32 INFECTION 



B. of Typhoid. B. of Dysentery. 



Spirillum Choleras. Meningococcus. 



Pneumococcus (Pneumonia) . 



Spiroch&ta of Relapsing Fever and of Syphilis 



There are several other organisms that are considered to be 

 the cause of specific disease, but they do not fulfill the postulates. 

 Among these are : 



The Protozoa of Malarial Fever 

 Amoeba Dysenteries. 



While the specifications outlined by Koch as indicating the 

 etiological role of an organism were sufficient for the period at 

 which they were laid down, advances in immunology have added 

 so much information about antigens and antibodies that it is 

 but right today to expect that a virus should behave as an 

 antigen by calling forth certain immunity reaction under spon- 

 taneous and experimental conditions. Such as expectation is 

 fulfilled in practically all cases, and indeed has been, even in 

 a few instances where all Koch's postulates could not be com- 

 pleted, typhoid fever being a notable example. 



In rheumatic fever, measles, mumps, yellow fever, chicken- 

 pox, rabies, and dengue, the specific cause has, thus far, eluded 

 discovery. In the case of measles, hog cholera, and some of 

 the eruptive diseases, it has been found that the cause of these 

 diseases resides in the blood, and if the serum of the latter is 

 carefully filtered through a Berkefeld filter, it is still capable of 

 producing the disease in susceptible animals. Careful micro- 

 scopic search fails to show any bodies in the serum that might be 

 considered the agents of infection, and it is thought that these 

 organisms are submicroscopic (see chapter on Filterable Viruses). 



If the invading organism is a pure saprophyte the various" 

 forces for internal defense immediately act upon and destroy it. 



Bacteria are disposed of in diverse ways. By means of the 



