Building a large practice was to Cooper an urgent necessity for this was his only means of garnering the money, patients and especially the recognition that his scheme to found a medical school required. He was confident that his anatomical knowledge and technical skill were unsurpassed by any of the local practitioners. What he needed to attract patients and especially referrals was an opportunity to demonstrate his surgical virtuosity. Surgery is a performing art and preeminence is most rapidly acquired by the safe execution of hazardous, difficult and well-publicized procedures. As a bold, deft and experienced operator, Cooper was well aware of this formula for success and welcomed opportunities to perform "capital" operations.
It was customary at the time for surgeons to invite medical colleagues to be present as observers during operations in order to have their advice and moral support, and to cultivate their referral of patients. Cooper's purpose in opening an Infirmary as soon as possible was to enable him from an early date to perform surgery in his own premises and be host - and instructor - to local and regional doctors. Aseptic techniques were unknown, of course, and there was no bar to the presence of even a considerable group, such as up to ten or twenty observers, crowding close around the operating table in their street clothes. Afterwards they discussed the operation freely outside among the profession in general, especially if there were some special features. Daily papers were always on the lookout for a good story and the surgeon's guests at the operation commonly provided explicit details to reporters. When report of an unusual operation appeared in the press, as it often did, the surgeon could righteously disavow responsibility for a gratuitous "puff" to his reputation if the case were successful. On the other hand, if the outcome was unfavorable, the surgeon could expect a scathing critique of his judgement and technique.
Operating before an audience lent itself to the dissemination not only of complimentary information but also of distortions and malicious gossip, as Cooper was to learn from the following case that occurred six months after his arrival in San Francisco.
The Case of Frank Travers
Cooper not only hosted practitioners at operations in his own Infirmary, but also attended the operating rooms of other surgeons at their invitation in order to broaden his clinical knowledge and to evaluate surgical practice in the community. It was on such a courtesy call that he by chance became involved in the Travers case. 
A man named Frank Travers was stabbed in the upper thigh (left or right not specified). His femoral artery was lacerated, resulting in repeated severe hemorrhages and development of a femoral artery aneurysm. Treatment of such a condition would require ligating the external iliac artery in the lower abdomen to control the flow of blood to the femoral artery - a difficult and truly "capital" operation at the time. According to Cooper: 
In December, 1855, I was invited to witness an operation for ligating the external iliac artery (on a patient named Travers). . . On my arrival there were present Drs. Knapp, Hubbard, Angle, Webster, Macauley, Sawyer, and twelve or fifteen others who were strangers to me. Through the politeness of Dr. Macauley, the attending surgeon in the case, I was invited to take the knife
Cooper was delighted with this unexpected opportunity, only six months after his arrival in San Francisco, to demonstrate his superior anatomical knowledge and surgical skill before a group of about twenty of the town's physicians. He recognized that his situation was similar to that of Brainard who, seventeen years before in Chicago, performed a difficult amputation on a canal worker's leg in the presence of many of the local doctors - with great benefit to his reputation.
Travers was anesthetized with chloroform by one of the doctors. Cooper, as well as the crowd of spectators, were all in ordinary street dress, although Cooper and his assistant did roll up their sleeves and don aprons to protect their clothes. Speed and dexterity being the hallmark of the master surgeon, he rapidly made an incision in the lateral aspect of the lower abdomen with a scalpel that he took from the instrument case he always carried with him. Pushing the superficial tissues aside in a swift and nearly bloodless maneuver, he reached the fibrous layer of the abdominal wall known as the "transversalis fascia" which is the last barrier covering the extraperitoneal space between the peritoneal membrane medially and the pelvic wall laterally. Within this space the iliac artery and vein course side-by-side to the lower limb where they become the femoral artery and vein. 
The transversalis fascia being unobscured by any flow of blood was now nicely exposed to view. As a matter of greater safety, I divided (the transversalis fascia) solely with my finger nail, according to the plan of Jobert and Lawrence, having previously laid down the knife. . . At this stage, however, I encountered the first difficulty of the operation.
The peritoneal membrane was markedly thickened and adherent to the side wall of the pelvis, effectively sealing off the space occupied by the iliac artery and vein which are normally easily exposed by detaching the peritoneum from the pelvic sidewall with the finger. While Cooper was carefully separating these thickened and adherent surfaces, the large and thin-walled iliac vein accompanying the artery was torn and dark blood gushed up in a torrent from deep in the pelvis. Dr. Sawyer, Cooper's panic-stricken assistant, froze and the horrified onlookers who now moved in close for a better view of the operative field, sensed that death from uncontrollable hemorrhage was imminent.
In the hands of any surgeon on the Pacific Coast except Cooper, a tragic outcome may well have been inevitable. No operator in the region aside from Cooper was so disciplined by countless hours of anatomical dissection and surgical procedures assiduously practiced in the animal laboratory, that equanimity and technical virtuosity were normal responses in an emergency. He knew that false or frantic moves would worsen bleeding or do irreparable damage to vital structures. While the observers watched in breathless anxiety, Cooper arrested the hemorrhage by calmly directing his assistant to press down a sea sponge firmly on the bleeding point in the pelvis while he coolly and adroitly enlarged the wound, exposed the iliac vessels, tied the vein above and below the tear and then ligated the artery. It was an impressive feat of damage control.
The patient made a rapid recovery, without a single untoward symptom. To Cooper, this favorable course was not only a source of gratification, but it also raised the physiological question of whether tying both the iliac artery and the vein at the same time, a procedure thought to be hazardous, was as harmful as generally believed. He knew that when the vein alone is tied and the artery remains open, congestion of the venous system often results and swelling of the limb, even clotting of the blood in the engorged veins may occur. When the artery alone is tied and venous return continues unimpeded, the limb is deprived of blood and may be cold and its sensation impaired.
Perhaps in Travers's case the tying of both vessels resulted in the retention of a more natural amount of blood in the extremity. Did this account for the good result? As was his custom, Cooper tried the experiment: 
This was the query and subject of speculation between my medical friends and myself, for some weeks, until at last I opened a channel for settling the matter by experiments upon dogs, with the following results.
Of fifteen dogs, I ligated the external iliac artery alone in six, one of which died, the balance recovered. In five I ligated the iliac artery and vein at the same time - all of these recovered. In the first six the extremity became cold in every instance, and the coldness was sometimes quite persistent for a day or two, in spite of externally stimulating applications. The sensibility of the limb was greatly impaired, so much so that the application of terebinthinic (turpentine) liniments would hardly disturb the animal during the first two or three days; but in the latter five the heat and sensibility of the limb remained nearly natural from the first.
According to the above experiment, the answer to the question posed by Cooper and his medical friends is probably "Yes, tying both iliac artery and vein at the same time did result in a more normal balance in the circulation of the extremity."
While it is clear that Cooper exhibited superior technical skill in controlling hemorrhage under difficult conditions, the most significant feature of the Travers episode is not in Cooper's surgical coup, but in his turning to the laboratory for an explanation of the clinical outcome of the case. Indeed it was Cooper's devotion to research and teaching that set him apart from his peers in San Francisco where, from the outset, he conducted programs to teach anatomy (the basic surgical science of his day) and to investigate clinical surgical problems in the animal laboratory. He is the first surgeon in the region to heed the admonition of John Hunter (1728-1793), founder of surgery as a science: "Why not try the experiment?" Cooper's experimental ligation of the iliac vessels, simplistic as it seems today, was evidence of a commitment to academic pursuits that earned him the respect and loyalty of a small coterie who later joined him in founding a medical school. 
But there is more to the Travers story. As usual in such cases, there was free discussion of the operation among the doctors, and sidewalk progress reports kept all informed. Interest on the street was particularly keen in this instance because Travers was a well-known figure in the downtown area, being the cabman on the corner of Broadway and Kearney. As we have seen, the operation was well attended. The many eye-witness accounts of the procedure generally varied only in the superlatives used to describe the surgeon's skill and poise. All of this was very gratifying to Cooper until the day when word reached him that a prominent physician, Dr. H.M. Gray who had been present at the operation, pronounced it the botched job of an inept surgeon - or words to that effect.
Although Cooper was not personally acquainted with Dr. Gray, he knew that criticism by him was a serious matter because Gray's arrival in San Francisco during the Gold Rush period conferred upon him and other doctors of this vintage a distinctly honorific status as "pioneers" within the medical profession of the city.
Henry M. Gray (1821-1863) was born in New York City, son of the Reverend William Gray, a Scotch Presbyterian clergyman. Soon after his birth his family moved to Seneca Falls in northeastern New York State where he spent his youth and early manhood. His medical education consisted of an apprenticeship with a private physician in nearby Almyra and graduation in 1842 from Geneva Medical College, a "country medical school" that was moved to Syracuse, New York, and became the Medical Department of Syracuse University in 1872. 
To commence the practice of medicine he moved back to New York City where his bright mind, pleasing frankness of manner and gratuitous practice among the poor soon won him a secure professional and enviable social position. Although he was assured of speedy eminence as a New York physician, his love of adventure and the excitement of the California gold discovery led him to close his office and organize an immigrant party of ten congenial spirits - college mates, friends and associates. They purchased the bark Hope and set sail in July 1849 on the six-months' voyage around Cape Horn to the gold fields of California, he acting as the surgeon of the expedition. Touching en route at Rio de Janiero, they reached San Francisco in December. Some of the party, including Dr. Gray, visited the mining regions, but he returned to San Francisco in a few months where he immediately commenced the practice of medicine, to which he thenceforth devoted himself.
His practice, at first limited, grew to be among the most extensive in San Francisco, and so lucrative that in a few years he acquired a considerable fortune that enabled him to support not only his expensive habits but to make liberal contributions to the many charities that appealed to him for aid. As in New York, he was generous in his services to needy patients so that his kind offices were legendary in the community. He was a member of the San Francisco Medical Society and San Francisco Pathological Society, associations that were initiated by the pioneer group of physicians.
Just as with Dr. John D. Arnold, Cooper's adversary in Peoria, Dr. Gray had a decided interest in political affairs. He identified himself with the Whig Party in California and was Secretary of the Whig State Central Committee and Chairman of the Whig General Committee. His popularity was such that the Whig Nominating Committee considered (but did not choose) him as the Party's candidate for Mayor of San Francisco in 1852. His talents as an orator were greatly admired and hearers were impressed by his polished eloquence and unstudied gracefulness of delivery. He was a devoted member of the Masonic Order and on many special occasions addressed its members in the fervent rhetoric for which he was distinguished. However, the genial disposition and collegial temperament attributed to him by biographers were apparently not evident to Dr. Cooper in his relations with Dr. Gray.
Dr. Gray died at the age of 42 after a lingering period of broken health. He was unmarried and the Society of California Pioneers received his body in their hall where it lay in state before the funeral.
With respect to Dr. Gray's surgical knowledge and skills, we are unable to find any writings by him or statements by contemporaries that would enlighten us in this regard. The only reference to his proficiency in a natural science is ambiguous: "He had a genuine appreciation of the grandeur and beauty of nature, and the correctness of an anatomist in the choice of fine horses, of which he was particularly fond."  
The barbs of Dr. Gray, a well-established and respected figure in San Francisco, were potentially ruinous when leveled at a newcomer such as Cooper who was beginning to annoy the old guard as an offensive upstart. Since coming to San Francisco, Cooper had indeed been "riding high." His whirlwind of activity (of which we have so far referred to only a small part) had gained him many friends and he had made great progress in implementing his long range plan. He had so far not been challenged for his extravagant advertising. Occupancy of his Infirmary and attendance at his Clinic on Sansome Street had grown so rapidly that he was arranging to move to more spacious quarters on near-by Mission Street. Students had been recruited for his Medical Course on Anatomy and Vivisection that had now been in session for several months. Therefore, the report that the silver-tongued Dr. Gray was slandering him to an ever-widening circle of practitioners and laymen who respected the 49er's judgement came as a shock and outrage to the sensitive Cooper.
As to Gray's criticisms of Cooper's surgical technique, they were in fact meaningless quibbles. Therefore, considering the distinction of the source, and counting on the generally favorable opinion of his operation to offset Gray's comments, Cooper took a cautious approach. He waited three months for the gossip to subside. But Gray's libel continued unabated and, inexplicably, there was a sinister persistence in his attack on Cooper's reputation. Finally, barely containing his anger, Cooper addressed the following letter to Dr. Gray: 
San Francisco, 10 April 1856
Dr. H. M. Gray
You were present, I believe, at an operation performed chiefly by myself upon Frank Travers some months since. At various times since I have been informed that you condemned in unmeasured terms the part of the operation performed by myself, making your allegations specific by isolating for condemnation certain parts of the operation such as opening the transverse fascia with the finger nail; separating the peritoneum from the outer side of the wound with the finger "instead of dissecting it away"; drawing the peritoneum towards the linea alba too far; the division of the epigastric artery, etc., etc.
Now I am not disposed to magnify into importance every trivial remark disparaging to myself purporting to have been made by a medical man but on the other hand am disposed to pay no attention to statements not proven at once, making it a rule never to be on unfriendly terms with any respectable medical man unless the responsibility clearly rests upon the other party. My object in sending you this note is to assure you that I have no desire to consider you as a malicious professional enemy.
In regard to the operation in question I have to say that no one present during its performance and close enough to obtain a correct view but knows very well that the epigastric artery was not cut and that no artery could have been divided by the scalpel when I made the incision but the arteria ad cutem abdominis or some of the branches of the epigastric or circumflex illii seeing that I laid the knife down 30-40 seconds before the hemorrhage began.
The transversalis fascia it would be folly to hesitate in saying to any well informed surgeon I saw fit to open solely with my finger nail. I then separated the peritoneum from the outer side of the wound entirely with my fingers and had it drawn as far towards the linea alba as was considered necessary at the time. A diseased condition of the epigastric and iliac veins involved the operation in a serious difficulty which though not the fault of the surgeon it was my misfortune at that time to encounter.
I have been thus minute in my explanations owing to the fact that I have been wrongly informed in regard to your statements. Otherwise you would be placed in the very unenviable light of assuming a groundless and most malicious opposition to one who has never desired to throw an obstacle in the way of your prosperity.
E. S. Cooper
To Cooper's increasing indignation, there was no reply or conciliatory gesture in response to his letter of 10 April; and Gray continued during the following weeks to make contemptuous allusions to the Travers operation and Cooper's alleged technical incompetence. Having previously been the victim of medical intrigues in Illinois, Cooper might be excused for his suspicion that the relentless Gray was the agent of a cabal determined to discredit him. Lesser provocations often led to lethal duels in mid-century America, but Cooper chose instead to engage in verbal combat. He wrote the following letter to the Editor of a San Francisco paper: 
May 1856 (approx.)
No medical man of honorable principles can be regardless of the rights of other members of the profession and no one deserving the name of Medical Man will calmly submit to a gross violation of his rights.
Some months since, I performed an operation for ligating the external iliac artery in the presence of several medical men of this city. Among the medical men present at the operation was Dr. H. M. Gray whom I was soon afterwards informed made himself very conspicuous by a most sweeping condemnation of myself as chief operator in that case, and did not limit his remarks to the profession but introduced the subject among his patients.
This I paid little attention to at the time having heard Dr. Gray spoken of as a well informed surgeon and as a gentleman, and considered the remarks as incompatible with one of his reputation.
As time passed on, however, the evidence of malignancy on the part of Dr. Gray accumulated until it was thought that justice to myself as well as to him demanded that I should give him an opportunity to either deny the accusations or give his reasons for making them which I did by a note to him stating what I had heard. No explanation, however, has been given and the evidence of Dr. Gray's guilt having become conclusive I consider it proper to give publicity to the facts of the case however extraordinary the step may at first appear.
The patient was Frank Travers cabman on the corner of Broadway and Kearney whose rapid recovery after the operation has long since convinced him that Dr. Gray is not a reliable medical prophet. But as rapid recovery after a surgical operation, however formidable it might be, is not sufficient evidence of its judicious performance, I shall now proceed to settle the matter by an appeal to disinterested authority.
The testimony of medical men present at the operation as well as others will now be offered and those who have heard Dr. Gray's version of the matter can have an opportunity of judging for themselves to what extent his statements in traducing my character were reliable, and whether I am not justifiable under the circumstances in arraigning him before the tribunal of public opinion seeing that he arrogated to himself the high privilege of asserting what he pleases derogatory to my character and of treating with silent contempt my most friendly appeals for an amicable explanation.
We the undersigned medical men present at the operation alluded to upon Frank Travers, feel in candor bound to state that, though we have been accustomed to witnessing important surgical operations, both in private and public hospitals by eminent surgeons, yet we have never seen a more skillful use of surgical instruments, or a greater degree of coolness and self-possession under sudden and alarming difficulties in the course of an operation than were exhibited by Dr. Cooper in that case.
Lorenzo Hubbard, M.D.
J. W. W. Gordon, M.D.
M. B. Angle, M.D.
John Lee Webster, M.D.
A. Atkinson, M.D.
The case of Travers was an unfortunate one in consequence of the condition of the blood vessels adjacent to the artery and though the operation terminated well it might not have done so had there been any alarm or confusion on the part of those principally concerned in the operation.
But had I failed to ligate the artery altogether it would not have been anything remarkable in the history of surgery though from the mean advantages that would have been taken of the case it might in that event have blasted my reputation as a surgeon in San Francisco for years to come, seeing that I was quite a stranger at that time.
Many of the most renowned surgeons of the world have failed to conclude successfully operations upon important blood vessels - sometimes not finding the artery at all in case of aneurysm. Sir Astley Cooper once failed to find the subclavian artery in case of aneurysm of that vessel and gave up the patient to die.
Dessault, White and Pelletan, three of the greatest surgeons that ever adorned the profession, failed on the same vessel (vide Pancoast's Operative Surgery). 
It is operations upon the important blood vessels in case of aneurysm that test the skill of the operative surgeon. It is in these that coolness, patience, perseverance, the most perfect knowledge of anatomy and the greatest dexterity in the use of instruments are required. And even with all these qualities combined in one man the operation has occasionally failed as above mentioned.
I shall not say that Dr. Gray has shown himself entirely ignorant of the more important operations of modern surgery, neither will I state that he has shown a decided willingness to make false statements in order to injure a professional brother - that may be a subject of comment to others after the evidence has been adjudged. But I will say that there are medical men in San Francisco of very fine personal address and more than ordinary general intelligence but without the least profundity either in the literature or practical skill of any branch of medicine who came here at an early day and attained a considerable degree of prominence among the people in spite of habits of libertinism and debauchery, and who seek self-protection by mutually concurring in their efforts to put down every medical stranger when their interest enjoins the same. Go ahead, Gentlemen, I hold both your principles and your puerile efforts in supreme contempt.
We have no record of a response by Gray to Cooper's sarcastic questioning of his motives and of his competence to judge the Travers operation, but we shall learn that the Cooper's seething resentment later erupted into a altercation with Gray who escaped physical harm only through the intervention of their medical colleagues. It is also of more than passing interest that the five doctors who signed the Testimonial were all co-founding members with Cooper of the San Francisco County Medico-Chirurgical Association, a society whose early history we shall shortly address.
The Gray episode was Cooper's first confrontation with San Francisco's medical "establishment" and we shall see to what lengths they will go in their intrigues to bring him down.