86 MEDICAL BACTERIOLOGY 



After a diphtheria patient has entirely recovered from the disease he may 

 still harbor the bacillus for days, weeks or months. 



In the vast majority of cases the diphtheria bacillus lodges upon the mucous 

 membranes of the nose or throat, mostly on the tonsils, not infrequently on the 

 larynx. If active it causes a false membrane to form on these surfaces. This 

 membrane is at first dirty white or grayish, as it ages it becomes darker. When 

 stripped off, the exposed mucous membrane is inflamed and may show bleeding 

 points. Although the diphtheria bacilli are confined to the mucous and false 

 membrane and do not penetrate underlying structures nor enter the blood- or 

 lymph-streams, diphtheria is a disease with profound systemic toxemia. The 

 toxin liberated by the bacilli upon the mucous membrane is absorbed and dis- 

 seminated through the blood-stream. 



Rare, isolated cases have been reported in which the diphtheria bacillus has 

 attacked the ear, the intestine and the genito-urinary canal. 



Occasionally the pus from chronic urethritis of long duration, when ex- 

 amined microscopically, shows, among other organisms, bacilli morphologically 

 indistinguishable from diphtheria bacilli. Most of these are not diphtheria 

 bacilli, some produce toxin in broth and apparently are true diphtheria bacilli. 

 Whether diphtheria bacilli or not, they do not cause false membrane forma- 

 tion and do not cause toxemia; they are active in maintaining the urethritis, 

 as evidenced by rapid recovery after they cease to exist in the urethra. 



The diphtheria bacillus, injected subcutaneously, is virulent for horses, 

 cattle, dogs, cats, rats, guinea-pigs, chickens and many other birds and animals. 

 Cats are said to be subject to diphtheria. 



Marked variations in virulence and toxin production are exhibited by dif- 

 ferent strains of diphtheria bacilli. The virulence and toxin production of any 

 diphtheria bacillus depends, to a large extent, upon little understood condi- 

 tions of environment. A diphtheria bacillus may exist in one person's throat 

 for days or weeks without injury to the host and immediately cause disease 

 when transferred to another. A diphtheria bacillus cultivated in bouillon may 

 produce so little toxin that 10 cc. or more of the filtrate is required to kill a 

 guinea-pig, but when the same organism is transplanted into a different bouillon, 

 one more nearly adapted to its requirements, so much toxin will be produced 

 that o.oi cc. or less of the filtrate will kill a guinea-pig. 



Some strains of diphtheria bacilli are more constant in their degree of viru- 

 lence and toxin production than others and less susceptible to changes in 

 environment. 



Diagnosis. When the diphtheria bacillus is present in the nose, throat or 

 tonsils, a sterile cotton swab passed over the infected surface and then smeared 

 on a glass slide may deposit bacteria on the slide that will be visible when 

 stained and examined microscopically, or it may not. If after passing a sterile 

 cotton swab over the infected area, the swab is then drawn across the surface 

 of Loeffler's blood serum and the medium incubated 16 to 24 hours at 37C., 

 any bacteria introduced will multiply and form colonies from which slides may 

 be prepared and stained for microscopic examination and the organism ex- 



