108 PRACTICAL HISTOLOGY. 



for permanent preservation it is better that they 

 should have been some days in Mtiller's fluid. The 

 mode of preparing the fresh specimens is as follows. 

 One of the long bones the femur, for instance is 

 removed, and, its cartilaginous head having been 

 cleared of the adherent soft structures, is split down 

 the middle with a strong scalpel, the split extending 

 a little distance into the subjacent bone. Then by 

 a movement of the scalpel one of the halves is broken 

 away, and the junction of the bone and cartilage is 

 brought clearly into view. One or two slices as thin 

 as possible are now taken from the surface thus pro- 

 duced, including the line of advancing ossification, 

 and are placed on a slide in salt solution and covered. 

 These sections are of course parallel with the long 

 axis of the bone ; but to complete the observation 

 others should be made across that axis, at and a 

 little below the level of the line of ossification, the 

 cartilaginous head being first sliced gradually away 

 until the line of ossification is reached, and then a, 

 series of sections taken of the part of the cartilage 

 which is undergoing ossification and of the newly- 

 formed bone. 



The fresh preparations are by far the most beau- 

 tiful and instructive if the sections are obtained 

 sufficiently thin. If it is wished permanently to 

 preserve a section made in this way, the salt solution 

 in which it is mounted must be drawn off by filter- 

 ing paper placed at one edge of the cover-glass, and 

 at the same time replaced by a solution of osmic 

 acid (one per cent.) applied at the opposite edge. 

 The preparation may then be left for an hour (the 

 filter paper being removed), after which time the 

 osrnic acid is in its turn withdrawn arid replaced by 

 water, and finally a drop of glycerine is put at the 

 edge of the covering-glass and suffered to take the 

 place of the water as this evaporates. 



Preparation 9. Sections, longitudinal and trans- 

 verse, of ossifying bones which have been in Mliller's 

 fluid for a few days, are prepared in exactly the 



