BACILLUS DIPHTHERIA 165 



inoculation, lymphatic glands congested, exudation into the pleurae, 

 peritoneum, and pericardium. Suprarenal capsules are enlarged and 

 show hsemorrhagic infiltration ; spleen is sometimes enlarged ; also fatty 

 degeneration of liver and kidneys. Rabbits are not so susceptible, and 

 generally recover after a small injection. When death does not follow 

 inoculation rapidly, the visceral changes are less marked, and we often get 

 nervous symptoms with paralysis progressing from behind forward. 

 Among common animals rats and mice alone are immune, but MM. 

 Borrel and Roux found that though rats were not affected by inoculation, 

 yet if they injected the toxine into the brain the animal died from 

 diphtheritic paralysis. 



Differential Diagnosis. In diphtheria we are specially liable to 

 get cases of mixed infection and pseudo-diphtheria. In the former we 

 may have streptococci, staphylococci, pneumococci, and B. coli communis. 



Pseudo-diphtheria is due to bacilli which resemble very closely in 

 their morphology the true Loffler's bacillus, but are distinguished as 

 follows : They are non-pathogenic for experimental animals, and when 

 grown in alkaline bouillon do not change the reaction of the medium. 

 The genuine bacillus changes slightly alkaline bouillon to acid, which 

 later (after some months) again becomes alkaline. 



Immunity. Fraenkel was the first to immunize guinea-pigs against 

 diphtheria by infecting them with a toxin modified by exposure to a tem- 

 perature of 70 C. ; but to Behring belongs the credit of the fundamental 

 discovery that the blood of an animal immunised for a certain infectious 

 disease may be employed for protective inoculation, and even in larger 

 quantity exercise a curative influence after infection has occurred. This 

 is one of the greatest discoveries of recent years in scientific medicine, 

 even if the practical results attained in human infectious diseases do not 

 justify all the expectations that were entertained regarding it. The 

 above discovery has been specially applied to prevent and mitigate the 

 ravages of diphtheria. A disease that can attack the same child more 

 than once, therefore, does not belong to the class of diseases producing 

 a permanent immunity after recovery. It is, however, well known that 

 after recovery from diphtheria a certain temporary immunity is conferred, 

 as the blood serum of children during convalescence has been found to 

 possess immunizing properties. 



The diphtheria toxin used for immunizing animals in the prepara- 

 tion of the antitoxin is obtained by cultivating the virulent diphtheria 

 bacillus in bouillon exposed to the air, or by making cultivations in a 

 current of moist air in 2 per cent, peptone alkaline bouillon placed in 

 flat-bottomed Fernbach flasks, and sterilized previous to inoculation. 

 In three weeks, or longer, the culture is rich enough in toxins to be 

 employed. The culture is next filtered through a Chamberland filter, 

 and the clear filtrate preserved in vessels well filled, and protected from 



