288 



PATHOGENIC BACTERIA. 



from the throat does not necessarily prove the patient to 

 be diseased. Virulent bacilli can often be discovered in 

 the throats of healthy persons who have knowingly or 

 unknowingly come in contact with the disease. The 

 bacteriologic examination is only an adjunct to the 

 , clinical diagnosis, and must never be taken as positive 

 in itself. 



The bacillus grows similarly upon blood-serum and 

 Loffler's mixture. Upon glycerin agar-agar and agar-agar 

 the colonies are much larger, more translucent, always 



FIG. 78. Diphtheria bacilli (from photographs taken by Prof. E. K. Dun- 

 ham, Carnegie Laboratory, New York) : a, pseudo-bacillus ; b, true bacillus ; 

 f, pseudo-bacillus. 



without the yellowish-white or china-white color of the 

 blood-serum cultures, and generally are distinctly divided 

 into a small elevated centre and a flatter surrounding zone 

 with indented edges, sometimes with a distinctly radiated 



