He was soon master of all his instructer’s knowledge, and was obliged to enlarge his acquaintance with plants, by observing them himself in the neighbourhood of Mans.  Having finished his grammatical studies, he was sent to learn philosophy at Paris, whither he travelled on foot like a student in botany, and was careful not to lose such an opportunity of improvement.

When his course of philosophy was completed, he was determined, by his love of botany, to the profession of physick, and, from that time, engaged in a course of life, which was never exceeded, either by the ostentation of a philosopher, or the severity of an anchoret; for he confined himself to bread and water, and, at most, allowed himself no indulgence beyond fruits.  By this method, he preserved a constant freedom and serenity of spirits, always equally proper for study; for his soul had no pretences to complain of being overwhelmed with matter.  This regimen, extraordinary as it was, had many advantages; for it preserved his health, an advantage which very few sufficiently regard; it gave him an authority to preach diet and abstinence to his patients; and it made him rich without the assistance of fortune; rich, not for himself, but for the poor, who were the only persons benefited by that artificial affluence, which, of all others, is most difficult to acquire.  It is easy to imagine, that, while he practised in the midst of Paris the severe temperance of a hermit, Paris differed no otherwise, with regard to him, from a hermitage, than as it supplied him with books and the conversation of learned men.

In 1662, he was admitted doctor of physick.  About that time Dr. Fagon, Dr. Longuet, and Dr. Galois, all eminent for their skill in botany, were employed in drawing up a catalogue of the plants in the Royal garden, which was published in 1665, under the name of Dr. Vallot, then first physician:  during the prosecution of this work, Dr. Morin was often consulted, and from those conversations it was that Dr. Fagon conceived a particular esteem of him, which he always continued to retain.

After having practised physick some years, he was admitted expectant at the Hotel-Dieu, where he was regularly to have been made pensionary physician upon the first vacancy; but mere unassisted merit advances slowly, if, what is not very common, it advances at all.  Morin had no acquaintance with the arts necessary to carry on schemes of preferment; the moderation of his desires preserved him from the necessity of studying them, and the privacy of his life debarred him from any opportunity.  At last, however, justice was done him, in spite of artifice and partiality; but his advancement added nothing to his condition, except the power of more extensive charity; for all the money which he received, as a salary, he put into the chest of the hospital, always, as he imagined, without being observed.  Not content with serving the poor for nothing, he paid them for being served.