212 MICEOBES, FERMENTS, AND MOULDS. 



It may be useful to retrace here the curious history 

 of vaccine, since it is directly interesting to us all 



. . . . . ;. . _ . 



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Fig. 91. .Section of skin covering a small-pox pustule, a, horny layer of the 

 epidermis ; d, adenoid tissue ; m, m, micrococci stained with methyl violet ( X 

 850 diam.). 



Before vaccine was discovered, inoculation with 

 small -pox was practised as a preventive measure. 



