KOCH'S POSTULATES 175 



The Infective Process 



With regard to disease-producing micro-organisms, 

 Koch laid down the following conditions, which have been 

 termed " Koch's postulates," which should be complied 

 with before the relation of an organism to a disease process 

 can be said completely to be demonstrated : 



(1) The organism in question must be present in the 

 tissues, fluids, or organs of the animal affected with, or 

 dead from, the disease. 



(2) The organism must be isolated and cultivated out- 

 side the body on suitable media for successive generations. 



(3) The isolated and cultivated organism, on inoculation 

 into a suitable animal, should reproduce the disease. 



(4) In the inoculated animal the same organism must 

 be found. 



To these may be added : 



(5) Chemical products with a similar physiological 

 action may be obtainable from the artificial cultures of the 

 micro-organism, and from the tissues of man or animals 

 dead of the disease. 



(6) Specific serum and other reactions, agglutinative, 

 bacteriolytic, complement fixative, etc., are generally 

 obtainable, under certain conditions, if the blood of the 

 infected person or animal be allowed to act on the specific 

 organism producing the infection. 



It. is true that there are diseases in which one or more 

 of these conditions are not fulfilled, but on general 

 evidence they are classed as infective. 



The modes of infection, or entrance of the infective 

 agent into the body, are varied. The infective agent 

 may enter by (1) the gastro-intestinal tract, e.g. typhoid 

 fever, cholera, and glanders ; (2) the respiratory tract, e.g. 

 pneumonia and influenza, and occasionally typhoid fever, 

 plague, etc. ; (3) by inoculation, not necessarily only of 



