290 BACTERIA AND DISEASE 



resistance, but when in a dry condition it can survive for long 

 periods. 



The bacillus is secured for diagnostic purposes by one of two 

 methods : (a) Either a piece of the membrane is detached, and after 

 washing carefully examined by culture as well as the microscope ; 

 or (b) a " swab " is made from the infected throat, cultured on serum, 

 and incubated at 37 C. for eighteen hours, and then microscopically 

 examined. Both methods and there is no further choice present 

 some difficulties owing to the large number of bacteria found in the 

 throat. Hence a negative result must be accepted with reserve. 

 Indeed the rule to follow is three examinations before deciding that 

 a throat is free from infectivity, and it should be remembered that 

 about 20 per cent, of all cases of diphtheria offer no bacteriological 

 evidence of infection.* It therefore comes back to the point of 

 broad judgment and common-sense. The clinical condition is the 

 main fact for guidance, and the bacteriological must not usurp 



itt 



Locally, the bacillus produces inflammatory change with fibrinous 

 exudation and some cellular necrosis. In the membrane a ferment 

 is probably produced which, unlike the localised bacilli, passes 

 throughout the body, and. by digestion of the proteids, produces 

 albumoses and an organic acid which have the toxic influence. The 

 toxins act on the blood-vessels, the nerves, the muscle fibres of the 

 heart (hyaline degeneration and even fatty changes), and many of the 

 more highly specialised cells of the body. Thus we get degenerative 

 changes in the kidney (cloudy swelling, and, clinically, albuminuria) 

 in cells of the central nervous system, in the peripheral nerves 

 (post -diphtheritic paralysis), and elsewhere, these pathological condi- 

 tions setting up, in addition to the membrane, the symptoms of the 

 disease. The bacillus is pathogenic for the horse, ox, rabbit, guinea- 

 pig, cat, and some birds. Cases are on record of supposed infection 

 of children by cats suffering from the disease. Eoux and Yersin 

 in 1888-89 showed that the diphtheria bacillus is capable of pro- 

 ducing the various phenomena associated with the disease, including 

 the formation of false membrane and diphtheritic paralysis. They 

 also succeeded in separating and studying the toxin, which they 

 found to be capable of producing all the effects produced by the 

 bacillus. In 1890 appeared the great work by Behring, to which 

 reference will be made subsequently ; and the observations in regard 

 to diphtheria made in that work were extended and strengthened in 

 a paper by Behring and Wernicke in 1892. At the Medical Congress 

 at Buda-Pesth in 1894, Roux read a paper on the treatment of diph- 

 theria by diphtheria antitoxin, which first proved to the medical 



* Jour. ofHyyiene, 1903, p. 217. 



t See also Brit. Med. Jour., 1900, ii., p. 907 (Andrewes). 



