CAUSE OF THE REAPPEARANCE OP CHOLERA. 95 



of the city of Manila offers one of the few conditions in which the latter 

 is assured during every day in the year. It is scarcely conceivable that 

 a pathologic cholera vibrio is propagated in the city water supply because 

 a much larger number of cases would surely occur. 



HYPOTHESIS. 



With the conditions then as set forth in the foregoing pages, the 

 following hypothesis is submitted : The cholera organism is continuously 

 present in some form in the sewer system of Manila either in its fluid 

 contents or in vermin; at certain stages of its atypical form, by passage 

 through the human intestine or otherwise, it first is capable of producing 

 a disease resembling cholera, but the organism can not be recognized by 

 the present laboratory methods. Successive passages through the human 

 intestine produce a typical cholera- vibrio. Possibly the disease disap- 

 pears because the population gradually becomes immune by eating fish 

 and other sea products which have been taken from cholera-infected 

 waters, or drinking the water itself. An immunity of this kind appears 

 probable from the fact that cholera organisms continuously passed 

 through the living, susceptible intestines either increase or retain their 

 virulence, and this should cause the mortality among those attacked 

 throughout an epidemic to remain the same. However, the reverse is 

 the case, as may be seen by referring to the history of the cholera out- 

 breaks in the Philippines and other countries (the rate at the beginning 

 being from 90 to 100 per cent and soon falling to 40 per cent or below), 

 so that the decline in the mortality would seem to be due rather to the 

 acquired resistance of the individual than to the change in the cholera 

 vibrio. 



CONDITIONS CONFIRMING THE HYPOTHESIS. 



It appears probable that the cholera organism is conveyed either di- 

 rectly or indirectly from the sewers to easily contaminated articles of food 

 or drink by the means of roaches, either through direct mechanical con- 

 tact with their feet or bodies, or by the deposition of their excretions, 

 thence it is passed to human beings; but flies, water bugs, and other 

 vermin commonly found in sewers are also no doubt partly responsible. 



When it is remembered that cholera organisms can live in the intestines 

 of such vermin for a number of weeks, it will be at once apparent that 

 many cases of cholera, the origin of which has heretofore been obscure, 

 will have at least a reasonable explanation. It has frequently happened 

 that only one case occurred in a house in which seventy-five persons or 

 more obtained their meals and the fact that rarely ever more than one case 

 occurs in a city block shows a limited infection which can be explained 

 by insect transmission. An outbreak of cholera such as occurred in 

 Honolulu during the latter part of December, 1907, might also be ex- 

 plained by the landing of infected roaches. 



