It clearly states that the author is Paul de Kruif (a very Dutch name), with Dutch translation by Dr C. Easton (an English name).
What I didn't know, was that Paul de Kruif was at that time a rather well know American micro-biologist who wrote "Microbe Hunters" in '26. So it was indeed written in English and translated into Dutch (by Dr. C. Easton).
Fifth printing in '39 of the Dutch translation, hardcover book with dust jacket. Still very readable stories about the discoverers and discoveries of the small world of microbes. About how human understanding and successes in battling disease were achieved - relatively recently.