ioo THE MICROSCOPE. 



excess of living matter at this particular point or that there is an in- 

 flammation of the living matter causing hypersensitiveness. 



Few teeth having this unpleasant characteristic in a marked de- 

 gree, were examined under the microscope, the specimen being 

 usually a longitudinal slab ground from the fresh tooth and includ- 

 ing both the soft and hard dentine, the softest outer portion being of 

 course ground away in bringing the specimen to the requisite thin- 

 ness. When the specimen had been reduced in thickness to about one 

 lanima of canaliculi it was immersed for a few moments in one 

 eighth per cent gold chloride, washed in distilled water and then 

 placed in glycerine and i p. c. acetic acid which was exposed to dif- 

 fuse daylight until the violet color was produced by the reduction 

 of the gold salt; the specimen was then mounted in glycerine and 

 distilled water, equal parts. If fresh teeth that are carious are 

 treated in this way, many very interesting facts concerning the pro- 

 cess of decay will be seen under the microscope, but in regard to 

 this subject it will be found after many specimens have been pre- 

 pared that there is a great difference in the density of tooth 

 structure and that this difference is largely due to the varying size 

 of the dentinal canaliculi. It will be found that the fibrillar in the 

 more dense dentine nearly or quite fill the tubuli, whereas in the 

 tooth of very loose structure the canaliculus may be twice the 

 diameter of the fibrilla that it contains. 



The violet color spoken of by straining with gold chloride is 

 only produced in the already softened or decayed portion, joined to 

 the sound portion in the specimen, the outside line of this color 

 showing definitely how far the process of decay has progressed. 

 Just inside this line of color will be found an apparently normal 

 amount of fibrillar, extending across the line from the sound 

 structure. Some of these fibers of living matter extending beyond 

 others for some distance into the colored dentine. 



[to be continued.] \P~ 1 



LABORATORY WORK. 



BY C. H. STOWELL. 

 KIDNEY. 



SECTIONS of the fresh kidney may be made with a Valentin's 

 knife, or a freezing microtome. The most instructive views 

 are obtained only from hardened injected specimens. The kidney 



