238 HOSACK ON THE LAWS OF CONTAGION. 



as far as such atmosphere extends, and the circumstances favourable to 

 such fermentative or assimilating process continue, so far those diseases 

 become epidemic, but no further. 



The same idea of an assimilating process appears to be expressed by 

 Lucretius, when, speaking of the contagiousness of the plague, he 

 observes, 



" Proinde, ubi se coelum, quod nobis forte venenum,. 



Conmovet, atque aer inimicus serpere coepit ; 



Ut nebula ac nubes paullatim repit, et omne, 



Qua graditur, conturbat, el immutare coactat. 



Fit quoque, ut in nostrum quom venit denique coelum 



Conrumpat, reddatque sui simile, atque alienum." 



Lucretius, de Nat. Rerum, lib. VI. 



Or, as it has been rendered by that learned burgeon and accom- 

 plished scholar, John Mason Good, Esq. 



" But when the heaven, of poisonous power to usj 

 First moves remote, its hostile effluence creeps 

 Slow, like a mist or vapour ; all around 

 Transforming as it passes, till, at length, 

 Reach'd our own region, it the total scene 

 Taints, and assimilates, and loads with death." 



If the view which has been taken of this subject be correct, a still 

 more important truth is the result; that, while by a rigid and well-exe- 

 cuted system of quarantine laws we have it in our power to guard 

 against the introduction of the spark that kindles the flame, we are 

 also enabled, by means of domestic cleanliness and ventilation, to ex- 

 tinguish it when introduced. For this purpose our magistrates and 

 guardians of the public health cannot be too attentive in their police 

 fegulations to have all noxious materials removed from our streets and 



