Medical therapies during the first three quarters of the 19th century, and throughout previous medical history as well, were based on one or another theory of the pathophysiology of disease. In the absence of observations based on scientific principles, these theoretical "systems" sought to account for the signs and symptoms of illness and to devise "logical" treatments to counteract them. Whether a treatment was in fact effective was not objectively evaluated. If patients recovered after receiving a treatment, the favorable response was attributed to the treatment - post hoc ergo propter hoc. As a result, the drugs and medical procedures prescribed were, with the exception of a few specifics, either useless or harmful, a circumstance obscured since prehistoric times by the healing power of nature - vis medicatrix naturae. In an address in 1860 to the Massachusetts Medical Society, Oliver Wendell Holmes reviewed the state of the Art and called on his colleagues to forego obnoxious treatments: 
On the whole, more harm than good is done by medication. Throw out opium, which the Creator himself seems to prescribe, for we often see the scarlet poppy growing in the cornfields, as if it were foreseen that wherever there is hunger to be fed there must also be pain to be soothed; throw out a few specifics which our art did not discover, and is hardly needed to apply; throw out wine, which is a food, and the vapors which produce the miracle of anaesthesia, and I firmly believe that if the whole materia medica, as now used, could be sunk to the bottom of the sea, it would be all the better for mankind - and all the worse for the fishes.
Several of the medical systems in vogue early in the 1800s will be cited as examples of the genre. Professor Wood's recommendation on leeches in puerperal fever calls attention to their use as definitive therapy in the medical system of the Prince of Leeching, François Joseph Victor Broussais (1772-1838). This colorful veteran of the Napoleonic campaigns was chiefly responsible for founding the famous Paris Clinical School. His style was vigorous and dictatorial. Even his civilian medical practice was conducted with military-like discipline. His dogmatic approach was temporarily persuasive and for a time he was the leading medical figure in Paris. The basis for his immense popularity was, in addition to his dynamic personality, the medical system he conceived and zealously propagated. The Broussais Doctrine, which gained a wide but short-lived prominence on the continent and in America, was merely one in a countless succession of theoretical systems proposed during the prescientific era to explain the manifestations of disease. The importance of systems lay in their determining influence, in the absence of basic facts, on the diagnosis and treatment of medical disorders. Groundless in a scientific sense, some systems were nevertheless remarkably durable as illustrated by the humoral doctrine which regarded the body as composed of four liquids or "humors": blood, phlegm, yellow bile and black bile. This often-refined doctrine survived in modified versions from Hippocrates in the fifth century B.C., through Galen in the second century A.D., and until Rudolf Virchow (1821-1902)) finally dealt a death blow to its surviving remnants with publication of his work on Cellular Pathology in 1858.  
After 1700 the validity of medical systems was increasingly challenged by the basic and clinical research of investigators who were in the vanguard of modern biomedical science. However, the still-limited scope of scientific information permitted systematists to continue filling the void well into the 19th century with theories such as the Broussais Doctrine. This Doctrine was a modification of the Brunonian theory, derived by John Brown (1735-1788) from the medical system of his teacher, William Cullen (1710-1790) of Edinburgh. Cullen's system assumed that the body is maintained in a normal state of health by "nervous energy". The nervous system, which is the source of this energy, reacts adversely to certain external stimuli and disease is the result. Cullen regarded almost every disease as a manifestation of nervous reaction.
The Brunonian theory claimed that the essential quality of living tissue is "excitability" and that life itself is non-existent except as the resultant of external and internal stimuli. If these exciting forces are withdrawn, death ensues. Health is defined as a moderate state of excitability resulting from a proper balance of stimuli. Disease is caused by an increase or decrease of excitability and falls into two main groups: "sthenic" diseases (asthenia) are associated with increased and "asthenic" diseases (asthenia) with decreased excitability. Treatment is simple - sedatives (e.g., opium) for sthenia and stimulants (e.g., alcohol) for asthenia. This mode of therapy soon gained many passionate adherents, and as many bitter opponents. Advocates and enemies of Brown's system tended to be noisy and combative. In 1802 a two-day riot between Brunonian and non-Brunonian medical students broke out at the University of Göttingen and had finally to be put down by a troop of cavalry.
As for the controversial Brown himself, his favorite remedies and personal adjuvants were, as might be expected, opium and alcohol. Of his lectures, which attracted many students, it is said:
His voice was in general hoarse and almost croaking. . . Before he began his lecture, he would take 40 or 50 drops of laudanum in a glass of whisky; repeating the dose four or five times during the lecture. Between the effects of these stimulants and voluntary exertion, he soon waxed warm, and by degrees his imagination was exalted into phrenzy.
Hopelessly addicted to drink and narcotic, his downward path led, by way of a term in debtors' prison, to death one night in his 53rd year after taking a very large dose of laudanum.   
Broussais simplified matters by claiming that individual diseases do not exist. For the Brunonian concept of stimulation as the agency of disease, he substituted inflammation. Based on clinical experience and extensive post mortem dissections he concluded that most diseases are merely the physiological expression of inflammation, usually localized in the gastrointestinal tract. For example, fevers in general are a symptom of gastroenteritis. He denied the Hippocratic doctrine of the healing power of nature and therefore thought it necessary to abort disease aggressively by active measures. His standard treatment (the rationale for which is incomprehensible in the present day) was to combat the underlying inflammation by antiphlogistic or weakening measures consisting of a very limited diet plus blood-letting by application of leeches all over the patient's body. From 10 to 50 leeches would be applied at a time. In the year 1833 alone, when Broussais was at the height of his fame, over 40 million leeches were imported into France. Yet eight years earlier, two or three million met all demands.  
It was also in 1833 that Oliver Wendell Holmes arrived in Paris for two and a half years of study. The first lectures he attended at the Ecole de Médecine were those of Professor Broussais about whom he wrote:  
Broussais was in those days like an old volcano, which has pretty nearly used up its fire and brimstone, but is still boiling and bubbling in its interior, and now and then sends up a spurt of lava and volley of pebbles. His theories of gastroenteritis, of irritation and inflammation as the cause of disease, and the practice which sprang from them ran over the fields of medicine for a time like flame over the grass of the prairies.
The authority and popularity of Broussais were just then being eroded by younger members of the faculty who set about exposing the absurdity of his doctrine and the dangerous consequences of treatment by starvation and leeching which reduced some patients to a deplorable state.  Among this new generation of clinicians in Paris was Rene Theophile Hyacinthe Laennec (1781-1826), expert pathologist and the most distinguished internist of his day. He is best remembered as inventor of the stethoscope in 1819, and author of classic treatises on auscultation and percussion. He had a low regard for his colleague, Broussais, to whom he referred in sarcastic terms.
However, it was Laennec's pupil, Pierre Charles Alexandre Louis (1787-1872), founder of medical statistics, who undermined Broussais's arbitrary system in 1835 when he published a memoir entitled Investigations on the Effects of Blood-letting in Some Inflammatory Disorders.  Here for the first time the effectiveness of the age-old practice of venesection was submitted to scientific evaluation. Louis's research consisted of a retrospective study of the response to blood-letting in two series of cases, one of pneumonia and the other of erysipelas of the face. He tabulated and analyzed the data according to his new "Numerical Method" which he described in detail.  By simple arithmetical calculations he compared the carefully observed outcome in untreated patients with similar patients who received treatment. The results showed that blood-letting was not of value in these cases. In the process, he demonstrated the need for rigorous evaluation of the theories and conventional wisdom of clinical medicine. Louis's Numerical Method served to establish the cardinal principle that "the edifice of medicine reposes entirely upon facts, and that truth cannot be elicited but from those which have been well and completely observed".  Medical systems could not withstand such a test and Louis's method of statistical analysis of objective data was now used to discredit them. By mid century systems were being labeled "quackery" and vigorously attacked by the enlightened elements of the profession. 
During the second quarter of the 19th century the hospitals and medical schools of Paris were the preferred destination of American students seeking advanced training abroad. Many future leaders in American medicine were inspired by the progressive spirit of French medicine. Louis, particularly, was respected for his devotion to science and his personal interest in American students, many of whom strengthened the faculties of American schools when they returned home. Holmes, for one, greatly admired Louis and after a few months' attendance at his rounds and lectures reported that "I have learned at least three principles since I have been in Paris; not to take authority when I can have facts; not to guess when I can know; not to think a man must take physic because he is sick."  In 1908 Osler recalled the contribution of the European schools to the development of American medicine and the changes that occurred in their appeal to American students: 
During the nineteenth century three schools in succession have molded the thoughts and opinions of the medical profession in this country. In the early period English ways and methods prevailed, and (as in the colonial days) the students who crossed the Atlantic for further study went to Edinburgh or to London. Then came a time between 1825 and 1860 when American students went chiefly to Paris, and the profession of the country was strongly swayed by the teaching of the French school. Since 1860 the influence of German medicine has been all-powerful, but of late American students are beginning to learn that their "Wanderjahre" should be truly such, and that when possible they should round their studies in France and England.
Discovery of Anesthesia
The discovery of the anesthetic property of ether was one of the most significant medical contributions in the first half of the 19th century. Ether anesthesia was first publicly demonstrated at the Massachusetts General Hospital in Boston on 16 October 1846. William T. G. Morton (1819-1869), a dentist, administered ether vapor (whose properties he had investigated), while Professor John Collins Warren (1778-1866), Harvard surgeon, painlessly ligated a cavernous hemangioma in the left side of the neck of Gilbert Abbott, age 20. Upon successful completion of the operation on the anesthetized patient, Dr. Warren turned to those present and said: "Gentlemen, this is no humbug." 
Dr. Warren published a report of the operation in the Boston Medical and Surgical Journal on 9 December 1846. The endorsement of ether by the highly respected Warren and his surgical colleagues at the MGH led to its immediate acceptance as an anesthetic agent on both sides of the Atlantic. Within a few months medical journals were filled with reports of operations performed under ether anesthesia. 
At the time of the demonstration at the MGH, Dr. Oliver Wendell Holmes was in medical practice in Boston. About a month after the operation he wrote to Dr. Morton with a suggestion on terminology: 
On 21 November 1856
My dear Sir:
Everybody wants to have a hand in a great discovery. All I will do is to give you a hint or two as to names, or name, to be applied to the state produced, and to the agent.
The state should, I think, be called anaesthesia. This signifies insensibility, more particularly (as used by Linnaeus and Cullen) to objects of touch. The adjective will be anaesthetic. Thus we might say the "state of anaesthesia," or the "anaesthetic state.". .
I would have a name pretty soon, and consult some accomplished scholar, such as President Everett, or Dr. Bigelow, Sr., before fixing upon the terms which will be repeated by the tongues of every civilized race of mankind. You could mention these words which I suggest, for their consideration; but there may be other more appropriate and agreeable.
O. W. Holmes
There is no evidence that other advice was sought and the words suggested by Dr. Holmes were readily accepted by the profession and the public. In due course the spelling was simplified to "anesthesia" and anesthetic.
James Young Simpson (1811-1870), Professor of Obstetrics at Edinburgh, first used ether for delivery in January 1847 but, being dissatisfied with its unpleasant odor and tendency to irritate the bronchi, set about looking for a more agreeable anesthetic. At the suggestion of David Waldie, a chemist at Liverpool, he and his assistants tested chloroform by inhaling it themselves in November 1847. Finding it highly effective and bland, they immediately began using it to provide analgesia in childbirth. Later that month he reported his experience to the Medico-Surgical Society of Edinburgh and then proceeded to wage a campaign on behalf of the use of chloroform analgesia to relieve the pangs of childbirth.  The Scottish Calvinist clergy objected on the basis of God's malediction to mothers in Genesis iii, 16 that "in sorrow shalt thou bring forth children; and thy desire shall be to thy husband, and he shall rule over thee," which he countered with the revelation in Genesis ii, 21 that God was the first anesthetist when he "caused a deep sleep to fall upon Adam, and he slept: and he took one of his ribs, and closed up the flesh instead thereof." When Simpson delivered Queen Victoria of her eighth child with the benefit of chloroform in 1853, the ecclesiastics were silenced and he was knighted, to be known thereafter as Sir James Young Simpson, Bart.  
In a letter to Professor Meigs at Jefferson Medical College in January 1848, Simpson, eager to encourage the use of chloroform in America, informed him that: 
In Great Britain and on the Continent of Europe, chloroform has everywhere entirely, or nearly entirely superseded the use of sulphuric ether, as an anaesthetic agent. . . In Midwifery, most or all of my brethren in Edinburgh employ it constantly. The ladies themselves, insist on not being doomed to suffer, when suffering is so totally unnecessary.
To which Meigs with his usual self-assurance replied in February:
And here allow me to say, I have been accustomed to look upon the sensation of pain in labor as a physiological relative of the power of force; and not-withstanding I have seen so many women in the throes of labor, I have always regarded a labor-pain as a most desirable, salutary, and conservative manifestation of life-force.
Once again, as he did with respect to contagion and blood-letting in puerperal fever, Professor Meigs came down on the wrong side of a significant medical issue of his day. He continued to be markedly antagonistic to the use of either chloroform or ether in childbirth and late in the 1840's arranged to demonstrate the danger of anesthesia to his students at Jefferson Medical College. S. Weir Mitchell (1829-1914), later to become the leading American neurologist, was a member of the class and made this note in his diary: 
(My father, Professor John K. Mitchell of the Jefferson faculty, was the first in Philadelphia to use ether in childbed.) Professor Meigs violently opposed it and one day undertook to show its peril to a class of three hundred or more at Jefferson Medical School. A big billy goat was brought into the arena, which was called the bull-ring, and Ellerslie Wallace, Dr. M's assistant, gave the ether. At last, Professor Meigs announced the demise of Billy, and the corpse was taken out and left in a small room at the half-way landing of the main stairway. The lecture over, we were noisily descending to the chemical lecture when Wallace opened the door of Billy's room. Out came Billy, very drunk, charged between Wallace's long legs into a mass of delighted students, and Billy and students went downstairs in one wild confusion. My father was never weary of inquiring of his colleague after his patient's health.
According to Professor Hodge of the University of Pennsylvania, Meigs continued 15 years later to protest against anesthesia in labor and predicted that, in the course of a few years, it would be banished from practice, except in a few extraordinary cases. 
Here we conclude our survey of the status of medicine and medical care from 1800-1850. We shall look ahead now to the three immortals of science whose contributions during the next half-century most clearly mark the transition to the modern era.