THE DIPHTHERIA BACILLUS 115 



While non- virulent diphtheria-like bacilli are frequently 

 present in milk and its products, virulent Klebs-Loffler 

 bacilli have several times been isolated from milk. Klein 

 stated that cows inoculated in the shoulder with the 

 bacillus are attacked with an eruptive disease of the 

 udder, and that the diphtheria bacillus could be isolated 

 from their milk. Abbott and Hitter, repeating Klein's 

 experiments, failed to find the bacilli in the milk. Dean 

 and Todd investigated a small outbreak of diphtheria, 

 in which the Klebs-Loffler bacillus was isolated from 

 the milk and from an eruption on the udders of two 

 cows supplying it. They seem to have proved, however, 

 that the eruptive disease was not due to the diphtheria 

 bacillus, but was an eruption which had become infected 

 with the bacillus, and they suggest that both the lesions 

 on the cows and the milk had become infected from some 

 outside source, possibly the milker. Milk epidemics are 

 generally attributed to a human rather than a bovine 

 origin. Experiments show that the bacillus may survive 

 for some weeks in spring waters of little organic impurity, 

 although during this time the virulence is gradually 

 attenuated. If, however, at any time previous to its 

 ultimate disappearance the organism be transplanted 

 into a suitable culture medium, it can reacquire its full 

 initial virulence. There is, however, no well- authenticated 

 instance in which water has been proved to be the source 

 of infection. 



Faulty sanitary conditions may also assist in the spread 

 of this disease by preparing the throat for the bacillus, 

 and may in this way apparently give rise to cases which 

 would never have arisen had it not been for the existence 

 of such conditions. 



It is not unusual for an epidemic of diphtheria to be 

 preceded by a prevalence of ' sore throat,' which seems 

 to gather in intensity till cases arise of undoubtedly 

 true diphtheria. 



Pathogenesis. The incubation period varies from two 

 to seven days, but is usually from about two to four days. 

 The mortality is about 0-20 per cent, of the total death- 

 rate. 



Mucous surfaces are most prone to infection. The 

 pharynx is most generally the area attacked, but infection 

 of the larynx (membranous croup) and of the nose 



