102 .Fermentation and Kindred Phenomena. 



statement that the disease is caused by the organisms, we must 

 be shown a most convincing and complete chain of proofs. 



Such a chain of complete proof seems to have been established. 

 As regards splenic fever, it is somewhat as follows : — 



1st. We always observe in the blood and tissues of animals 

 suffering from the disease, rod-like organisms or bacilli. 



2nd. It is possible to inoculate (with every precaution) an 

 artificial nourishing medium— say nutrient gelatine — with this 

 blood, and we find characteristic colonies from which we can 

 obtain a pure culture of the bacillus, with which we can inoculate 

 a sterile nourishing fluid like broth. 



3rd. On injecting this broth into a healthy animal — a mouse, 

 a guinea pig, a sheep, or an ox, we find after a short interval all 

 the characteristics of splenic fever. The animal usually dies, 

 and in its blood are found countless bacilli of the kind from 

 which we originally started. 



The argument appears complete, and I believe that Koch was 

 the first to maintain that no organism could be considered as 

 the cause of a disease, unless all the above conditions are fulfilled. 



Koch has formulated the above conditions, thus — 



(1) It is absolutely necessary that the micro-organisms in 

 question be present in the blood or diseased tissues of man or 

 animal suffering or dead from the disease. [In this respect 

 great differences exist, for in some infectious diseases the micro- 

 organisms, although absent in the blood are present in the 

 diseased tissues, whilst in others they are present in large 

 numbers in the blood only, or in the lymphatics only — Klein.] 



(2) It is necessary to take these organisms from their nidus — 

 from the blood or tissues as the case may be — to cultivate them 

 artificially, i.e. outside the animal body, but by such methods 

 as exclude the accidental introduction into these media of other 

 micro-organisms ; to go on cultivating them from one cultivation 

 to another, for several successive generations, in order to obtain 

 them free from every kind of matter derived from the animal 

 body from which they have been taken in the first instance. 



(3) After having thus cultivated the micro-organisms, it is 

 necessary to re-introduce them into the body of a healthy 



