NATURAL SCIENCES OF PHILADELPHIA. 



Sections of Hard Tissues and other Substances for the Microscope. 

 BY CHRISTOPHER JOHNSON, M. D. 



As hard substances cannot be examined microscopically in their natural 

 state, they must undergo preparation by the investigator before the secrets of 

 their physical and vital condition can be mastered. The end or object of 

 this '• preparation " is the production of a lamina so thin as to be translu- 

 cent, and yet sufficiently thick to retain every physical characteristic. To 

 accomplish this desired end much patience is called for in each of the seve- 

 ral processes especially adapted to the particular and diflerent states of 

 hardness, with or -n-ithout brittleness, or toughness, and finally to the condi- 

 tion of preservation of objects, whether receut or fossil. 



It must be evident to every student in microscopy, that certain qualities 

 of objects oppose a barrier to the facile disentanglement of their web and 

 woof, and such, for e.xample, is the absorption of light, as totally Jjy blnck or 

 partially by colored bodies. Wherefore a knowledge of these qualities is 

 requisite ; and success will reward the operator in proportion as he adapts 

 modes of preparation to tissues offered for examination, if he possess the 

 amount of skill and patience indispensable in delicate manipulations. 



It may be observed, before proceeding to develop any method of section 

 making, thai perfect sections, even, of some objects, such as biliary and 

 vesical calculi, as well as certain pathological concretions, require the aid 

 of a suitable mounting before their intimate constitution can be exhibited; 

 so that the work of the microscopist does not always end with the production 

 of a successful section, but must not be regarded as complete until the prep- 

 aration be secured and displayed in some proper way upon a slide. 



When I needed the aid of guides in directing ray unskilled manipulations 

 I was very often embarrassed by the meagreness of the assistance afforded by 

 authors of works on practical microscopy ; inexperienced readers, however, 

 will find in my attention to detail that help which will secure me exonora- 

 tion from the charge of tedious minuteness, and I beg to add that I theorize 

 in nothing, but give the results of my own personal experience. 



Hard substances may be divided into two groups, ihe first comprising all 

 such as require the emery wheel for their reduction, and the second, all other 

 and less resisting structures. Among the former are to be found the flints and 

 siliceous petrifactions, as also very hard calcareous bodies, whether petrifac- 

 tions or of recent and normal constitution, as the porcelain-like shell of 

 many molluscs. In the succeeding group may be ranged recent or non-sili- 

 cified teeth and bone, calculi of various kinds, brain sand and calcareous de- 

 posits, hard seed capsules, and the like. Whatever be the process employed 

 to subdue these refractory substances, the resulting section must possess cer- 

 tain qualities or fulfil certain conditions. It must be perfectly flat, of suita- 

 ble and equal thinness, and ought, if possible, to be polished on both sides. 

 I say if possible, because there are many hard and tough substances which 

 are not susceptible of a polish ; and it is almost needless to add that, ia the 

 study of structure, sections cut in several directions are indispensable for its 

 correct appreciation. 



The apparatus I have employed is of very simple description. For the 

 preparation of sections of objects of the^Vs^ class, I necessarily have recourse 

 to the lathe fitted with a " true " disc of thin soft steel, for emery on the side 

 or edge, as I might wish to grind a surface or cut a slice ; with an Ayrshire 

 stone for grinding, and a wooden disc cut across the grain to bear the polish- 

 ing powder, the tin powder in use by stone cutters. But to save time I 

 have frequently availed myself of the steadily revolving fine stones in a 

 glass-cutting establishment, which readily "cut" the chalk-flint by which 

 they are sharpened and corrected. The lathe is a part of a former watch- 

 maker's, and similar to those commonly in vogue with dentists. The emery 



