26 PROTOZOOLOGY 



in 6.8 days as a result of the infection and the amoebae disappear in 

 from 4 to 10 days if removed from a host Hydrsi. Costia necatrix 

 (p. 297) often occurs in an enormous number, attached to various 

 freshwater fishes especially in an aquarium, by piercing through the 

 epidermal cells and appears to disturb the normal functions of the 

 host tissue. Ichthyophthirius muUifiliis (p. 568), another ectoparasite 

 of freshwater fishes, goes further by completely burying themselves 

 in the epidermis and feeds on the host's tissue cells and, not infre- 

 quently, contributes toward the cause of the death of the host fishes. 



The endoparasites absorb by osmosis the vital body fluid, feed on 

 the host cells or cell-fragments by pseudopodia or cytostome, or 

 enter the host tissues or cells themselves, living on the cj^oplasm or 

 in some cases on the nucleus. Consequently they bring about abnor- 

 mal or pathological conditions upon the host which often succumbs 

 to the infection. Endoparasitic Protozoa of man are Entamoeba 

 histolytica, Balantidium coli, species of Plasmodium and Leishmania, 

 Trypanosoma gamhiense, etc. The Sporozoa, as was stated before, are 

 without exception coelozoic, histozoic, or cytozoic parasites. 



Because of their modes of living, 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 de- 

 velop into abscesses and the ulcers formed by the rupture of ab- 

 scesses, may reach 2 cm. or more in diameter, completely destroying 

 the tissues of the colon wall. Similar pathological changes are also 

 noticed in the case of infection by Balantidium coli. In Leishmania 

 donovani, the victim shows an increase in number of the large macro- 

 phages and mononuclears and also an extreme enlargement of the 

 spleen. Trypanosoma cruzi brings about the degeneration of the in- 

 fected host cells and an abundance of leucocytes in the infected 

 tissues, followed by an increase of fibrous tissue. T. gambiense, the 

 causative organism of African sleeping sickness, causes enlargement 

 of lymphatic glands and spleen, followed by changes in meninges 

 and an increase of cerebro-spinal fluid. Its most characteristic 

 changes are the thickening of the arterial coat and the round-celled 

 infiltration around the blood vessels of the central nervous system. 



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

 pathogenic trj^panosomes tends to show that the sugar is only par- 

 tially oxidized in the presence of oxygen and that the carbohydrate 

 metabolism of the infected host is disturbed, as shown mainly by 

 the unbalanced condition of the blood sugar, by lowering of the 

 glycogen reserves, and by reduced ability to build glycogen from 



