332 BACTERIOLOGY. 
applied, and exclusively applied, to that acute infectious 
disease usually associated with pseudomembranous affec- 
tion of the mucous membranes which is primarily 
caused by the bacillus diphtherie of Loffler. Other 
bacteria do, indeed, occasionally produce lesions which 
simulate in one way or another those caused by the 
diphtheria bacillus, but none of them ever produce 
lesions similar in their totality to those of a charac- 
teristic case of diphtheria. 
Morphology. When cover-glass preparations made 
from the cultures grown on blood-serum are examined 
the diphtheria bacilli are found to possess the following 
morphological characteristics: The diameter of the 
bacilli varies from 0.2 to 0.8 and the length usually 
Fie. 41, 
4. 
One of very characteristic forms of 
diphtheria bacilli from blood-serum 
cultures, showing clubbed ends and 
irregular stain. X 1100 diameters 
Stain, methylene-blue. 
Fie. 42. 
Extremely long form of diphtheria 
bacillus. This culture hasgrown on 
artificial media for four -years and 
produces strong toxin. 1100 diam- 
eters, 
from ly to 6u, but exceptionally even longer (see 
Fig. 42). They occur singly and in pairs (see Figs. 41 
to 44), and very infrequently in chains of three or four. 
At times, especially in the tissues, branching forms are 
