INTRODUCTION TO THE PROTOZOA 



19 



been done in Euglena, for instance, by 

 treatment with streptomycin or simply by 

 growing the organisms at 34 to 35° C 

 (Pringsheim and Pringsheim, 1952). This 

 change of a plant into an animal would be 

 just as astounding as the metamorphosis 

 of Cinderella's pumpkin into a golden 

 coach if the differences between the lower 

 forms were as great as those between 

 higher plants and animals. However, the 

 principal difference is one of nutrition, 

 and many species are quite plastic, their 

 form of nutrition depending on circum- 

 stances. Indeed, many of the metabolic 

 pathways of the phytoflagellate, Ochro- 

 monas Dialhaniensis, aside from those in 

 which its chlorophyll takes part, are so 

 similar to those of men that Hutner has 

 facetiously called it a humanoid! 



In recognition of this situation, Ernst 

 Haeckel proposed that the name Protista 

 be applied to all single-celled organisms 

 and that the group be considered inter- 

 mediate between the animal and plant 

 kingdoms. Relatively few modern taxon- 

 omists subscribe to this idea, perhaps 

 less because of any defect in the idea itself 

 than because they have been trained either 

 as botanists or zoologists and not as biol- 

 ogists. 



Since their discovery by Leeuwenhoek, 

 some 30,000 species of protozoa have been 

 described. They occur in practically all 

 habitats where life can exist and are among 

 the first links of the food chain on which 

 all higher life depends. Floating in the 

 plankton of tropic seas, they cause the 

 luminous glow of waves and ship-wakes. 

 Blooming off our coasts, they cause the 

 red tide which deposits windrows of dead 

 fish on shore. They abound in ponds and 

 streams and in the soil. Their role in 

 sewage purification is just beginning to be 

 understood. Their skeletons cover the 

 ocean floor and form the chalk we use in 

 classrooms. 



As parasites, protozoa play a double 

 role. Malaria is still the world's most 

 important disease. Trypanosomes have 

 interdicted vast African grazing lands for 

 livestock. Amoebae cause dysentery in 

 man, and coccidia cause it in his domes- 



tic animals. But other protozoa, packing 

 the termite's hind-gut almost solidly, di- 

 gest the cellulose that it eats and feed it 

 with their wastes and dead bodies. Fabu- 

 lous numbers of protozoa swarm in the 

 rumen and reticulum of cattle and sheep 

 and in the cecum and colon of the horse, 

 but their role is still not clear. 



In this book we are concerned with the 

 protozoan parasites of domestic animals. 

 Our understanding of these forms can be 

 enhanced by knowledge of the parasites of 

 other animals and of free-living forms. 

 For further information on the protozoa in 

 general, reference is made to Doge'l (1951), 

 Grasse (1952-53), Grell (1956), Hall (1953), 

 Hyman (1940), Kudo (1954), Reichenow 

 (1949-53) and Wenyon (1926). 



STRUCTURES 



The structures of protozoa are not 

 referred to as organs as in higher animals 

 but as organelles, organs being composed 

 of cells and organelles being differentiated 

 portions of a cell. 



NUCLEI 



Protozoa contain one or more nuclei, 

 which may be of several types. In the 

 protozoa other than ciliates, the nucleus 

 is vesicular, and all the nuclei in the same 

 individual look alike. There are two types 

 of vesicular nuclei. In one type, an endo- 

 some is present. The endosome is a more 

 or less central body with a negative Feul- 

 gen reaction and therefore without deoxy- 

 ribonucleic acid. The chromatin, which 

 is Feulgen positive and which forms the 

 chromosomes, lies between the nuclear 

 membrane and the endosome. This type 

 of nucleus is found in the trypanosomes, 

 parasitic amoebae and phytoflagellates. 

 In the other type of vesicular nucleus, 

 there is no endosome, but there may be 

 one or more Feulgen-positive nucleoli. 

 In these, the chromatin is distributed thru- 

 out the nucleus. This type of nucleus is 

 found in the Telosporasida, hypermasti- 

 gorid flagellates, opalinids, dinoflagel- 

 lates, and radiolaria. 



