MYCOBACTERIACE^: THE BACILLUS OP DIPHTHERIA 309 



The Schick Reaction. — In an outbreak of diphtheria it is often 

 helpful to ascertain which of the exposed persons may be sus- 

 ceptible to the disease. For this purpose the diphtheria toxin 

 is diluted with salt solution so that 0.2 c-c. of the solution contains 

 Ho M. L. D. (minimum lethal dose for a 250-gram guinea pig). 

 This amount is injected through a fine needle into the person's 

 skin so that a white swelling is produced. A control injection may 

 be made in another place with the same toxin previously rendered 

 inert by heating at 75° C. for 5 minutes. A positive reaction is 

 manifested by a red, swollen and infiltrated area 7 to 20 mm. in 

 diameter after 48 to 96 hours at the test area without a similar 

 reaction at the control site and this result indicates that the , 

 individual is susceptible to diphtheria. 



Bacillus (Corynebacterium) Xerosis. — This organism occurs 

 on the normal mucous membranes, particularly the conjunctiva. 

 It resembles B. diphtheria very closely, simulating the granular 

 morphological type. Its cultures are not poisonous. 



Bacillus Hofmaimi.^ — This organism is also called the pseudo- 

 diphtheria bacillus. It occurs frequently in cultures from the 

 nose and pharynx, and resembles the short solid-staining morpho- 

 logical types of B. diphtheria. It does not produce toxin, nor 

 does it produce acid from dextrose. 



The Morax-Axenfeld Bacillus. — This is a small non-motile 

 diplo-bacillus, the individuals measuring abdut i X 2ju, which 

 occurs in one form of epidemic conjimctivitis. It can be cultured 

 on LofSer's serum, which it liquefies, and the disease has been 

 produced in man by inoculation with pure cultures. 



The Koch-Weeks Bacillus.— This a non-motile rod 0.25m 

 wide and i to 2/1 long, which occurs in epidemic conjunctivitis. 

 It is cultivated with difficulty and abundant moisture is essential 

 to success. Inoculation with pure cultures causes conjunctivitis. 



Bacillus (Hemophilus) Pertussis (Bordet-Gengou Bacillus).— 

 Bordet and Gengou in 1906 described a minute, non-mo tjle 

 bacillus 0.3, X I •5m which occurs in the sputum and on the mucous 

 membrane of the trachea and bronchi in whooping cough. They 



