MALARIAL FEVER. 525 



In both the quartan and tertian fevers all the stages of development 

 can be readily observed in the peripheral blood. 



3. The Parasite of Malignant or /Estivo-autumnal Fever, or Tropical 

 Malaria. — The cycle in the human subject probably occupies forty- 

 eight hours, though this cannot be definitely stated to be always the case 

 (vide supra). The amoebulse in the red corpuscles are of small size, 

 and their amoeboid movements are very active ; they often, however, 

 pass into the quiescent ring form (Fig. 163). The pigment granules, 

 even in the larger forms, are few in number and very fine ; the infected 

 red corpuscles have a tendency to shrivel and assume a deeper or coppery 

 tint. The fully developed sporocyte occupies less than half the red 

 corpuscle, and gives rise to usually from six to twelve spores, somewhat 

 irregularly arranged and of minute size. Sporulation takes place almost 

 exclusively in the internal organs, spleen, etc., so that, as a rule, no sporo- 

 cytes can be found in the blood taken in the usual way. The proportion 

 of red corpuscles infected by the amcebute is also much larger in the inter- 

 nal organs. The gametes have the crescentic form, as already described. 



Cases of infection with the malignant parasite sometimes assume a 

 pernicious character, and then the number of organisms in the interior 

 of the body may be enormous. In certain fatal cases with coma the 

 cerebral capillaries appear to be almost filled with them, many being in 

 process of sporulation, and in so-called algid cases, characterised by great 

 collapse, a similar condition has been found in the capillaries of the 

 omentum and intestines. The process of blood destruction present in 

 all malarial fevers, reaches its maximum in the malignant class, and the 

 brown or black pigment elaborated by the parasites — in part after being 

 taken up by leucocytes, chiefly of the mononuclear class — becomes 

 deposited in various organs, spleen, liver, brain, etc., especially in the 

 endothelium of vessels and the perivascular lymphatics. In the severer 

 forms also brownish-yellow pigment is apparently derived from liberated 

 haemoglobin, and accumulates in various parts, especially in the liver 

 cells ; most of this latter gives the reaction of an iron salt. 



General Considerations. — The developments of the malarial parasites 

 in the mosquito and infection of the human subject through the bites of 

 this insect have, by the work of Ross and others, as detailed above, 

 become established scientific facts. These facts, moreover, point to 

 certain definite methods of prevention of infection, and these methods 

 have to a certain extent already been practically tested. The extensive 

 observations recently carried out go to show that all the mosquitoes 

 which act as hosts of the parasite belong to the genus anopheles ; of 

 these there are a large number of species, and in at least eight or nine 

 the parasite has been found. The breeding places of these insects are 

 chiefly in stagnant pools and other collections of standing water, and 



