HOW TO PREVENT DISEASE. 167 



tion to the laws of health, and will continue to germinate 

 and grow if not arrested by the strictest compliance with 

 those laws, not only of individuals, but of communities as 

 well. In view of the fact that by the observance of sanitary 

 laws disease may be prevented, it is obvious that education 

 on this subject should be widely diffused. It should begin 

 in childhood with the parent, by precept and example. It 

 should be continued in the school-room, from the lowest 

 grades upward, and the wise and prudent man will be a 

 student of hygiene all his life. 



2. Infectious and Contagious Diseases. The terms 



infectious and contagious have a separate and distinct mean- 

 ing, although they are commonly used synonymously. The 

 distinction is important in so far as each term indicates 

 the means whereby the poison which invades the system is 

 developed. 



The poison of an infectious disease is developed external to 

 the human body, and is introduced to the system irrespective 

 of a pre-existing case. Typhoid fever and cholera are types 

 of this class. In a contagious disease the germs of the poison 

 are received directly or indirectly from a person having the 

 disease. The germs, having been received into the system, 

 undergo a process of development and multiplication. There 

 is always a period, longer or shorter, between catching the 

 disease and its actual appearance. It is a period of incuba- 

 tion or hatching. Familiar types of this class are scarlet 

 fever, measles and small-pox. 



Some diseases are more distinctly contagious than others, 

 as scarlet fever and small-pox; some, as diphtheria, seem to 

 be both infectious and contagious, while cholera is ^believed 

 by some to be contagious as well as infectious. 



The poison of infection, developed external to the body, 

 requires suitable soil in which the germs may take root and 

 grow. This soil consists of dead matter which has formed a 



