In the 17e century van Leeuwenhoek discovered with his microscope new kind of animals and cells. How was this discovery of van Leeuwenhoek received by the ordinary people when there seemed to be more animals than human kind could ever think of? Was it a bit like discovering extraterrestrial life would be nowadays, or was his whole discovery only interesting for the scientists of those days?
Short answer: no. They did not have TV, internet, twitter, public schools or even scientific journals back then, so the group of people that got information about such things was very narrow to begin with, mostly scientists gathered in royal academies and societies. "Ordinary people" had more pressing concerns with surviving day to day. Gest describes the early days of microbilology in The Discovery of Microorganisms by Robert Hooke and Antoni van Leeuwenhoek.
Leeuwenhoek in 1676 was not the first to observe microorganisms under the microscope, Hooke published his observations of microfungus about a decade earlier in Micrographia (1665):
"These spots appear’d, through a good Microscope, to be a very pretty shap’d Vegetative body, which, from almost the same part of the Leather, shot out multitudes of small long cylindrical and transparent stalks, not exactly streight, but a little bended with the weight of a round and white knob that grew on the top of each of them... The whole substance of these pretty bodies was of a very tender constitution, much like the substance of the softer kind of common white Mushroms, for by touching them with a Pin, I found them to be brused and torn; they seem’d each of them to have a distinct root of their own; for though they grew neer together in a cluster..."
Leeuwenhoek's submitted his first letter to the Royal Society in 1673, and his descriptions of "mould" indicate that he was familiar with Micrographia. When he later (1676) observed "very little animals of divers kind" (bacteria) his letter was originally met with skepticism. Hooke could not observe the creatures through his microscope until he left the sample be for five to six days. He daoes express fascination and wonderment, but not of the kind associated today with extraterrestrials:
"I examined again the said water; and then much to wonder I discovered vast multitudes of thoseexceeding small creatures, which Mr. Leeuwenhoeck had described; and upon making use of other lights and glasses, as I shall by and by shew, I not only magnified those I had thus discovered to a very great bigness, but I discovered many other sorts very much smaller than those I first saw, and some of these so exceeding small, that millions of millions might be contained in one drop of water. I was very much surprized at this so wonderful a spectacle, having never seen any living creature comparable to these for smallness: nor could I indeed imagine that nature had afforded instances of so exceedingly minute animal productions."
Modern scholarship suggests more generally that Hooke deserves more credit as a co-founder of microbiology, for instance what was later commonly called a (single-lens) ‘Leeuwenhoek microscope’ was already described by Hooke, and while Leeuwenhoek was notoriously secretive about how he polished his lenses, Hooke published detailed descriptions of his microscopes and their making. What "ordinary people" were not in a position to appreciate right away was still assimilated, but slower. Boorstin in The Discoverers even compares Hooke to Galileo:
"What Galileo’s Sidereus Nuncius had done for the telescope and its heavenly vistas, Hooke’s Micrographia now did for the microscope. Just as Galileo did not invent the telescope, neither did Hooke invent the microscope. But what he described seeing in his compound microscope awakened learned Europe to the wonderful world within. Fifty-seven amazing illustrations drawn by Hooke himself revealed for the first time the eye of a fly, the shape of a bee’s stinging organ,the anatomy of a flea and a louse, the structure of feathers, and the slantlike form of molds. When he discovered the honeycomb structure of cork, he said it was made of ‘cells.’ Frequently reprinted, Hooke’s illustrations remained in textbooks into the nineteenth century"