BACTERIUM DIPHTHERIA 457 



it is sometimes comparatively regular in shape, appearing 

 as straight or slightly curved rods with more or less pointed 

 ends. More frequently, however, spindle- and club-shapes 

 occur, and not rarely many of these rods stain irregularly; 

 in some of them very deeply stained round or oval points 

 can be detected. 



When cultures are examined microscopically it is especially 

 characteristic to find irregular, bizarre forms, such as rods 

 with one or both ends swollen, and very frequently rods 

 broken at irregular intervals into short, sharply defined 

 segments, either round, oval, or with straight sides. Some 

 forms stain uniformly, others in various irregular ways, the 

 most common being the appearance of deeply stained 

 granules in a lightly stained bacillus. 



By a series of studies upon this organism when cultivated 

 under artificial conditions we have found that its form and 

 size depend very largely upon the nature of its environment. 

 That is to say, its morphology is always more regular, and 

 it is smaller on glycerin-agar-agar than on other media used 

 for its cultivation; while upon Loffler's blood-serum the 

 other extremes of development appear: here one sees, 

 instead of the very short, spindle-, lancet-, club-shaped, 

 always segmented and regularly staining forms as seen upon 

 glycerin-agar-agar, long, sometimes extremely slender, some- 

 times thicker, irregularly staining threads that may be either 

 clubbed or pointed at their extremities. They are, as a rule, 

 marked by areas that stain more intensely than does the 

 rest of the rod, and at times they may be a little swollen 

 at the centre. These differences are so conspicuous that 

 microscopic preparations from cultures from the same source, 

 but cultivated in the one case on glycerin-agar-agar and in 

 the other upon blood-serum, when placed side by side would 



