348 SUMMARY OF CURRENT RESEARCHES RELATING TO 



which the increment of motion is given. It consists of (a) A bed- 

 plate of iron about 15 in. long by 6 in. in breadth, having elevated 

 walls on each side and running the entire length. The cores of two 

 or more magnets project through this bed-plate, being fastened be- 

 neath, (h) A rectangular plate moving freely between the walls of 

 the bod-plate, and resting directly upon the cores of the magnets. 

 (c) A Microscope-arm attached to the bed-plate in such a way that a 

 ruled metal plate attached to the moving plate can be brought under 

 the objective, (rf) A simi^lc means, either by a lever or a screw, of 

 running the rectangular plate over any distance indicated by the 

 scale, (e) The mechanism for holding tho object upon the rectangular 

 plate and for moving the knife. 



The object being mounted for cutting, each increment of motion 

 is obtained by moving the rectangular plate over a given distance 

 under the Microscope. There can be no mistake about the magnitude 

 of this motion, because it can be at any time verified by reading the 

 scale. In order to fasten the plate, preparatory to making the section, 

 we have only to turn a switch and complete the circuit. By the 

 principle employed there can be no disturbance during this operation, 

 and this fact can be verified by again reading the scale. 



Preparing Thin Sections of Shells and Teeth.* — E. Ehrenbaum 

 recommends that before grinding thin sections of teeth, shells of 

 molluscs, foraminifera, &c. (especially small objects), they should be 

 placed in a vei'y fluid and not too warm mixture of 10 parts colo- 

 phonium (rosin) and 1 part ordinary wax, the latter serving to 

 reduce the brittleness of the former. It is quite transparent, and the 

 object can be oriented in any desired position in the grinding. The 

 objects should be placed in the mixture and after a short time lifted 

 out with the forceps with as much as possible of the mixture hanging 

 to them, and allowed to cool. Or the mixture with the object may be 

 poured in a very small paper box. 



The grinding is done on a glass plate with emery powder of 

 various degrees of fineness. When one side is smooth, the section is 

 attached to the slide, and the other side similarly ground down and 

 polished. It is then washed with oil of turpentine and (moistened 

 with the oil) left under a bell glass to clear and render it transparent. 

 The remainder of the imbedding material is best removed with 

 chloroform. 



If the section is damaged and likely not to hold together, it can be 

 mounted without dissolving the colophonium, which when pure is little 

 inferior to Canada balsam. In this case the slide should be warmed 

 very gently or some drops of chloroform run over it before the cover- 

 glass is put on. 



Rapid Method for Making Bone and Teeth Sections.! — Under 

 this heading E. T. Nealey describes a process which consists of using 

 only perfectly fresh tissue and grinding down first one side and then 

 the other of the tooth or sawn section of bone on a dentist's lathe 



* Zeitscbr. f. Wiss. Mikr., i. (1884) pp. 414-5. 

 t Amer. Mon. Micr. Journ., v. (1884; pp. 142-4. 



