218 CLINICAL BACTERIOLOGY. 



nosis, however, should be made only with great reserve 

 after the lapse of only six hours (M. Neisser). After 

 eighteen or twenty hours smear-preparations are made, and 

 these are treated by the method of double staining already 

 described (p. 207). Typical granules in typical bacilli may 

 be considered as conclusive, although Neisser himself issues 

 a warning against dependence upon double staining alone 

 until his observations have been amply confirmed by others. 

 If, in accordance with older methods, dependence is placed 

 upon simple staining of an ordinary cover-slip preparation 

 from a plate or a test-tube of Loffler's serum, the possi- 

 bility of confusion with pseudo-diphtheria-bacilli must con- 

 stantly be borne in mind. It is then, necessary to scrutinize 

 carefully the peculiarities that have been described as in- 

 dicating either diphtheria or pseudo-diphtheria. No single 

 feature should be accepted as conclusive in the diagnosis ; 

 but the conjunction of all should be required. Frequently, 

 experiments on animals must be resorted to in order to 

 determine whether the bacilli are virulent or not. If they 

 prove virulent, the organisms are probably without question 

 true diphtheria-bacilli. * 



Immunity and Specific Therapy. Diphtheria may 

 attack the same child on several occasions. It is not one 

 of those diseases that leave behind them permanent immu- 

 nity, but rather one of those that predispose to recurrence. 

 Nevertheless, it is certain that after recoveiy from diph- 

 theria some degree of immunity exists temporarily. This 

 is demonstrated by the observations of Escherich, Kle- 

 mensiewicz, and others, who showed that the blood- 

 serum of children convalescent from diphtheria exhibits 

 immunizing properties. 



Experimental animals are readily immunized to diph- 

 theria. Behring and, later, Roux conferred such immunity 

 on a large scale upon horses by preliminary treatment with 

 diphtheria-toxin whose toxicky was attenuated by addition 

 of iodin trichlorid or solution of iodin and potassium iodid. 

 By the introduction of gradually increasing amounts of 

 diphtheria-toxin the immunity of these animals was in- 

 creased to a high degree. 



* The method commonly practised in public laboratories consists in inocula- 

 tion of a tube of Loffler' s serum with a previously sterilized swab applied to the 

 suspicious membrane, cultivation in the incubator overnigh't, and microscopic 

 examination of cover-slip preparations stained with Loffler' s solution. A. A. E. 



