DIPHTHERIA BACILLUS. 343 
culture of one bacillus will kill a guinea-pig, while it 
would require 1 cc. of the culture of another bacillus 
to kill. The same marked variation occurs in the 
amount of toxin produced by different bacilli in their 
growth in media outside of the body. There are also 
bacilli which produce no specific toxin whatever and 
yet appear to have all the other characteristics of viru- 
lent bacilli. Moreover, the diphtheria bacilli differ 
greatly in the tenacity with which they retain their 
virulence when grown outside the body. The bacillus 
that we have used in the laboratory of the health de- 
partment has retained its virulence unaltered for four 
years in frequently renewed bouillon cultures. Other 
bacilli have lost 50 per cent. of their virulence after 
being kept for only a few months. The passage of 
diphtheria bacilli through the bodies of susceptible 
animals does not increase their virulence to any con- 
siderable extent, this being probably due to the fact 
that the bacilli multiply but little iu the tissues. 
At the autopsy of animals dying from the poisons 
produced by the bacilli the characteristic lesions de- 
scribed by Léffler are found. At the seat of inocula- 
tion there is a grayish focus surrounded by an area of 
congestion; the subcutaneous tissues for some distance 
around are cedematous; the adjacent lymph-nodes are 
swollen; and the serous cavities, especially the pleural 
and the pericardial, frequently contain an excess of 
fluid, usually clear, but at times turbid; the lungs are 
generally congested. In the organs are found numer- 
ous smaller and larger masses of necrotic cells, which 
are permeated by leucocytes. The heart and voluntary 
muscular fibres usually show degenerative changes. 
Occasionally there is fatty degeneration of the liver and 
