SECTION III. 

 RELATION OF BACTERIA TO DISEASE. 



CHAPTER IX. 

 TRANSMISSIBLE DISEASES. 



Bacteria are classified according to their manner of nu- 

 trition into saprophytes and parasites. The saprophytic 

 forms live on dead organic matter, the parasites live in 

 the bodies of other living forms which may be either 

 plants or animals. The form affected is known as the 

 host, and the invading organism as the parasite. There 

 are many forms of bacteria that may live in the animal 

 body and cause no disturbance. Still other forms, 

 known as pathogenic or disease-producing organisms, by 

 their growth in the body of an animal cause changes that 

 may injure the body or cause the death of the animal it- 

 elf. 



Transmissible diseases. Diseases traceable to such 

 causes are capable of being communicated from one sus- 

 ceptible host to another, and are known as transmissible 

 or communicable diseases. Many forms of disease are 

 the result of some physiological disturbance of the body 

 such as poor digestion, circulation, etc. These are not 

 transmissible and no danger of spread from one animal 

 to another exists. All transmissible diseases are caused 

 by the infection of the proper host with the parasite, and 

 ~by the growth of the parasite. In order that infection 



