INTRODUCTION. xxxvii 



Method of Imbedding. Press the tissue to be imbedded between folds of blotting-paper, 

 to remove all the alcohol, and see that its surface is thoroughly dry. It is a good plan to dip 

 it for a moment into a weak solution of gum arabic, and allow the gum to dry as a film on 

 its surface. This prevents the paraffin from penetrating the tissue, and also causes it to 

 separate more readily from the section. Fold a piece of paper in the form of an oblong box, 

 and pour into it a little of the previously melted paraffine. Place a needle into the tissue, fix 

 it conveniently in the paraffine mixture in the paper box, add more paraffine until the tissue is 

 well covered. Use the needle to keep the tissue in its place until the mixture sets. The 

 paraffine block is then removed from the paper, and sections cut through it and the imbedded 

 tissue. The sections are floated off into spirit or water. 



(&} Other imbedding mixtures are sometimes used, as two parts of paraffine mixed with 

 one of vaseline, which gives a transparent mass, in which the position of the tissue can be 

 detected. 



MICROTOMES. 



When a large number of sections is required, or when a complete section is wanted through 

 an organ, there can be no doubt that a microtome of some kind is required. One of the earliest 

 microtomes introduced (fig. 17) is that of Mr. A. B. Stirling, of the Anatomical Museum, 

 Edinburgh University. It consists of a strong brass tube, with a broad, smooth, metal plate 

 fixed at right angles to it at one end. In this cylinder a plug is moved by a very fine- 

 threaded screw, which works in the lower end of the tube. The instrument is so made that it 

 can be clamped to a table. The tissue to be cut is imbedded in the well of the microtome in 

 paraffine and lard, in the same way as a tissue is imbedded for cutting hand sections. Melt 

 the imbedding mixture, and fill the well of the microtome, and whilst still fluid put in the 

 tissue to be cut using the same precautions as to drying and hold it in position till the 

 mixture sets. By turning the screw the mass and included tissue are elevated ; and a sharp knife 

 carried along on the flat brass plate shaves off a section, which can be made as thin as desired 

 by having a screw of sufficient fineness. The knife must be kept flooded with spirit, and the 

 sections are floated off by means of a camel-hair brush into spirit or water. 



Fig. 18. RANVIER'S HAND MICROTOME. 

 Fig. 17. MR. A. B. STIRLING'S MICROTOME. Half Natural Size. 



Ranvier's Microtome is simply a smaller instrument, working on the same principle, and 

 designed to be held in the hand (fig. 18). The whole apparatus can be inverted in spirit, if it 

 be desired to make sections of the same tissue from time to time. 



