68 Phylum Protozoa 



1921b. The cultivation of Trichomonas hominis. Amer. J. Trop. Med. 



1:211. 



1922a. A study of Trichomonas hominis, its cultivation, its inoculation into 



animals, and its staining reaction to vital dyes. Johns Hopkins Hosp. Bull. 



33:437- 



■ 1922b. Spirochaeta eurygyrata. J. Exper. Med. 36:617. 



1926. Studies on Trichomonas buccalis. Amer. J. T-rop. Med. 6:75. 



1933. A new variety of Retortamonas (Embadomonas) intestinalis from 



man. Amer. J. Hyg. 18:433. 



FROG AND TOAD TADPOLES AS SOURCES OF 

 INTESTINAL PROTOZOA FOR TEACHING PURPOSES* 



R. W. Hegner, School 0) Hygiene and Public Health 



MANY teachers of protozoology and invertebrate zoology use frogs 

 for the purpose of obtaining intestinal Protozoa for class use, 

 but it does not seem to be generally known that the tadpoles of frogs 

 and toads are even more valuable than the adults as sources of material. 

 Unfortunately tadpoles are most abundant late in the spring and in 

 early summer when classes are usually not in session, but two species 

 of frogs that are more or less common throughout the United States pass 

 two or more seasons in the tadpole stage and hence are available in 

 the autumn and, in the southern part of the country, at any time of the 

 year; these are the green frog, Rana clamitans, and the bullfrog, R. 

 catesbiana. A breeding place once found will serve as a source of supply 

 year after year. 



Sample tadpoles should be collected some time before the class meets so 

 as to determine the incidence of infection and numbers present of the 

 various species of Protozoa, since these vary from year to year. The 

 specimens for class use may be collected several days before they are 

 needed but should not be kept more than a week or two since they tend 

 to lose their infections under laboratory conditions. The writer has 

 found dishes about 10 inches in diameter and 3 inches deep containing 

 a quart of tap water to be suitable for about 20 tadpoles each. The 

 dishes should not be covered with glass plates, but the water should be 

 changed every day or two. Tadpoles may be killed very quickly, as 

 adult frogs usually are, by destroying the brain and spinal cord with a 

 heavy needle. The ventral body wall may then be opened from the 

 anterior to the posterior end. The intestine is coiled within the body 

 cavity, being several hundred millimeters in length. The rectum, or 

 posterior portion of the alimentary tract, is tightly coiled and is separated 

 from the intestine by a constriction. The different species of intestinal 

 Protozoa are rather definitely distributed within the intestine and rectum. 



* Reprinted from Science 56:439, 1922, with slight changes by the author. 



