34 ESSENTIALS OF BACTERIOLOGY 



ing a disease peculiar to the micro-organism. 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 

 serpents; highly poisonous in minute doses (TWO* gram of 

 tetanus toxin will kill a horse weighing 600 kilos 1200 

 pounds). At first toxins were called ptomains, 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 w r ere called toxal- 

 bumins, 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 that the albumin part 

 of the toxin is furnished by the blood or albuminous media in 

 which it is formed. The term toxin is to be preferred in 

 speaking of bacterial poisons. 



CHAPTER IV 

 IMMUNITY 



Ordinary Defenses to Bacterial Invasion. The un- 

 broken skin and the connective tissue underneath prevent 

 the passage of bacteria. The unbroken mucous surface of 

 eye, nose, and mouth, because of the continuous washing, 

 prevents the numerous bacteria that are constantly present 

 in the discharge from finding suitable lodgment. The hairs 

 and ciliated epithelium in upper respiratory tract retain 

 many a dust particle and pathogenic cell on its way to the 

 lungs. The acid gastric juice is destructive to most bacteria, 

 and protects not only the stomach, but the intestines as well. 



