CHAPTER X. 



CAUSES OF DISEASE. 



Inflammation and Fever. Thus far we have been con- 

 cerned with diseases and malformations arising mainly 

 from structural alterations due to the combined effects 

 of variability and inheritance. We will now consider 

 some examples of disease due to other causes. 



Biological researches of the last few years have shown 

 that many diseases of animals are due to the entrance, 

 and subsequent multiplication in the system, of micro- 

 scopic bodies known collectively as bacteria, or micro- 

 organisms. It has been clearly established by an 

 overwhelming amount of evidence that such conditions 

 as tuberculosis, glanders, actinomycosis and other 

 contagious diseases are due to the action of these 

 minute bodies. 



For our purpose bacteria may be divided into two 

 groups those which when introduced into the body 

 cause no harm, and those which produce disturbance 

 either local or general. The latter are said to be 

 pathogenic, or disease-producing. A study of the 

 relation of bacteria to disease is of great interest, and 

 sheds abundant light, not only on the nature of specific 

 diseases, but also on the nature of a very remarkable 

 condition known generally as inflammation. 



