306 



OUR BODIES AND HOW WE LIVE 



Under certain conditions bacteria reproduce themselves 

 by minute round bodies called "spores" or eggs. These 

 spores become dried without losing their vitality, and as 

 dust may be carried everywhere by the winds. Under 

 favorable conditions they germinate and become bacteria. 1 

 421. Importance of Bacteria in Nature. Bacteria exist 

 in the soil and in water. They are wafted as dust in the 

 air all over the face of the earth. We eat myriads of 

 them in our food, drink them in water, and breathe them 

 in the dust of the street, the house, and the workshop. 

 These tiny organisms break down all dead organic matter 

 into simple chemical substances which are thus made more 

 fit for the food of plants. In other words, bacteria act 

 as scavengers which serve to make the face of the earth 

 clean and sweet for all living things. If it were not so, 

 life upon the earth would be impossible. Like countless 

 other species of living organisms, bacteria obey the relent- 



less law of nature which 

 allows only the fittest to sur- 

 vive. The rains, the winds, 



1 Bacteria consist of many varieties 

 roughly divided into groups accord- 

 ing as they are spherical, rodlike, or 

 spiral in shape. The word " bacillus " 

 is commonly applied to rod-shaped 

 bacteria. Each bacterium consists of 

 a mass of protoplasm surrounded by 

 an ill-defined cell wall. 



The bacteria vary considerably in 

 size. Some of the rod-shaped varie- 

 ties are from T^TTO to ~5~3o~o f an mcn 

 in length and average about ^^ff 

 of an inch in diameter. It has been calculated that a cubic space of ^ of 

 an inch would contain 250,000,000 of these minute organisms and that 

 they would not weigh more than ?fa of a grain. 



FIG. 191. Various Forms of 



Bacteria. 



Magnified about 1000 diameters. 

 A, spheroidal bacteria in pairs ; B, same 

 kind of bacteria in chains ; C, bacteria 

 found in pus (grouped in masses like a 

 bunch of grapes). 



