162 PRACTICAL HISTOLOGY. 



tions should always be manipulated with camel-hair pencils. 

 Much practice is required before dexterity is attained, but 

 it is very important to thoroughly practise this mode of 

 section ; for, when only small slices are required, they can 

 be made very perfectly in this simple way. 



297. Imbedding. The piece of tissue is often so 

 small that it is impossible to hold it in the hand, and it is 

 sometimes so brittle that it is apt to go to pieces when cut. 

 To overcome these difficulties, it is necessary to imbed the 

 tissue, so as to support and hold it firm during the section. 



298. Imbedding in Carrot. A carrot is an excellent 

 imbedding agent. For holding in the hand a piece of 

 softened bone or hardened spinal cord, etc., it is extremely 

 convenient. A hole rather smaller than the organ should 

 be scooped in the carrot, near its centre. An incision 

 should then be carried from the hole to the periphery, so 

 that the hole may be enlarged for the admission of the 

 organ, round which the carrot closes like a hollow spring. 

 The carrot does not cling either to the knife or to the texture ; 

 and the knife is wetted at every slice by passing through the 

 carrot. It is not suitable, however, for delicate tissues. 



299. Imbedding in elder pith is recommended by 

 Ranvier. A hole somewhat larger than the tissue is made 

 in the pith, and the piece of tissue e.g., a hardened nerve 

 is placed in it. The whole is then immersed in water, 

 to cause the pith to swell up and clasp the tissue firmly. 



300. Imbedding in Paraffin. Paraffin is the imbedding 

 agent most commonly employed. Ordinary solid paraffin 

 is too hard. Five parts of it should therefore be mixed 

 with one part of hog's lard with the aid of a gentle heat. 

 The addition of a little clove oil renders the mixture less 

 liable to adhere to the knife. A mixture of equal parts of 

 bees'-wax and sweet oil is often recommended, and no 

 doubt it answers very well for hand sections ; but it is not 

 so suitable as paraffin for imbedding in a microtome, be- 

 cause the wax and oil, having a higher melting point than 

 the paraffin mixture, contracts so much when it cools, 

 that it separates from the metal around the well of the 

 microtome. 



