II42 



THE MALARIAL FEVERS 



Then by the Poisson-Pearson formula the percentage error will be ;— 



Latent Malaria. — ^This term is employed to denote cases in which, 

 without any sign of illness, malarial parasites can be found in the 

 blood in small numbers. These cases form a reservoir of transmis- 

 sion to the anopheline. Craig states that out of 1,267 cases in 

 which malarial parasites were demonstrated in the blood, 21 per 

 cent, were latent, and the majority of these were found to be caused 

 by the subtertian parasite. 



Congenital Infection. — The question of congenital malaria has 

 been much debated, but Dumolard and Viallet have recorded a 

 case in which a woman suffering from malaria gave birth to a child, 

 in which blood from the umbilical cord during life and from the 

 heart after death contained malarial parasites identical with those 

 in the maternal blood and placenta. A similar case has been 

 recently reported by Leger. 



II. Predisposing Causes. — These may be classified into: — 



1. Those which promote infection with the parasite. 



2. Those which promote the increase of the parasite in man after 

 its inoculation. 



1. Those which Promote Infection with the Parasite.- — 

 The first of these is residence in an area which contains not merely 

 persons with gametocytes in their blood, but also mosquitoes 

 capable of carrying the disease, associated with an atmospheric 

 temperature suitable for the development of the parasite in the 

 mosquito. 



The second is any cause which produces large numbers of mos- 

 quitoes capable of spreading the disease. This will be not merely 

 a suitable air-temperature, but also moisture. Hence low-lying, 

 marshy places, and the wet season, are important predisposing 

 causes. 



The third is occupation, for this may compel people to live in 

 malarial countries, to reside in the low-tying marshy portions of the 

 same, to work in rice-fields covered with water, etc. Age is a pre- 

 disposing factor, as mosquitoes have more opportunity of biting a 

 young child than an adult. Sex has no influence. 



2. Those which Promote the Increase of the Parasite 

 AFTER ITS Inoculation. — -These predisposing causes are subdi- 

 visible into: {a) racial; {b) personal; (c) meteorological. 



{a) Racial. — There is no doubt that the native races suffer less 

 than an immigrant race in a tropical country, where there is always 

 malaria present, and this we believe to be mainly due to the acquired 

 partial immunity of the native races, as already explained. 



(6) Personal. — It will be obvious from the above remarks that the 

 parasite cannot produce the markedly deleterious effects which we 

 term malarial fever, unless there be a sufficiently large number 

 present. Further, there appears to be a tendency on the part of 



