REPORT ON THE LAWS OP CONTAGION. 85 



casioual long fasts, excessive evacuations, and intemperate in- 

 dulgences of every sort. The depressing passions of fear, grief, 

 and anxiety are powerful auxiliaries of contagious poisons. So 

 also are religious creeds that lead to gloom or despondency, or 

 that inculcate observances requiring abstinence, or other prac- 

 tices unfavourable to health*. But of all predisposing causes, 

 poverty, with its attendant physical and moral evils, prepares 

 the greatest numbers of victims to contagious diseases, and most 

 widely spreads their destructive ravages. 



It may be received, then, as a general conclusion, to be applied 

 to all our reasonings in special instances, that no one malady 

 IS invariably and under all circumstances conta- 

 gious ; in other words, that a contagious poison is such 

 only in a limited and qualified sense. 



XXXIII. Beside the general causes promoting or counteract- 

 ing the ef&ciency of contagious poisons, there are others of li- 

 mited operation, affecting chiefly certain individuals or classes of 

 men. 1. From peculiarities of structure or constitution not at 

 all understood, some persons enjoy an exemption from particu- 

 lar contagious diseases. Before the preventive powers of cow- 

 pox were known, it was not unusual to meet with instances in 

 which persons had entirely escaped the contagion of smallpox, 

 though repeatedly exposed to it, and even after being inoculated 

 with its virus. By diligent and careful inquiry. Dr. Haygarth 

 was led to estimate the proportion of persons who had reached 

 the middle age without taking the smallpox, at one in twenty- 

 three ; and if it be admitted that in some instances the excep- 

 tions were only apparent, there will still remain a sufl&cient num- 

 ber to establish the general observation. During the prevalence 

 of typhus fever a similar proportion of persons has been esti- 

 mated to escapef. 2. Whole tribes and classes of men share in 

 liability to be infected by some diseases, and in the power of 

 resisting others. In hot climates the negro resists certain mor- 

 bid poisons which the European is unable to withstand. The 

 Bedouin Arabs, we are told, wear with impunity the cast-off 

 clothes of persons who have died of plague, without even at- 

 tempting to purify themj ; but the soldiers of the French army 

 in Egypt fell victims to the same practice, which all the autho- 

 rity of the General-in-chief could not suppress§. 3. Difi^erent 

 periods of life modify the predisposition to infectious diseases. 

 Old persons enjoy an exemption from some contagions, but not 



* Instance in Howard On Lazarettos, p. 25, and in the Doctrine of Fatalism. 

 t Letter ioPercival, pp. 32, 33. J Blane's Medical Logic, p. 176, note. 



§ Larry, Memoires, p. 333. 



