CH. II] THE CHARACTERS OF BACTERIA 27 



showed them to a greater degree than those isolated earlier in 

 the attack or from the tonsils at the same time. After cultiva- 

 tion on blood-agar it was noticed that the strains from the 

 tonsils soon lost any distinctive peculiarities, whilst those from 

 the exudate retained them longer." He concludes that the 

 unusual character of the organism was directly due to residence 

 in the body fluids and was accentuated as the disease advanced. 



Leutscher (1911) found that pneumococci isolated from 

 the lung in acute pneumonia after the crisis were more virulent 

 than those isolated earlier in the illness. 



(/) In some cases — the so-called " carriers"— &iter all 

 symptoms of a disease have subsided, the particular organism 

 concerned resists all attempts to eradicate it and continues 

 for an indefinite period to grow and multiply at the site of 

 the original lesion. In such cases the organism may become 

 modified in the course of time. This is true more especially 

 of its virulence, but other characters may be involved. Wilson 

 (1910) mentions a strain of B. typhosus, isolated from the 

 urine of a typhoid carrier, which had acquired the power to 

 ferment lactose. 



