272 NATURE STUDY REVIEW [8:7— Oct., 1912 



priest, or pastor in their language, about teeth when these men 

 pay a visit to their homes. The functions of the different groups 

 of teeth may be inductively studied with profit by following the 

 suggestion of Mr. Dearness in the December, 1911, number of 

 The Nature- Study Review (p. 271), namely, supplying each 

 member of the class with grains of wheat, pieces of thread and 

 strips of bread, and noting the uses and groups of teeth employed 

 in dealing with these materials. 



(d). As a further study, now that the names of the teeth 

 are known, the pupils can be directed to find out, so far as they 

 can, when their own and their playmates' various second teeth 

 came in. At the class hour, a tabulation can be made on the 

 blackboard, of all the results reported. There will be variation, 

 of course, but the final table should- average up about as follows 

 for the upper jaw : 



Two middle incisors — T years. 



Two lateral incisors — 8 years. 



Two canines, or cuspids — 11 years. 



Two first bicuspids — 9 years. 



Two second bicuspids — 10 years. 



Two first molars — (J years. 



Two second molars — VI years. 



Two third molars — 17 to 45 years. 



(2). Stnicfnre of a Tooth. 



(a). The parts of a tooth can best be studied by providing 

 the pupils with human teeth obtained from an obliging dentist. 

 Indeed, it would not be difficult to get a full set of extracted 

 teeth in fairly good condition and have a small hole drilled 

 through them transversely so they could be strung on a wire in 

 their proper order. After the parts of the teeth have beeln. 

 decided upon by the pui)ils, the terms crown, neck and fang may 

 be supplied. 



(b). The structure and materials of a tooth can be grossly 

 studied from teeth that have been ground in transverse and longi- 

 tudinal planes, and the names enamel, dentine and pulp cavity 

 supplied. 



C. Hygienic Studies. 



(1). Conditions and Effects of Decay. 



(a). Secure from the laboratory or the druggist some blue 

 litmus ])ai)er, and, in the presence of the class demonstrate its 

 use in discovering acid substances. 



