MORPHOLOGY. 329 



diphtheria bacilli; and in approximately 6000 blood- 

 serum cultures from cases of diphtheria that have been 

 examined during the past two years by three competent 

 bacteriologists at the laboratory of the Board of Health 

 of Philadelphia, the branching forms of this organism 

 were not observed in a single instance. It is fair to 

 assume, therefore, that this peculiar morphological 

 variation of bacillus diphtherice is comparatively rare. 



FIG. 65. 



f 



S Of 



f 



Bacillus diphtheriae. a. Its morphology when cultivated on glycerin-agar- 

 agar. 5. 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 com- 

 merce, 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 bouillon to 

 which a bit of hard-boiled egg has been added, the mor- 

 phology of the organism is about intermediate, in both 

 size and outline, between the forms seen upon glycerin- 

 agar-agar and upon Loeffler's blood-serum. There 

 will appear about an equal number of short segmented 

 and longer irregularly staining forms, but in general 

 the longest are rarely as long as the long forms seen on 

 blood-serum, and throughout they are not so conspicu- 

 ous for the irregularity of their staining. 



