t^O PRACTICAL PARASITOLOGT 



, ; Classification is based mainly upon the structural peculiarities of 

 the flagjella. The subclass Euflagellata is the only group which 

 includes parasitic forms, and of this subclass we shall concern our- 

 selves with the orders Protomonadina, Polymastigina, and Binucleata, 



Order 1. Protomonadina. 



The Protomonadines, which must be regarded as the most primi- 

 tive of the Flagellates, are capable of more or less definite changes 

 of body-form, some varieties performing characteristic amoeboid move- 

 ments. These, organisms are ext^mely minute ; they have a single 

 nucleus; they do not possess an undulating membrane ; and they are 

 furnished with two flagella, placed at the anterior end. The parasitic 

 varieties are the Cercomonades and the Bodonides, the former possess- 

 ing one flagellum, the latter being furnished with two, one principal 

 and one a .trailing flagellum. Very little, however, is known about 

 these varieties, and this applies particularly to those forms observed 

 in human excreta. The best known is Bodo lacertce (Grassi), 1 which 

 occurs with great frequency in the cloaca and in the terminal portion 

 of the intestinal canal of lizards. Being readily obtainable, it is 

 useful for demonstration purposes, illustrating as it does the simplest 

 form of flagellate apparatus. 



A small quantity of faeces is expelled by gentle pressure from the 

 anus of the lizard and caught in a clean watch-glass. If the material 

 is to be examined fresh, the faeces should be diluted with a little 

 normal saline. To reduce the motility of the parasites, add a small 

 quantity of carragheen which has been previously soaked in normal 

 saline. 



In addition to B. lacertce, and the Amoebae (already described), 

 two varieties of Polymastigina are found in preparations of this kind. 

 These are easily recognizable by the large number of their flagella and 

 their more compact appearance (fig. 7). 



B. lacertce (fig. 7, a) appears at a first glance to be pear-shaped, but r 

 as a matter of fact, is flattened and rolled inwards in a spiral fashion, 

 so that the parasite resembles a coarse gimlet. Two flagella of equal 

 thickness spring from the anterior end, one of which is usually pro- 

 jected forward, while the other and shorter of the two trails behind. 

 There is no cytostome, and it is assumed that nutrition takes place by 

 endosmosis. 



The more intimate structural details are best seen in finished 

 cover-glass specimens. These should be fixed in alcoholic solution of 



1 S. Prowazek, " Untersuchungen ueber einige parasitische Flagellaten," Arb 

 a. d. Kaiserl. Gesundh.-Amte, vol. xxi, 1904, pp. 1-41. 



