II34 



THE MALARIAL FEVERS 



no fever exists unless these forms exceed some hundreds per cuhic 

 centimetre of blood. These forms persist through the apyretic in- 

 terval before a relapse, but in small numbers, which increase for 

 some days before the relapse takes place. The pigmentation of the 

 cells and organs is due to the hsemozoin liberated by the disruption 

 of the infected red cell. The liberated spores attack new erythro- 

 cytes, and so the numbers of the parasites may increase, until in 

 certain pernicious cases it appears as though the majority of the 

 red cells were infected with parasites, and, indeed, two or more 

 may be noted in one cell. Such a condition must, of course, lead 



to death. ^ ^ r • - ^^ 



But this does not by any means always happen; lor it is well 

 known that a malarial, especially a quartan fever may wear itself 



out, the attacks becoming less and 

 less severe until they cease. 



This would appear to be due to 

 acquired immunity, which no doubt 

 explains the known fact that the 

 European in West Africa on first 

 arrival generally suffers from repeated 

 attacks of fever, but he gradually 

 becomes partially immune, and can 

 then live there, with care, for years. 

 Further, it would certainly explain, 

 in part, the relative immunity of the 

 native races in that region who are 

 infected from earliest childhood, and 

 no doubt this is the true cause of the 

 racial immunity which some allege 

 to exist. It is now known that 

 the merozoites can, although very 

 rarely, penetrate the placenta, and 

 infect the foetus, giving rise to con- 

 genital malaria. 



The three parasites produce very 

 different results, apparently due to 

 their habitats. Thus Plasmodium malaricB and P. vivax as a rule 

 live mainly in the circulating blood, in which the former sporulates, 

 while the latter develops in the spleen; their toxins will therefore 

 produce general symptoms. Laverania malarice, on the other hand, 

 seems to affect the red corpuscles so profoundty that they are liable 

 to adhere to the walls of the capillaries of the organs in which the 

 parasite sporulates. Hence this parasite may produce severe 

 local symptoms, due to the mechanical blocking of capillaries or to 

 the more intense local action of the toxin, or to both of these causes, 

 and therefore it is associated with what are called the pernicious 

 fevers — that is to say, the fevers which produce severe effects on one 

 or more organs — e.g., on the brain, causing coma or paralysis; or on 

 the pancreas, causing haemorrhagic pancreatitis. 



Fig. 6ii. — Plasmodium vivax. 

 (X i,ooo Diameters.) 



Schizont or sporulation stage 

 is shown enclosed in a red blood- 

 corpuscle, which will presently 

 rupture and liberate the pyroge- 

 netic toxins, which will cause the 

 fever. At the same time the 

 merozoites and haemozoin will 

 be liberated. 



(From a photomicrograph 

 by Norman.) 



