Diphtheria, long no doubt a plague among mankind, was not carefully described until by Pierre Bretonneau in 1826; and since his time our conception of this disease has been extended by the study of later, secondary and incidental phases of it, such as neuritis, which had always formed part of the diphtheritic series, though the connexion had not been detected.
In this connexion it is interesting to note the behaviour of the diphtheritic contagion in soil.
Thus if a little diphtheritic sputum were coughed into a person's eye, or some blood containing anthrax bacilli were to touch a raw spot upon the hand, the removal of microbes in either case by washing with simple water might be regarded as a means of passive defence, whilst washing them away with an antiseptic lotion might be regarded as active defence, because the antiseptic would tend not only to remove but to destroy the microbes.