296 MICROBIOLOGY 



half of the serum cultures grow readily in broth slightly alka- 

 line to litmus ; the other cultures grow very feebly. The char- 

 acteristic growth in neutral bouillon is in fine granules. These 

 deposit along the sides and bottom of the tube, leaving the 

 broth nearly clear. Occasionally after twenty-four or forty- 

 eight hours the bouillon becomes more or less diffusly clouded, 

 and frequently a film forms over the surface of the broth. On 

 shaking the tube this film breaks up and slowly sinks to the 

 bottom. 



Milk. Diphtheria bacteria grow readily in milk but do 

 not change its appearance. As they begin to multiply at a 

 comparatively low temperature (20 G.) milk that has become 

 infected is a very favorable medium for the transmission of 

 the virus. 



Life conditions and properties. Bact. diphtheriae grows 

 best in the presence of oxygen. It is a strong aerobe but it 

 will multiply to a limited extent under anaerobic conditions. 

 It grows best at a temperature of about 37 C. but it is said 

 to multiply between 19 and 42 C. This organism elaborates 

 a very poisonous soluble toxin. It is this toxin which causes 

 the general symptoms in case of infection. The production of 

 toxin has been investigated very carefully by Madsen, 8 Mar- 

 tin, 9 Smith, 10 and Park and Atkinson n who have described 

 their methods for preparing it. A very efficient therapeutic 

 and immunizing serum is obtained from the horse after proper 

 immunization with the toxin. 



Resistance. Bact. diphtheriae is killed by boiling for one 

 minute, by heating to 70 C. for five minutes or 60 C. for ten 

 minutes. It resists drying in bits of the membrane removed 

 from the throat, for several months. They are destroyed in a 

 ifew minutes with a 1-1000 corrosive sublimate or a 5 per cent 

 carbolic acid solution. 



Pathogenesis. The diphtheria bacterium through its 



:I Madsen. Kraus und Levaditi. Handbuch d. Technic, etc., 1907. 



"Martin. Ann de 1'Inst. Pasteur, Vol. XII (1898) p. 26. 



"Th. Smith. Jour. Exp. Med., Vol. IV (1899) p. 373. 



"Park and Atkinson. Jour. Exp. Med., Vol. Ill (1898) p. 513. 



