Careless and stupid people often take, by mistake, with serious, and often fatal, results, poisonous doses of carbolic acid, bed-bug poison, horse-liniment, oxalic acid, and other poisons.  A safe rule is to keep all bottles and boxes containing poisonous substances securely bottled or packed, and carefully labeled with the word POISON plainly written in large letters across the label.  Fasten the cork of a bottle containing poison to the bottle itself with copper or iron wire twisted into a knot at the top.  This is an effective means of preventing any mistakes, especially in the night.

This subject of poisons assumes nowadays great importance, as it is a common custom to keep about stables, workshops, bathrooms, and living rooms generally a more or less formidable array of germicides, disinfectants, horse-liniments, insect-poisons, and other preparations of a similar character.  For the most part they contain poisonous ingredients.

Bacteria.

394.  Nature Of Bacteria.  The word bacteria is the name applied to very low forms of plant life of microscopic size.  Thus, if hay be soaked in water for some time, and a few drops of the liquid are examined under a high power of the microscope, the water is found to be swarming with various forms of living vegetable organisms, or bacteria.  These microscopic plants belong to the great fungus division, and consist of many varieties, which may be roughly divided into groups, according as they are spherical, rod-like, spiral, or otherwise in shape.

Each plant consists of a mass of protoplasm surrounded by an ill-defined cell wall.  The bacteria vary cably in size.  Some of the rod-shaped varieties are from 1/12,000 to 1/8,000 of an inch in length, and average about 1/50,000 of an inch in diameter.  It has been calculated that a space of one cubic millimeter would contain 250,000,000 of these minute organisms, and that they would not weigh more than a milligram.

[Illustration:  Fig. 168.—­Examples of Micro-Organisms called Bacteria.  (Drawn from photographs.)

  A, spheroidal bacteria (called cocci) in pairs;
  B, same kind of bacteria in chains;
  C, bacteria found in pus (grouped in masses like a bunch of grapes).
     [Bacteria in A, B, and C magnified about 1000 diameters]. 
  D, bacteria found in pus (tendency to grow in the form of chains).
     [Magnified about 500 diameters.]
]

Bacteria are propagated in a very simple manner.  The parent cell divides into two; these two into two others, and so on.  The rapidity with which these organisms multiply under favorable conditions, makes them, in some cases, most dangerous enemies.  It has been calculated that if all of the organisms survived, one bacterium would lead to the production of several billions of others in twenty-four hours.

395.  The Struggle of Bacteria for Existence.  Like all kinds of living things, many species of bacteria are destroyed if exposed to boiling water or steam, but seem able to endure prolonged cold, far below the freezing-point.  Thus ice from ponds and rivers may contain numerous germs which resume their activity when the ice is melted.  Typhoid fever germs have been known to take an active and vigorous growth after they have been kept for weeks exposed in ice to a temperature below zero.