MTIOLOCY 



system in the place, and if faecal pollution of the drinking-water is 

 possible, the disease may easily become epidemic, for it has been 

 shown that the vibrios can not merely live, but multiply, in water, 

 though the conditions under which they do this are not perfectly 

 understood. 



Two classical instances are usually quoted as evidence of the 

 spread of the disease by water. The first of these is the infection 

 in 1854 of a lady and her servant in Hampstead, where there was 

 no cholera, by drinking the water of the Broad Street well, which 

 was infected, the water being carried all the way from Broad Street 

 to Hampstead because the lady in question had a special liking 

 for it. The second is the infection of Hamburg in 1892 from the 

 waters of the Elbe, in which cholera vibrios were found in the river- 

 water and that of the hydrants. 



As water is a method of infection, it is quite easy to understand 

 that milk is specially dangerous, for it is often diluted with water, 

 and, moreover, forms an excellent medium in which the germs can 

 grow. Thus Haffkine and Simpson found that an outbreak of 

 cholera in the Gaya Gaol was due to the contamination of the milk, 

 from which they obtained the vibrio. 



The Carrier. — -Of great importance in the dissemination of the 

 malady are the so-called vibrio-carriers — viz., persons who, though 

 themselves in good health, still harbour the germ in their intestines, 

 or individuals who continue to harbour the germ for months and 

 years after an attack is over. 



Greig has demonstrated that carriers can show an increased titre 

 for the agglutination of the vibrio. His researches also show that 

 the vibrio can live for long in the gall-bladder of animals, and he 

 has also demonstrated it in the human gall-bladder. 



The fact that the germs can live for a long time in faecal matter 

 enables them to infect insects such as flies, and perhaps ants. With 

 regard to flies, the germs have been found not merely on the ex- 

 terior of the body, but also in the alimentary canal, in which they 

 are believed to multiply. The habits of flies make them, therefore, 

 an important possible means of dissemination of the disease. 



Barber, in 1914, brought forward experimental evidence showing 

 that the germ could live for a time in the alimentary canals of 

 Periplaneta americana (the cockroach) and Monomorium latinode 

 Mayr (the red ant). 



Faecal matter may also pollute green vegetables, for in the East 

 vegetable-gardens are often contaminated with human faecal matter. 

 The most dangerous vegetables are those which are eaten raw, such 

 as lettuces, watercress, and tomatoes. While, however, the above 

 methods explain many points in the epidemiology of cholera, they 

 do not afford a full explanation of the spread of the disease. As we 

 have already said, the principal endemic centre is Lower Bengal, 

 whence it can spread through India, and, indeed, over the greater 

 part of the world, by human agency and along lines of human inter- 

 communication, but in so doing it may miss places on the direct 



