156 PATHOGENIC ORGANISMS 



The fermentation and hsemolytic reactions of the best- 

 known types of streptococci, excepting Str. lacticus, are shown 

 in Table LIX. 



B. DIPHTHERIA 



Milk has, on several occasions, been proved to be a vehicle 

 for B. diphtheria and responsible for epidemics of diphtheria, 

 and it is consequently sometimes necessary for the bacteriolo- 

 gist to examine milk for this organism. 



There is no satisfactory evidence that diphtheria organisms 

 may invade the udder and so cause infection of the milk, but 

 it is more than probable that milk has become accidentally in- 

 fected from human sources and that the organisms have rapidly 

 increased in number. Milk is not an ideal medium for the 

 development of B. diphtheria but fairly rapid multiplication 

 does occur until checked by the metabolic products of the acid 

 producers. 



The number of authentic cases in which B. diptherise has 

 been isolated from milk are comparatively few. Bowhill, 10 

 in 1899, isolated diphtheria organisms from milk and prepared 

 broth cultures that were fatal to guinea pigs in forty-eight hours. 

 The same year Eyre n isolated a virulent diphtheritic bacillus 

 from milk and, later, cases were reported by Klein, 12 Dean and 

 Todd 13 and Marshall. 14 



For the isolation of the organisms, Bowhill directly inocu- 

 lated Loeffler's blood serum with the sample. Eyre, and Dean 

 and Todd concentrated the organisms by centrifugalising and 

 afterwards streaked the sediment over a number of tubes of 

 blood serum. The cream layer was treated in a similar man- 

 ner. Characteristic colonies were fished and those mor- 

 phologically resembling B. diphtheria isolated as pure cultures 

 and tested for pathogenicity. Klein and Marshall used the 

 animal inoculation method. The former inoculated two guinea 

 pigs with one sample, one subcutaneously in the groin, and the 

 other intraperitoneally. The latter pig remained well, but the 

 former, on the fifth day, showed swollen inguinal glands sur- 



