84 TROPICAL MEDICINE AND HYGIENE 



diseases, such as kala-azar, trypanosomiasis, &c., are also 

 causes of enlargement- of the spleen, and that therefore 

 where these diseases are prevalent the value of the test is 

 greatly reduced ; and (2) that the examinations should be 

 limited to children, as in adults of many races, Indians, 

 &c., chronic enlargement of the spleen, whether as a 

 result of early infection of malaria or not, persists 

 throughout adult life, and may even increase. 



With negro races the results obtained by the spleen 

 test are of high value. With other races only the ex- 

 aminations made of children up to 15 are valuable 

 (fig. 26). The advantages of the method of spleen 

 examination are that : (i) There is less opposition to 

 palpation of the abdomen in children than to blood 

 examination ; (2) that the examinations can be made 

 more quickly than the examination of blood for parasites, 

 and far more quickly than differential leucocyte counts ; 

 (3) that with little training moderately reliable results may 

 be obtained by trustworthy men with no medical educa- 

 tion ; (4) that the condition of the spleen does not vary so 

 rapidly as the number of parasites in the blood. Thus a 

 spell of cold or wet weather will often result in an increase 

 in the proportion of persons in whose blood the parasites 

 are sufficiently numerous to be readily found, whilst the 

 probabilities of a new infection are not affected by such 

 meteorological changes. The size of the spleen is affected 

 by such changes to a very slight extent. 



(C) The period of residence or exposure required in 

 the average European or other susceptible person before 

 an attack of malaria develops is a very fair measure of 

 the endemic index. Most Europeans are able to give 

 fairly definitely the period that elapsed between their 

 arrival in the country and the onset of their first attack 

 of fever. The first attack of fever is usually a marked 

 one, and comparatively few errors in diagnosis are made 

 with this attack in a malarious country. The shorter the 

 period of average residence required, the higher the 

 endemic index. 



