364 DIPHTHERIA 



obtained from the spleen, but in higher degree. Martin con- 

 siders 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. In the present state of knowledge we are not in a 

 position to give an interpretation of such experiments, and we 

 cannot even say whether the proteids obtained by precipitation 

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

 whether the true 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 toxins, can be 

 produced in various animals by gradually increasing doses either 

 of the bacilli or of their filtered toxins (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 glycerin agar. Roux and Yersin found that, 

 when the bacilli were grown at an abnormally high temperature, 

 namely, 39'5 C., and in a current of air, the virulence diminished 

 so much that they became practically innocuous. When the 

 virulence was much diminished, these observers found that it 

 could be restored if the bacilli were inoculated into animals along 

 with streptococci, inoculation of the bacilli alone not being 

 successful for this purpose. If, however, the virulence had fallen 

 very low, even the presence of the streptococci was insufficient 

 to restore it. As a rule, the cultures most virulent to guinea- 

 pigs are obtained from the gravest cases of diphtheria, though to 

 this rule there are frequent exceptions. Perhaps the majority of 

 observers have found that the bacilli of the larger form are 

 usually more virulent than those of the shorter form ; but this is 

 not invariably the case, as sometimes short forms are obtained 

 which possess an extremely virulent character. It has been 

 abundantly established that after the cure of the disease, the 

 bacilli may persist in the mouth for weeks, though they often 

 quickly disappear. Roux and Yersin found, by making cultures 



