334 INFECTIVE DISEASES. 



Dried diphtheritic membrane and cultures dried on silk threads 

 retain their vitality for several months. 



A brotli-culture in forty-eight hours may be used for inoculating 

 guinea-pigs. A few drops will cause death in from three to five 

 days ; there is hypersemia and cedema at the seat of inoculation, the 

 lymphatic glands are enlarged, there is fluid in the peritoneal, 

 pleural and pericardial cavities, and the lungs are congested. The 

 bacillus is found at the seat of inoculation, but not, as a rule, in the 

 blood or internal organs. Inoculation of rabbits produces extensive 

 local oedema, enlargement of the lymphatic glands, and death in 

 from four days to three weeks. Roux and Yersin pointed out that in 

 less acute cases there was paralysis of the hind limbs. Mice and 

 rats have an immunity. Cultures lose their virulence with age, but 

 the filtrate from old cultures contains more toxic substance than 

 that from fresh cultures. The toxin has been described in a 

 previous chapter (p. 46). 



Old cultures sterilised by heating for an hour to 60° 0. or 

 70° C. will render guinea-pigs immune in two weeks. The toxic 

 substance is believed to be destroyed by this process, while according 

 to Frankel the immunity-giving substance which is also present in 

 the culture is not affected. 



According to Behring's researches, the blood of immune animals 

 contains diphtheria antitoxin, consequently the blood of an im- 

 mune animal is caj)able of neutralising the toxic properties in a 

 filtered culture, not only in the living animal but when added to the 

 culture in a test-tube. These researches led to the employment of 

 the serum of an immune animal as a therapeutic agent in the treat- 

 ment of diphtheria in man (p. 58). 



Bacteriological Diagnosis. — The diphtheritic bacilli are not only 

 found in the throat while the lesions exist, but they are found after 

 all sign of the disease has disappeared. In some cases they 

 persist for a few days, in others for three or four weeks, and 

 in rarer cases they have been found several months afterwards. 

 They have also been found in the throats of persons in health, 

 especially of those who have been in contact with cases of diph- 

 theria, such as healthy children in' infected families and healthy 

 nurses. 



The bacilli which persist in the throat after recovery may be 

 virulent up to the time of their disappearance, or they may gradu- 

 ally become attenuated, and entirely lose their pathogenic properties. 

 The value of a microscopical examination as an aid in the diagnosis 

 of diphtheria has been considerably exaggerated, and unless the 



