BY DR. KLEIN. 63 



cartilages of the symphyses, etc. The mode of preparation is 

 the same. 



Bone. In the investigation of the structure of bone, one 

 of two courses may be followed, according as we have in view 

 the bony framework, i. e., the bone substance proper, or the 

 soft parts, viz., the periosteum, medulla, bloodvessels, and 

 nerves. The bone substance proper ma}* be studied satisfac- 

 torily by means of thin sections, for the preparation of which 

 the method is as follows: A human long bone, a vertebra, or 

 one of the flat bones of the skull, is cleared of the soft parts 

 and dried. The bone is then fixed in a vise, and thin lamella" 

 are cut in various directions with the aid of a fine saw. These 

 are rubbed down with moist emery powdered on a ground- 

 glass plate, against which they are pressed either with the 

 finger alone, or with a bit of cork, or with a, second glass 

 plate, until they are extremely fine. Having been polished 

 on a wet hone, they are washed in water and pencilled with a 

 camel-hair brush, in order to get rid of adhering dirt. They 

 must next be dried and placed under a cover-glass, either 

 without the addition of any liquid, or in glycerin. As ex- 

 amples, transverse and longitudinal sections of a human 

 radius may be taken. In the one, the Haversian canals are 

 seen cut across ; in the other, they appear as broad channels, 

 which communicate with each other by cross channels, the 

 latter running obliquely or at right angles to the former. 



The clear ground substance consists of lamella} arranged 

 concentrically around the Haversian canals (primary lamellae), 

 and secondary lamellae, which run longitudinally in various 

 planes, occupying the spaces which are left between contiguous 

 systems of concentric lamellae. The lamellae contain an im- 

 mense number of dark cavities (lacunae) at equal distances 

 from each other, which, as longitudinal sections show, are of 

 elliptical form. These communicate with each other by dark, 

 somewhat convoluted canaliculi, many of which run in the 

 same layer, but many also in such a direction as to form com- 

 munications between one lamella and the next. In dry prepa- 

 rations, the whole system of lacume and canaliculi is filled 

 with air. We shall s-. e afterwards that in the living state they 

 contain protoplasmic branching cells. 



A second method of preparing bone is that of maceration. 

 A fresh bone is separated from the surrounding muscles and 

 placed in a large quantity of a quarter to half per cent, solu- 

 tion of chromic acid, to which a few drops of hydrochloric acid 

 have been added. The bone acquires a consistence suitable 

 for the preparation of sections with the razor in from a week 

 to a fortnight, according to its size. If too soft, it can be 

 placed in diluted alcohol. Bones prepared in this way may 



