242 THE SPOROZOA 



with the actual sporulation of the parasite, when vast numbers of 

 merozoites are set free in the blood, and are attacking fresh, 

 healthy corpuscles. The result of the rapid multiplication of the 

 parasite in the blood, and the consequent destruction of the 

 corpuscles, is a condition of anaemia which tends to produce 

 general cachexy, and may terminate fatally. At the same time 

 the melanin-granules produced by the parasite, and dispersed in 

 the blood when the sheltering corpuscle disintegrates and the 

 merozoites scatter (see below, p. 245), become deposited in the 

 spleen and liver, which become hypertrophied, and also in the 

 lungs, kidneys, and brain, causing a pigmentation of these organs. 

 In pernicious malaria death may ensue from the accumulation of 

 the parasites in the capillaries of the brain to such an extent 

 that the circulation is hindered or completely blocked. Finally, it 

 should be mentioned that the fevers may be acute or chronic, and 

 that in the latter condition the disease may be masked or latent 

 for a considerable period. What exactly happens to the parasite 

 during this time is now the only obscure part of its life-history. 



Fevers similar to malaria appear to be produced in birds and 

 in various mammals by Haemosporidian parasites. In birds, 

 according to Macallum [84], characteristic changes take place in the 

 internal organs, resulting from the destruction of blood-corpuscles 

 and the deposition of pigment. The spleen and liver are the 

 parts chiefly affected ; the bone-marrow and other organs less so. 

 In cattle an acute and rapidly fatal disease, the so-called Texas- 

 fever (" Tick-fever," " Tristeza," " Redwater," etc.), is produced by 

 Piroplasma bigeminum, manifesting itself in high body-temperature, 

 loss of appetite, and jaundice of the sclerotics, accompanied by 

 general dulness and emaciation, and in many, though not in all 

 cases, by pronounced haemoglobinuria, the urine being the colour 

 of port-wine. In horses a fever similar to malaria is produced by 

 Piroplasma equi, and in dogs Piroplasma canis is the cause of the so- 

 called "malignant jaundice," very similar in its symptoms to Texas- 

 fever in cattle. Interesting discoveries with regard to the life- 

 histories of these parasites are probably to be expected in the near 

 future. 



(b) Morphology and Life-history. The forms that have been 

 most fully worked out, and of which the life-histories are best 

 known, are those infesting the human blood. They may there- 

 fore serve as types of the structural and developmental character- 

 istics of the whole order, and the distinctive features of other 

 forms will be described briefly afterwards. 



It is still a matter of controversy how many species of these 

 parasites occur in the blood of man. Their discoverer, Laveran, 

 regards them all as one species ; some authorities, on the other 

 hand, believe in the existence of as many as five different kinds. 



