He found in a drop of water, in the fluid in the intestines of frogs and birds, and in his evacuations, objects of great minuteness which differed from each other in form and size and in the peculiar motion which some of them possessed.

In the year 1683 he presented to the Royal Society of London a paper describing a certain minute organism which he found in the tartar of his teeth.

After these observations of Loewenhoeck became known to the world they quickly found application in disease, although the author had expressed himself very cautiously in this regard.

The strongest exponent of the view of a living contagion was Plenciz, 1762, a physician of Vienna, basing his belief not only on the demonstration of minute organisms by Loewenhoeck which he was able to verify, but on certain shrewdly conceived theoretical considerations.

He was the first to recognize the specificity of the epidemic diseases, and argued from this that each disease must have a specific cause.