Pasteur Changes His Mind

5. Pasteur Changes His Mind

As previously mentioned, around 1860. Pasteur discovered facts which were not in accord with his previous conception that disease germs were unchangeable. He found that microbial species can undergo many transformations; this discovery destroyed the basis for the germ theory. Since a coccus (pneumonia germ) could change to a bacillus (typhoid germ) and back again (and, indeed, since
any germ could turn into another)—and since their virulence could be altered, often at the will of the experimenter, the whole theory exploded.

It is frequently overlooked that Pasteur by then had changed his direction, and his more mature conception of the cause of disease, as given by Dr. Duclaux, was that a germ was “ordinarily kept within bounds by natural laws, but, when conditions change, when its virulence is exalted, when its host is enfeebled, the germ was able to “invade” the territory which was barred to it up to that time. This, of course, is the premise that a healthy body is resistant to disease or not susceptible to it.

After the change in his outlook, and numerous experiments along this line, Pasteur was at last convinced that controllable physiological factors were basic in the assessment of vulnerability to disease and concluded, “The presence in the body of a pathogenic agent is not necessarily synonymous with infectious disease.” (The presence of certain germs is not proof that they are the cause of a disease.)

So Pasteur did finally reverse his position and acknowledge that germs are not the specific and primary cause of disease, and he abandoned the germ theory. He is reported to have said on his deathbed, “Bernard was right. The seed is nothing, the soil is everything.”

Although Pasteur abandoned his early immature and erroneous theory in the 1880s, it was accepted, developed, fostered, and perpetuated by others, and the mischief, medical misunderstanding, and error continue to this day (the ultimate irony!).