INFECTION. 71 



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. 



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 certain number are peculiarly inclined to 

 give rise to pus, and are known as pyogenic organisms. 



Infective bacteria are as a rule specific, the particular toxin 

 having a specific action and causing a disease peculiar to the 

 microorganism. Thus typhoid fever is a disease distinctly 

 different from tuberculosis ; the infective organisms are distinct 

 and the poisons they produce have specific characteristics. 



The Nature of Toxins. Very similar to the venom of ser- 

 pents; highly poisonous in minute doses ( ^ & gramme of 

 tetanus toxin will kill a horse weighing 600 kilos (1200 pounds;). 

 At first toxins were called ptomaines, or cadaveric alkaloids ; but 

 this term is applied now to such poisons as have a basic nature 

 and arise in decomposing meat, cheese, and cream as a result 

 of chemical change in the material, the bacteria causing the 

 change. Then they were called toxalbumins, and were supposed 

 to belong to an albumin series ; but when the bacteria are grown 

 in non-albuminous media the toxins correspond more in their 

 chemical composition to a ferment, and therefore it is supposed 



