SPIRILLUM CHOLERJE ASIATICS. 453 



Nevertheless we notice the very striking fact that Irregularity 

 cholera does not necessarily develop in an epidemic form {Jution of " 



in the region to which it gains access ; that all the regions 



which lie along the main channels of trade, and to which, 



in the case of cholera spreading over Europe, there is no 



douht that cholera patients and cholera dejecta frequently 



gain access, are not attacked by an epidemic ; hut that, 



on the contrary, large tracts of territory and numbers 



of towns remain completely free, while neighbouring 



provinces and cities are violently attacked. Even within 



the same town similar local differences may be found. 



There are also a number of places where trade is great, Local pmii*- 



which even during the repeated epidemics which have pc 



come into Europe have always remained immune, for 



example Lyons, Stuttgart, Hanover, &c. These facts 



give rise to the impression that in addition to the intro- 



duction of the contagium there are some other local 



conditions necessary for the epidemic spread of the 



disease in fact a local predisposition. 



In like manner there is a peculiar seasonal distribu- Seasonal 

 tion of the cholera epidemics. As the result of careful P redis i )0sition - 

 statistical calculations it has been shown that the cholera 

 epidemics which have attacked the northern part of 

 Germany always attain their highest point in the latter 

 part of summer and harvest, while during the spring 

 months from February to May the number of cases 

 is very few.* In other regions the maxima and minima 

 as regards season are different: thus in Calcutta the 

 constant minimum is from June to October, and the 

 maximum in April ; in Bombay also the cases diminish 

 in number from June to November, and rise again from 

 November to June ; in Lahore there is a marked rise 

 from July to October, which attains its height in August, 

 and an almost complete absence of cholera during the 

 rest of the year. These numbers give rise to the im- 



* Of the 167,000 fatal cases of cholera which occurred in Prussia 

 between 1848 and 1859, the following was the relation to the various 

 months : January, 1'4 per cent. ; February, March, April, and May 

 together 1 per cent. ; June, 2'6 per cent. ; July, 5 per cent. ; August, 

 20 per cent. ; September, 34 per cent. ; October, 21 per cent. ; Novem- 

 ber, 10 per cent. ; December, 5 per cent. 



