Germicide
Aiton's Encyclopedia (1910)
a germ killer. Current discussions divide germicides into three classes--mechanical, physical, and chemical. Germs are so minute that no process of grinding or pounding can be effective. Prolonged shaking prevents multiplication in many cases, and even kills germs. Of physical agencies, heat, light, cold, and electricity are the most important. Heat is the most effective; electricity the least so. No germ can withstand a high degree of heat. Nearly all germs are killed by the temperature of boiling water. Speaking in a general way, bacteria can stand more heat than animal germs. Freezing kills some germs; others live dormant in ice. Some live even in liquid air . There is no practical method of killing bacteria by freezing. Prolonged sunlight is nature's great germicide. Some forms of disease seem to yield to the influence of red light, X-rays, radium, etc., but the nature of their action is not understood, nor are the results certain. Strong, white sunlight is the greatest of physical germ destroyers. Electrical currents cannot be depended upon to kill germs. Polluted water, through which a powerful current has been passed, is found to be full of germs. Of chemical germicides, carbolic acid is without a superior. Other anti-bacterial agents are ammonia, chloride of lime, creosote, formaldehyde, alcohol, hydrogen peroxide, mercury, and iodine. Sulphur is less in favor than formerly. A number of oils, as of peppermint, pennyroyal, turpentine, and mustard are effective. Quinine and its ally, salicylic acid, are the standard remedies for malarial germs. Fortunately the blood itself, or rather the serum of the blood, is one of the most efficient germicides in nature.
What Has Changed in the Last Century
Aiton's 1910 entry called carbolic acid "without a superior" and listed mercury and iodine among the best chemical agents; the great shift since is that medicine stopped relying on killing germs on surfaces and learned to kill them inside the body, with the sulfa drugs from 1935 and penicillin brought into mass production in the early 1940s. Steam under pressure in an autoclave, not merely boiling water, is now the standard for sterilising instruments, and municipal chlorination did far more for waterborne disease than any of the oils of peppermint or pennyroyal named here. The 1910 hunch that ultraviolet light in "strong, white sunlight" is the greatest physical destroyer was sound: germicidal UV lamps are used today in ventilation ducts and water treatment. Mercury compounds have largely been withdrawn as too toxic, and the newest problem is one the entry could not foresee — bacteria that evolve resistance to the agents used against them.
Written for this edition, 2026.