28 BACTERIA, YEASTS, AND MOLDS 



many experiences where a knowledge of distribution of 

 diseases is of even more importance to her than to the 

 physician himself. The physician is directly concerned in 

 the cure and only indirectly in the prevention of contagion ; 

 the housewife must always have upon her shoulders the 

 duty of keeping her family in health, and when an instance 

 of contagious disease appears she must try to protect the 

 rest of the household. For these reasons it follows that 

 a knowledge of disease germs is of more vital significance 

 to one who cares for the home than it is to the physician, 

 who is only concerned in curing the disease. The physi- 

 cian or the Board of Health may give suggestions and 

 directions, but the successful application of these direc- 

 tions depends upon the intelligence of the home keeper. 



This brief outline of the relation of bacteria to various 

 household problems is sufficient to show why a knowledge 

 of microorganisms should be a part of the equipment of 

 any one who is to conduct the affairs of a well-regulated 

 household. For the development and preparation of some 

 foods, for the preservation of all foods, and for the pro- 

 tection of the health of those under her care, the head of 

 a modern well-equipped home needs to understand bac- 

 teria and kindred organisms. A knowledge of molds, 

 yeasts, and bacteria has become a vital if not a necessary 

 part of training in domestic economy. 



Different Classes of Microorganisms 



Nearly all the microorganisms with which we are here 

 concerned have this characteristic : they are what botanists 

 call colorless plants. This does not mean that they are 



