386 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



spores makes it relatively nonresistant to drying at a high 

 temperature. Gelatin is not liquefied. It is readily de- 

 stroyed at the temperature of pasteurization. 



Pathogenesis. The disease diphtheria is one of the best 

 examples of a true toxemia, that is, a disease in which a 

 microorganism produces a powerful poison without itself 

 invading the tissues to any great degree. It localizes usually 

 in the throat, less commonly in the nose and still less fre- 

 quently on other mucous surfaces and in wounds. Diphtheria 

 as it attacks the throat produces a poison which causes the 

 death of the epithelial cells of the mucous membrane. These 

 are thrown off, leaving a raw surface, plasma is exuded, 

 coagulation of the fibrinogen takes place and there is 

 gradually built up a relatively thick membrane. In most 

 cases the severe reaction in diphtheria is due to the absorp- 

 tion of the toxin. In some cases asphyxiation due to devel- 

 opment of the false membrane may occur. In this membrane 

 conditions are favorable for the growth of the microorgan- 

 ism and unless the body produces antitoxin rapidly or anti- 

 toxin is introduced artificially, the case will probably prove 

 fatal. 



A discussion has already been given of the method of 

 manufacture of the diphtheria toxin and the antitoxin 

 under the general heading of " Immunity. " It is well 

 known that persons that have had diphtheria once do not 

 frequently contract the disease a . second time ; in other 

 words, such individuals have an acquired immunity. An 

 immunity conferred by the injection of the diphtheria anti- 

 toxin does not last for more than a few months at the most. 



The disease diphtheria is usually diagnosed by means of 

 cultures taken from the throat of the patient. Usually the 

 medium employed is Loffler's blood serum. Mounts made 

 from such slants after incubation for 8 to 18 hours, 

 stained with methylene blue show the characteristic meta- 

 chromatic granules. Occasionally it is possible to grow 



