and these were far more in number." In the mouth of one of the old men, Leeuwenhoek found "an unbelievably great company of living animalcules, a-swimming more nimbly than any I had ever seen up to this time. The biggest sort. . . bent their body into curves in going forwards. . . Moreover, the other animalcules were in such enormous numbers, that all the water. . . seemed to be alive." These were among the first observations on living bacteria ever recorded. Leeuwenhoek looked at animal and plant tissues, at mineral crystals and at fossils. He was the first to see microscopic foraminifera, which he described as "little cockles. . . no bigger than a coarse sand-grain." He discovered blood cells, and was the first to see living sperm cells of animals. He discovered microscopic animals such as nematodes and rotifers. The list of his discoveries goes on and on. Leeuwenhoek soon became famous as his letters were published and translated. In 1680 he was elected a full member of the Royal Society, joining Robert Hooke, Henry Oldenburg, Robert Boyle, Christopher Wren, and other scientific luminaries of his day -- although he never attended a meeting. In 1698 he demonstrated circulation in the capillaries of an eel to Tsar Peter the Great of Russia, and he continued to receive visitors curious to see the strange things he was describing. He continued his observations until the last days of his life. After his death on August 30, 1723, the pastor of the New Church at Delft wrote to the Royal Society:. . . . Antony van Leeuwenhoek considered that what is true in natural philosophy can be most fruitfully investigated by the experimental method, supported by the evidence of the senses; for which reason, by diligence and tireless labour he made with his own hand certain most excellent lenses, with the aid of which he discovered many secrets of Nature, now famous throughout the whole philosophical World.