THE THREE HUMAN PARASITES 635 



occupies forty-eight hours, though this cannot be definitely stated 

 to be always the case (vide supra}. The amcebulse 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. 180). 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, sometimes they are swollen and decolorised. The 

 fully developed schizont usually occupies less than half the red 

 corpuscle, and gives rise to from six to twenty or more merozoites, 

 somewhat irregularly arranged and of minute size. Schizogony 

 takes place almost exclusively in the internal organs, spleen, 

 etc., so that, as a rule, no schizonts can be found in the blood 

 taken in the usual way. The proportion of red corpuscles infected 

 by the amoebuke is also much larger in the internal organs. The 

 gametocytes 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 parasites being in process of schizogony ; 

 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 hsemosiderin. 



Cultivation. Bass and Johns have recently announced that 

 they have succeeded in obtaining growths of the parasites of 

 tertian and malignant fevers outside the body. The first 

 cultures were obtained in defibrinated blood from malarial 

 patients to which was added 1 per cent, of a 50 per cent, 

 solution of dextrose in water. Growth of the parasites took 

 place within the red corpuscles, but only under anaerobic 

 conditions, and there must be a layer of serum at least half an 

 inch in depth above the sedimented corpuscles. Under such 

 circumstances, the parasites underwent enlargement and after- 

 wards passed through the stage of schizogony. The merozoites 



