range, but also due to patent laws (especially in North America). It was common for manufacturers to patent the action mechanism used on their instruments, thus requiring any new manufacturer to develop their own version; as the number of manufacturers grew, this led to some instruments having hugely complex arrays of levers, cranks, rods and shafts, which made replacement with an electronic instrument even more attractive. The last mass-producer of harmoniums in North America was