60 MICROBES AND TOXINS 



and thus produces the miracle of the bleeding host, multiplies 

 very quickly in alkaline media, producing coccal forms ; these 

 cocci, reinoculated on a faintly acid medium, multiply less 

 rapidly and produce bacillary forms. Bacteria are then 

 multiform or pleomorphic organisms. 



In old cultures or in cultures on unfavourable media, forms 

 are seen diverging from the typical : a micrococcus may give 

 relatively enormous globules ; a bacillus may give forms racket- 

 shaped, club-shaped, pear-shaped, &c. A bacillus which 

 ordinarily never branches may show branching forms. These 

 abnormal shapes are called involution forms, again examples of 

 pleomorphism. 



In the early days of bacteriology this pleomorphism was 

 copiously discussed. Nageli held that there were no bacterial 

 species, but that the bacteria formed an immense group in 

 which neither species nor families nor genera were to be 

 distinguished. A coccus might give, under suitable conditions, 

 a rod form or a spirillum and the function might be as variable 

 as the form. He would not admit that a given fermentation 

 always corresponded to a definite bacterial form, but held that 

 the same microbe might be in its turn an acetic ferment, a 

 lactic ferment, or a butyric ferment. For him bacterial speci- 

 ficity did not exist. Hence arose the belief that it was easy to 

 render pathogenic an inoffensive bacterium like the B. subtilis 

 of hay infusions. 



The botanist Cohn exaggerated the stability of bacterial 

 species as much as Nageli exaggerated their pleomorphism, and 

 bacteriologist-physicians, in their desire to discover for each 

 infectious disease a specific agent, followed Cohn's idea. It 

 was obviously impossible to hold precise opinions about the 

 pathogenic bacteria if there existed no stability in their forms. 

 R. Koch accused the " pleomorphists " of making their 

 observations on impure cultures or on infusions containing 

 already a very numerous flora ; it was not pleomorphism that 

 was present, but confusion. 



Another observer, Kurth, however, demonstrated the 

 pleomorphism of the Bacterium Zopfii in pure cultures ; there- 



