Peace being declared, he was released, and came back to Paris in 1763, where he attended the Abbe Mollet's course of natural philosophy, the chemical course of the Brothers Douille, and the botanical lectures of the celebrated Bernard de Jussieu. At this time, however, his poverty was so great, that he had to endure the severest privations, to enable him to pay the necessary fees, and to purchase such books as he required, without interfering with the pecuniary aid which he felt it alike his duty and his privilege to afford his mother. In 1766, he became a candidate for a situation as medical attendant at the Hotel des Invalides, and was almost unanimously elected. In this position, he gave the utmost satisfaction; and not only did the skill he displayed obtain for him professional reputation, but his playful, yet never satirical wit, and the charm of his gentle and affectionate disposition, made him a universal favorite. He was the object of respectful attachment to the disabled veterans, and also to the good Sisters of Charity who attended the hospital. In 1769, he received, as the reward of his labors, the appointment of apothecary-in-chief, which permanently fixed him in the Hotel des Invalides. With a little more leisure, and comparative freedom from pecuniary care, came back the recollection of his former plans with regard to the potato. This now well-known and almost universally-used tubercle had been introduced into Europe from Peru early in the sixteenth century, and had at once been cultivated in Italy and Germany. Brought from Flanders into France, its culture was promoted in the southern provinces by the encouragement given by the great Turgot; but the dogged pertinacity with which ignorance so often resists the introduction of any thing new, had in every other part of the kingdom interfered with its propagation. Indeed, the popular prejudice against it was so high as to lead to the belief that it had a baleful effect on any soil in which it was planted, and produced in those who used it as food leprosy and other loathsome diseases. Such were the absurd and groundless prejudices which Parmentier had to encounter, but he prepared himself to carry on the contest with the boldness and perseverance of one who knew that, however difficult it may be to struggle with old opinions and long-established customs, yet nothing is impossible to the spirit of enterprise, guided by sound judgment, and animated by genuine philanthropy. Parmentier was not unmindful that to attain his object he would, in the first instance, need high patronage; and this patronage he sought and found in no less a personage than Louis XVI. himself. At his earnest solicitation, the monarch placed at his disposal, as a field for his experiment, fifty acres of the Plaine des Sablons. For the first time, this sterile soil was tilled by Parmentier, and the plant he so ardently desired to naturalize committed to it. In due time the long-wished-for blossoms appeared.