88 ENTOZOA FOUND IN MAN. 



of water, as compared with the rural districts ; in 

 large to^viis the water is often passed through filters 

 before it is distributed to the inhabitants, whilst in 

 the country the unfiltered water of wells, and veiy 

 often the impure water of brooks or of marshy places, 

 forms the only means of supply. These wells or 

 brooks are frequently fed by the rain-water which 

 falls around the neighbouring houses ; and, as no 

 system of sewerage exists, the water which is used 

 for drinking purposes must necessarily become at 

 times, and especially after heavy rains, contaminated 

 with excrementitious matter, in which the ova exist. 



Dr. Davaine's opinion, with which I fully coin- 

 cide, serves to throw some light upon the cause 

 of the epidemics which occasionally prevail in large 

 armies during a campaign. It will also serve to 

 explain the reason why negroes who are not over- 

 delicate in their habits, and who drink the water 

 which they obtain from any source nearest to their 

 habitations, are so frequently affected with lumbrici, 

 whilst the Europeans who reside in the same country, 

 but who make use of fermented liquors imported 

 from abroad, of tea, and of filtered water, enjoy a 

 comparative immunity from these entozoa. 



The age, temperament, and state of the health of 

 a person may have some influence upon the develop- 

 ment of lumbrici ; but it must be remembered that 

 they do not occur spontaneously, and that the ova 

 must be conveyed into the intestine before the lum- 

 brici can be developed there. 



Generally speaking, when the lumbrici are not 

 very numerous, and when they still remain in their 

 usual habitat, they do not give rise to any pain, nor 



