334 THE POPULAR SCIENCE MONTHLY. 



were formerly considered independent of the soil, because their specific 

 germs are communicable and are actually communicated by human 

 intercourse and trade, are still in some way connected with it, although 

 the nature of the connection is yet to be found out. The explanation 

 of the frequent, sharply defined local limitations of cholera and typhoid 

 has been sought first, in influences not of soil but of water and air, to 

 which the germs of disease have been impai'ted from men ; but a clear 

 and impartial examination of the local prevalence of these diseases in 

 circles of greater or lesser extent has now furnished evidence that in 

 many cases air and water can no longer be maintained to be the causes 

 of the localization, but that the sources of the epidemic must be sought 

 i.i the soil. 



In the occurrence of cholera on ships at sea, where any influence of 

 soil would seem to be absolutely out of the question, that influence 

 often makes itself apparent in a striking manner by the fact that only 

 persons who have come from certain places are attacked, while other 

 persons on the ships do not even have a diarrhoea, although they are 

 all the time with the sick, and use the same food and water and air. 

 Ships at sea may be considered as in themselves safe from cholera ; 

 usually sickness brought upon them in individual cases dies out ; and 

 it is regarded in seafaring practice as an excellent prophylactic meas- 

 ure to go to sea, taking the sick along and breaking up all communica- 

 tion of the men with the infected port or shore. Exceptional cases of 

 epidemics breaking out on ships can not be regarded as arising from 

 contagion from person to person, but always from previous communi- 

 cation of the ship or its crew or passengers with some place infected 

 with the disease. 



Not less plainly and frequently is the real influence of the soil 

 shown in inland regions and towns that enjoy immunity from cholera. 

 Permit me to bring forward as a well-known but pregnant example 

 the great manufacturing and commercial city of Lyons, in Southern 

 France, which has constantly maintained with impunity the most active 

 intercourse by sea and land with cities infected with cholera ever since 

 the disease first appeared in Europe. Often as cholera-epidemics have 

 prevailed in Paris and Marseilles, the disease has never yet gained an 

 epidemic footing in Lyons, which lies right between those two cities, 

 notwithstanding many cases have been brought into it from without. 

 Even in 1849, when the city was in revolt and was besieged and occu- 

 pied by cholera-infected regiments from Paris and Marseilles, and the 

 civil population were suffering from disorder, want, and misery of 

 every kind, the disease did not spread. 



The immunity of Lyons is now a generally recognized fact in 

 France, and the city derives a considerable profit from it ; for the 

 rich people of Paris and Marseilles, whose circumstances permit it, 

 are accustomed to flock to Lyons like sheep as soon as cholera breaks 

 out in their homes, and readily pay a good price for the patient hospi- 





