SPIRILLUM CHOLER-E ASIATICS. 463 



quarter of tlie town where numerous individuals come 

 in contact with the patient and with the dejecta, where 

 the methods of cleanliness are by no means sufficient, 

 where the food is prepared and eaten in the same room, 

 where there are numbers of flies which aid in the 

 transport of the germs, and where consequently it is 

 only rarely that direct contamination does not take 

 place. It is evident that in the latter case the chances 

 of a sudden and great extension of the disease are 

 present, and hence the effect is so very different from 

 that of the former case, in which at most only an 

 isolated further infection occurs. 



If now the disease has attacked several individuals Difference due 



. . , ,. , . tothesucceed- 



these unequal chances continue to act in an increasing i ng cases. 

 degree, because from every new case where the chances 

 continue favourable there is a marked multiplication of 

 the number of individuals affected, and along with this 

 an enormous increase in the number of sources of 

 infection. In the one town the primitive arrangements 

 for the removal of faeces, badly constructed wells, small 

 dwellings, poverty of the population, bad nutritive con- 

 ditions, &c., can readily so act that almost every new 

 case forms a source of infection and a means of trans- 

 port, and that susceptible individuals are constantly 

 present in the neighbourhood of the sick. In other 

 towns or at other seasons, on the contrary, a very 

 much smaller number of cases may occur, on account of 

 the presence of a drainage system, a good supply 

 of water, well-built houses, well-to-do, cleanly popula- 

 tion, or on account of the fact that the individuals in 

 contact with the sick are in great part insusceptible or 

 immune ; in this way the chances are against the further 

 spread of the disease, and favour the interruption in 

 the chain. 



Circumstances which are apparently trivial and Influence of 

 accidental, and which readily escape observation, may tSviai ntly 

 often exert such an influence on the spread of a cholera accident*, 

 epidemic that the presence of local and seasonal pre- 

 disposing conditions may be of absolutely no impor- 

 tance. Thus to mention some examples of these 



