CLIMA TOLOGY—mriOLOGY 



tropical and subtropical Africa, especially in Senegambia, Algeria, 

 and Egypt. It is common in Mauritius and Ceylon, and is possibly 

 not as rare in India as it is alleged to be. It is common in China, 

 Indo-China, and the Philippines, and not infrequent in North 

 America, but is said to be rare in Central America, in the West 

 Indies, and the Guianas, while common in Brazil and Chili. In 

 Europe it is endemic in Russia and Germany, and fairly frequently 

 met with in the south, especially in Italy and in the Balkans. 

 Sporadic indigenous cases have been reported also from Great 

 Britain, where carriers of Loeschia histolytica cysts are not very 

 rare especially among miners. 



Our observations do not lend support to the theory that amoebic 

 dysentery is more common in the hills than in the plains of the 

 tropics, as we have frequently met with it in persons residing in 

 the low country. We have noted the disease all the year round, 

 but it would appear to be more prevalent towards the end of the 

 dry and the beginning of the wet seasons, which probably merely 

 means that the chance of drinking polluted water is greater at that 

 time, for though the climatological characters are not well under- 

 stood, the disease appears to bear a relationship to contaminated 

 water, though flies are also very important. 



Amoebic dysentery is generally endemic, and does not spread 

 m epidemic, still less in pandemic, form. Probably, as medical 

 science advances, it will be found to be of more frequent occurrence 

 and of wide distribution. 



etiology. — The prevalent opinion at the present time is that 

 amoebic dysentery is generally caused by Loeschia histolytica Schau- 

 dinn, 1903, but the possibility is not excluded of there being other 

 pathogenic Loeschice. The life-histories of the various species, as 

 far as they are known, have already been described in Chapter XVII., 

 p. 285. The most common source of infection is the drinking- 

 water, which has been contaminated by faeces, and contaminated 

 food, and especially green vegetables, which may be infected prin- 

 cipally by the agency of flies carrying the cysts in their intestine 

 and depositing them upon the food, and less frequently by actual 

 human faecal contamination. 



Woodcock has called attention to the importance of a hot, damp 

 climate as a factor in the spread of amoebic dysentery, as cysts 

 survive much longer in a hot, damp climate than in a dry climate. 

 Cysts cannot withstand drying; while the experiments of Penfold, 

 Woodcock and Drew have shown that cysts of Loeschia histolytica 

 can retain their vitality for more than a fortnight in water. 



There does not appear to be any well-established racial or age 

 predisposition, but the disease is less common in women than in 

 men, perhaps because they are in some way less exposed to infection. 



Pathology. — ^The spores of the amoebae enter the body by the 

 drinking-water, and by food contaminated with cysts, often 

 deposited by flies, and produce the young amoebae on arrival 

 in the large bowel. These young forms enter the mucosa. 



