76 ESSENTIALS OF BACTERIOLOGY 



in the same individual to the different forms of disease germs. 

 Susceptibility may be natural to the race, it may be acquired, it 

 may be inherited. Mice are naturally susceptible to anthrax. 

 Acquired susceptibility occurs upon exposure to conditions 

 which lower vitality, as hunger, cold, advanced age, and sur- 

 gical shock. Inherited susceptibility is a less important factor 

 now than formerly. Many diseases were at one time considered 

 inherited which now are known to be acquired during the life- 

 time of an individual. Still, certain physical characteristics, 

 such as narrow chest, mouth-breathing, etc. clearly inheritable 

 characters predispose to disease. Given a susceptible individ- 

 ual and an infective microorganism producing toxins in suffi- 

 cient amount, disease is certain to result. 



Fourth, the infecting organism must gain entrance into the 

 tissues or find lodgment on some portion of the body that has 

 been injured; on the skin, in the nose, and in the throat are 

 at all times bacteria that are more or less pathogenic, but 

 they fail to cause disease until, through a traumatism or 

 lessened resistance, they are allowed to enter the tissues or 

 the blood and then they act. 



Local Effects of Bacteria. By mechanical obstruction from 

 rapid growth, thrombosis, with its consequences, may occur. 

 Destruction of a part of the cells of a tissue with necrosis can 

 arise from irritation, as from a foreign body. 



General Effects. Sapremia, when toxic products of local 

 suppuration are absorbed into the system. Septicemia, when 

 the infective agent itself enters the blood-stream and causes 

 general disturbance. 



Suppurative bacteria are those which give rise to inflamma- 

 tion and suppuration locally at the point of entrance, and 

 secondarily through metastasis. Any organism may cause 

 suppuration, but a number are peculiarly inclined to give rise 

 to pus, and are known as pyogenic organisms. 



Specific Bacteria. Infective bacteria are, as a rule, specific, 

 the particular toxin having a specific action and causing a dis- 

 ease peculiar to the microorganism. Thus typhoid fever is a 

 disease distinctly different from tuberculosis; the infective 



