880 PROTOZOOLOGY 



Intestinal Protozoa of man are usually studied in the faeces of an 

 infected person. Natural movement should be collected. Do not use 

 oily purgatives in obtaining faecal specimens, as they make the 

 microscopical examination difficult by the presence of numerous oil 

 droplets. The receptacle must be thoroughly cleaned and dry, and 

 provided with a cover. Urine or water must be excluded completely. 

 The faeces must be examined as soon as possible, since the active 

 trophozoites degenerate quickly once leaving the human intestine. 

 If dysenteric or diarrhoeic stools are to be examined, they must not 

 be older than one hour or two. In case this is not possible, wrap the 

 container with woolen cloth while transporting, the organisms may 

 live for several hours. Care must however be exercised during the 

 microscopical examination, as there will be present unavoidably a 

 large number of degenerating forms. If the stool is formed and nor- 

 mal, it would contain usually encysted forms and no trophozoites if 

 the host is infected by a protozoan, unless mucus, puss, or blood is 

 present in it. Examination of such faeces can be delayed, as the cysts 

 are quite resistant (p. 450). 



Cultivation 



For extensive study or for class work, a large number of certain 

 species of Protozoa are frequently needed. Detection and diagnosis 

 of human Protozoa are often more satisfactorily made by culture 

 method than by microscopical examination of the collected material. 

 Success in culturing Protozoa depends upon several factors. First an 

 abundant supply of proper food material must be made available. 

 For example, several species of Paramecium live almost exclusively 

 on bacterial organisms, while Didinium and allied ciliates depend 

 upon Paramecium and other ciliates as sources of food supply. For 

 cultivating chromatophore-bearing forms successfully, good light 

 and proper kinds and amount of inorganic substances are necessary. 

 In the second place, the temperature and chemical constituents of 

 the culture medium must be adjusted to suit individual species. As a 

 rule, lower temperatures seem to be much more favorable for culture 

 than higher temperatures, although this is naturally not the case 

 with those parasitic in homoiothermal animals. Furthermore, proper 

 hydrogen ion concentration of the culture must be maintained. In 

 the third place, both Protozoa and Metazoa which prey upon the 

 forms under cultivation must be excluded from the culture. For in- 

 stance, it is necessary to remove Didinium nasutum in order to ob- 

 tain a rich culture of Paramecium. For successful culture of Amoeba 

 proteus, Aeolosoma, Daphnia, Cyclops, etc., must be excluded from 

 the culture. 



