230 QUARANTINE AND SMALLPOX. 



be left out of account, since the danger does not consist so much 

 in numbers as in the state as to disease of individuals. In the 

 present case, a man living in Hobart and under necessity to read 1 

 the mainland might very probably sail in the usual way, trusting 

 to the supposed cleanness of that city to escape arrest, and so 

 would fall under detention on arrival ; but a man who lived in 

 Launceston, knowing that he could not escape detention nor yet, 

 perhaps, afford to suffer it, would be likely to seek some irregular 

 means of transit. He could easily escape the quarantine officers; 

 and he would be one of the very persons it is most desirable to 

 exclude. This illustration is not fanciful or rhetorical, but on 

 the contrary represents universal experience ; and the opinion is 

 warranted that the more urgent the danger from infection, and the 

 more stringent the measures taken under ancient quarantine to 

 exclude it, the greater in reality becomes the likelihood that the 

 latter will be evaded and the disease introduced ; while the more 

 quarantine is relied upon to entirely exclude infection, the more 

 are other and truer and better means of defence likely to be 

 overlooked. 



****'** 4s-*'# 



I have hitherto spoken designedly, not of epidemic disease, but 

 of contagion. To some casual local spread of contagious disease 

 two conditions alone are necessary ; viz., the presence of the specific 

 contagium, and of personal and local susceptibility. Against 

 epidemics of small-pox thus arising ( I speak now of shore 

 populations) our limited quarantine, or policy of isolation with 

 vaccination, is doubtless a sufficient protection usually; that is to say, 

 when the members of the quarantine service are themselves also 

 rendered invulnerable by vaccination and re-vaccination. But to 

 pandemic extensions of disease at all events, and probably therefore 

 to any very wide and uncontrollable spread even in a particular 

 city, a third condition is necessary. What this is, is not yet known.; 

 although it may fairly be supposed to consist in conditions which 

 prolong the life of the contagion after it has parted from the 

 animal body in which it has been propagated. But its existence 

 may be inferred from the observation that whereas small-pox is 

 endemic in many places yet it becomes formidable only from time 

 to time. Now if such accessions of virulence were merely local, 

 they might be accounted for by accumulation of susceptible persons^ 

 newly born for the most part since the last preceding outbreak, 

 when the then susceptible either got immunity after suffering, or 

 were killed off. But it is not in isolated spots that such accessions 

 are observed as a rule ; on the contrary, many widely separated 

 places begin to suffer about the same time ; and hence it must be 

 concluded that a third, not local, condition is necessary to them. 

 This being so, if we have hitherto escaped any serious epidemic 



