344 



DIPHTHERIA. 



medullary sheaths are involved, and may break across, so 

 that degeneration occurs in the peripheral portion of the 

 nerve fibres. Such changes occur irregularly in patches, 

 both sensory and motor fibres being affected. Fatty change 

 takes place in the associated muscle fibres. There may 

 also be a similar condition in the cardiac muscle. The 

 organic acid has a similar but weaker action. Substances 

 obtained from diphtheritic membrane have an action like 

 that of the bodies obtained from the spleen, but in higher 

 degree. Martin considers that this is due to the presence 

 in the membrane of an enzyme which has a proteolytic 

 action within the body, resulting in the formation of 

 poisonous albumoses. According to this view the actually 

 toxic bodies are not the direct product of the bacillus, but 

 are formed by the enzyme which is produced by it locally 

 in the membrane. Cartwright Wood has also found that 

 when diphtheria cultures in an albumin-containing medium 

 are filtered germ-free and exposed to 65 C. for an hour 

 (the supposed ferments being thus destroyed), there still ' 

 remain albumoses which produce febrile reaction and 

 are active in developing immunity. The existence of 

 ferments, though highly probable, cannot, however, be 

 considered to be yet completely proved. Nor is it certain 

 whether the proteids obtain'ed by precipitation from cultures 

 and from the tissues are in themselves toxic, or whether the 

 toxic bodies are carried down along with them. 



Immunity. This is described in the general chapter 

 on immunity. It is sufficient to state here that a high 

 degree of immunity, against both the bacilli and their 

 toxines, can be produced in various animals by gradually 

 increasing doses either of the bacilli or of their filtered 

 toxines (vide Chap. XIX.). 



Variations in the Virulence of the Diphtheria Bacillus. 

 In cultures on serum the diphtheria bacilli retain their 

 virulence fairly well, but they lose it much more quickly 

 on less suitable media, such as glycerine agar. Roux and 

 Yersin in their experiments had some difficulty in attenuat- 

 ing the virulence ; but they succeeded in doing so by grow- 



