212 



MICROBES, FERMENTS, AND MOULDS. 



It may be useful to retrace here the curious history 

 of vaccine, since it is directly interesting to us all 





'A 



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

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

 850 diam.)- 



Before vaccine was discovered, inoculation with 

 small -pox was practised as a preventive measure. 



