HISTORICAL INTRODUCTION. 9 



ing and by cross division. Further, that in the blood or in serum 

 or in aqueous humour they not only grew into long leptothrix 

 filaments, but they produced enormous numbers of seeds or spores. 

 He traced, by continuous observation on the warm stage, the whole 

 life cycle, from the fission of the rods to the formation of spores and 

 the sprouting of the spores into fresh rods. Further, he cax-ried 

 on the disease by inoculating from mouse to mouse for several 

 generations, and observed that in the blood of the animal and in 

 the swollen spleen the glass-like rods were always to be found. 



Pasteur also studied the microbe of splenic fever, and amply 

 confirmed and extended the observations of Koch by his researches 

 on the attenuation of the anthrax virus. 



Pasteur also met with adverse criticism. Paul Bert argued 

 that the bacilli were of no importance, because he could destroy 

 them by exposing material containing them to great pressvire, and 

 yet the material produced the disease on inoculation. But such 

 measures did not destroy the spai'es; and finally, Paul Bert was 

 convinced of his error when Pasteur demonstrated cultures of the 

 anthrax bacillus in urine, from which successive generations were 

 started, and that with such cultivations the disease could always be 

 produced. 



It was, however, principally the researches of Koch which 

 placed the doctrine of contagium vivum on a scientific basis. 



Koch's improvements in the methods of cultivation, his recom- 

 mendation of the necessary microscopical apparatus, his histological 

 methods for examining these minute organisms, and his famous 

 postulates for proving beyond controversy the existence of specific 

 pathogenic micro-organisms, elevated the theory of contagium vivum 

 to a demonstrated and established fact. The chain of evidence 

 regarded by Koch as essential for proving the existence of a 

 pathogenic organism was as follows : — 



1. The micro-organism must be found in the blood, lymph, or 

 diseased tissue of man or animal suffering from or dead of the 

 disease. 



2. The micro-organisms must be isolated from the blood, lymph, 

 or tissues, and cultivated in suitable media — i.e., outside the animal 

 body. These pure cultivations must be carried on through successive 

 generations of the organism. 



3. A pure cultivation thus obtained must, when introduced into 

 the body of a healthy animal, produce the disease in question. 



4. In the inoculated animal the same micro-oi'ganism must 

 again be found. 



