A quick word of warning: today's bookmark contains not safe for work (NSFW) images. I'm posting it with a blur, but you if you want to see it uncensored, click here.
Order form from the "Model of the Month" photograph service, based on Sunset Boulevard in Hollywood, California. They offer 100 color slides for $30.00 or 100 negatives for $8.00. The images in question are all nude photographs of women. My best guess, based on the small amount of information I was able to find online, is that the company sold these photographs as "art supplies," but many of the buyers were just people looking for some pornography at a time when it was hard to purchase.
Found in "The Outlook for American Prose" by John Warren Beach. Published by the University of Chicago, 1926.
-Click to enlarge photos-