Sullivan Donald H Sullivan 
Man With Two Minds Plus Mindswitch 

Here are two stories: The Man With Two Minds and Mindswitch. 1. Man With Two Minds: An alien attempts to take over the mind of Jake Stewart but is only partially successful. The two fight for full possession and Jake comes to realize that the fate of Planet Earth hinges on the outcome of their struggle. 2. Mindswitch: An alien kidnaps Jack Ramsey and swaps minds with him. The alien, in the body of Jack, leaves his space ship in orbit to spy on Earth. Jack, in the body of the alien, is left imprisoned on the space ship. Jack now possesses the body of the alien, far larger and more powerful than his own, but he cannot use his powerful body against the alien, as he would be attacking his own body. He awaits the return to the space ship of the alien while trying to figure out how to use his powerful body to his advantage.