I've posted another Dr. Martinus story to the project page.
In The Doll That Came to Life, Dr. Martinus must contend with both a malicious, doll-possessing poltergeist, and a fraudulent spiritualist who keeps giving their mutual client the wrong advice. Will he prevail?
This is, unfortunately, the last Dr. Martinus story I could find, other than the first installment of "The House of the Living Dead." It seems cruel to post that with giving you the rest of the story, so I won't. If you really want to read it, I have the original publication info of all the published stories on the project page. Maybe someday more issues of Ghost Stories magazine will come to light, and we will find more Martinus tales.
If Rousseau's pattern holds, he likely killed Dr. Martinus off at the end of this serial; but over the next few years, he wrote at least another two occult researcher stories. Both of them bear a strong resemblance to Dr. Martinus, at least in their setup and their modus operandi. I will share those with you as well, as time permits.
In the meantime, enjoy!