"Box Car Blues" is the 6th Bosko cartoon and the 5th to be shown theatrically. It seems that the very first one was only made to show executives and distributors.
Like nearly all of the Harmon-Ising cartoons of the 1930s, this one sticks to a formula that incudes cutesy animals, anthropomorphic characters (such as the train with arms and legs), singing and dancing as well as minimal plots. This is typical of many 30s cartoons...which is why the 1940s offered such a huge advance over the 1930s when it came to animated shorts.
In this one, a train is struggling to go up amazingly impossible hills. Bosko is hitching a ride and when one of the cars becomes detached, he goes for a wild ride. This ride seems to go on forever and frequently reuses animation cels in order to save money.
All in all, this short seemed like a step back for the franchise and comes off as pretty cheap and plotless. The only outstanding thing about it is the music...which is actually quite nice when combined with the animation.