312 BACTERIA. 



diphtheria poison. On the other hand, the diphtheritic virus 

 applied to an abraded mucous membrane even after fourteen 

 days was capable of producing typical local symptoms. These 

 points, if confirmed, indicate that the immunity against 

 diphtheria may not be so easily acquired as in some other 

 diseases, or, if acquired, it must be through the application 

 of methods different from those hitherto described. 



Another feature that is brought into special prominence 

 by the recent researches on diphtheria is, that the attenuated 

 diphtheria bacillus requires the fulfilment of certain con- 

 ditions before it can again acquire the virulent form, one of 

 these being that it shall be allowed to grow on the surface of 

 the fauces, or outside the body altogether, in the presence 

 of certain organisms, such as the streptococci found in 

 erysipelas, or those streptococci that occur in the throat 

 affections of scarlet fever, measles, and similar diseases. It 

 is quite possible that other organisms have the same effect, 

 and that the attenuated diphtheria bacillus growing outside 

 the body may become so virulent that it is capable of pro- 

 ducing a very grave form of diphtheria, but from what 

 occurs in outbreaks of diphtheria — in which the first cases, as 

 a rule, are mild, successive cases becoming gradually tnore 

 and more severe until an extremely fatal form of diphtheria 

 attacks susceptible individuals — it would appear that the 

 growth on mucous surfaces of this bacillus, along with these 

 streptococci, is specially favourable to the development of the 

 virulent form of the organism. 



These experiments exemplify in a most remarkable manner the use that 

 bacteriological investigations have been to medicine, and Roux and Yersin 

 sum up the practical outcome of their researches as follows : — " The best 

 method of arresting the spread of diphtheria is to recognize the disease 

 as early as possible ; consequently a precise diagnosis should be made by 

 microscopic examination of the false membranes, and this should be con- 

 firmed by cultivations on blood serum." As the former takes only a few 

 minutes, and as the latter gives results in twenty-four hours, both these 

 methods are available in private practice or where patients can be sent to 

 an observation ward. 



" Active diphtheritic virus can remain in the mouth for a long time after 

 the malady is cured. Consequently diphtheritic patients should only be 

 allowed to resume their ordinary mode of life when they are no longer 

 bearers of the bacillus. 



" Diphtheritic virus retains its virulence for a long time when kept in a 

 dried state. It is therefore necessary to disinfect in a steam sterilizing 

 apparatus the linen and all articles that have been in contact with diphtheri- 

 tic patients. 



