His reputation was unusually flattering to one who had not yet entered upon the practice of his profession, and upon his return to the United States, in 1809, he was met with an offer of the chair of surgery in Columbia College, his alma mater. He promptly accepted the position, and held it until 1813, when the medical department of Columbia College was merged in the College of Physicians and Surgeons. He was at once called to the same chair in the new college, and occupied it until 1826. In that year he resigned his place in the faculty, in consequence of a misunderstanding between the professors and the trustees of the college on the principles of college government. Withdrawing entirely from the school, he united with Drs. Hosack, Mitchell, Francis, and several others, in founding the Rutgers Medical College. This college, after a short career of four years, was compelled by the Legislature to discontinue its operations, in consequence of an alleged invalidity in its charter.

In 1830, Dr. Mott returned to the College of Physicians and Surgeons as Professor of Surgery, and in 1840 he became President of the Faculty and Professor of Surgery and Relative Anatomy in the new University Medical School. The science of Relative Anatomy is of the highest importance to the surgeon, and of this science Dr. Mott is generally regarded as the author. He held his position in the University for twenty years, and in 1860, after a period of fifty years spent in the active duties of his professorship, retired from the immediate discharge of them, and was made Professor Emeritus, in which capacity he occasionally lectured to the classes during each of the remaining years of his life.

As a professor and teacher of surgical science Dr. Mott won a brilliant reputation, and was considered one of the most thoroughly successful instructors in the Union. He had the power of winning the attention of his pupils at the opening of his lectures and of retaining it until the close. He made even the most difficult operations so clear and simple in his lectures that the dullest intellects could comprehend them; and his system of practical demonstration of his subjects was vastly superior to any thing that had ever been seen in America. He was the first to introduce into this country the system of delivering clinical lectures, or lectures at the bedside of the patient, whose ailments were operated upon during the course of his remarks. This system is naturally the most repugnant to the patient, but its advantages to the student are so great that they outweigh all other considerations. Other professors had shrunk from subjecting their patients to such an ordeal, but Dr. Mott had seen enough, during his attendance upon such lectures abroad, to satisfy him that it was the only method by which a thorough knowledge of the profession of surgery could be imparted, and immediately upon establishing himself in this country he introduced it. He met with opposition at first, but he gradually overcame it, and made the advantages of his system so apparent to all that at length the opposition entirely ceased.

The greatest difficulty to which American medical schools have always been subject has been the almost utter impossibility of procuring dead bodies for dissection. It was this want that compelled Dr. Mott, as it has compelled so many others, to seek a practical education in Europe; and when he came back to the college as professor, he was met by the same drawback to thorough instruction. The law forbade the taking of dead bodies for dissection, under severe penalties. If a student was ever found in possession of a limb, he was liable to fine and imprisonment; and popular sentiment was so strong against the practice of dissection that those who engaged in it ran serious risk of incurring violence at the hands of the mob. Dr. Mott was often driven to desperate expedients in the procuring of subjects. He was fond of relating one of his adventures of this kind, which will show the reader how he was enabled to carry on his lectures.

It was in the winter of 1815, and it had been found impossible to procure a supply of subjects for the season. They could not be obtained at any price, and it was evident that if any were to be had, the doctor and his pupils would have to take the matter in their own hands. There was a grave-yard just outside the city, in which a number of interments had recently been made, and the doctor resolved upon securing these bodies for his dissecting-room. It was a dangerous undertaking, as discovery would subject all engaged in it to the direst penalties of the law, if, indeed, they should be lucky enough to escape being lynched by the people. In spite of the dangers, however, the students volunteered to assist the doctor in the attempt, and at an appointed time proceeded to the cemetery, properly disguised, and began the removal of the bodies from the graves. The night was intensely dark, and the wind was high, both of which circumstances favored their undertaking, but every sound, every snapping of a twig or rustling of a leaf caused them to start with alarm and gaze anxiously into the darkness. It was near midnight when they had finished their task, and, this done, they waited in anxious silence for the arrival of the means of removing their prey. Their movements had been accurately timed, and they had scarcely completed their labors when a cart, driven by a man dressed in the rough clothing of a laborer, approached the cemetery at a rapid pace. Signals were exchanged between the driver and the students, and the latter fell to work to place the bodies, eleven in number, in the cart. Having accomplished this, they covered them over in such a manner as to make it appear that the cart was loaded with country produce, bound for the city markets. When every thing was properly arranged, the students disappeared in the darkness, each seeking the means by which he had come out from the city, and the driver, turning his cart about, drove off rapidly in the direction of New York. It was a long ride, and to an imaginative man, carrying eleven dead bodies that had been torn from their quiet graves through the darkness of that winter night would have been a terrible undertaking. But this man was not imaginative, and, besides this, he was keenly alive to the tremendous consequences of discovery. He knew that he was carrying his life in his hand, and that he needed all the coolness and decision of which he was master. Reaching the city long after midnight, he drove rapidly down Broadway and turned into Barclay Street. The lights of the college shone out brightly, and they had never seemed so welcome as then. The cart was driven rapidly to the college entrance, where the students were in readiness to receive it. In a few moments the bodies were removed from the cart and conveyed to the dissecting-room, and the cart turned over to its owner. The driver accompanied the students to the dissecting-room, and, throwing off his disguise, revealed the handsome but excited and eager countenance of Dr. Mott. He had shared the dangers to which his pupils had subjected themselves, and had even borne the part in the enterprise attended with the greatest risk. The affair had succeeded admirably, a winter's supply of "subjects" had been obtained, and after this the lectures went on without interruption.

"A story is told of his readiness in the lecture-room. A mother brought into the amphitheater, one morning, an extremely dirty, sickly, miserable-looking child, for the purpose of having a tumor removed. He exhibited the tumor to the class, but informed the mother that he could not operate upon the child without the consent of her husband. One of the students, in his eagerness to examine the tumor, jumped over into the little inclosure designed for the operator and his patients. Dr. Mott, observing this intrusion, turned to the student and asked him, with the most innocent expression of countenance: 'Are you the father of this child?' Thunders of applause and laughter greeted this ingenious rebuke, during which the intruder returned to his place crestfallen."

He was equally as successful in his private practice as in his labors in the medical school. His brilliant reputation preceded him in his return to his native country, and immediately upon opening his office in New York he entered upon a large and lucrative practice. His skill as a surgeon was in constant demand, and it is said that during his long career he tied the common carotid artery forty-six times, cut for stone one hundred and sixty-five times, and amputated nearly one thousand limbs. His old preceptor, Sir Astley Cooper, proud of the distinction won by his favorite pupil, said of him exultingly: "He has performed more of the great operations than any man living, or that ever did live."

When he was but thirty-three years old (in 1818) he placed a ligature around the bracheo-cephalic trunk or arteria innominata, within two inches of the heart, for aneurism of the right subclavian artery. This was the first time this wonderful operation had ever been performed, and the skill and success with which he accomplished it stamped him as one of the brightest lights of his profession. "The patient survived the operation twenty-eight days, and thus demonstrated the feasibility of this hazardous and thus far unparalleled undertaking. He discovered in this case that, though all supply of blood to the blood-vessels of the right arm was apparently cut off, the circulation was kept up by the interosculating blood-vessels, the pulsation at the wrist maintained, and no evidence of loss of vitality or warmth manifested in the limb. The patient finally died from secondary hemorrhage."

In 1828 he performed successfully the most difficult and dangerous operation known to surgery. A clergyman called upon him to remove an enormous tumor in the neck, in which were imbedded and twisted many of the great arteries. In this operation it became necessary to take out entire the right clavicle or collar bone, to lay bare the membrane which surrounds the lungs, to search for and dissect around the arteries which ran through the tumor, to make forty ligatures, and to remove an immense mass of diseased matter. This terrible operation had never been attempted before, and was performed by Dr. Mott without the aid of chloroform; yet it was done so skillfully that the patient survived it, and in 1865 was still living and discharging his ministerial duties. It was thirty years before it was attempted again in any part of the world. It was a great triumph of the genius of the operator, and won him praises from men of science in all countries.

In 1821 "he performed the first operation for osteo-sarcoma of the lower jaw. In 1822 he introduced his original operation for immobility of the lower jaw. He was the first surgeon who removed the lower jaw for necrosis, and the first to tie successfully the primitive iliac artery for aneurism. Other of his original operations were cutting out two inches of the deep jugular vein, inseparably imbedded in a tumor, and tying both ends of the vein, and closing, with a fine ligature, wounds of large veins of a longitudinal or transverse kind, even where an olive-sliced piece had been cut out."