CHAPTER XIX 



* 



THE BIOLOGY OP DISEASE 1 



STUDENT KEPORT 



How many in the class have been sick during the past year ? Of how 

 many different diseases ? What was done to aid each one in getting 

 well ? What was done to prevent others from taking the same diseases ? 

 What was done by your Board of Health officer ? (Consult the reports 

 of the State Board of Health and of the local health official.) 



173. Disease. — Usually people go through their daily 

 occupations without feeling pain or bodily discomfort. 

 Such a condition is known as health. Sometimes, how- 

 ever, they go about their usual duties when they do not 

 feel well and the indisposition gradually passes away. 

 But in other cases the ill feeling becomes severe, the usual 

 activities are given up, and we say that they are sick. 

 Sickness may last for only a short time or for many years. 

 The usual conditions of the body are changed, and we say 

 that the body is diseased. The apple, the tree, the dog, 

 the horse, each has its own diseases. 



174. Cause of Disease. — While there are many causes of 

 disease, all of them may be grouped under four headings: 

 (1) Inherited diseases, i.e. those transmitted from parent 

 to child, as certain forms of insanity and imbecility where 

 the exact cause is not known. (2) Diseases caused 

 by such poisons as lead, arsenic, mercury, phosphorus, 

 opium, cocaine, alcohol, and the like. The disturbances 

 which these chemical agents set up in animal tissues are 



1 Chapter XXII, Bacteria, may be read in connection with this chapter. 



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