Having furnished himself with this preparatory knowledge, he began to read the ancient physicians, in the order of time, pursuing his inquiries downwards, from Hippocrates through all the Greek and Latin writers. Finding, as he tells us himself, that Hippocrates was the original source of all medical knowledge, and that all the later writers were little more than transcribers from him, he returned to him with more attention, and spent much time in making extracts from him, digesting his treatises into method, and fixing them in his memory. He then descended to the moderns, among whom none engaged him longer, or improved him more, than Sydenham, to whose merit he has left this attestation, "that he frequently perused him, and always with greater eagerness." His insatiable curiosity after knowledge engaged him now in the practice of chymistry, which he prosecuted with all the ardour of a philosopher, whose industry was not to be wearied, and whose love of truth was too strong to suffer him to acquiesce in the reports of others. Yet did he not suffer one branch of science to withdraw his attention from others: anatomy did not withhold him from chymistry, nor chymistry, enchanting as it is, from the study of botany, in which he was no less skilled than in other parts of physick. He was not only a careful examiner of all the plants in the garden of the university, but made excursions, for his further improvement, into the woods and fields, and left no place unvisited, where any increase of botanical knowledge could be reasonably hoped for. In conjunction with all these inquiries, he still pursued his theological studies, and still, as we are informed by himself, "proposed, when he had made himself master of the whole art of physick, and obtained the honour of a degree in that science, to petition regularly for a license to preach, and to engage in the cure of souls;" and intended, in his theological exercise, to discuss this question, "why so many were formerly converted to Christianity by illiterate persons, and so few at present by men of learning." In pursuance of this plan he went to Hardewich, in order to take the degree of doctor in physick, which he obtained in July, 1693, having performed a publick disputation, "de utilitate explorandorum excrementorum in aegris, ut signorum." Then returning to Leyden, full of his pious design of undertaking the ministry, he found, to his surprise, unexpected obstacles thrown in his way, and an insinuation dispersed through the university, that made him suspected, not of any slight deviation from received opinions, not of any pertinacious adherence to his own notions in doubtful and disputable matters, but of no less than Spinosism, or, in plainer terms, of atheism itself.