114 MICROBES AND TOXINS 



are to be found ; the name of pseudo-diphtheria has been 

 agreed upon for them. Are they capable of becoming toxic ? 

 Under the conditions in which we can experiment it is 

 scarcely possible to give an answer. There is a possibility, 

 and even a probability. But once the natural selection has 

 occurred, it is undoubtedly the toxic bacilli which get all the 

 chances of passing from mouth to mouth and of maintaining 

 their hereditary privileges. 



The specificity of the meningococcus has had to be defended 

 against a group of bacteria resembling it in form and cultural 

 characters — the pseudo-meningococci. The true meningococcus 

 may be distinguished from these by various biological reactions, 

 but it is certain that the principal character from our point of 

 view is the property of causing meningitis, and it is difficult to 

 say whether or not, and under what conditions, the " pseudo " 

 forms may acquire this power. 



Not only have there been distinguished three pathogenic 

 types of the dysentery bacillus (Shiga, Flexner, and Strong), 

 but a whole group of pseudo-dysentery bacilli has been 

 admitted, and side by side with the true bacillary dysentery 

 there have been decribed dysenterifcrm affections caused by 

 these " pseudo-bacilli." In reality the biological reactions 

 have proved that there is only one fundamental type of patho- 

 genic dysentery bacillus, but that there exist none the less 

 satellites of this which possess biological importance, although 

 of less importance from the point of view of medicine. 



Hygiene cannot afford to neglect the non-pathogenic 

 cholera vibrios, often very difficult to distinguish from the vibrios 

 isolated from genuine fatal cases of cholera. Since the 

 prophylaxis is based on the discovery of the microbe, and 

 since no laboratory animal exists which readily takes cholera, 

 it has been necessary to employ refined diagnostic procedures, 

 and these do not solve the scientific question of the relations 

 in nature between these different vibrios. In certain maladies 

 closely resembling typhoid fever (but almost always benign, 

 rarely fatal), bacilli have been found which only differ from the 

 typhoid bacillus in certain cultural peculiarities, differing also 



