THE SPOROZOA 241 



upon various species of Lacerta, which from its effects upon the 

 nucleus of the host-cell has been termed Karyolysus lacertarum. In 

 blood -corpuscles infected with Karyoiysus, the nucleus becomes 

 hypertrophied and divides amitotically into two or more fragments, 

 which ultimately degenerate (Fig. 76). 



In the sub-order Acystosporea the parasite retains the endo- 

 globular or intracellular situation throughout the whole endo- 

 genous generation, except for the brief period during which the 

 merozoites are seeking fresh corpuscles to attack. But in the 

 sub-order Haemosporea the parasite leaves its first host-cell and 

 becomes free in the blood -plasma. It then penetrates other 

 corpuscles, which it may abandon again, but as a rule it comes to 

 rest finally within a corpuscle or cell, and undergoes schizogony 

 in this situation, though sometimes even the reproductive stages 

 may be free in the spleen-pulp or bone-marrow. 



The effects produced by Haemosporidia upon their hosts seem 

 to diifer markedly in the case of cold-blooded and warm-blooded 

 animals. In the former there is no evidence that these parasites, 

 however numerous, produce any pathological effect upon their 

 hosts at all. But in birds and mammals they cause fevers and 

 agues of various kinds, of which those that trouble the human species 

 are naturally the best known. The varieties of malarial fevers and 

 their symptoms will be found described in medical treatises, but a 

 few points may be briefly summarised here. At least three types 

 of fever are generally recognised, each caused by a distinct form 

 of parasite (see below, p. 243) the two so-called benign inter- 

 mittent fevers, tertian and quartan ague, and the pernicious 

 aestivo -autumnal fever or tropical malaria. In each case the 

 parasite is introduced into the human body by the bite of a 

 mosquito, and not, so far as is known, in any other way. After 

 a period of incubation, varying from six to twelve days, according 

 to the species of parasite, the fever makes its appearance. In 

 the benign forms the feverish symptoms appear at regular 

 intervals, dependent on the time occupied by a complete repro- 

 ductive cyc;le of the parasite. Thus in the parasite of tertian 

 ague the schizogony takes forty-eight hours, and the fever recurs 

 every other day. In quartan ague the schizogony takes seventy- 

 two hours, and the attacks of fever recur once every three days. 

 There may, however, be double or triple infections, the result of 

 distinct inoculations ; or again there may be mixed infections of 

 the two forms, so that distinct generations of the parasites occur 

 contemporaneously in a given patient, producing every possible 

 variation in the frequency of the attacks of fever. In pernicious 

 malaria, on the other hand, the sporulation takes place irregularly, 

 and the fever is consequently irregular or continuous in its 

 manifestations. In all cases the fever coincides in its appearance 



16 



