ANIMAL PARASITES. 133 



IV. INFUSORIA. 



The infusoria are the most highly different iated of the protozoa. They 

 have numerous motor appendages or cilia, which may persist through 

 life or in some forms be replaced in the adult stage by suctoria. They 

 reproduce chiefly by fission, or budding. Among the ciliated infu- 

 soria, few if any are pathogenic in man. The Balantidium coli is an 



F1G.56A. BALANTIDTFM COLI. After Braun. 



ovoidal organism from 0.06 to 0.1 mm. long; it is a common parasite of 

 swine in some regions, and has been found a few times in the intestinal 

 tract of man under conditions which indicated its possible pathogenic 

 significance. 



Methods of Study of the Protozoa. 



The protozoa may be studied in the living condition either in the fluids in which 

 they are found or in three-quarter-per-cent salt solution. They may be killed and pre- 

 served by allowing a drop of one-per-cent osmic acid to run under the cover glass, and 

 replacing this after an hour by glycerin lightly tinged with eosin. Or they may be 

 killed by sublimate solution and stained. 



Many of the smaller forms show well when dried on the cover glass and stained by 

 the anilin dyes by the methods used for bacteria (see p, 152). 



The movements of the Amoeba coli in the freces or in the contents of abscesses 

 which frequently contain them in enormous numbers, may be studied on the warm 

 stage in three-quarter-per-ceut salt solution. Its morphology may be studied in tissue 

 containing it, such as intestinal ulcers, abscesses, etc., which have been hardened in 

 alcohol and stained either with methylene blue or haernatoxylin, the former being espe 

 cially commended by Councilman and Lafleur. 



The attempts to obtain pure cultures of certain forms of Amo?ba and similar or 

 allied forms of protozoa have been partially successful. The method by which McNeal 

 and Xovy obtained pure culture of trypanosomes, namely, by the use of ordinary nutri- 

 ent agar containing rabbits' blood, is of high promise in related forms of protozoa. For 

 details of this method as well as a resume of the cultivation of protozoa, consult McNeal 

 and Novy, "Contributions to Medical Kesearch, Vaughan Anniversary Volume," 1903, 

 p. 549. 



Worms. 



TBEMATODA (Flukes). 



These worms are small, flat, tongue-shaped, or leaf-like creatures, 

 with an intestine, and a discoidal structure on the under surface, by 



