106 METHODS. 



the alcohol, as has been already stated. When gelatin is used, 

 the mode of procedure, so far as relates to the preparation of 

 the solution, is similar. The bit having been fixed into the 

 box and surrounded with the solution, the whole is allowed to 

 stand until it becomes solid. Whichever material is used, the 

 mass is freed from the paper box as soon as it has acquired 

 sufficient firmness, and the ends of the needle are snipped off 

 above and below. 



Preparation of Sections of Hardened Tissues. For 

 making sections, razors are most used. Other instruments 

 are also employed, the purpose of which is to make up for 

 want of skill in the operator. The principal ones are Valentin's 

 knife, the microtome of Hensen, that of His, another micro- 

 tome lately described by Brandt, and the section cutter of 

 Stirling, lately improved by Rutherford. Of these, the most 

 useful is that of His, which has the advantage that it is possi- t 

 ble to cut with it successive sections of an organ in equidistant 

 planes, parallel to each other, with the greatest exactitude. 



The razor or section knife, in the hands of a skilful operator, 

 is superior to any of these contrivances. The knife I use is of 

 the form shown in Fig. 1 6. The blade measures eight inches ; 

 the wooden handle is massive, so that it can be firmi3 r grasped. 

 One side of it is flat, the others slightly concave, it is thus ex- 

 tremely thin to a considerable distance from the cutting edge. 

 When sections are to be made of objects embedded in wax- 

 mass, the knife must be wetted with common alcohol, in which 

 liquid each section must be immersed as soon as it is made. 

 Sections of objects which have been embedded in gum or gela- 

 tin must be placed in water, but the knife wetted with alcohol. 



Coloring of the Sections. It is quite unnecessary to 

 refer to all the colored liquids which have been used for stain- 

 ing. It will be sufficient to describe the mode of using carmine 

 and anilin. 



Carmine. The most simple solution for the purpose is the 

 following: Two grammes of carmine in fine powder are tho- 

 roughly mixed in a beaker, with a few drops of water. Four 

 cubic centimetres of liquor ammonite are then added, and forty- 

 eight cubic centimetres of distilled water. The liquid is filtered 

 into the stoppered bottle, in which it is to be kept. The bottle 

 is then left open for a few days, in order to get rid of the excess 

 of ammonia. One or two drops of this solution are introduced 

 into a watch-glass, and diluted with distilled water to such an 

 extent, that when it is placed on a written or printed sheet of 

 paper, the letters can only just be distinguished through it. 

 The sections are immersed in the diluted liquid till, on inspec- 

 tion, they appear to have the tint desired. Prolonged steeping 

 in dilute solution gives, as a rule, better results than rapid 

 straining in strong solution; for, in the former case, although 



