ECOLOGY 25 



was stated before, are without exception coelozoic, histozoic, 

 or cytozoic parasites. 



Because of their modes of Uving, the endoparasitic Protozoa 

 cause certain morphological changes in the cells, tissues, or organs 

 of the host. The active growth of Entamoeba histolytica in the 

 glands of the colon of the victim, produces slightly raised nodules 

 first which develop into abscesses and the ulcers formed by the 

 rupture of abscesses, may reach 2 cm. or more in diameter, com- 

 pletely destroying the tissues of the colon wall. Similar patho- 

 logical changes are also noticed in the case of infection by 

 Bala?itidium coli. In Leishmania donovani, the victim shows an 

 increase in number of the large macrophages and mononuclears 

 and also an extreme enlargement of the spleen. Trypanosoma 

 cruzi brings about the degeneration of the infected host cells and 

 an abundance of leucocytes in the infected tissues, followed by 

 an increase of fibrous tissue. T. gamhiense, the causative organ- 

 ism of African sleeping sickness, causes enlargement of lymphatic 

 glands and spleen, followed by changes in meninges and an in- 

 crease of cerebro-spinal fluid. Its most characteristic changes are 

 the thickening of the arterial coat and the round-celled infiltra- 

 tion around the blood vessels of the central nervous system. Von 

 Brand's (1938) summary of the carbohydrate metabolism of the 

 pathogenic trypanosomes tends to show that the sugar is only 

 partially oxidized in the presence of oxygen and that the carbo- 

 hydrate metabolism of the infected host is disturbed, as shown 

 mainly by the unbalanced condition of the blood sugar, by lower- 

 ing of the glycogen reserves, and by reduced ability to build 

 glycogen from sugar. Malarial infection is invariably accom- 

 panied by an enormous enlargement of the spleen ("spleen 

 index"); the blood becomes watery; the erythrocytes decrease in 

 number; the leucocytes, subnormal; but mononuclear cells in- 

 crease in number; pigment granules which are set free in the 

 blood plasma at the time of merozoite-liberation are engulfed by 

 leucocytes; and enlarged spleen contains large amount of pig- 

 ments which are lodged in leucocytes and endothelial cells. In 

 Plamodium falciparum, the blood capillaries of brain, spleen and 

 other viscera may completely be blocked by infected erythro- 

 cytes. 



In Myxosporidia which are either histozoic or coelozoic para- 

 sites of fishes, the tissue cells that are in direct contact with highly 



