Although I have not found the 1st edition, the second edition of Eliott Joslin’s book is available for free. The book Joslin’s Diabetes Mellitus is still considered a classic and the 15th edition is anticipated soon. It is interesting that the diet recommended by Joslin (and others) at the time was very low carb and Joslin himself fought to have patients still be very careful with diet. Unfortunately the knowledge from that era was essentially lost and it took us literally decades to find it again.
There was a history display at the ADA scientific sessions in June and I took lots of pictures of many of the things that @Richard157 mentions in his post. I wrote a blog with those pictures.