698 SUMMAEY OF CURRENT RESEARCHES RELATING TO 



consists of a copper plate, 20 em. by 10 cm., supporting at one end the 

 lamp as described above, and on the rest of its length a horizontal com- 

 plementary rheostat. The latter consists of a long tube of serpentine 

 inclosing 120 discs of graphite, and gives a range of resistance from 

 1/4 ohm to 1000 ohms. 



Leach, W.— A substage Condenser for the Microscope. 



Trans. Manchester Micr. Soc, 1888, pp. 76-8 (6 figs.). 

 Miles, J. L. W.— Sub-stage Illumination by simple devices. 



Ibid., 1888, pp. 78-80 (1 pi.). 



(4) Photomicrograpliy. 



"Artistic Photomicrography attained."* — Dr. W. X. Sudduth 

 recently gave a lecture on histology before an American Dental Society, 

 illustrated with the aid of the stereopticon, which is reported as 

 follows : — 



" He exhibited the results of his experiments in colouring slides in 

 facsimile of the stained specimens which had been photographed. The 

 Microscope is undoubtedly valuable in investigating tissues ; never- 

 theless the reported discoveries of microscopists are not always reliable. 

 Great obstacles arise in the use of the instrument, even after the speci- 

 men has been mounted, not the least being the fact that focusing is 

 necessary, and that no two men see exactly alike. Therefore, when A 

 focuses on a specimen to show a certain peculiarity,which he claims to be 

 able to discern, he finds it difficult to demonstrate his discovered fact to 

 B, because B cannot tell when he focuses whether he is viewing the 

 same plane seen by A. Of course, when examiners are experienced 

 microscopists the difficulties are lessened, because the trained eye is 

 familiar with the appearances of different tissues, and this materially 

 assists in obtaining the true focus. For example, suppose A claims to 

 show lacunse and canaliculi in a specimen of cementum. B is ac- 

 quainted with the microscopic appearance of dentine, and in focusing 

 aims to get the tubuli of the dentine which is adjacent to the cementum 

 distinctly outlined, and having done so, knows that the cementum also 

 is in focus, and should be able to see the lacunae if present. Again, it 

 is only the trained eye which is able to distinguish breaks, tears, or 

 foreign bodies (as shreds of lint, &c.), and the surfaces of the tissues 

 from the sides or thickness; profile views look flat, not only at the 

 edges of the specimen, but at all points over the surfaces; shadows 

 become lines, and resemble special features of tissues. To lessen these 

 difficulties various methods of staining are resorted to, it being known 

 that different kinds of tissues are differently acted on by the same agent, 

 thus producing various tints, and materially aiding in the differentiation 

 of tissues, which may thus be recognized by their known colours if the 

 stain used be known. It also shows plainly breaks, tears, and foreign 



bodies. 



" Havino' prepared and mounted a specimen, in order to show what 

 he sees with his instrument, the investigator may reproduce as accurately 

 as possible with his pencil the picture in the field of his vision. These 

 drawings from specimens, however, only carry weight in proportion to 

 the honesty and ability of the artist. Therefore, as Dr. Sudduth truly 

 says, drawings male by photolithographic processes are the more 

 valuable, being above suspicion of inexactness or perversion through 



* Odontographic Journal, x. (1889) pp. 44-8. 



