The Modern Hygiene was built by Royal for Modern Hygiene Sales Corporation of Boston. Like Health-Mor (filter queen) before them, Modern Hygiene just had Royal manufacture an 'exclusive' version for their door to door sales force. It was a fairly pricey machine for what you got, which was a Lamb motor, a cloth bag, and a stove pipe.
Modern Hygiene as a sales company was gone by the mid 1950's. I believe there were three tank cleaners (I may be wrong, there may only have been two tank models), a hand vac, and I believe an upright. All Royals just private labeled.
Your Modern Hygiene is the less desired model of the tank types. The model that followed yours was gorgeous, designed by a very famous industrial designer, and is very valuable in excellent condition. I see a number of Modern Hygiene tank cleaners the same model as yours on eBay over the course of a year. Unfortunately, none of them bring over about $50.
This is a picture of the valuable model from 1950, you can see how much more refined it is. It's also a huge monster, very long - longer than any Electrolux.
