1869.] The Future Water-supphj of London. 235 



they were actually drunk withiu six days afterwards, that is, before 

 July 4th. Moreover, the period of incubation of the j^oison in the 

 body is believed to be short. Dr. Farr says on this subject, '' There 

 is reason to believe that the period of incubation is as brief as the 

 term of attack in fatal cases of cholera ; the cholrine often acts as 

 suddenly as any of the poisons."* And again, in another place, 

 " It may now be laid down as an established law, that water into 

 which cholera dejections find their way produces cases of cholera 

 aU over the district in which it is distributed for a certain period 

 of time ; and that if the distribution is in any way cut short, the 

 deaths from cholera begin to decline within about three days of 

 the date at which the distribution is stopped." f 



Mr. Eadchffe, indeed, instances the outbreak at Theydon Bois, in 

 order to show that the period of incubation may be somewhat longer 

 than is here suggested, for in that instance several persons were 

 attacked on the sixth day after the disuse of the water. If, however, 

 we assume the utmost in every respect, and allow six days for the 

 period diu'ing which the chohine retained its activity in the water, 

 seven days for the period of incubation, and three for the duration of 

 the attack, J we are still compelled to admit that the Priory Street 

 cases could only have led to those deaths which took place within 

 sixteen days after the 27th of June, that is, at the outside, before 

 the 14th of July. The above-quoted table shows us that only forty- 

 four deaths occurred in this period, and it is difficult to imagine how 

 the special contamination of the Old Ford reservoir can be made 

 accountable for more than this number. If the view of the case be 

 correct, the cause, or rather perhaps the causes, of this terrible 

 mortality which followed are still to seek. Yery probably the bad 

 sanitary condition of the district aggravated the epidemic, and the 

 mere estabhshment of the disease in a place is almost sure to lead to 

 its increase by personal contact, the influence of impregnated soil, 

 sewer gases, &c. But none of these, or even all of these combined, 

 apj)ear to me to account for the singularly well-marked and ail-but 

 universal prevalence of the disease in the districts supplied with the 

 Old Ford water ; and, in spite of some difficulties and apjDarent 

 contradictions which beset the question, I find myself constantly 

 led back to the belief that the Old Ford water must have contained 

 choh'ine. We can never know the exact truth of the matter, and 

 must be contented to accept probabihties as our guide ; and it 

 appears to me much more ]:)robable that the Old Ford water should, 

 either by infiltration from the Lea, or in some other manner, have 

 become impregnated with cholera poison, than that the remarkable 



* ' Cholera Eeport,' xsxiii. t Ibid., xxxix. 



X About four-iilths of the deaths from cholera in England in 186G, excluding 

 cases in which no return was made on the subject, took place within three days of 

 the first attack, vide ' Cholera Report,' Table 12. 



