A physician's subject of study is necessarily the patient, and his first field for observation is the hospital.
But if clinical observation teaches him to know the form and course of diseases, it cannot suffice to make him understand their nature; to this end he must penetrate into the body to find which of the internal parts are injured in their functions.
That is why dissection of cadavers and microscopic study of diseases were soon added to clinical observation.
But today these various methods no longer suffice; we must push investigation further and, in analyzing the elementary phenomena of organic bodies, must compare normal with abnormal states.
We showed elsewhere how incapable is anatomy alone to take account of vital phenenoma, and we saw that we must add study of all physico-chemical conditions which contribute necessary elements to normal or pathological manifestations of life.
This simple suggestion already makes us feel that the laboratory of a physiologist-physician must be the most complicated of all laboratories, because he has to experiment with phenomena of life which are the most complex of all natural phenomena.
By Claude Bernard
An Introduction to the Study of Experimental Medicine (1865), trans. Henry Copley Green (1957) 140-1.