THE BACILLI'S AM) Till-: HM'TI'.illOLOGY OF DIPHTHERIA 189 



but also without it. It does not form spores. It begins to develop, but 

 grows slowly at a temperature of 20 C., or even less. It attains 

 its maximum development at 37 C. In old cultures in fluid media, 

 Williams has observed fusion of one bacillus with another. The fused 

 forms live the longest. 



Ibxixtance to Heat, Drying, and Chemicals. Its thermal death point 

 with ten minutes' exposure is about 60 C. Boiling kills in one minute. 



FIG. 78 



Fro. 79 



FIG. 78. Diphtheria bacilli from agar culture. X 1000 diameters. 



FIG. 79. B. diphtherias. No. 31. Forty-eight hours' agar culture. Thick, medium-clubbed rods and 

 moderate number of segments. One year on artificial culture media. X 1410 diameters. 



FIG. <ij 



FIG. 81 





FIG. 80. B. diphtheria, No. 57. Forty-eight hours' agar culture. Many segments; long, medium- 

 clubbed ends. One year on artificial media. X 1410 diameters. 



FIG. 81. B. diphtheria, S. Twenty-four hours' agar culture. Coccus forms. Segmented granular 

 forms on Loeffler's serum. Only variety found ; cases of diphtheria at Children's Home. X 1410 

 diameters. 



It is more easily destroyed by disinfectants than many other bacteria. 

 In the dry state and exposed to diffuse light diphtheria bacilli 

 usually die in a few days or may live for weeks or months; when 

 in the dark, or protected by a film of mucus or albumin, they may 

 live for even longer periods. Thus we found scrapings from a dry 

 bit of membrane to contain vigorous and virulent living bacilli for a 

 period of four months after removal from the throat, and if the mem- 

 brane had not been at that time completely used, living bacilli could 



