远行☆Echo,
They are called hot because they are served hot off the grill. Hot dogs are sausages. Back in the days before there were government meat inspections, people wondered what exactly was in those sausages. Often the meat was not of good quality and people began to accuse the sausage makers of using dog meat. That is how they got their name!
Today, "most recipes for hot dogs combine together a tasty blend of favorite meats (pork, beef, chicken, or turkey), meat fat, a cereal filler which could be either bread crumbs, flour, or oatmeal, a little bit of egg white, and a mouth-watering array of herbs and seasonings including garlic, pepper, ground mustard, nutmeg, salt, and onion."
Choppy's explanation is interesting and except for the fact that no one has ever produced a copy of Mr. Dorgan's cartoon, and the fact that the term "hot dog" was already in use ( the first mention in print was in 1893 in the Knoxville Journal ) it would be believable.
By 1840 the term "dog sandwich" was already in use.
Here is a song popular in 1860 that gives the clue to the real origin of the word 'hot dog'.
Oh where oh where has my little dog gone?
Oh where oh where can he be?
Now sausage is good, baloney, of course.
Oh where oh where can he be?
They make them of dog, they make them of horse,
I think they made them of he.