112 THE AMEKICAN MONTHLY [May, 



MEDICAL MICROSCOPY.* 



The Etiology of Diphtheria. — A valuable paper with the above 

 title, by Dr. Samuel N. Nelson, of Boston, appears in the. Jotir. Am. 

 Med. Ass'n for April 6. The paper consists partly of citations of au- 

 thorities and partly of records of experiments, both tending to prove 

 the bacterial nature of diphtheritic contagion. There are still many 

 who deny the contagiousness of diphtheria, and who would, of course, 

 deny that its bacterium was discoverable. To such we commend a 

 perusal of Dr. Nelson's paper, and particularly the part which records 

 the following experiment : 



Sterilized beef-bouillon was inoculated with pseudo-membrane from 

 a child who died of diphtheria. The culture was carried to the sixth 

 generation ; guinea pigs were inoculated with the sixth culture, and the 

 pigs developed diphtheria. Further, on the third day after dissecting 

 the diseased pigs, the doctor himself was attacked with diphtheria. 



The Structure of Dentine. — Mr. F. J. Bennett read a paper 

 recently at the Odontological Society on " Certain Points con- 

 nected with the Structure of Dentine." Mr. Bennett employed 

 a new, and what may in future prove a valuable, method of de- 

 calcification, namely, by glycerine. The idea was suggested by 

 some papers by Dr. Ord, in which it was shown that glass, mother of 

 pearl, ivory, and other substances became slowly etched by immersing 

 them in a solution of subcarbonate of potash in glycerine. Mr. Bennett 

 applied this solution to the dental tissues, and in the course of experi- 

 mentation was surprised to find that precisely the same results could be 

 obtained by using glycerine, alone, and thenceforward confined himself 

 to the use of this reagent. His method of pi'ocedure was as follows : 

 i. Freshly-extracted teeth were ground and polished sufficiently thin to 

 allow of microscopical examination ; these wer.e suspended in glycerine 

 for pei"iods of from one to six months, washed, and mounted in glycer- 

 ine for examination. 2. Freshly-ground teeth were immersed whole in 

 pure glycerine for similar periods, then ground, polished, and mounted 

 as before. 3. Whole teeth were placed in extremely dilute solutions of 

 glycerine, the strength of which was daily increased until pure glycer- 

 ine was used ; the specimens were then kept in this for one or two months. 

 It is interesting to note that cementum which is poorest in inorganic mat- 

 ter is most readily acted on by glycerine. Thus treated, dentine, espec- 

 ially that portion nearest the pulp and that newly formed, shows veiy 

 distinctly the outlines of the dentinal tubules, and the matrix, which is 

 generally stated to be absolutely structureless, is apparently made up of 

 superimposed layers of membranes, with a number of stellate cells. The 

 tubules perforate these layers, and can be seen in some sections to com- 

 municate with or arise from the cells. In the discussion which ensued. 

 Dr. Ord, referring to the cells, said he could not express an opinion un- 

 til the specimens had been examined by polarized light to see whether 

 the cells were organic spheroids or inorganic matter, suggesting that 

 the appearances might be due to a rearrangement of the earthy matter. 

 — Lancet, Jan., '89. 



*This department is conducted by F. Blanchard, M. D. 



