and Laboratory Methods. 2487 



GENERAL LABORATORY TECHNIQUE. 



RAYMOND PEARL, University of Michigan. 



Books and Papers for Review should be Sent to Raymond Pearl, Zoological Laboratory, 

 University of Michigan, Ann Arbor, Mich. 



^, ., , ^ ^, , , Dr. R. O. Moody describes in the Bul- 



The Use of Clay Modeling in the Study of , . , , ^ , ^^ , . xt ■ i 



letin of the Johns Hopkins Hospital 

 Osteoloev J r r 



(Vol. xiv, pp. 78-81) the results of his 



experience in having students of human osteology make clay models of bones as 

 a part of their laboratory work in the subject. He commends the plan highly 

 on pedagogical grounds, and gives a very interesting and suggestive account of 

 how the work is carried on in the Medical Department of the University of 

 California. In this work the " outfit of the student consists of a paraffined 

 board and two modeling tools, Boxwood 64 and E. & B. No. 3. The first of the 

 instruments may be easily made by any one who can use a jack-knife, and the 

 second by any one who has in addition a little manual dexterity. The board 

 should be a piece of kiln-dried finished wood about 60 centimeters long, 50 cen- 

 timeters wide, and 2 centimeters thick. It is well to have it coated with boiling 

 paraffin to prevent the clay from sticking or the board from warping. We have 

 found it desirable to use the best potter's clay that can be obtained. This 

 should be free from stains and foreign bodies. It is prepared by grinding it 

 into a fine powder and, after passing it through a sieve, adding a sufficient quan- 

 tity of water. This mode of preparation not only removes foreign bodies but 

 permits the water to act evenly on the clay. It is important to have the two 

 homogeneously mixed. Clay that is more moist in some parts than others is 

 difficult to mold and liable to crack when dry, thus destroying the model. It is 

 ready for use when it contains enough water to mold easily but not sufficient to 

 make it sticky. When there is a little too much moisture, kneading will often 

 bring it to a proper consistency, but if it is very wet and sticky some powdered 

 clay may be added to take up the excess. In this case, however, the kneading 

 should be thorough in order that the clay shall have throughout a uniform moist- 

 ure. When given to the students, the clay should be in the proper state of plas- 

 ticity for immediate use, but it is well, however, to have the student thoroughly 

 work it over with his hands, for the better the clay is worked, the more readily 

 it can be molded. The bones should be completed while the clay is still in a 

 plastic condition. This state can be maintained indefinitely by covering the 

 model with wet cloths during the various stages of its preparation. There is a 

 notable tendency among the students, especially before they have learned how 

 to handle soft clay, to outline the bone roughly, let the clay harden, and then 

 carve and finish the model. This, however, is unsatisfactory, as the student 

 who carves loses the training of the tactile sense and often cannot make the 

 necessary changes which the instructor suggests to improve the model or make 

 it conform more closely to the original specimen. In fact, the less modeling 

 the student does with his tools and the more he does with his fingers, the greater 



