What enabled scientist to see one celled animals

The invention of the microscope, contributed to the discovery and accelerated research of microscopic, single cell and multi-cell organisms that are found all around our planet, this also led to our better understanding of pathogens such as germs, viruses, bacteria, fungi, parasites, and much more.   

Use a microscope to see one-celled animals.

He made the polygraph too,but thomas edison was not falsely credited for the light buld