86 ENTOZOA FOUND IN MAN. 



tion of entozoa. It has also been observed that they 

 are frequent in the spring. 



It has been generally supposed that the inhabi- 

 tants of cold, damp countries are more subject to 

 lumbrici than people living in warm countries. This 

 supposition is not, however, supported by facts ; 

 for although these worms are very common in Hol- 

 land and in Sweden, which countries have been 

 mentioned in confirmation of the theory, they are 

 certainly not less frequent in tropical latitudes, as 

 has been shown by different observers in Brazil, 

 Cayenne, Jamaica, and elsewhere. 



Again, if we consider that in some districts (the 

 province of Smaland, in Sweden, for instance) almost 

 every inhabitant is affected with lumbrici, it will be 

 evident that the influence of climate alone is small in 

 determining the frequency or rarity of these entozoa. 

 Besides this, as has been pointed out by Dr. Davaine, 

 the ascaris lumbricoides is comparatively rare in 

 Paris, whilst in some of the French provinces it is 

 very common ; the same comparison holds good with 

 regard to London and some parts of England, and 

 most probably depends upon certain local circum- 

 stances which favour the development of the lumbricus 

 in the rural districts. 



According to the evidence of most authors upon 

 the diseases of negroes, they are much more subject 

 to round-worms than the whites are ; but no decided 

 reason has been given for this difference between the 

 two races. Dyer, in the " London Medical Gazette " 

 for 1834, states his belief that it is due to the fact 

 that the negroes do not eat any salt, and Dazille 

 attributes it to their insipid, unfermented diet. 



