MORPHOLOGY. 299 



more regular, and it is smaller on glycerin agar-agar 

 than on other media used for its cultivation; while 

 upon Loeffler's blood-serum the other extremes of devel- 

 opment 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, irregularly staining threads, that are sometimes 

 clubbed and sometimes pointed at their extremities. 

 They are usually marked by areas that stain more in- 

 tensely than do 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 hardly be 

 recognized as of the same organism, unless its peculiar 

 behavior under these circumstances was already known. 



FIG. 58. 



./- 



a 



Bacillus diphtheria, a. Its morphology when cultivated on glycerin-agar- 

 agar. b. Its morphology as seen in cultures on Loeffler's blood-serum. 



On plain nutrient agar-agar (that is, nutrient agar- 

 agar without glycerin) ; on solidified egg-albumin ; on 

 a medium consisting of dried albumin, as found in 

 commerce, dissolved in bouillon (about 10 grammes 

 albumin to 100 c.c. of bouillon containing 1 per cent, 

 of grape-sugar) ; in bouillon without glycerin, and in 



