abstract undiscovered alien microorganism

microorganism microbe organism microscopic exist single-celled colony existence microbial life suspected ancient times jain scriptures century india scientific microorganisms observation microscope anton leeuwenhoek louis pasteur food spoilage debunking theory spontaneous generation robert koch discovered diseases tuberculosis cholera diphtheria anthrax abstract undiscovered alien size may form cells unseen sixth india study began 1670s van leeuwenhoek 1850s found caused generation 1880s anthrax