I think most of the buildings pictured here are gone. They did a lot of rebuilding of this area in the past century, and extended Spring Street to meet Middle Street, probably somewhere in the 1950s. During this period urban renewal made a lot of changes to Portland, and a lot of historic architecture was destroyed in the name of progress.

The numbers on this map go up to the high 200s - Middle Street only goes up to about 200 now, before it intersects with Spring Street.

Now Middle Street ends at Temple Street, and the straightaway turns into Spring Street. The bend, what was once Middle Street, now runs in front of One City Center (built in the early 1980s), and through Monument Square, before intersecting with Preble Street. You can still see it on an aerial map of Portland.

When I was a little kid, I remember my dad being able to drive on this segment of Middle Street, but now it's all pedestrian right of way, bricks, with storefronts on the right, One City Center on the left, facing southeast as in the direction of this photo. A few of the buildings pictured on the right of this photo probably still exist, but none on the left; the street was pretty much decimated.

This 1885 map shows the bend in Middle Street that definitely doesn't exist now.

Page 18 here has a little more info.

I like that the little building that housed the Dentists office still stands after all these years. From the way it looks in the first picture, you'd think it would have been taken down long before the more architecturally atractive buildings shown. I wish there was an easy way to see these things side by side!

I believe it is has something to do with window treatments. This is based on this Maine Chamber Of Commerce article from that timeframe, which referenced the business.

I wonder if it still exists?

Below is the same view from October of 2008 (looking NE from Market Street).