THE DIPHTHERIA BACILLUS 435 
I)i])htheria is a generalized toxemia with a local infection. The 
baciUi cause coagulation necrosis of the superficial cells, and an inflam- 
matory membrane consisting of a serofibrinous exudate in which 
fibrin and leukocytes are prominent, together with epithelial cells, 
pyogenic cocci, and diphtheria bacilli in the deeper layers adjacent 
to the denuded epithelium. At times the membrane strips off without 
serious injury to the underlying epithelium, but in severe cases the 
membrane tears away, leaving a bleeding, raw surface. 
There are four principal types of diphtheria: the faucial, laryngeal, 
nasal, and tracheal. The incubation period is from two days to a week. 
An important sequelum is the postdiphtheritic paralysis, which is sup- 
posed to be caused by the toxone component of the diphtheria toxin. 
This is anatomically a toxic neuritis and it occurs in from 10 to 20 
per cent of all cases of diphtheria from two to four weeks after the 
attack. There is no apparent relation between the severity of the 
attack and the paralysis. The pharynx is most commonly affected, 
next in order the eyes, leading to strabismus (ptosis). In a smaller 
number of cases the heart is affected. When the heart is affected the 
patients not infrequently drop dead during heavy exertion as the result 
of cardiac failure. The early use of antitoxin usually prevents or 
greatly modifies the development of postdiphtheritic paralysis. 
Bacteriological Diagnosis. —The principle involved in the bacterio- 
logical diagnosis of diphtheria (and the diagnosis can only be definitely 
established by bacteriological examination) is to make cultures trom 
the suspected lesions on Loffler's alkaline blood serum, to incubate 
the cultures from twelve to eighteen hours at 37° C, to stain the result- 
ing growths with Loffler's methylene blue or the Albert stain, anfl to 
diagnose the organisms by their characteristic morphology. 
The Technique of Inoculation.— Rub a sterile swab on the under surface 
of the diphtheritic membrane, avoiding extraneous organisms, and 
also avoid touching the tongue or other parts of the mouth. Do not 
overlook the nose. Smear this infected swab gently over the surface of 
the serinn, rotating the swab while floing so to bring every part of it in 
contact with the medium. It shoidd be remembered that the crypts of 
the tonsils and the naso-pharynx are more frequently the site of diph- 
theria bacilli in carriers than the throat ; a firm application of the swab 
is necessary to insure an infection of its surface with the diphtheria 
bacilli in such cases. The infected serum is incubated at 37° C. for 
twelve to eighteen hours. It is customary in many laboratories to 
make a preliminary examination of the growth on the serimi after five 
hours' incubation, and also to make a smear from the swab itself after 
the serum has been inoculated with it. By these preliminary examina- 
tions from 30 to 60 per cent of diagnoses may be correctly anticipated. 
During the first eighteen hours of incubation diphtheria bacilli out- 
grow practically all other organisms. After this time the other organ- 
isms tend to outgrow the diphtheria bacillus. 
