PBEPAEING SECTIONS OF SHELL, ETC. 331 



CHAPTEE XL 



TO MAKE SECTIONS OF SHELL AND OTHER HARD TISSUES. 



For this purpose nearly all the apparatus described for 

 making sections of bone and teeth will be required. By 

 far the most important instruments, however, will be found to 

 be the file and the hone. Shell, although generally much 

 softer than bone or tooth, is, nevertheless, very brittle, and 

 thin sections require to be handled with very great care. 

 The best plan of proceeding is to make a portion flat on one 

 surface, and polish it first on the hone and then with putty 

 powder, and to cement this surface to the slide on which the 

 section is intended to be mounted by means of Canada balsam, 

 the file may then be employed to reduce its thickness, and the 

 hone to finish it; the section should be examined from time to 

 time by the microscope, to see when it is thin enough, and, if 

 required, the slide may be placed either in ether or turpentine 

 to dissolve away the old balsam without separating it from the 

 slide ; but should the specimen be very brittle, it should be 

 allowed to remain on the slide on which it was ground, and 

 after having been made as clean as possible, some new balsam 

 may dropped upon it, and a cover of thin glass laid over it 

 in the usual way ; but if the section be sufficiently strong, it 

 may be removed by ether from the slide, and be mounted in 

 balsam as a fresh object; the latter plan will be found the 

 neatest and best, provided it can be accomplished without 

 injury to the specimen. When it is required to investigate 

 the arrangement of the animal matter in any section, it should 

 be subjected to the action of dilute muriatic acid, this is 

 termed by Dr. Carpenter the decalcifying process ; such speci- 

 mens, after soaking in water to get rid of the acid, may be 

 mounted with fluid in the thin glass cell. The structure of 

 many shells of the oyster kind can be very weU made out by 

 selecting some of the thinnest of the flakes or laminas found 



