October 20, 1922] 



SCIENCE 



439 



When school science has this outlook it -will 

 lie closer to the human heart than it does at 

 present, and a common bond of sympathy will 

 be formed between all who are guiding the 

 growth of young minds for both beauty and 

 strength. So will the community of educa- 

 tional aims be established and the place of 

 science in modern life be understood by a gen- 

 eration which will be entrusted with the task of 

 making a new heaven and a new earth. If 

 these trustees for the future learn to know 

 science in spirit as well as in truth we may 

 look forward with happy confidence to the 

 social structure they will build, in which knowl- 

 edge will be the bedrock of springs of action 

 and wisdom will make man the worthy monarch 

 of the world. 



Richard Gregoet 



FROG AND TOAD TADPOLES AS 

 SOURCES OF INTESTINAL PRO- 

 TOZOA FOR TEACHING 

 PURPOSES 



Many teachers of protozoology and inverte- 

 brate zoology use frogs for the purpose of ob- 

 taining intestinal protozoa for class use, but it 

 does not seem to be generally known that the 

 tadpoles of frogs and toads are even more val- 

 uable than the adults as sources of ma/terial. 

 Unfortunately tadpoles are most abundant late 

 in the spring and in early summer when classes 

 are usually not in session, tout 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, 

 B. eatesbiana. The former is common through- 

 out eastern North Amerca, inhaibiting swamps 

 and large and small ponds; the latter has a 

 similar distribution but is limited to swamps 

 and the larger and deeper ponds. Tadpoles 

 should be looked for in these habitats. The 

 identification of these, so far as their use as 

 material for intestinal protozoa is concerned, 

 is of little importance, but it may be stated here 

 that the tadpoles of the two species are very 

 similar and difficult to distinguish from each 

 other. Full descriptions of them are given 'by 



Wright (1914). 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 deter- 

 mine the incidence of infection and numbers 

 present of the various species of protozoa, since 

 this varies from year to year. The specimens 

 for class use may be collected several days 

 before they are needed tout should not be kept 

 in the laboratory for more than a week or two 

 since they tend to lose their infections under 

 laboratory conditions. The writer has found 

 dishes about ten inches in diameter and three 

 inches deep containing a quart of tap water 

 to be suitable for albout twenty 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 destroy- 

 ing the brain and spinal cord with a heavy 

 needle. The ventral toody wall can then be 

 opened from tlie 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 ali- 

 mentary tract, is tightly coiled and is separated 

 from the intestine by a constriction. The dif- 

 ferent species of intestinal protozoa are rather 

 definitely distributed within the intestine and 

 rectum. The anterior portion of the intestine 

 is inhabited by a flagellate, Giardia agilis; in 

 various parts of the intestine and rectum Enda- 

 ■mceba ranarum may be found; the rectum is 

 the principal habitat of two genera of ciliates, 

 Opalina and Nyctotherws, of two genera of 

 flagellates. Trichomonas and Hexamitus, and 

 of several green flagellates resembling members 

 of the genera Euglena and Phacus. To study 

 any of these species in the living condition, 

 the part of the digestive tract containing them 

 should be teased out in a drop of 0.7 per cent, 

 salt solution and covered with a cover glass. 

 Any of the species mentioned can be found 

 with low magnification, such as obtained with 

 a 16 mm. objective and a number 5 ocular. To 

 study the details of most of these protozoa, 

 however, the Schaudinn iron-htemotoxylin 

 method is necessary. This in torief is as fol- 

 lows: Spread the intestinal or rectal contents 

 in a thin layer over about one balf the area of 



