.30 PROTOZOOLOGY 



Hydra which, according to Reynolds and Looper (1928), die on an 

 average in 6.8 days as a result of the infection and the amoebae dis- 

 appear in from 4 to 10 days if removed from a host Hydra. Costia 

 necatrix (p. 372) 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 func- 

 tions of the host tissue. Ichthyophthirius multifiliis (p. 709), another 

 ectoparasite of freshwater and marine fishes, goes further by com- 

 pletely burying themselves in the epidermis and feeds on the host's 

 tissue cells and, not infrequently, 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 cytoplasm 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 gambiense, 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 first slightly raised nodules 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 may also 

 occur 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. 



Malarial infection is invariably accompanied by an enormous 

 enlargement of the spleen ("spleen index"); the blood becomes 

 watery; the erythrocytes decrease in number; the leucocytes, sub- 

 normal; but mononuclear cells increase in number; pigment granules 



