j68 THE STORY OF GERM LIFE. 



spread of disease. Its value is seen in the fact that 

 there has been a constant decrease in the death 

 rate since modern ideas of sanitation began to 

 have any influence, and in the fact that our 

 general epidemics are less severe than in former 

 years, as well as in the fact that more people 

 escape the diseases which were in former times 

 almost universal. 



The study of preventive medicine takes into 

 view several factors, all connected with the 

 method and means of contagion. They are the 

 following : 



The Source of Infectious Material. It has been 

 learned that for most diseases the infectious ma- 

 terial comes from individuals suffering with the 

 disease, and that except in a few cases, like ma- 

 laria, we must always look to individuals suffering 

 from disease for all sources of contagion. It is 

 found that pathogenic bacteria are in all these 

 cases eliminated from the patient in some way, 

 either from the alimentary canal or from skin se- 

 cretions or otherwise, and that any nurse with 

 common sense can have no difficulty in deter- 

 mining in what way the infectious material is 

 eliminated from her patients. When this fact is 

 known and taken into consideration it is a com- 

 paratively easy matter to devise valuable precau- 

 tions against distribution of such material. It is 

 thus of no small importance to remember that the 

 simple presence of bacteria in food or drink is of 

 no significance unless these bacteria have come 

 from some source of disease infection. 



The Method of Distribution. The bacteria must 

 next get from the original source of the disease to 

 the new susceptible individual. Bacteria have no 

 independent powers of distribution unless they 



