There he continued for two years, labouring with such diligence and success, that he not only secured the high approbation of his instructors, but on the 11th October 1663, was admitted to the rank of a candidate of physic. At this time the study of human anatomy seems chiefly to have engaged his attention, and he made various trials to accomplish an object which has frequently been attempted since, namely, to preserve anatomical dissections in such a way that they might serve for demonstrations, and supersede the necessity of employing so many subjects. His zeal for anatomy led him to cultivate the friendship of every one eminent in that department, and they, in their turn, were not slow in appreciating his genius and enthusiasm. He formed a lasting friendship with Nicholas Steno, and was likewise intimate, for a time, with Rynier de Graaf, two of the most distinguished anatomists of that age.
About this time he appears to have first engaged in experiments on the respiratory system of frogs, a subject to which he often reverted, and which he illustrated with great diligence and success.
In 1664, he made a journey into France, and resided for some time in the house of Tanaquil Faber, at Saumur. While there, his attention was much occupied with the examination of the internal structure of insects, in which he made several discoveries. Of these, the most important was the valves of what Boerhaave calls the lymphatic vessels, which he detected by means of very slender tubes, which he had now acquired the art of employing, with great effect, for the
