DISTRIBUTION OF CONTAGIOUS DISEASES 233 



power, then, depends upon the vigor of the physical 

 health. Hence it is of the greatest practical importance 

 for every one to remember that robust physical health is 

 the best protection against many types of disease due to 

 the invasion of bacteria. It is true that persons in appar- 

 ently perfect health may take these diseases, but it is never- 

 theless the rule that the stronger the physical vigor the 

 less is the likelihood of being attacked. At any rate a 

 person of strong constitution will have a milder attack of 

 the disease than one whose physical activity is weakened. 



Distribution of Contagious Diseases 



While these problems are of the utmost importance in 

 every household, hygiene does not properly belong to 

 the field of our study. There is one phase of the subject 

 of bacterial diseases, however, that is of vital interest to 

 every housewife. If contagious diseases are due to the 

 growth of bacteria or other microorganisms, it is clear 

 that they may be avoided if we can prevent the disease 

 germs from reaching the healthy individual. We have 

 already noticed how one bit of decaying fruit contaminates 

 another, the spores passing to the perfect fruit and caus- 

 ing that also to decay. We have seen how the minute * 

 spores of molds and yeasts are scattered through the air 

 and blown about by the winds until they are almost sure 

 to be found everywhere. We have noticed, also, how 

 readily bacteria are distributed, and how surely the air 

 of our houses is filled with them. We have learned that 

 these microorganisms are so abundant in the air that they 

 are sure to get into any exposed bit of food, and we have 



