be assumed that each of the long list of diseases known as infectious is caused by its own specific virus, and that no other material or combination of agencies can produce it. This fact is universally recognized. Furthermore, it has been demonstrated in a large proportion of these diseases that the essential principle of infection in the virus is the living germ called the pathogenic microbe.
The literally vital relation of microbic to human life can be observed in the following general statement: The pathogenic microbes cause four fifths of all diseases of the human family; they destroy more lives than war, famine, fire, murders, shipwreck, and all other casualties; and they actually abbreviate the average natural term of human life by three fourths, and constantly depress the health average of the world's population far below its natural standard.
They are an insidious but powerful and relentless enemy to human kind, holding sway over a large part of the most beautiful and fertile portions of the earth, excluding man at the peril of his life; while, as if with malicious discrimination, ferocious animals and venomous reptiles find there their congenial home, and vegetation reaches its acme of luxuriance. Like some diabolical spirit, in the form of the epidemic, it leaves its native habitat, and with insatiate malignity, sometimes with slow but irresistible progress, and again by rapid flight, passes all barriers of mountain, sea, and distance in its pursuit of man, its only known object, and whose destruction is its only visible effect. This is shown in Asiatic cholera, the plague, yellow fever, and the lesser scourges. The strife for possession in some coveted regions has been progressing for ages. Man may advance his outposts under the favoring light of sunshine, but must retreat, or fortify himself against the dangerous shades of night, until, by slow degrees, advantages are gained over the invisible enemy.
The Italian Pontine marshes, the jungles of India, the banks and shores of the tropics, our own Southern lowlands and fertile, new prairies are the strongholds of Bacillus malarial.
"The pestilence that walketh in darkness, and the sickness that wasteth at noonday," are known to be the work of the armies of the microbes.
Some of the means and methods of the micrologist, in his researches, must be mentioned. His outfit is extensive and novel. It includes the best known microscopes and a well-constructed incubator with heater and thermometer, numerous test-glasses, beakers, filters, acids, alkalies, deep-colored dyes, and a good supply of prepared cotton.
In studying the life history of his microbes he will require a well-supplied commissariat. He must be a professional caterer