BACILLUS DIPHTEEBIM. 389 



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 cul- 

 tivated 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 de- 

 velopment appear : here one sees, instead of the very 

 short, spindle,- lancet,- club-shaped, always segmented 

 land regularly staining forms as seen upon glycerin-agar- 

 lagar, long, sometimes extremely slender, sometimes 

 [thicker, irregularly staining threads that are usually 

 'clubbed and frequently 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 diflFerences 

 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- 



