PATHOGENIC BACTERIA 



125 



of bacilli. In twenty-four hours small round colonies are found 

 which seem to arrange themselves concentrically. The growth 

 becomes more abundant, and the individual colonies larger and 

 yellowish. On blood-coagidum the growth 

 is usually gray and the margins of the 

 culture crenated. Often a diagnosis can 

 be made in four hours if the serum-tubes 

 are kept in a brood-oven. 



Serum-agar. Joos finds senim-agar 

 better than Loffler's serum: 300 c.c. 

 blood-serum mixed with 50 c.c. normal 

 soda solution and 150 c.c. water, heated 

 in water-bath for two to three hours at 

 60 to 70 C., then raised to 100 C., or 

 in steam-chest one-half hour. Then 500 

 c.c. peptone bouillon (slightly alkaline) 

 and 20 gm. agar. When the agar is 

 dissolved by heat, avoiding prolonged 

 boiling, the mixture is filtered and steril- 

 ized one-quarter hour at 100 to 110 C. 

 in autoclave; then poured into Petri 

 dishes. Streptococci do not grow on 

 this medium, whereas diphtheria bacilli 

 will grow in from six to twelve hours. 



Bouillon. In bouillon an abundant 

 growth takes place, and this medium is 

 used to obtain the toxins. 



Staining. Is positive by Gram's 

 method. Stained best with Loffler's-alka- 

 line methylene-blue. Neisser's double 

 stain (see p. 34) shows granules, blue black, and body, 

 brown. 



Pathogenesis. By inoculation, animals, which naturally are 

 not subject to diphtheria, have had diphtheritic processes 

 develop at the site of infection; hemorrhagic edema then 

 follows, and death. 



No agglutinins are developed in the serum. 



Fig. 63. Bacillus 

 diphtherias; agar-agar 

 culture (photograph by 

 Dr. Henry Koplik). 



