The human being is a machine. An automatic machine. It is composed of thousands of complex and delicate mechanisms, which perform their functions harmoniously and perfectly, in accordance with laws devised for their governance, and over which the man himself has no authority, no mastership, no control. For each one of these thousands of mechanisms the Creator has planned an enemy, whose office is to harass it, pester it, persecute it, damage it, afflict it with pains, and miseries, and ultimate destruction. Not one has been overlooked.

From cradle to grave these enemies are always at work; they know no rest, night or day. They are an army: an organized army; a besieging army; an assaulting army; an army that is alert, watchful, eager, merciless; an army that never relents, never grants a truce.

It moves by squad, by company, by battalion, by regiment, by brigade, by division, by army corps; upon occasion it masses its parts and moves upon mankind with its whole strength. It is the Creator's Grand Army, and he is the Commander-in-Chief. Along its battlefront its grisly banners wave their legends in the face of the sun: Disaster, Disease, and the rest.

Disease! That is the force, the diligent force, the devastating force! It attacks the infant the moment it is born; it furnishes it one malady after another: croup, measles, mumps, bowel troubles, teething pains, scarlet fever, and other childhood specialties. It chases the child into youth and furnishes it some specialties for that time of life. It chases the youth into maturity, maturity into age, and age into the grave.
- Letters from the Earth