CHAPTER III. 



BRIEF DESCRIPTIONS OF THE MOST IMPOR- 

 TANT PATHOGENIC BACTERIA. 



THE starting-point of the discoveries enu- 

 merated in this chapter was the observation that 

 definite bacteria with well-marked character- 

 istics occur in certain diseases. For example, 

 spirally twisted filaments were observed by 

 Obermeier in the disease known as relapsing 

 fever, rodlets were found by Koch in anthrax, 

 and chain-cocci in erysipelas. The microbes 

 which have been brought to light by investiga- 

 tion of this kind belong mostly to the class of 

 bacteria. Such microbes found accompanying 

 disease have been discovered successively not 

 only in many epidemic diseases, but also in so- 

 called organic diseases like pneumonia, and in 

 constitutional diseases like consumption ; and 

 they have been found so situated that their 

 causal connection with these diseases is gener- 

 ally acknowledged. Koch claimed that three 

 points must be determined in order to afford 



proof of this causal relation : (i). The microbes 

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