150 PUBLIC HEALTH BACTERIOLOGY 



necessary to trace it back to some parent fungus or mould. 

 This not improbable theory was, even in its crude form, 

 not easily met, as at that time no one was working with 

 pure cultures. Klebs in 1872 described in pus, rod-like 

 bodies and " microspores," grouped in short chains or in 

 longer threads ; and he filtered the pus through baked clay 

 cylinders, and found that the filtrate on injection into the 

 blood or under the skin gave constitutional symptoms, but 

 did not induce suppuration nor cause death ; though if to 

 it were added a small quantity of the micro-organisms, a 

 true pyaemia was produced. 



Koch in 1876 demonstrated the specificity of the anthrax 

 bacillus by making it satisfy the following four conditions, 

 commonly called Koch's postulates, namely : 



1. The anthrax bacillus was invariably found in the 

 blood or tissues of animals affected with the disease. 



2. The bacillus was cultivated in artificial media for an 

 indefinite number of successive generations. 



3. The same disease was produced by inoculation of a 

 susceptible animal with the last cultivation. 



4. In every such inoculated animal the specific microbe 

 was found, and similarly distributed as in animals infected 

 in the ordinary way. 



To these Martin adds : 



5. The secondary infective agent or toxin separable 

 from the tissues in the natural disease, should have similar 

 chemical and physiological actions to the products 

 obtained from a pure cultivation of the organism. 



Koch succeeded in doing this by being able to make 

 pure cultures of the anthrax bacillus on the aqueous humour 

 of the eye of the ox, and in this way was able to carry 

 out the further procedures, and to accept the results as due 

 to the single substance inserted. 



Numerous similar investigations were now made, and 

 served to corroborate the soundness of the germ theory of 

 disease. 



The introduction of solid media by Koch in 1882 paved 

 the way for an enormous advance in bacteriological 

 technique, and numerous discoveries of specific organisms 

 followed, or specificity wa^i established : Staphylococci in 

 1880-83, Streptococci 1881-84, Micrococcus tetragenus 



