Leeuwenhoek called the organisms he saw under the microscope

animals
germs
animalcules
really small

He called them animalcules. I googled it its legit XD.

i believe the answer is:   psychological  experiment

in this experiment, wilhelm wundt became the first person that implement scientific method in analyzing the pyschological phenomenon.

due to this result, wilhelm wundt also able to make psychology to be acknowledged as a separate scientific field from biology.

answer; genetics;