450 BACTERIOLOGY. 
of irregular size and shape, giving a peculiar mottling 
to the organ when present in large numbers. By micro- 
scopical examination these were found to represent 
places where the liver cells had undergone necrosis, 
accompanied by emigration of leucocytes, and the cells 
about them were in a condition of fatty degeneration. 
In sections of the liver, masses of the bacilli were dis- 
covered in and about the necrotic foci. The bacilli 
were not found generally distributed through the body, 
but only in the bile, liver, and occasionally in the 
spleen. Gilbert and Lion found in addition that hemi- 
plegia and paraplegia were often produced in conse- 
quence of atrophy of the cells of the cord. These 
observations have been confirmed by Thoinot and 
Massilin, but in their experiments the nerve-lesions 
were not commonly present. 
From experiments on animals it would, therefore, 
appear that the true explanation of the pathogensis of 
the colon bacillus is undoubtedly to be found in the 
toxic effects of the chemical products of the organism 
rather than in its mechanical presence in the tissues. 
Variation in Virulence. The virulence of the colon 
bacillus varies considerably. as derived from different 
sources. An attempt has been made to establish 
certain rules for this. Thus, Lesage and Macaigne 
express the opinion that when obtained from a healthy 
body it is only slightly virulent, while that isolated 
from a diseased person is much more virulent. The 
infective power is thought to bear a definite relation 
to the severity of the disease with which the organism 
is associated; for instance, to be greatest in cultures 
taken from cholera patients and least in those obtained 
from pus. Dreyfus also confirms this view. He found 
