CHAPTER V. 



ANIMAL, PARASITES. 

 Protozoa. 1 



THIS class of unicellular organisms, some of which belong in the bor- 

 derland between plants and animals, are for the most part microscopic, 

 though a few forms are large enough to be visible to the naked eye. 

 Many of them are parasitic in man, though few forms are as yet of known 

 pathogenic significance. There is, however, much reason for the grow- 

 ing belief that many forms are the inciting factors in some of the serious 

 infectious diseases whose etiology is still obscure. 



The protozoa may be divided into four classes: 

 I. SARCODINA OR EHIZOPODA. 

 IT. MASTIGOPHORA. 



TIT. SPOROZOA. 



IV. INFUSORIA. 



I. SARCODINA (Rhizopoda). 



The protozoa of this class are the simplest in structure and move 

 about or feed by the protrusion of broad or slender processes called pseu- 

 dopodia. Reproduction takes place by simple division and by spore for- 

 mation. One of the lowest orders in this class contains forms Amoeba 

 which are parasitic in man. 



The Amoeba coU (Amoeba dysenterica, Councilman and Lafleur) is of 

 considerable pathological significance. It has been repeatedly found in 

 acute and chronic dysentery, in the intestinal contents, at the bottom of 

 the intestinal ulcers, and in the secondary abscesses, especially of the 

 liver, which may accompany ulcerative colitis. The amoaba is believed 

 to be the inciting factor, in some cases, in both the primary ulcerative 

 colitis and its complicating abscesses (see p. 555). 



The Amoeba coli (Fig. 52) is a spheroidal cell, from five to eight 

 times the diameter of a red blood cell, with granular protoplasm and a 

 vesicular nucleus. It often contains larger and smaller vacuoles. Fre- 



1 For a resume of our present knowledge of the parasitic and other protozoa, consult 

 Calkins, "The Protozoa," 1902; also Mannnberg, Lubarsch and Ostertag's "Ergebnisse 

 der allg. Aetiologie der menschlichen und Thierkrankheiten," Jahrg. I., Abth. 1, p. 916, 

 1896; Kruse in Fliigge's "Mikroorganismen," vol. ii. ; Clarke, "Protozoa and Disease," 

 1903; and Doflein and -c. Prowazek in Kolle and Wassermanu's "Handbuch der Mikro- 

 organismen," Bd. i., S. 865. 



