“Medicine, guarded too by preliminary impediments, and frightful medusa-heads of quackery, which deter many generous souls from entering, is of the half-articulate professions, and does not much invite the ardent kinds of ambition. The intellect required for medicine might be wholly human, and indeed should by all rules be,—the profession of the Human Healer being radically a sacred one and connected with the highest priesthoods, or rather being itself the outcome and acme of all priesthoods, and divinest conquests of intellect here below. As will appear one day, when men take off their old monastic and ecclesiastic spectacles, and look with eyes again! In essence the Physician's task is always heroic, eminently human: but in practice most unluckily at present we find it too become in good part beaverish,—yielding a money-result alone. And what of it is not beaverish,—does not that too go mainly to ingenious talking, publishing of yourself, ingratiating of yourself; a partly human exercise or waste of intellect, and, alas, a partly vulpine ditto;—making the once sacred… Human Healer, more impossible for us than ever!”
1850s, Latter-Day Pamphlets (1850), Stump Orator (May 1, 1850)
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Thomas Carlyle 481
Scottish philosopher, satirical writer, essayist, historian… 1795–1881Related quotes
2009 speech at the opening ceremony for Chekhov Studio International Los Angeles ( online http://chekhovstudio.com/2013/07/inspiring-quotes/ and books.google.com http://books.google.com/books/about/The_Spirit_of_Creation_Discipline_and_At.html?id=jqMInoDQoxMC)

On being a lawyer, as quoted by Claire Birge in The Stevensons : A Biography of an American Family (1997) by Jean H. Baker, p. 262

Les médecins administrent des médicaments dont ils savent très peu, à des malades dont ils savent moins, pour guérir des maladies dont ils ne savent rien.
This attribution to Voltaire appears in Strauss' Familiar Medical Quotations (1968), p. 394, and in publications as early as 1956 http://books.google.pt/books?id=lCtCAQAAIAAJ&q=%22Doctors+are+men+who+prescribe+medicine+of%22&dq=%22Doctors+are+men+who+prescribe+medicine+of%22&hl=pt-PT&sa=X&ei=mbnWUsvDIfTB7Aaw_YD4Dw&redir_esc=y; the quotation in French does not, however, appear to be original, and is probably a relatively modern invention, only quoted in recent (21st century) published works, which attribute it to "Voltaire" without citing any source.
Attributed

“Human nature is the same in all professions.”
Source: The Life and Opinions of Tristram Shandy, Gentleman

This attribution to Voltaire appears in Strauss' Familiar Medical Quotations (1968), p. 394, and in publications as early as 1956 http://books.google.pt/books?id=lCtCAQAAIAAJ&q=%22Doctors+are+men+who+prescribe+medicine+of%22&dq=%22Doctors+are+men+who+prescribe+medicine+of%22&hl=pt-PT&sa=X&ei=mbnWUsvDIfTB7Aaw_YD4Dw&redir_esc=y; the quotation in French does not, however, appear to be original, and is probably a relatively modern invention, only quoted in recent (21st century) published works, which attribute it to "Voltaire" without citing any source.
Original: (fr) Les médecins administrent des médicaments dont ils savent très peu, à des malades dont ils savent moins, pour guérir des maladies dont ils ne savent rien.

Source: The Postman (1985), Section 3, “Cincinnatus”, Chapter 9 (p. 225)
Kenneth Boulding (1967) "The Concept of Need for Health Services" in: The Milbank Memorial Fund Quarterly. Vol. 44, No. 4, Part 2, pp. 202
1960s