REHO'.IT ON THE LAWS OF CONTAGION. 



Report on the State of our Knowledge of the Laws of Conta- 

 gion. ^«/ William Henrv, M.D., F.R.S.,&;c., late Phy- 

 sician to the Manchester Roy id Infirmary and Pever- ffards. 



The subject of the following pages may perhaps appear, on first 

 view, not to fall Avithin those boundaries, wliich have been as- 

 signed by the British Association to- the field of its labours. I 

 hasten therefore to avow, at the outset, that it is no part of my 

 object to trespass upon the province of practical medicine, or to 

 treat the topic of contagion in any other light, than in that of a 

 purely philosophical question. Under this point of view, the in- 

 quiry is open to all, whose education has embraced the principles 

 of chemical and physical science, and who possess a general ac- 

 quaintance with the laws of the animal oeconomy. Much valu- 

 able information has indeed been already contributed to the 

 history of contagion by persons of this class ; among whom the 

 late John Howard, the enlightened and devoted philanthropist, 

 is an eminent example. 



The establishment of sound conclusions on this subject is of 

 the highest importance, not only to individuals and to small 

 communities, but to the interests of whole nations. On such 

 principles alone can wise and salutary measures for obviating the 

 importation, and checking the spread, of contagious m;iladies, 

 be based ; and it is for want of them that legislators and execu- 

 tive governments have enforced regulations, some of which are 

 nugatory and absurd, and others positively mischievous. The 

 quarantine law^s of every civilized country call, indeed, loudly 

 for revisal and remodelling ; and this can only be effected by 

 mutual agreement between different nations. In their present 

 state, those laws are both inadequate and oppressive. They lay 

 great stress upon observances that are of no value, and overlook 

 others that would be really efficacious. They impose grievous 

 restraints on personal freedom ; fetter our commerce ; abridge 

 the demand for produce and manufactures ; and, by diminishing 

 employment over wide and populous districts, increase the suf- 

 ferings attendant on poverty, and give rise to inborn diseases, 

 even more formidable than those,] against which they are in- 

 tended to act as barriers. 



An inquiry into the laws of contagion, it must however be ad- 

 mitted, is beset with many pressing difficulties. Our senses, the 

 great inlets of our knowledge of the material world, give us no 

 insight into the properties of this subtile agent ; nor do we derive 



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