There are no words in regard to which there is more misconception, or more nonsense talked and written, than the two words “contagion” and “infection;” and as the word “infectious” has been used in these Notes, it is necessary to say what it does mean, and what it does not mean. The word “contagion” appears to have been first used by certain classical writers to signify the spread of scab among sheep; and it would have been well for humanity if the word had been restricted to this very primitive bucolic signification. It was not till centuries after Virgil’s death that the common sense of men had descended so low as to introduce it into the Medical vocabulary. This took place at a period when, from the neglect of sanitary arrangements, pestilence attacked whole masses of people, and when no one appears to have considered that nature had any laws for her guidance whatever. It was not until human intelligence had descended to this depth that men seem to have bethought themselves of Virgil’s term as affording them an adequate explanation for pestilence, and sufficient reason for not exerting themselves to prevent its recurrence. So it has continued ever since. The little word used in all innocence by the poet for poetic purposes has become the ground-work of every manner of false observation, false reasoning, neglect of sanitary laws, lazarettos, quarantine, and continually-threatened interruption to the commercial intercourse of mankind. No single word has ever done so much harm to the human race, or given such a proof of what a mighty thing a word is! One would have thought that, after the sanitary experience of the last fifteen years, the word “contagion” would have disappeared from our language; but, even in the last document issued by the expiring Board of Health, written by their Medical Officer, Mr. Simon, and based on erroneous statistical evidence (Papers relating to the Sanitary state of the People of England, 1858), it is stated that “a further--practically speaking, unavoidable--cause of premature death in every civilized country is the risk of its _current contagions_.” [The italics are not mine.] And this refers to small pox, hooping cough, measels, and scarlatina, the mortality from which we are to presume, is “unavoidable.” If this be Board of Health doctrine, it is certainly not sanitary doctrine. It would have astonished the Health of Towns Commission, and the first Board of Health.