viii.] THE INFECTIVENESS OF CHOLERA. 155 



number of cholera cases becomes less, 1 is manifestly illogical. 

 That Koch should have used an argument of this nature to 

 build up his theory is only intelligible if we remember how 

 little convinced some of the medical public appeared to be 

 of Koch's theory and that it required, as it were, a much 

 stronger argument to support it. This discovery of the 

 comma-bacillus in the water of that tank was considered 

 such an argument, as is clear from the manner in which at 

 the time the daily and some of the medical papers wrote 

 about it. 



That the cholera virus, whatever this is, can find entrance 

 into a person by being conveyed there by water is in perfect 

 harmony with the known facts, and that pure drinking water not 

 contaminated with any extraneous material is of the greatest 

 importance finds many a good illustration in the Reports of 

 the Privy Council Office, in the Broad Street Pump cases in 

 London, in Dr. Macnamara's work on Cholera, and in the 

 various Indian Sanitary Reports. 



Another curious illustration how even a very experienced 

 observer like Koch sometimes becomes unable correctly to 

 interpret plain facts, is furnished in the same reports sent to 

 the German Government. Koch stated that at Fort William, 

 in Calcutta, cholera abated as soon as a good water-supply to 

 the fort was introduced, and takes this of course as proof 

 that, previous to the introduction of the good water-supply, 

 many cholera cases were due to contaminated water. Now, 

 had he taken the precaution as he might easily have done, 



1 This last statement of Koch's requires a certain amount of correc- 

 tion. The tank of \\hich Koch speaks was visited by him on the I3th 

 February, and again on the 2Oth February. During the week the 

 comma-bacilli had greatly diminished, but in the records of the police 

 office I find that the epidemic in the bustees surrounding this tank broke 

 out on the 2ist of January, and lasted till the 27th of April. It lasted, 

 therefore, fully two months more after this conspicuous diminution of 

 the comma-bacilli. 



