This would be code for old, plain MS DOS which would query if the mouse driver (mouse.com/mouse.sys) is loaded or not.
To talk to mouse.sys, you had to fill some processor registers with specific contents, execute interrupt 0x33, then check the processor registers for return values. That's what the function does. You can find a list of most possible register contents and functions here: http://www.delorie.com/djgpp/doc/rbinter/ix/33/00.html