shaped, and have at the front end several flagella, 

 one of which extends backward along the edge of an 

 undulating membrane. The body is supported by an 

 internal stiflf rod, projecting at the rear, which also 

 anchors the animal in feeding. Trichomonas vaginalis 

 is found in the vagina of from 20 to 40 per cent of all 

 women examined and in 50 to 70 per cent of those 

 who complain of leucorrhea. It sometimes causes ir- 

 ritation and discomfort, but whether it does more 

 serious harm we do not definitely know. Since the 

 flagellate does not thrive in the acid condition of the 

 normal vagina, weak acetic acid is the usual treat- 

 ment; but it does not always help, and then various 

 drugs or antibiotics are tried. This flagellate also oc- 

 curs in the male urinary tract, in the urethra and in 

 the prostate. Trichomonas tena.x lives in the mouth 

 of man and may be involved in some way in pyor- 

 rheal conditions. Trichomonas hominis is present 

 suspiciously often in cases of human diarrhea. 



The diplomonads. which have paired sets of or- 

 ganelles and look as if two simpler flagellates were 

 joined together in the middle, include Giardia intes- 

 tinalis and other species of Giardia that live in all 

 kinds of vertebrates. They inhabit the upper part of 

 the small intestine instead of the large intestine, 

 which attracts the other intestinal protozoans. Seen 

 from the side, Giardia looks like a half-pear with the 

 broad end directed forward and the flat side indented 

 by a concavity, which helps the animal to adhere 

 tightly to the intestinal lining. The eight flagella, at- 

 tached at the middle and at the hind end, are in ac- 

 tive use when the animal is seen in the liquid feces 

 that attend the diarrhea it apparently causes. The 

 lashing of these flagella was vividly described by the 

 indefatigably curious Leeuwenhoek. Ill with mild 

 diarrhea, he was not content merely to complain, 

 like the rest of us. Instead he set about to examine 

 his watery feces and in them saw Giardia. In the ab- 

 sence of diarrhea, only the cysts of Giardia are found 



An ameba is never the same from moment to moment as it 

 moves along by protoplasmic flow. (Ralph Buchsbaum) 



in the feces. In one case a single stool was estimated 

 to contain 14 billion cysts, but in a moderate infec- 

 tion the number would be closer to 300.000,000. 

 An effective cure for G/a/Y//a-caused diarrhea is 

 atebrin or other drugs used also for malaria. A group 

 of related flagellates, the hypermastiginads, which 

 live in the gut of termites, cockroaches, and wood- 

 roaches, are certainly among the most remarkable of 

 protozoans both in the complexity of their structure 

 and in their habits. Trichonympha campanula, from 

 the gut of termites, is pear-shaped, with the fore end 

 narrower than the rear, and is covered with hundreds 

 of long flagella. The front end of the body is very 

 complex and composed of structurally specialized 

 layers. The large, rounded rear end has thin proto- 

 plasm and engulfs the minute wood particles that 

 surround the animal in the termite gut. The flagellate 

 has enzymes that digest the cellulose in wood to 

 soluble carbohydrates. These are then shared with 

 the termite host, which eats wood but cannot digest 

 its chief constituent, cellulose, without the interven- 

 tion of its protozoan guests. Such mutualistic rela- 

 tionships, in which two organisms are so closely asso- 

 ciated for mutual benefit, are fairly unusual in the 

 animal kingdom, but they are common in this group 

 of flagellates that inhabit wood-eating insects. 



The Ameboid Protozoans 



{Class Sarcodina or Rhizopoda) 



The word "ameba" is derived from a Greek word 

 meaning "change," and the ameboid protozoans are 

 those that move about and capture their food by 

 means of "false feet" or pseudopods, temporary ex- 

 tensions of the body, that may never appear the 

 same from moment to moment, or may appear stiff 

 and fixed yet show a constant streaming of the proto- 

 plasm. Members of this group never move by flagella 

 in the principal phase of the life cycle, though they 

 may have flagellated stages or sex cells. Most are 

 free-living in fresh and salt waters and in soil. Some 

 are parasitic or live as supposedly harmless commen- 

 sals, mostly in the digestive tracts of larger animals. 

 A few very small amebas live as parasites within the 

 bodies of other protozoans. 



THE LOBOSE AMEBAS 



The lobose amebas have no fixed shape and move 

 along by extending lobose or finger-like pseudopods, 

 now at one point, now at another. As new pseudo- 

 pods form, the old ones flow back into the general 

 mass of protoplasm, and the animal appears to flow 

 about in irregular fashion with no permanent front 

 or rear. Lobose amebas may at times have long, 

 pointed pseudopods, especially when they are float- 

 ing in water. But typically they are bottom-dwellers 



