Louis Pasteur versus Claude Bernard on the Causes of Disease

Two giants of scientific medicine in the 19th century, both French, propounded radically different paradigms for the understanding and treatment of disease, that are still relevant today. Louis Pasteur (1822-1895), chemist and microbiologist, put forward the germ theory, according to which diseases are caused by infectious microbes, that impair the functioning and structures of different organ systems. This paradigm is the basis for the use of antibiotics to destroy these invasive microbes and vaccines with low doses of the microbe to challenge the body’s immune defenses and thereby prevent systemic infection.

Pasteur’s contemporary and friend, the physiologist Claude Bernard (1813-1878), argued instead for the importance of balance in the body’s internal environment – what he called le milieu intérieur. “The constancy of the interior environment is the condition for a free and independent life.” Bernard thought that the body becomes susceptible to infectious agents only if the internal balance – or homeostasis as we now call it – is disturbed. After all, there are billions of microbes and bacteria inhabiting our guts, our blood, our whole body. Why do we sometimes sicken from them, sometimes not? When a bacterial or viral agent is “going around,” as we say, why do some people sicken and others remain healthy ?

There is an apocryphal story that Pasteur renounced his germ theory on his death-bed, saying that “Bernard is right. The microbe is nothing. The environment is everything.” The renowned 20th century French-American microbiologist René Dubos (1901-1982) agreed with Bernard’s principle: “Most microbial diseases are caused by organisms present in the body of a normal individual. They become the cause of disease when a disturbance arises which upsets the equilibrium of the body.”

Today, Pasteur’s germ theory of disease provides the rationale for the pharmaceutical industry’s billions of dollars research and sales programs for ever more potent anti-bacterial and anti-viral drugs, the use of these antibiotics as a feed-additive in the disease-prone, overcrowded environments of industrial farming – with the predictable consequence that bacterial evolution is out-stripping the discovery rate of effective antidotes.

The Bernard/Dubos theory that health and resilience is a function of homeostatic balance in the internal environment is reflected in the growing influence of the ancient medical systems of India and China, as well as homeopathy and Dr. Andrew Weil’s integrative medicine. In all these approaches, the maintenance of health and prevention of disease involves conscious attention given to factors of life-style, environment, nutrition, exercise and recreation, as well as psychological well-being and spiritual practice.