Day and night, sleeping and waking, the white knights of life are constantly on the alert, for on their vigilance hangs our existence.

Sometimes, however, the invading microbes come in, not in companies but in platoons, innumerable as Xerxes' Persians, and then "e'en Roderick's best are backward borne," and we die.

For our life is the prize of the combat in these novel lists which science has revealed to our view through the microscope, and health is but the token of the triumphant victory of the phagocyte over the microbe.
But far more enthralling is the suggestion which psychical science has made as to the existence of a combat not less grave in the very inmost centre of our own mental or spiritual existence.

The strife between the infinitely minute bacilli that swarm in our blood has only the interest which attaches to the conflict of inarticulate and apparently unconscious animalculae.

The strife to which researches into the nature and constitution of our mental processes call attention concerns our conscious selves.