MICEOBES— INFECTION— IMMUNITY 451 



Bacteriacem | ^^cfermwi ; No spores are produced. 

 I Bacillus : Spores are produced. 



f Vibrione : A short curved cell. 

 Spinllacece I Spirillum : A long' curved spiral cell. 

 I Spirochcete : A screw shaped cell. 



Some bacteria are motile, and this is usually due to the 

 presence of flagells. 



The above groups of organism contain all the known 

 pathogenic bacteria, but it is convenient here to note that 

 all pathogenic bacteria are not visible, in fact the organisms 

 of some of the most highly infectious diseases have never 

 been seen, for example, rinderpest, foot and mouth disease, 

 small-pox, sheep-pox, and pleuro-pneumonia ; nor have the 

 organisms been seen which produce such highly inoculable 

 diseases as rabies and South African horse sickness. The 

 organisms of the above diseases are invisible owing to their 

 extreme minuteness, yet we know of their existence, and 

 are sometimes able to filter them off from the fluids in 

 which they are found ; even this is not yet possible for the 

 organism of 'horse sickness,' which passes through the 

 pores of the finest filter. 



Coccacece. — The principal representatives of this group 

 are Streptococcus and Micrococcus pyogenes found in con- 

 nection with septic processes. There is a specific disease 

 of the horse, ' Strangles,' caused by the Str. equi, and a 

 disease of cattle and goats, known as Agalactia, which is 

 due to the Str. agalactia. In agalactia the organism causes 

 atrophy of the milk cells of the mammary gland, and sub- 

 sequent induration of the organ. 



Bacteriacece. — This group contains several species which 

 cause disease, viz. the bacterium of hsemorrhagic septieasmia, 

 glanders, swine fever, and swine erysipelas, and the bacillus 

 of anthrax, quarter-evil, tetanus, malignant oedema, and 

 others. 



Sp>irillacece. — In this group is found the organism of 

 a disease resembling fowl cholera, another affecting geese 

 and fowls and one affecting cattle, but it has not been 



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