720 Reading-Course for Farmers' Wives. 



Dust plants are micro-organisms. There are large numbers of minnte 

 organisms so small that they cannot be seen by the naked eye, and which 

 require the aid of a powerful microscope to show their presence, hence 

 the name micro-organisms. Various names have been given to these 

 minute living bodies, as germs and microbes. Literally, germ means 

 the beginning, the first living cell which produces a more complex form. 

 The plant micro-organisms we shall consider are: — 



Bacteria, Molds and Yeasts 

 Not a great many years ago little was known about these minute living 

 things. Even now but few persons know much of the practical science 

 of bacteriology. A growing knowledge of the subject has done much 



\ • _ - 



*•• 



Fig. 44. — I'arious, forms of bacteria or germs. Much magnified 



toward preserving or prolonging life. Modern ])acteriology has devel- 

 oped practically since i8<So. although as early as the 17th century some- 

 thing was known of this little world. 



Bacteria. These are micro-organisms, of very simple structure, 

 belonging to the vegetable kingdom and are the smallest and simplest 

 plants known. They live in soil and in water and are found on many 

 food-stufifs, and some varieties prey upon man and beast and plant. 

 There are hundreds of species of them. Some are of great value in 

 nature's economy and of great benefit to man, while others are sources 

 of danger to the health of man. They take food, change it into their 

 own substance and give off waste products, either gases or liquids, 

 which, dissolved in blood or other liquids, bring about changes which 

 may be either good or bad. Ptomaine poisoning is a common illustra- 

 tion of this. Certain bacteria have fed u|)on the food and produced 

 active poisons in it. 



Bacteria are reproduced by a process of division. This process of 

 division is known as fission and will be seen in some of the different 

 forms in Fig. 44. 



